research paper about environmental factors

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Environmental and Health Impacts of Air Pollution: A Review

Ioannis manisalidis.

1 Delphis S.A., Kifisia, Greece

2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece

Elisavet Stavropoulou

3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland

Agathangelos Stavropoulos

4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

Eugenia Bezirtzoglou

One of our era's greatest scourges is air pollution, on account not only of its impact on climate change but also its impact on public and individual health due to increasing morbidity and mortality. There are many pollutants that are major factors in disease in humans. Among them, Particulate Matter (PM), particles of variable but very small diameter, penetrate the respiratory system via inhalation, causing respiratory and cardiovascular diseases, reproductive and central nervous system dysfunctions, and cancer. Despite the fact that ozone in the stratosphere plays a protective role against ultraviolet irradiation, it is harmful when in high concentration at ground level, also affecting the respiratory and cardiovascular system. Furthermore, nitrogen oxide, sulfur dioxide, Volatile Organic Compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) are all considered air pollutants that are harmful to humans. Carbon monoxide can even provoke direct poisoning when breathed in at high levels. Heavy metals such as lead, when absorbed into the human body, can lead to direct poisoning or chronic intoxication, depending on exposure. Diseases occurring from the aforementioned substances include principally respiratory problems such as Chronic Obstructive Pulmonary Disease (COPD), asthma, bronchiolitis, and also lung cancer, cardiovascular events, central nervous system dysfunctions, and cutaneous diseases. Last but not least, climate change resulting from environmental pollution affects the geographical distribution of many infectious diseases, as do natural disasters. The only way to tackle this problem is through public awareness coupled with a multidisciplinary approach by scientific experts; national and international organizations must address the emergence of this threat and propose sustainable solutions.

Approach to the Problem

The interactions between humans and their physical surroundings have been extensively studied, as multiple human activities influence the environment. The environment is a coupling of the biotic (living organisms and microorganisms) and the abiotic (hydrosphere, lithosphere, and atmosphere).

Pollution is defined as the introduction into the environment of substances harmful to humans and other living organisms. Pollutants are harmful solids, liquids, or gases produced in higher than usual concentrations that reduce the quality of our environment.

Human activities have an adverse effect on the environment by polluting the water we drink, the air we breathe, and the soil in which plants grow. Although the industrial revolution was a great success in terms of technology, society, and the provision of multiple services, it also introduced the production of huge quantities of pollutants emitted into the air that are harmful to human health. Without any doubt, the global environmental pollution is considered an international public health issue with multiple facets. Social, economic, and legislative concerns and lifestyle habits are related to this major problem. Clearly, urbanization and industrialization are reaching unprecedented and upsetting proportions worldwide in our era. Anthropogenic air pollution is one of the biggest public health hazards worldwide, given that it accounts for about 9 million deaths per year ( 1 ).

Without a doubt, all of the aforementioned are closely associated with climate change, and in the event of danger, the consequences can be severe for mankind ( 2 ). Climate changes and the effects of global planetary warming seriously affect multiple ecosystems, causing problems such as food safety issues, ice and iceberg melting, animal extinction, and damage to plants ( 3 , 4 ).

Air pollution has various health effects. The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).

The long-term effects associated with air pollution are chronic asthma, pulmonary insufficiency, cardiovascular diseases, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure ( 5 ). Moreover, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders ( 3 ), leading to infant mortality or chronic disease in adult age ( 6 ).

National reports have mentioned the increased risk of morbidity and mortality ( 1 ). These studies were conducted in many places around the world and show a correlation between daily ranges of particulate matter (PM) concentration and daily mortality. Climate shifts and global planetary warming ( 3 ) could aggravate the situation. Besides, increased hospitalization (an index of morbidity) has been registered among the elderly and susceptible individuals for specific reasons. Fine and ultrafine particulate matter seems to be associated with more serious illnesses ( 6 ), as it can invade the deepest parts of the airways and more easily reach the bloodstream.

Air pollution mainly affects those living in large urban areas, where road emissions contribute the most to the degradation of air quality. There is also a danger of industrial accidents, where the spread of a toxic fog can be fatal to the populations of the surrounding areas. The dispersion of pollutants is determined by many parameters, most notably atmospheric stability and wind ( 6 ).

In developing countries ( 7 ), the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization. This leads to poor air quality, especially in countries with social disparities and a lack of information on sustainable management of the environment. The use of fuels such as wood fuel or solid fuel for domestic needs due to low incomes exposes people to bad-quality, polluted air at home. It is of note that three billion people around the world are using the above sources of energy for their daily heating and cooking needs ( 8 ). In developing countries, the women of the household seem to carry the highest risk for disease development due to their longer duration exposure to the indoor air pollution ( 8 , 9 ). Due to its fast industrial development and overpopulation, China is one of the Asian countries confronting serious air pollution problems ( 10 , 11 ). The lung cancer mortality observed in China is associated with fine particles ( 12 ). As stated already, long-term exposure is associated with deleterious effects on the cardiovascular system ( 3 , 5 ). However, it is interesting to note that cardiovascular diseases have mostly been observed in developed and high-income countries rather than in the developing low-income countries exposed highly to air pollution ( 13 ). Extreme air pollution is recorded in India, where the air quality reaches hazardous levels. New Delhi is one of the more polluted cities in India. Flights in and out of New Delhi International Airport are often canceled due to the reduced visibility associated with air pollution. Pollution is occurring both in urban and rural areas in India due to the fast industrialization, urbanization, and rise in use of motorcycle transportation. Nevertheless, biomass combustion associated with heating and cooking needs and practices is a major source of household air pollution in India and in Nepal ( 14 , 15 ). There is spatial heterogeneity in India, as areas with diverse climatological conditions and population and education levels generate different indoor air qualities, with higher PM 2.5 observed in North Indian states (557–601 μg/m 3 ) compared to the Southern States (183–214 μg/m 3 ) ( 16 , 17 ). The cold climate of the North Indian areas may be the main reason for this, as longer periods at home and more heating are necessary compared to in the tropical climate of Southern India. Household air pollution in India is associated with major health effects, especially in women and young children, who stay indoors for longer periods. Chronic obstructive respiratory disease (CORD) and lung cancer are mostly observed in women, while acute lower respiratory disease is seen in young children under 5 years of age ( 18 ).

Accumulation of air pollution, especially sulfur dioxide and smoke, reaching 1,500 mg/m3, resulted in an increase in the number of deaths (4,000 deaths) in December 1952 in London and in 1963 in New York City (400 deaths) ( 19 ). An association of pollution with mortality was reported on the basis of monitoring of outdoor pollution in six US metropolitan cities ( 20 ). In every case, it seems that mortality was closely related to the levels of fine, inhalable, and sulfate particles more than with the levels of total particulate pollution, aerosol acidity, sulfur dioxide, or nitrogen dioxide ( 20 ).

Furthermore, extremely high levels of pollution are reported in Mexico City and Rio de Janeiro, followed by Milan, Ankara, Melbourne, Tokyo, and Moscow ( 19 ).

Based on the magnitude of the public health impact, it is certain that different kinds of interventions should be taken into account. Success and effectiveness in controlling air pollution, specifically at the local level, have been reported. Adequate technological means are applied considering the source and the nature of the emission as well as its impact on health and the environment. The importance of point sources and non-point sources of air pollution control is reported by Schwela and Köth-Jahr ( 21 ). Without a doubt, a detailed emission inventory must record all sources in a given area. Beyond considering the above sources and their nature, topography and meteorology should also be considered, as stated previously. Assessment of the control policies and methods is often extrapolated from the local to the regional and then to the global scale. Air pollution may be dispersed and transported from one region to another area located far away. Air pollution management means the reduction to acceptable levels or possible elimination of air pollutants whose presence in the air affects our health or the environmental ecosystem. Private and governmental entities and authorities implement actions to ensure the air quality ( 22 ). Air quality standards and guidelines were adopted for the different pollutants by the WHO and EPA as a tool for the management of air quality ( 1 , 23 ). These standards have to be compared to the emissions inventory standards by causal analysis and dispersion modeling in order to reveal the problematic areas ( 24 ). Inventories are generally based on a combination of direct measurements and emissions modeling ( 24 ).

As an example, we state here the control measures at the source through the use of catalytic converters in cars. These are devices that turn the pollutants and toxic gases produced from combustion engines into less-toxic pollutants by catalysis through redox reactions ( 25 ). In Greece, the use of private cars was restricted by tracking their license plates in order to reduce traffic congestion during rush hour ( 25 ).

Concerning industrial emissions, collectors and closed systems can keep the air pollution to the minimal standards imposed by legislation ( 26 ).

Current strategies to improve air quality require an estimation of the economic value of the benefits gained from proposed programs. These proposed programs by public authorities, and directives are issued with guidelines to be respected.

In Europe, air quality limit values AQLVs (Air Quality Limit Values) are issued for setting off planning claims ( 27 ). In the USA, the NAAQS (National Ambient Air Quality Standards) establish the national air quality limit values ( 27 ). While both standards and directives are based on different mechanisms, significant success has been achieved in the reduction of overall emissions and associated health and environmental effects ( 27 ). The European Directive identifies geographical areas of risk exposure as monitoring/assessment zones to record the emission sources and levels of air pollution ( 27 ), whereas the USA establishes global geographical air quality criteria according to the severity of their air quality problem and records all sources of the pollutants and their precursors ( 27 ).

In this vein, funds have been financing, directly or indirectly, projects related to air quality along with the technical infrastructure to maintain good air quality. These plans focus on an inventory of databases from air quality environmental planning awareness campaigns. Moreover, pollution measures of air emissions may be taken for vehicles, machines, and industries in urban areas.

Technological innovation can only be successful if it is able to meet the needs of society. In this sense, technology must reflect the decision-making practices and procedures of those involved in risk assessment and evaluation and act as a facilitator in providing information and assessments to enable decision makers to make the best decisions possible. Summarizing the aforementioned in order to design an effective air quality control strategy, several aspects must be considered: environmental factors and ambient air quality conditions, engineering factors and air pollutant characteristics, and finally, economic operating costs for technological improvement and administrative and legal costs. Considering the economic factor, competitiveness through neoliberal concepts is offering a solution to environmental problems ( 22 ).

The development of environmental governance, along with technological progress, has initiated the deployment of a dialogue. Environmental politics has created objections and points of opposition between different political parties, scientists, media, and governmental and non-governmental organizations ( 22 ). Radical environmental activism actions and movements have been created ( 22 ). The rise of the new information and communication technologies (ICTs) are many times examined as to whether and in which way they have influenced means of communication and social movements such as activism ( 28 ). Since the 1990s, the term “digital activism” has been used increasingly and in many different disciplines ( 29 ). Nowadays, multiple digital technologies can be used to produce a digital activism outcome on environmental issues. More specifically, devices with online capabilities such as computers or mobile phones are being used as a way to pursue change in political and social affairs ( 30 ).

In the present paper, we focus on the sources of environmental pollution in relation to public health and propose some solutions and interventions that may be of interest to environmental legislators and decision makers.

Sources of Exposure

It is known that the majority of environmental pollutants are emitted through large-scale human activities such as the use of industrial machinery, power-producing stations, combustion engines, and cars. Because these activities are performed at such a large scale, they are by far the major contributors to air pollution, with cars estimated to be responsible for approximately 80% of today's pollution ( 31 ). Some other human activities are also influencing our environment to a lesser extent, such as field cultivation techniques, gas stations, fuel tanks heaters, and cleaning procedures ( 32 ), as well as several natural sources, such as volcanic and soil eruptions and forest fires.

The classification of air pollutants is based mainly on the sources producing pollution. Therefore, it is worth mentioning the four main sources, following the classification system: Major sources, Area sources, Mobile sources, and Natural sources.

Major sources include the emission of pollutants from power stations, refineries, and petrochemicals, the chemical and fertilizer industries, metallurgical and other industrial plants, and, finally, municipal incineration.

Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

Finally, natural sources include, as stated previously, physical disasters ( 33 ) such as forest fire, volcanic erosion, dust storms, and agricultural burning.

However, many classification systems have been proposed. Another type of classification is a grouping according to the recipient of the pollution, as follows:

Air pollution is determined as the presence of pollutants in the air in large quantities for long periods. Air pollutants are dispersed particles, hydrocarbons, CO, CO 2 , NO, NO 2 , SO 3 , etc.

Water pollution is organic and inorganic charge and biological charge ( 10 ) at high levels that affect the water quality ( 34 , 35 ).

Soil pollution occurs through the release of chemicals or the disposal of wastes, such as heavy metals, hydrocarbons, and pesticides.

Air pollution can influence the quality of soil and water bodies by polluting precipitation, falling into water and soil environments ( 34 , 36 ). Notably, the chemistry of the soil can be amended due to acid precipitation by affecting plants, cultures, and water quality ( 37 ). Moreover, movement of heavy metals is favored by soil acidity, and metals are so then moving into the watery environment. It is known that heavy metals such as aluminum are noxious to wildlife and fishes. Soil quality seems to be of importance, as soils with low calcium carbonate levels are at increased jeopardy from acid rain. Over and above rain, snow and particulate matter drip into watery ' bodies ( 36 , 38 ).

Lastly, pollution is classified following type of origin:

Radioactive and nuclear pollution , releasing radioactive and nuclear pollutants into water, air, and soil during nuclear explosions and accidents, from nuclear weapons, and through handling or disposal of radioactive sewage.

Radioactive materials can contaminate surface water bodies and, being noxious to the environment, plants, animals, and humans. It is known that several radioactive substances such as radium and uranium concentrate in the bones and can cause cancers ( 38 , 39 ).

Noise pollution is produced by machines, vehicles, traffic noises, and musical installations that are harmful to our hearing.

The World Health Organization introduced the term DALYs. The DALYs for a disease or health condition is defined as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences ( 39 ). In Europe, air pollution is the main cause of disability-adjusted life years lost (DALYs), followed by noise pollution. The potential relationships of noise and air pollution with health have been studied ( 40 ). The study found that DALYs related to noise were more important than those related to air pollution, as the effects of environmental noise on cardiovascular disease were independent of air pollution ( 40 ). Environmental noise should be counted as an independent public health risk ( 40 ).

Environmental pollution occurs when changes in the physical, chemical, or biological constituents of the environment (air masses, temperature, climate, etc.) are produced.

Pollutants harm our environment either by increasing levels above normal or by introducing harmful toxic substances. Primary pollutants are directly produced from the above sources, and secondary pollutants are emitted as by-products of the primary ones. Pollutants can be biodegradable or non-biodegradable and of natural origin or anthropogenic, as stated previously. Moreover, their origin can be a unique source (point-source) or dispersed sources.

Pollutants have differences in physical and chemical properties, explaining the discrepancy in their capacity for producing toxic effects. As an example, we state here that aerosol compounds ( 41 – 43 ) have a greater toxicity than gaseous compounds due to their tiny size (solid or liquid) in the atmosphere; they have a greater penetration capacity. Gaseous compounds are eliminated more easily by our respiratory system ( 41 ). These particles are able to damage lungs and can even enter the bloodstream ( 41 ), leading to the premature deaths of millions of people yearly. Moreover, the aerosol acidity ([H+]) seems to considerably enhance the production of secondary organic aerosols (SOA), but this last aspect is not supported by other scientific teams ( 38 ).

Climate and Pollution

Air pollution and climate change are closely related. Climate is the other side of the same coin that reduces the quality of our Earth ( 44 ). Pollutants such as black carbon, methane, tropospheric ozone, and aerosols affect the amount of incoming sunlight. As a result, the temperature of the Earth is increasing, resulting in the melting of ice, icebergs, and glaciers.

In this vein, climatic changes will affect the incidence and prevalence of both residual and imported infections in Europe. Climate and weather affect the duration, timing, and intensity of outbreaks strongly and change the map of infectious diseases in the globe ( 45 ). Mosquito-transmitted parasitic or viral diseases are extremely climate-sensitive, as warming firstly shortens the pathogen incubation period and secondly shifts the geographic map of the vector. Similarly, water-warming following climate changes leads to a high incidence of waterborne infections. Recently, in Europe, eradicated diseases seem to be emerging due to the migration of population, for example, cholera, poliomyelitis, tick-borne encephalitis, and malaria ( 46 ).

The spread of epidemics is associated with natural climate disasters and storms, which seem to occur more frequently nowadays ( 47 ). Malnutrition and disequilibration of the immune system are also associated with the emerging infections affecting public health ( 48 ).

The Chikungunya virus “took the airplane” from the Indian Ocean to Europe, as outbreaks of the disease were registered in Italy ( 49 ) as well as autochthonous cases in France ( 50 ).

An increase in cryptosporidiosis in the United Kingdom and in the Czech Republic seems to have occurred following flooding ( 36 , 51 ).

As stated previously, aerosols compounds are tiny in size and considerably affect the climate. They are able to dissipate sunlight (the albedo phenomenon) by dispersing a quarter of the sun's rays back to space and have cooled the global temperature over the last 30 years ( 52 ).

Air Pollutants

The World Health Organization (WHO) reports on six major air pollutants, namely particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Air pollution can have a disastrous effect on all components of the environment, including groundwater, soil, and air. Additionally, it poses a serious threat to living organisms. In this vein, our interest is mainly to focus on these pollutants, as they are related to more extensive and severe problems in human health and environmental impact. Acid rain, global warming, the greenhouse effect, and climate changes have an important ecological impact on air pollution ( 53 ).

Particulate Matter (PM) and Health

Studies have shown a relationship between particulate matter (PM) and adverse health effects, focusing on either short-term (acute) or long-term (chronic) PM exposure.

Particulate matter (PM) is usually formed in the atmosphere as a result of chemical reactions between the different pollutants. The penetration of particles is closely dependent on their size ( 53 ). Particulate Matter (PM) was defined as a term for particles by the United States Environmental Protection Agency ( 54 ). Particulate matter (PM) pollution includes particles with diameters of 10 micrometers (μm) or smaller, called PM 10 , and extremely fine particles with diameters that are generally 2.5 micrometers (μm) and smaller.

Particulate matter contains tiny liquid or solid droplets that can be inhaled and cause serious health effects ( 55 ). Particles <10 μm in diameter (PM 10 ) after inhalation can invade the lungs and even reach the bloodstream. Fine particles, PM 2.5 , pose a greater risk to health ( 6 , 56 ) ( Table 1 ).

Penetrability according to particle size.

Multiple epidemiological studies have been performed on the health effects of PM. A positive relation was shown between both short-term and long-term exposures of PM 2.5 and acute nasopharyngitis ( 56 ). In addition, long-term exposure to PM for years was found to be related to cardiovascular diseases and infant mortality.

Those studies depend on PM 2.5 monitors and are restricted in terms of study area or city area due to a lack of spatially resolved daily PM 2.5 concentration data and, in this way, are not representative of the entire population. Following a recent epidemiological study by the Department of Environmental Health at Harvard School of Public Health (Boston, MA) ( 57 ), it was reported that, as PM 2.5 concentrations vary spatially, an exposure error (Berkson error) seems to be produced, and the relative magnitudes of the short- and long-term effects are not yet completely elucidated. The team developed a PM 2.5 exposure model based on remote sensing data for assessing short- and long-term human exposures ( 57 ). This model permits spatial resolution in short-term effects plus the assessment of long-term effects in the whole population.

Moreover, respiratory diseases and affection of the immune system are registered as long-term chronic effects ( 58 ). It is worth noting that people with asthma, pneumonia, diabetes, and respiratory and cardiovascular diseases are especially susceptible and vulnerable to the effects of PM. PM 2.5 , followed by PM 10 , are strongly associated with diverse respiratory system diseases ( 59 ), as their size permits them to pierce interior spaces ( 60 ). The particles produce toxic effects according to their chemical and physical properties. The components of PM 10 and PM 2.5 can be organic (polycyclic aromatic hydrocarbons, dioxins, benzene, 1-3 butadiene) or inorganic (carbon, chlorides, nitrates, sulfates, metals) in nature ( 55 ).

Particulate Matter (PM) is divided into four main categories according to type and size ( 61 ) ( Table 2 ).

Types and sizes of particulate Matter (PM).

Gas contaminants include PM in aerial masses.

Particulate contaminants include contaminants such as smog, soot, tobacco smoke, oil smoke, fly ash, and cement dust.

Biological Contaminants are microorganisms (bacteria, viruses, fungi, mold, and bacterial spores), cat allergens, house dust and allergens, and pollen.

Types of Dust include suspended atmospheric dust, settling dust, and heavy dust.

Finally, another fact is that the half-lives of PM 10 and PM 2.5 particles in the atmosphere is extended due to their tiny dimensions; this permits their long-lasting suspension in the atmosphere and even their transfer and spread to distant destinations where people and the environment may be exposed to the same magnitude of pollution ( 53 ). They are able to change the nutrient balance in watery ecosystems, damage forests and crops, and acidify water bodies.

As stated, PM 2.5 , due to their tiny size, are causing more serious health effects. These aforementioned fine particles are the main cause of the “haze” formation in different metropolitan areas ( 12 , 13 , 61 ).

Ozone Impact in the Atmosphere

Ozone (O 3 ) is a gas formed from oxygen under high voltage electric discharge ( 62 ). It is a strong oxidant, 52% stronger than chlorine. It arises in the stratosphere, but it could also arise following chain reactions of photochemical smog in the troposphere ( 63 ).

Ozone can travel to distant areas from its initial source, moving with air masses ( 64 ). It is surprising that ozone levels over cities are low in contrast to the increased amounts occuring in urban areas, which could become harmful for cultures, forests, and vegetation ( 65 ) as it is reducing carbon assimilation ( 66 ). Ozone reduces growth and yield ( 47 , 48 ) and affects the plant microflora due to its antimicrobial capacity ( 67 , 68 ). In this regard, ozone acts upon other natural ecosystems, with microflora ( 69 , 70 ) and animal species changing their species composition ( 71 ). Ozone increases DNA damage in epidermal keratinocytes and leads to impaired cellular function ( 72 ).

Ground-level ozone (GLO) is generated through a chemical reaction between oxides of nitrogen and VOCs emitted from natural sources and/or following anthropogenic activities.

Ozone uptake usually occurs by inhalation. Ozone affects the upper layers of the skin and the tear ducts ( 73 ). A study of short-term exposure of mice to high levels of ozone showed malondialdehyde formation in the upper skin (epidermis) but also depletion in vitamins C and E. It is likely that ozone levels are not interfering with the skin barrier function and integrity to predispose to skin disease ( 74 ).

Due to the low water-solubility of ozone, inhaled ozone has the capacity to penetrate deeply into the lungs ( 75 ).

Toxic effects induced by ozone are registered in urban areas all over the world, causing biochemical, morphologic, functional, and immunological disorders ( 76 ).

The European project (APHEA2) focuses on the acute effects of ambient ozone concentrations on mortality ( 77 ). Daily ozone concentrations compared to the daily number of deaths were reported from different European cities for a 3-year period. During the warm period of the year, an observed increase in ozone concentration was associated with an increase in the daily number of deaths (0.33%), in the number of respiratory deaths (1.13%), and in the number of cardiovascular deaths (0.45%). No effect was observed during wintertime.

Carbon Monoxide (CO)

Carbon monoxide is produced by fossil fuel when combustion is incomplete. The symptoms of poisoning due to inhaling carbon monoxide include headache, dizziness, weakness, nausea, vomiting, and, finally, loss of consciousness.

The affinity of carbon monoxide to hemoglobin is much greater than that of oxygen. In this vein, serious poisoning may occur in people exposed to high levels of carbon monoxide for a long period of time. Due to the loss of oxygen as a result of the competitive binding of carbon monoxide, hypoxia, ischemia, and cardiovascular disease are observed.

Carbon monoxide affects the greenhouses gases that are tightly connected to global warming and climate. This should lead to an increase in soil and water temperatures, and extreme weather conditions or storms may occur ( 68 ).

However, in laboratory and field experiments, it has been seen to produce increased plant growth ( 78 ).

Nitrogen Oxide (NO 2 )

Nitrogen oxide is a traffic-related pollutant, as it is emitted from automobile motor engines ( 79 , 80 ). It is an irritant of the respiratory system as it penetrates deep in the lung, inducing respiratory diseases, coughing, wheezing, dyspnea, bronchospasm, and even pulmonary edema when inhaled at high levels. It seems that concentrations over 0.2 ppm produce these adverse effects in humans, while concentrations higher than 2.0 ppm affect T-lymphocytes, particularly the CD8+ cells and NK cells that produce our immune response ( 81 ).It is reported that long-term exposure to high levels of nitrogen dioxide can be responsible for chronic lung disease. Long-term exposure to NO 2 can impair the sense of smell ( 81 ).

However, systems other than respiratory ones can be involved, as symptoms such as eye, throat, and nose irritation have been registered ( 81 ).

High levels of nitrogen dioxide are deleterious to crops and vegetation, as they have been observed to reduce crop yield and plant growth efficiency. Moreover, NO 2 can reduce visibility and discolor fabrics ( 81 ).

Sulfur Dioxide (SO 2 )

Sulfur dioxide is a harmful gas that is emitted mainly from fossil fuel consumption or industrial activities. The annual standard for SO 2 is 0.03 ppm ( 82 ). It affects human, animal, and plant life. Susceptible people as those with lung disease, old people, and children, who present a higher risk of damage. The major health problems associated with sulfur dioxide emissions in industrialized areas are respiratory irritation, bronchitis, mucus production, and bronchospasm, as it is a sensory irritant and penetrates deep into the lung converted into bisulfite and interacting with sensory receptors, causing bronchoconstriction. Moreover, skin redness, damage to the eyes (lacrimation and corneal opacity) and mucous membranes, and worsening of pre-existing cardiovascular disease have been observed ( 81 ).

Environmental adverse effects, such as acidification of soil and acid rain, seem to be associated with sulfur dioxide emissions ( 83 ).

Lead is a heavy metal used in different industrial plants and emitted from some petrol motor engines, batteries, radiators, waste incinerators, and waste waters ( 84 ).

Moreover, major sources of lead pollution in the air are metals, ore, and piston-engine aircraft. Lead poisoning is a threat to public health due to its deleterious effects upon humans, animals, and the environment, especially in the developing countries.

Exposure to lead can occur through inhalation, ingestion, and dermal absorption. Trans- placental transport of lead was also reported, as lead passes through the placenta unencumbered ( 85 ). The younger the fetus is, the more harmful the toxic effects. Lead toxicity affects the fetal nervous system; edema or swelling of the brain is observed ( 86 ). Lead, when inhaled, accumulates in the blood, soft tissue, liver, lung, bones, and cardiovascular, nervous, and reproductive systems. Moreover, loss of concentration and memory, as well as muscle and joint pain, were observed in adults ( 85 , 86 ).

Children and newborns ( 87 ) are extremely susceptible even to minimal doses of lead, as it is a neurotoxicant and causes learning disabilities, impairment of memory, hyperactivity, and even mental retardation.

Elevated amounts of lead in the environment are harmful to plants and crop growth. Neurological effects are observed in vertebrates and animals in association with high lead levels ( 88 ).

Polycyclic Aromatic Hydrocarbons(PAHs)

The distribution of PAHs is ubiquitous in the environment, as the atmosphere is the most important means of their dispersal. They are found in coal and in tar sediments. Moreover, they are generated through incomplete combustion of organic matter as in the cases of forest fires, incineration, and engines ( 89 ). PAH compounds, such as benzopyrene, acenaphthylene, anthracene, and fluoranthene are recognized as toxic, mutagenic, and carcinogenic substances. They are an important risk factor for lung cancer ( 89 ).

Volatile Organic Compounds(VOCs)

Volatile organic compounds (VOCs), such as toluene, benzene, ethylbenzene, and xylene ( 90 ), have been found to be associated with cancer in humans ( 91 ). The use of new products and materials has actually resulted in increased concentrations of VOCs. VOCs pollute indoor air ( 90 ) and may have adverse effects on human health ( 91 ). Short-term and long-term adverse effects on human health are observed. VOCs are responsible for indoor air smells. Short-term exposure is found to cause irritation of eyes, nose, throat, and mucosal membranes, while those of long duration exposure include toxic reactions ( 92 ). Predictable assessment of the toxic effects of complex VOC mixtures is difficult to estimate, as these pollutants can have synergic, antagonistic, or indifferent effects ( 91 , 93 ).

Dioxins originate from industrial processes but also come from natural processes, such as forest fires and volcanic eruptions. They accumulate in foods such as meat and dairy products, fish and shellfish, and especially in the fatty tissue of animals ( 94 ).

Short-period exhibition to high dioxin concentrations may result in dark spots and lesions on the skin ( 94 ). Long-term exposure to dioxins can cause developmental problems, impairment of the immune, endocrine and nervous systems, reproductive infertility, and cancer ( 94 ).

Without any doubt, fossil fuel consumption is responsible for a sizeable part of air contamination. This contamination may be anthropogenic, as in agricultural and industrial processes or transportation, while contamination from natural sources is also possible. Interestingly, it is of note that the air quality standards established through the European Air Quality Directive are somewhat looser than the WHO guidelines, which are stricter ( 95 ).

Effect of Air Pollution on Health

The most common air pollutants are ground-level ozone and Particulates Matter (PM). Air pollution is distinguished into two main types:

Outdoor pollution is the ambient air pollution.

Indoor pollution is the pollution generated by household combustion of fuels.

People exposed to high concentrations of air pollutants experience disease symptoms and states of greater and lesser seriousness. These effects are grouped into short- and long-term effects affecting health.

Susceptible populations that need to be aware of health protection measures include old people, children, and people with diabetes and predisposing heart or lung disease, especially asthma.

As extensively stated previously, according to a recent epidemiological study from Harvard School of Public Health, the relative magnitudes of the short- and long-term effects have not been completely clarified ( 57 ) due to the different epidemiological methodologies and to the exposure errors. New models are proposed for assessing short- and long-term human exposure data more successfully ( 57 ). Thus, in the present section, we report the more common short- and long-term health effects but also general concerns for both types of effects, as these effects are often dependent on environmental conditions, dose, and individual susceptibility.

Short-term effects are temporary and range from simple discomfort, such as irritation of the eyes, nose, skin, throat, wheezing, coughing and chest tightness, and breathing difficulties, to more serious states, such as asthma, pneumonia, bronchitis, and lung and heart problems. Short-term exposure to air pollution can also cause headaches, nausea, and dizziness.

These problems can be aggravated by extended long-term exposure to the pollutants, which is harmful to the neurological, reproductive, and respiratory systems and causes cancer and even, rarely, deaths.

The long-term effects are chronic, lasting for years or the whole life and can even lead to death. Furthermore, the toxicity of several air pollutants may also induce a variety of cancers in the long term ( 96 ).

As stated already, respiratory disorders are closely associated with the inhalation of air pollutants. These pollutants will invade through the airways and will accumulate at the cells. Damage to target cells should be related to the pollutant component involved and its source and dose. Health effects are also closely dependent on country, area, season, and time. An extended exposure duration to the pollutant should incline to long-term health effects in relation also to the above factors.

Particulate Matter (PMs), dust, benzene, and O 3 cause serious damage to the respiratory system ( 97 ). Moreover, there is a supplementary risk in case of existing respiratory disease such as asthma ( 98 ). Long-term effects are more frequent in people with a predisposing disease state. When the trachea is contaminated by pollutants, voice alterations may be remarked after acute exposure. Chronic obstructive pulmonary disease (COPD) may be induced following air pollution, increasing morbidity and mortality ( 99 ). Long-term effects from traffic, industrial air pollution, and combustion of fuels are the major factors for COPD risk ( 99 ).

Multiple cardiovascular effects have been observed after exposure to air pollutants ( 100 ). Changes occurred in blood cells after long-term exposure may affect cardiac functionality. Coronary arteriosclerosis was reported following long-term exposure to traffic emissions ( 101 ), while short-term exposure is related to hypertension, stroke, myocardial infracts, and heart insufficiency. Ventricle hypertrophy is reported to occur in humans after long-time exposure to nitrogen oxide (NO 2 ) ( 102 , 103 ).

Neurological effects have been observed in adults and children after extended-term exposure to air pollutants.

Psychological complications, autism, retinopathy, fetal growth, and low birth weight seem to be related to long-term air pollution ( 83 ). The etiologic agent of the neurodegenerative diseases (Alzheimer's and Parkinson's) is not yet known, although it is believed that extended exposure to air pollution seems to be a factor. Specifically, pesticides and metals are cited as etiological factors, together with diet. The mechanisms in the development of neurodegenerative disease include oxidative stress, protein aggregation, inflammation, and mitochondrial impairment in neurons ( 104 ) ( Figure 1 ).

Impact of air pollutants on the brain.

Brain inflammation was observed in dogs living in a highly polluted area in Mexico for a long period ( 105 ). In human adults, markers of systemic inflammation (IL-6 and fibrinogen) were found to be increased as an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins ( 106 ). The progression of atherosclerosis and oxidative stress seem to be the mechanisms involved in the neurological disturbances caused by long-term air pollution. Inflammation comes secondary to the oxidative stress and seems to be involved in the impairment of developmental maturation, affecting multiple organs ( 105 , 107 ). Similarly, other factors seem to be involved in the developmental maturation, which define the vulnerability to long-term air pollution. These include birthweight, maternal smoking, genetic background and socioeconomic environment, as well as education level.

However, diet, starting from breast-feeding, is another determinant factor. Diet is the main source of antioxidants, which play a key role in our protection against air pollutants ( 108 ). Antioxidants are free radical scavengers and limit the interaction of free radicals in the brain ( 108 ). Similarly, genetic background may result in a differential susceptibility toward the oxidative stress pathway ( 60 ). For example, antioxidant supplementation with vitamins C and E appears to modulate the effect of ozone in asthmatic children homozygous for the GSTM1 null allele ( 61 ). Inflammatory cytokines released in the periphery (e.g., respiratory epithelia) upregulate the innate immune Toll-like receptor 2. Such activation and the subsequent events leading to neurodegeneration have recently been observed in lung lavage in mice exposed to ambient Los Angeles (CA, USA) particulate matter ( 61 ). In children, neurodevelopmental morbidities were observed after lead exposure. These children developed aggressive and delinquent behavior, reduced intelligence, learning difficulties, and hyperactivity ( 109 ). No level of lead exposure seems to be “safe,” and the scientific community has asked the Centers for Disease Control and Prevention (CDC) to reduce the current screening guideline of 10 μg/dl ( 109 ).

It is important to state that impact on the immune system, causing dysfunction and neuroinflammation ( 104 ), is related to poor air quality. Yet, increases in serum levels of immunoglobulins (IgA, IgM) and the complement component C3 are observed ( 106 ). Another issue is that antigen presentation is affected by air pollutants, as there is an upregulation of costimulatory molecules such as CD80 and CD86 on macrophages ( 110 ).

As is known, skin is our shield against ultraviolet radiation (UVR) and other pollutants, as it is the most exterior layer of our body. Traffic-related pollutants, such as PAHs, VOCs, oxides, and PM, may cause pigmented spots on our skin ( 111 ). On the one hand, as already stated, when pollutants penetrate through the skin or are inhaled, damage to the organs is observed, as some of these pollutants are mutagenic and carcinogenic, and, specifically, they affect the liver and lung. On the other hand, air pollutants (and those in the troposphere) reduce the adverse effects of ultraviolet radiation UVR in polluted urban areas ( 111 ). Air pollutants absorbed by the human skin may contribute to skin aging, psoriasis, acne, urticaria, eczema, and atopic dermatitis ( 111 ), usually caused by exposure to oxides and photochemical smoke ( 111 ). Exposure to PM and cigarette smoking act as skin-aging agents, causing spots, dyschromia, and wrinkles. Lastly, pollutants have been associated with skin cancer ( 111 ).

Higher morbidity is reported to fetuses and children when exposed to the above dangers. Impairment in fetal growth, low birth weight, and autism have been reported ( 112 ).

Another exterior organ that may be affected is the eye. Contamination usually comes from suspended pollutants and may result in asymptomatic eye outcomes, irritation ( 112 ), retinopathy, or dry eye syndrome ( 113 , 114 ).

Environmental Impact of Air Pollution

Air pollution is harming not only human health but also the environment ( 115 ) in which we live. The most important environmental effects are as follows.

Acid rain is wet (rain, fog, snow) or dry (particulates and gas) precipitation containing toxic amounts of nitric and sulfuric acids. They are able to acidify the water and soil environments, damage trees and plantations, and even damage buildings and outdoor sculptures, constructions, and statues.

Haze is produced when fine particles are dispersed in the air and reduce the transparency of the atmosphere. It is caused by gas emissions in the air coming from industrial facilities, power plants, automobiles, and trucks.

Ozone , as discussed previously, occurs both at ground level and in the upper level (stratosphere) of the Earth's atmosphere. Stratospheric ozone is protecting us from the Sun's harmful ultraviolet (UV) rays. In contrast, ground-level ozone is harmful to human health and is a pollutant. Unfortunately, stratospheric ozone is gradually damaged by ozone-depleting substances (i.e., chemicals, pesticides, and aerosols). If this protecting stratospheric ozone layer is thinned, then UV radiation can reach our Earth, with harmful effects for human life (skin cancer) ( 116 ) and crops ( 117 ). In plants, ozone penetrates through the stomata, inducing them to close, which blocks CO 2 transfer and induces a reduction in photosynthesis ( 118 ).

Global climate change is an important issue that concerns mankind. As is known, the “greenhouse effect” keeps the Earth's temperature stable. Unhappily, anthropogenic activities have destroyed this protecting temperature effect by producing large amounts of greenhouse gases, and global warming is mounting, with harmful effects on human health, animals, forests, wildlife, agriculture, and the water environment. A report states that global warming is adding to the health risks of poor people ( 119 ).

People living in poorly constructed buildings in warm-climate countries are at high risk for heat-related health problems as temperatures mount ( 119 ).

Wildlife is burdened by toxic pollutants coming from the air, soil, or the water ecosystem and, in this way, animals can develop health problems when exposed to high levels of pollutants. Reproductive failure and birth effects have been reported.

Eutrophication is occurring when elevated concentrations of nutrients (especially nitrogen) stimulate the blooming of aquatic algae, which can cause a disequilibration in the diversity of fish and their deaths.

Without a doubt, there is a critical concentration of pollution that an ecosystem can tolerate without being destroyed, which is associated with the ecosystem's capacity to neutralize acidity. The Canada Acid Rain Program established this load at 20 kg/ha/yr ( 120 ).

Hence, air pollution has deleterious effects on both soil and water ( 121 ). Concerning PM as an air pollutant, its impact on crop yield and food productivity has been reported. Its impact on watery bodies is associated with the survival of living organisms and fishes and their productivity potential ( 121 ).

An impairment in photosynthetic rhythm and metabolism is observed in plants exposed to the effects of ozone ( 121 ).

Sulfur and nitrogen oxides are involved in the formation of acid rain and are harmful to plants and marine organisms.

Last but not least, as mentioned above, the toxicity associated with lead and other metals is the main threat to our ecosystems (air, water, and soil) and living creatures ( 121 ).

In 2018, during the first WHO Global Conference on Air Pollution and Health, the WHO's General Director, Dr. Tedros Adhanom Ghebreyesus, called air pollution a “silent public health emergency” and “the new tobacco” ( 122 ).

Undoubtedly, children are particularly vulnerable to air pollution, especially during their development. Air pollution has adverse effects on our lives in many different respects.

Diseases associated with air pollution have not only an important economic impact but also a societal impact due to absences from productive work and school.

Despite the difficulty of eradicating the problem of anthropogenic environmental pollution, a successful solution could be envisaged as a tight collaboration of authorities, bodies, and doctors to regularize the situation. Governments should spread sufficient information and educate people and should involve professionals in these issues so as to control the emergence of the problem successfully.

Technologies to reduce air pollution at the source must be established and should be used in all industries and power plants. The Kyoto Protocol of 1997 set as a major target the reduction of GHG emissions to below 5% by 2012 ( 123 ). This was followed by the Copenhagen summit, 2009 ( 124 ), and then the Durban summit of 2011 ( 125 ), where it was decided to keep to the same line of action. The Kyoto protocol and the subsequent ones were ratified by many countries. Among the pioneers who adopted this important protocol for the world's environmental and climate “health” was China ( 3 ). As is known, China is a fast-developing economy and its GDP (Gross Domestic Product) is expected to be very high by 2050, which is defined as the year of dissolution of the protocol for the decrease in gas emissions.

A more recent international agreement of crucial importance for climate change is the Paris Agreement of 2015, issued by the UNFCCC (United Nations Climate Change Committee). This latest agreement was ratified by a plethora of UN (United Nations) countries as well as the countries of the European Union ( 126 ). In this vein, parties should promote actions and measures to enhance numerous aspects around the subject. Boosting education, training, public awareness, and public participation are some of the relevant actions for maximizing the opportunities to achieve the targets and goals on the crucial matter of climate change and environmental pollution ( 126 ). Without any doubt, technological improvements makes our world easier and it seems difficult to reduce the harmful impact caused by gas emissions, we could limit its use by seeking reliable approaches.

Synopsizing, a global prevention policy should be designed in order to combat anthropogenic air pollution as a complement to the correct handling of the adverse health effects associated with air pollution. Sustainable development practices should be applied, together with information coming from research in order to handle the problem effectively.

At this point, international cooperation in terms of research, development, administration policy, monitoring, and politics is vital for effective pollution control. Legislation concerning air pollution must be aligned and updated, and policy makers should propose the design of a powerful tool of environmental and health protection. As a result, the main proposal of this essay is that we should focus on fostering local structures to promote experience and practice and extrapolate these to the international level through developing effective policies for sustainable management of ecosystems.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

IM is employed by the company Delphis S.A. The remaining authors declare that the present review paper was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

REVIEW article

Environmental and health impacts of air pollution: a review.

• 1 Delphis S.A., Kifisia, Greece
• 2 Laboratory of Hygiene and Environmental Protection, Faculty of Medicine, Democritus University of Thrace, Alexandroupolis, Greece
• 3 Centre Hospitalier Universitaire Vaudois (CHUV), Service de Médicine Interne, Lausanne, Switzerland
• 4 School of Social and Political Sciences, University of Glasgow, Glasgow, United Kingdom

One of our era's greatest scourges is air pollution, on account not only of its impact on climate change but also its impact on public and individual health due to increasing morbidity and mortality. There are many pollutants that are major factors in disease in humans. Among them, Particulate Matter (PM), particles of variable but very small diameter, penetrate the respiratory system via inhalation, causing respiratory and cardiovascular diseases, reproductive and central nervous system dysfunctions, and cancer. Despite the fact that ozone in the stratosphere plays a protective role against ultraviolet irradiation, it is harmful when in high concentration at ground level, also affecting the respiratory and cardiovascular system. Furthermore, nitrogen oxide, sulfur dioxide, Volatile Organic Compounds (VOCs), dioxins, and polycyclic aromatic hydrocarbons (PAHs) are all considered air pollutants that are harmful to humans. Carbon monoxide can even provoke direct poisoning when breathed in at high levels. Heavy metals such as lead, when absorbed into the human body, can lead to direct poisoning or chronic intoxication, depending on exposure. Diseases occurring from the aforementioned substances include principally respiratory problems such as Chronic Obstructive Pulmonary Disease (COPD), asthma, bronchiolitis, and also lung cancer, cardiovascular events, central nervous system dysfunctions, and cutaneous diseases. Last but not least, climate change resulting from environmental pollution affects the geographical distribution of many infectious diseases, as do natural disasters. The only way to tackle this problem is through public awareness coupled with a multidisciplinary approach by scientific experts; national and international organizations must address the emergence of this threat and propose sustainable solutions.

Approach to the Problem

The interactions between humans and their physical surroundings have been extensively studied, as multiple human activities influence the environment. The environment is a coupling of the biotic (living organisms and microorganisms) and the abiotic (hydrosphere, lithosphere, and atmosphere).

Pollution is defined as the introduction into the environment of substances harmful to humans and other living organisms. Pollutants are harmful solids, liquids, or gases produced in higher than usual concentrations that reduce the quality of our environment.

Human activities have an adverse effect on the environment by polluting the water we drink, the air we breathe, and the soil in which plants grow. Although the industrial revolution was a great success in terms of technology, society, and the provision of multiple services, it also introduced the production of huge quantities of pollutants emitted into the air that are harmful to human health. Without any doubt, the global environmental pollution is considered an international public health issue with multiple facets. Social, economic, and legislative concerns and lifestyle habits are related to this major problem. Clearly, urbanization and industrialization are reaching unprecedented and upsetting proportions worldwide in our era. Anthropogenic air pollution is one of the biggest public health hazards worldwide, given that it accounts for about 9 million deaths per year ( 1 ).

Without a doubt, all of the aforementioned are closely associated with climate change, and in the event of danger, the consequences can be severe for mankind ( 2 ). Climate changes and the effects of global planetary warming seriously affect multiple ecosystems, causing problems such as food safety issues, ice and iceberg melting, animal extinction, and damage to plants ( 3 , 4 ).

Air pollution has various health effects. The health of susceptible and sensitive individuals can be impacted even on low air pollution days. Short-term exposure to air pollutants is closely related to COPD (Chronic Obstructive Pulmonary Disease), cough, shortness of breath, wheezing, asthma, respiratory disease, and high rates of hospitalization (a measurement of morbidity).

The long-term effects associated with air pollution are chronic asthma, pulmonary insufficiency, cardiovascular diseases, and cardiovascular mortality. According to a Swedish cohort study, diabetes seems to be induced after long-term air pollution exposure ( 5 ). Moreover, air pollution seems to have various malign health effects in early human life, such as respiratory, cardiovascular, mental, and perinatal disorders ( 3 ), leading to infant mortality or chronic disease in adult age ( 6 ).

National reports have mentioned the increased risk of morbidity and mortality ( 1 ). These studies were conducted in many places around the world and show a correlation between daily ranges of particulate matter (PM) concentration and daily mortality. Climate shifts and global planetary warming ( 3 ) could aggravate the situation. Besides, increased hospitalization (an index of morbidity) has been registered among the elderly and susceptible individuals for specific reasons. Fine and ultrafine particulate matter seems to be associated with more serious illnesses ( 6 ), as it can invade the deepest parts of the airways and more easily reach the bloodstream.

Air pollution mainly affects those living in large urban areas, where road emissions contribute the most to the degradation of air quality. There is also a danger of industrial accidents, where the spread of a toxic fog can be fatal to the populations of the surrounding areas. The dispersion of pollutants is determined by many parameters, most notably atmospheric stability and wind ( 6 ).

In developing countries ( 7 ), the problem is more serious due to overpopulation and uncontrolled urbanization along with the development of industrialization. This leads to poor air quality, especially in countries with social disparities and a lack of information on sustainable management of the environment. The use of fuels such as wood fuel or solid fuel for domestic needs due to low incomes exposes people to bad-quality, polluted air at home. It is of note that three billion people around the world are using the above sources of energy for their daily heating and cooking needs ( 8 ). In developing countries, the women of the household seem to carry the highest risk for disease development due to their longer duration exposure to the indoor air pollution ( 8 , 9 ). Due to its fast industrial development and overpopulation, China is one of the Asian countries confronting serious air pollution problems ( 10 , 11 ). The lung cancer mortality observed in China is associated with fine particles ( 12 ). As stated already, long-term exposure is associated with deleterious effects on the cardiovascular system ( 3 , 5 ). However, it is interesting to note that cardiovascular diseases have mostly been observed in developed and high-income countries rather than in the developing low-income countries exposed highly to air pollution ( 13 ). Extreme air pollution is recorded in India, where the air quality reaches hazardous levels. New Delhi is one of the more polluted cities in India. Flights in and out of New Delhi International Airport are often canceled due to the reduced visibility associated with air pollution. Pollution is occurring both in urban and rural areas in India due to the fast industrialization, urbanization, and rise in use of motorcycle transportation. Nevertheless, biomass combustion associated with heating and cooking needs and practices is a major source of household air pollution in India and in Nepal ( 14 , 15 ). There is spatial heterogeneity in India, as areas with diverse climatological conditions and population and education levels generate different indoor air qualities, with higher PM 2.5 observed in North Indian states (557–601 μg/m 3 ) compared to the Southern States (183–214 μg/m 3 ) ( 16 , 17 ). The cold climate of the North Indian areas may be the main reason for this, as longer periods at home and more heating are necessary compared to in the tropical climate of Southern India. Household air pollution in India is associated with major health effects, especially in women and young children, who stay indoors for longer periods. Chronic obstructive respiratory disease (CORD) and lung cancer are mostly observed in women, while acute lower respiratory disease is seen in young children under 5 years of age ( 18 ).

Accumulation of air pollution, especially sulfur dioxide and smoke, reaching 1,500 mg/m3, resulted in an increase in the number of deaths (4,000 deaths) in December 1952 in London and in 1963 in New York City (400 deaths) ( 19 ). An association of pollution with mortality was reported on the basis of monitoring of outdoor pollution in six US metropolitan cities ( 20 ). In every case, it seems that mortality was closely related to the levels of fine, inhalable, and sulfate particles more than with the levels of total particulate pollution, aerosol acidity, sulfur dioxide, or nitrogen dioxide ( 20 ).

Furthermore, extremely high levels of pollution are reported in Mexico City and Rio de Janeiro, followed by Milan, Ankara, Melbourne, Tokyo, and Moscow ( 19 ).

Based on the magnitude of the public health impact, it is certain that different kinds of interventions should be taken into account. Success and effectiveness in controlling air pollution, specifically at the local level, have been reported. Adequate technological means are applied considering the source and the nature of the emission as well as its impact on health and the environment. The importance of point sources and non-point sources of air pollution control is reported by Schwela and Köth-Jahr ( 21 ). Without a doubt, a detailed emission inventory must record all sources in a given area. Beyond considering the above sources and their nature, topography and meteorology should also be considered, as stated previously. Assessment of the control policies and methods is often extrapolated from the local to the regional and then to the global scale. Air pollution may be dispersed and transported from one region to another area located far away. Air pollution management means the reduction to acceptable levels or possible elimination of air pollutants whose presence in the air affects our health or the environmental ecosystem. Private and governmental entities and authorities implement actions to ensure the air quality ( 22 ). Air quality standards and guidelines were adopted for the different pollutants by the WHO and EPA as a tool for the management of air quality ( 1 , 23 ). These standards have to be compared to the emissions inventory standards by causal analysis and dispersion modeling in order to reveal the problematic areas ( 24 ). Inventories are generally based on a combination of direct measurements and emissions modeling ( 24 ).

As an example, we state here the control measures at the source through the use of catalytic converters in cars. These are devices that turn the pollutants and toxic gases produced from combustion engines into less-toxic pollutants by catalysis through redox reactions ( 25 ). In Greece, the use of private cars was restricted by tracking their license plates in order to reduce traffic congestion during rush hour ( 25 ).

Concerning industrial emissions, collectors and closed systems can keep the air pollution to the minimal standards imposed by legislation ( 26 ).

Current strategies to improve air quality require an estimation of the economic value of the benefits gained from proposed programs. These proposed programs by public authorities, and directives are issued with guidelines to be respected.

In Europe, air quality limit values AQLVs (Air Quality Limit Values) are issued for setting off planning claims ( 27 ). In the USA, the NAAQS (National Ambient Air Quality Standards) establish the national air quality limit values ( 27 ). While both standards and directives are based on different mechanisms, significant success has been achieved in the reduction of overall emissions and associated health and environmental effects ( 27 ). The European Directive identifies geographical areas of risk exposure as monitoring/assessment zones to record the emission sources and levels of air pollution ( 27 ), whereas the USA establishes global geographical air quality criteria according to the severity of their air quality problem and records all sources of the pollutants and their precursors ( 27 ).

In this vein, funds have been financing, directly or indirectly, projects related to air quality along with the technical infrastructure to maintain good air quality. These plans focus on an inventory of databases from air quality environmental planning awareness campaigns. Moreover, pollution measures of air emissions may be taken for vehicles, machines, and industries in urban areas.

Technological innovation can only be successful if it is able to meet the needs of society. In this sense, technology must reflect the decision-making practices and procedures of those involved in risk assessment and evaluation and act as a facilitator in providing information and assessments to enable decision makers to make the best decisions possible. Summarizing the aforementioned in order to design an effective air quality control strategy, several aspects must be considered: environmental factors and ambient air quality conditions, engineering factors and air pollutant characteristics, and finally, economic operating costs for technological improvement and administrative and legal costs. Considering the economic factor, competitiveness through neoliberal concepts is offering a solution to environmental problems ( 22 ).

The development of environmental governance, along with technological progress, has initiated the deployment of a dialogue. Environmental politics has created objections and points of opposition between different political parties, scientists, media, and governmental and non-governmental organizations ( 22 ). Radical environmental activism actions and movements have been created ( 22 ). The rise of the new information and communication technologies (ICTs) are many times examined as to whether and in which way they have influenced means of communication and social movements such as activism ( 28 ). Since the 1990s, the term “digital activism” has been used increasingly and in many different disciplines ( 29 ). Nowadays, multiple digital technologies can be used to produce a digital activism outcome on environmental issues. More specifically, devices with online capabilities such as computers or mobile phones are being used as a way to pursue change in political and social affairs ( 30 ).

In the present paper, we focus on the sources of environmental pollution in relation to public health and propose some solutions and interventions that may be of interest to environmental legislators and decision makers.

Sources of Exposure

It is known that the majority of environmental pollutants are emitted through large-scale human activities such as the use of industrial machinery, power-producing stations, combustion engines, and cars. Because these activities are performed at such a large scale, they are by far the major contributors to air pollution, with cars estimated to be responsible for approximately 80% of today's pollution ( 31 ). Some other human activities are also influencing our environment to a lesser extent, such as field cultivation techniques, gas stations, fuel tanks heaters, and cleaning procedures ( 32 ), as well as several natural sources, such as volcanic and soil eruptions and forest fires.

The classification of air pollutants is based mainly on the sources producing pollution. Therefore, it is worth mentioning the four main sources, following the classification system: Major sources, Area sources, Mobile sources, and Natural sources.

Major sources include the emission of pollutants from power stations, refineries, and petrochemicals, the chemical and fertilizer industries, metallurgical and other industrial plants, and, finally, municipal incineration.

Indoor area sources include domestic cleaning activities, dry cleaners, printing shops, and petrol stations.

Mobile sources include automobiles, cars, railways, airways, and other types of vehicles.

Finally, natural sources include, as stated previously, physical disasters ( 33 ) such as forest fire, volcanic erosion, dust storms, and agricultural burning.

However, many classification systems have been proposed. Another type of classification is a grouping according to the recipient of the pollution, as follows:

Air pollution is determined as the presence of pollutants in the air in large quantities for long periods. Air pollutants are dispersed particles, hydrocarbons, CO, CO 2 , NO, NO 2 , SO 3 , etc.

Water pollution is organic and inorganic charge and biological charge ( 10 ) at high levels that affect the water quality ( 34 , 35 ).

Soil pollution occurs through the release of chemicals or the disposal of wastes, such as heavy metals, hydrocarbons, and pesticides.

Air pollution can influence the quality of soil and water bodies by polluting precipitation, falling into water and soil environments ( 34 , 36 ). Notably, the chemistry of the soil can be amended due to acid precipitation by affecting plants, cultures, and water quality ( 37 ). Moreover, movement of heavy metals is favored by soil acidity, and metals are so then moving into the watery environment. It is known that heavy metals such as aluminum are noxious to wildlife and fishes. Soil quality seems to be of importance, as soils with low calcium carbonate levels are at increased jeopardy from acid rain. Over and above rain, snow and particulate matter drip into watery ' bodies ( 36 , 38 ).

Lastly, pollution is classified following type of origin:

Radioactive and nuclear pollution , releasing radioactive and nuclear pollutants into water, air, and soil during nuclear explosions and accidents, from nuclear weapons, and through handling or disposal of radioactive sewage.

Radioactive materials can contaminate surface water bodies and, being noxious to the environment, plants, animals, and humans. It is known that several radioactive substances such as radium and uranium concentrate in the bones and can cause cancers ( 38 , 39 ).

Noise pollution is produced by machines, vehicles, traffic noises, and musical installations that are harmful to our hearing.

The World Health Organization introduced the term DALYs. The DALYs for a disease or health condition is defined as the sum of the Years of Life Lost (YLL) due to premature mortality in the population and the Years Lost due to Disability (YLD) for people living with the health condition or its consequences ( 39 ). In Europe, air pollution is the main cause of disability-adjusted life years lost (DALYs), followed by noise pollution. The potential relationships of noise and air pollution with health have been studied ( 40 ). The study found that DALYs related to noise were more important than those related to air pollution, as the effects of environmental noise on cardiovascular disease were independent of air pollution ( 40 ). Environmental noise should be counted as an independent public health risk ( 40 ).

Environmental pollution occurs when changes in the physical, chemical, or biological constituents of the environment (air masses, temperature, climate, etc.) are produced.

Pollutants harm our environment either by increasing levels above normal or by introducing harmful toxic substances. Primary pollutants are directly produced from the above sources, and secondary pollutants are emitted as by-products of the primary ones. Pollutants can be biodegradable or non-biodegradable and of natural origin or anthropogenic, as stated previously. Moreover, their origin can be a unique source (point-source) or dispersed sources.

Pollutants have differences in physical and chemical properties, explaining the discrepancy in their capacity for producing toxic effects. As an example, we state here that aerosol compounds ( 41 – 43 ) have a greater toxicity than gaseous compounds due to their tiny size (solid or liquid) in the atmosphere; they have a greater penetration capacity. Gaseous compounds are eliminated more easily by our respiratory system ( 41 ). These particles are able to damage lungs and can even enter the bloodstream ( 41 ), leading to the premature deaths of millions of people yearly. Moreover, the aerosol acidity ([H+]) seems to considerably enhance the production of secondary organic aerosols (SOA), but this last aspect is not supported by other scientific teams ( 38 ).

Climate and Pollution

Air pollution and climate change are closely related. Climate is the other side of the same coin that reduces the quality of our Earth ( 44 ). Pollutants such as black carbon, methane, tropospheric ozone, and aerosols affect the amount of incoming sunlight. As a result, the temperature of the Earth is increasing, resulting in the melting of ice, icebergs, and glaciers.

In this vein, climatic changes will affect the incidence and prevalence of both residual and imported infections in Europe. Climate and weather affect the duration, timing, and intensity of outbreaks strongly and change the map of infectious diseases in the globe ( 45 ). Mosquito-transmitted parasitic or viral diseases are extremely climate-sensitive, as warming firstly shortens the pathogen incubation period and secondly shifts the geographic map of the vector. Similarly, water-warming following climate changes leads to a high incidence of waterborne infections. Recently, in Europe, eradicated diseases seem to be emerging due to the migration of population, for example, cholera, poliomyelitis, tick-borne encephalitis, and malaria ( 46 ).

The spread of epidemics is associated with natural climate disasters and storms, which seem to occur more frequently nowadays ( 47 ). Malnutrition and disequilibration of the immune system are also associated with the emerging infections affecting public health ( 48 ).

The Chikungunya virus “took the airplane” from the Indian Ocean to Europe, as outbreaks of the disease were registered in Italy ( 49 ) as well as autochthonous cases in France ( 50 ).

An increase in cryptosporidiosis in the United Kingdom and in the Czech Republic seems to have occurred following flooding ( 36 , 51 ).

As stated previously, aerosols compounds are tiny in size and considerably affect the climate. They are able to dissipate sunlight (the albedo phenomenon) by dispersing a quarter of the sun's rays back to space and have cooled the global temperature over the last 30 years ( 52 ).

Air Pollutants

The World Health Organization (WHO) reports on six major air pollutants, namely particle pollution, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Air pollution can have a disastrous effect on all components of the environment, including groundwater, soil, and air. Additionally, it poses a serious threat to living organisms. In this vein, our interest is mainly to focus on these pollutants, as they are related to more extensive and severe problems in human health and environmental impact. Acid rain, global warming, the greenhouse effect, and climate changes have an important ecological impact on air pollution ( 53 ).

Particulate Matter (PM) and Health

Studies have shown a relationship between particulate matter (PM) and adverse health effects, focusing on either short-term (acute) or long-term (chronic) PM exposure.

Particulate matter (PM) is usually formed in the atmosphere as a result of chemical reactions between the different pollutants. The penetration of particles is closely dependent on their size ( 53 ). Particulate Matter (PM) was defined as a term for particles by the United States Environmental Protection Agency ( 54 ). Particulate matter (PM) pollution includes particles with diameters of 10 micrometers (μm) or smaller, called PM 10 , and extremely fine particles with diameters that are generally 2.5 micrometers (μm) and smaller.

Particulate matter contains tiny liquid or solid droplets that can be inhaled and cause serious health effects ( 55 ). Particles <10 μm in diameter (PM 10 ) after inhalation can invade the lungs and even reach the bloodstream. Fine particles, PM 2.5 , pose a greater risk to health ( 6 , 56 ) ( Table 1 ).

Table 1 . Penetrability according to particle size.

Multiple epidemiological studies have been performed on the health effects of PM. A positive relation was shown between both short-term and long-term exposures of PM 2.5 and acute nasopharyngitis ( 56 ). In addition, long-term exposure to PM for years was found to be related to cardiovascular diseases and infant mortality.

Those studies depend on PM 2.5 monitors and are restricted in terms of study area or city area due to a lack of spatially resolved daily PM 2.5 concentration data and, in this way, are not representative of the entire population. Following a recent epidemiological study by the Department of Environmental Health at Harvard School of Public Health (Boston, MA) ( 57 ), it was reported that, as PM 2.5 concentrations vary spatially, an exposure error (Berkson error) seems to be produced, and the relative magnitudes of the short- and long-term effects are not yet completely elucidated. The team developed a PM 2.5 exposure model based on remote sensing data for assessing short- and long-term human exposures ( 57 ). This model permits spatial resolution in short-term effects plus the assessment of long-term effects in the whole population.

Moreover, respiratory diseases and affection of the immune system are registered as long-term chronic effects ( 58 ). It is worth noting that people with asthma, pneumonia, diabetes, and respiratory and cardiovascular diseases are especially susceptible and vulnerable to the effects of PM. PM 2.5 , followed by PM 10 , are strongly associated with diverse respiratory system diseases ( 59 ), as their size permits them to pierce interior spaces ( 60 ). The particles produce toxic effects according to their chemical and physical properties. The components of PM 10 and PM 2.5 can be organic (polycyclic aromatic hydrocarbons, dioxins, benzene, 1-3 butadiene) or inorganic (carbon, chlorides, nitrates, sulfates, metals) in nature ( 55 ).

Particulate Matter (PM) is divided into four main categories according to type and size ( 61 ) ( Table 2 ).

Table 2 . Types and sizes of particulate Matter (PM).

Gas contaminants include PM in aerial masses.

Particulate contaminants include contaminants such as smog, soot, tobacco smoke, oil smoke, fly ash, and cement dust.

Biological Contaminants are microorganisms (bacteria, viruses, fungi, mold, and bacterial spores), cat allergens, house dust and allergens, and pollen.

Types of Dust include suspended atmospheric dust, settling dust, and heavy dust.

Finally, another fact is that the half-lives of PM 10 and PM 2.5 particles in the atmosphere is extended due to their tiny dimensions; this permits their long-lasting suspension in the atmosphere and even their transfer and spread to distant destinations where people and the environment may be exposed to the same magnitude of pollution ( 53 ). They are able to change the nutrient balance in watery ecosystems, damage forests and crops, and acidify water bodies.

As stated, PM 2.5 , due to their tiny size, are causing more serious health effects. These aforementioned fine particles are the main cause of the “haze” formation in different metropolitan areas ( 12 , 13 , 61 ).

Ozone Impact in the Atmosphere

Ozone (O 3 ) is a gas formed from oxygen under high voltage electric discharge ( 62 ). It is a strong oxidant, 52% stronger than chlorine. It arises in the stratosphere, but it could also arise following chain reactions of photochemical smog in the troposphere ( 63 ).

Ozone can travel to distant areas from its initial source, moving with air masses ( 64 ). It is surprising that ozone levels over cities are low in contrast to the increased amounts occuring in urban areas, which could become harmful for cultures, forests, and vegetation ( 65 ) as it is reducing carbon assimilation ( 66 ). Ozone reduces growth and yield ( 47 , 48 ) and affects the plant microflora due to its antimicrobial capacity ( 67 , 68 ). In this regard, ozone acts upon other natural ecosystems, with microflora ( 69 , 70 ) and animal species changing their species composition ( 71 ). Ozone increases DNA damage in epidermal keratinocytes and leads to impaired cellular function ( 72 ).

Ground-level ozone (GLO) is generated through a chemical reaction between oxides of nitrogen and VOCs emitted from natural sources and/or following anthropogenic activities.

Ozone uptake usually occurs by inhalation. Ozone affects the upper layers of the skin and the tear ducts ( 73 ). A study of short-term exposure of mice to high levels of ozone showed malondialdehyde formation in the upper skin (epidermis) but also depletion in vitamins C and E. It is likely that ozone levels are not interfering with the skin barrier function and integrity to predispose to skin disease ( 74 ).

Due to the low water-solubility of ozone, inhaled ozone has the capacity to penetrate deeply into the lungs ( 75 ).

Toxic effects induced by ozone are registered in urban areas all over the world, causing biochemical, morphologic, functional, and immunological disorders ( 76 ).

The European project (APHEA2) focuses on the acute effects of ambient ozone concentrations on mortality ( 77 ). Daily ozone concentrations compared to the daily number of deaths were reported from different European cities for a 3-year period. During the warm period of the year, an observed increase in ozone concentration was associated with an increase in the daily number of deaths (0.33%), in the number of respiratory deaths (1.13%), and in the number of cardiovascular deaths (0.45%). No effect was observed during wintertime.

Carbon Monoxide (CO)

Carbon monoxide is produced by fossil fuel when combustion is incomplete. The symptoms of poisoning due to inhaling carbon monoxide include headache, dizziness, weakness, nausea, vomiting, and, finally, loss of consciousness.

The affinity of carbon monoxide to hemoglobin is much greater than that of oxygen. In this vein, serious poisoning may occur in people exposed to high levels of carbon monoxide for a long period of time. Due to the loss of oxygen as a result of the competitive binding of carbon monoxide, hypoxia, ischemia, and cardiovascular disease are observed.

Carbon monoxide affects the greenhouses gases that are tightly connected to global warming and climate. This should lead to an increase in soil and water temperatures, and extreme weather conditions or storms may occur ( 68 ).

However, in laboratory and field experiments, it has been seen to produce increased plant growth ( 78 ).

Nitrogen Oxide (NO 2 )

Nitrogen oxide is a traffic-related pollutant, as it is emitted from automobile motor engines ( 79 , 80 ). It is an irritant of the respiratory system as it penetrates deep in the lung, inducing respiratory diseases, coughing, wheezing, dyspnea, bronchospasm, and even pulmonary edema when inhaled at high levels. It seems that concentrations over 0.2 ppm produce these adverse effects in humans, while concentrations higher than 2.0 ppm affect T-lymphocytes, particularly the CD8+ cells and NK cells that produce our immune response ( 81 ).It is reported that long-term exposure to high levels of nitrogen dioxide can be responsible for chronic lung disease. Long-term exposure to NO 2 can impair the sense of smell ( 81 ).

However, systems other than respiratory ones can be involved, as symptoms such as eye, throat, and nose irritation have been registered ( 81 ).

High levels of nitrogen dioxide are deleterious to crops and vegetation, as they have been observed to reduce crop yield and plant growth efficiency. Moreover, NO 2 can reduce visibility and discolor fabrics ( 81 ).

Sulfur Dioxide (SO 2 )

Sulfur dioxide is a harmful gas that is emitted mainly from fossil fuel consumption or industrial activities. The annual standard for SO 2 is 0.03 ppm ( 82 ). It affects human, animal, and plant life. Susceptible people as those with lung disease, old people, and children, who present a higher risk of damage. The major health problems associated with sulfur dioxide emissions in industrialized areas are respiratory irritation, bronchitis, mucus production, and bronchospasm, as it is a sensory irritant and penetrates deep into the lung converted into bisulfite and interacting with sensory receptors, causing bronchoconstriction. Moreover, skin redness, damage to the eyes (lacrimation and corneal opacity) and mucous membranes, and worsening of pre-existing cardiovascular disease have been observed ( 81 ).

Environmental adverse effects, such as acidification of soil and acid rain, seem to be associated with sulfur dioxide emissions ( 83 ).

Lead is a heavy metal used in different industrial plants and emitted from some petrol motor engines, batteries, radiators, waste incinerators, and waste waters ( 84 ).

Moreover, major sources of lead pollution in the air are metals, ore, and piston-engine aircraft. Lead poisoning is a threat to public health due to its deleterious effects upon humans, animals, and the environment, especially in the developing countries.

Exposure to lead can occur through inhalation, ingestion, and dermal absorption. Trans- placental transport of lead was also reported, as lead passes through the placenta unencumbered ( 85 ). The younger the fetus is, the more harmful the toxic effects. Lead toxicity affects the fetal nervous system; edema or swelling of the brain is observed ( 86 ). Lead, when inhaled, accumulates in the blood, soft tissue, liver, lung, bones, and cardiovascular, nervous, and reproductive systems. Moreover, loss of concentration and memory, as well as muscle and joint pain, were observed in adults ( 85 , 86 ).

Children and newborns ( 87 ) are extremely susceptible even to minimal doses of lead, as it is a neurotoxicant and causes learning disabilities, impairment of memory, hyperactivity, and even mental retardation.

Elevated amounts of lead in the environment are harmful to plants and crop growth. Neurological effects are observed in vertebrates and animals in association with high lead levels ( 88 ).

Polycyclic Aromatic Hydrocarbons(PAHs)

The distribution of PAHs is ubiquitous in the environment, as the atmosphere is the most important means of their dispersal. They are found in coal and in tar sediments. Moreover, they are generated through incomplete combustion of organic matter as in the cases of forest fires, incineration, and engines ( 89 ). PAH compounds, such as benzopyrene, acenaphthylene, anthracene, and fluoranthene are recognized as toxic, mutagenic, and carcinogenic substances. They are an important risk factor for lung cancer ( 89 ).

Volatile Organic Compounds(VOCs)

Volatile organic compounds (VOCs), such as toluene, benzene, ethylbenzene, and xylene ( 90 ), have been found to be associated with cancer in humans ( 91 ). The use of new products and materials has actually resulted in increased concentrations of VOCs. VOCs pollute indoor air ( 90 ) and may have adverse effects on human health ( 91 ). Short-term and long-term adverse effects on human health are observed. VOCs are responsible for indoor air smells. Short-term exposure is found to cause irritation of eyes, nose, throat, and mucosal membranes, while those of long duration exposure include toxic reactions ( 92 ). Predictable assessment of the toxic effects of complex VOC mixtures is difficult to estimate, as these pollutants can have synergic, antagonistic, or indifferent effects ( 91 , 93 ).

Dioxins originate from industrial processes but also come from natural processes, such as forest fires and volcanic eruptions. They accumulate in foods such as meat and dairy products, fish and shellfish, and especially in the fatty tissue of animals ( 94 ).

Short-period exhibition to high dioxin concentrations may result in dark spots and lesions on the skin ( 94 ). Long-term exposure to dioxins can cause developmental problems, impairment of the immune, endocrine and nervous systems, reproductive infertility, and cancer ( 94 ).

Without any doubt, fossil fuel consumption is responsible for a sizeable part of air contamination. This contamination may be anthropogenic, as in agricultural and industrial processes or transportation, while contamination from natural sources is also possible. Interestingly, it is of note that the air quality standards established through the European Air Quality Directive are somewhat looser than the WHO guidelines, which are stricter ( 95 ).

Effect of Air Pollution on Health

The most common air pollutants are ground-level ozone and Particulates Matter (PM). Air pollution is distinguished into two main types:

Outdoor pollution is the ambient air pollution.

Indoor pollution is the pollution generated by household combustion of fuels.

People exposed to high concentrations of air pollutants experience disease symptoms and states of greater and lesser seriousness. These effects are grouped into short- and long-term effects affecting health.

Susceptible populations that need to be aware of health protection measures include old people, children, and people with diabetes and predisposing heart or lung disease, especially asthma.

As extensively stated previously, according to a recent epidemiological study from Harvard School of Public Health, the relative magnitudes of the short- and long-term effects have not been completely clarified ( 57 ) due to the different epidemiological methodologies and to the exposure errors. New models are proposed for assessing short- and long-term human exposure data more successfully ( 57 ). Thus, in the present section, we report the more common short- and long-term health effects but also general concerns for both types of effects, as these effects are often dependent on environmental conditions, dose, and individual susceptibility.

Short-term effects are temporary and range from simple discomfort, such as irritation of the eyes, nose, skin, throat, wheezing, coughing and chest tightness, and breathing difficulties, to more serious states, such as asthma, pneumonia, bronchitis, and lung and heart problems. Short-term exposure to air pollution can also cause headaches, nausea, and dizziness.

These problems can be aggravated by extended long-term exposure to the pollutants, which is harmful to the neurological, reproductive, and respiratory systems and causes cancer and even, rarely, deaths.

The long-term effects are chronic, lasting for years or the whole life and can even lead to death. Furthermore, the toxicity of several air pollutants may also induce a variety of cancers in the long term ( 96 ).

As stated already, respiratory disorders are closely associated with the inhalation of air pollutants. These pollutants will invade through the airways and will accumulate at the cells. Damage to target cells should be related to the pollutant component involved and its source and dose. Health effects are also closely dependent on country, area, season, and time. An extended exposure duration to the pollutant should incline to long-term health effects in relation also to the above factors.

Particulate Matter (PMs), dust, benzene, and O 3 cause serious damage to the respiratory system ( 97 ). Moreover, there is a supplementary risk in case of existing respiratory disease such as asthma ( 98 ). Long-term effects are more frequent in people with a predisposing disease state. When the trachea is contaminated by pollutants, voice alterations may be remarked after acute exposure. Chronic obstructive pulmonary disease (COPD) may be induced following air pollution, increasing morbidity and mortality ( 99 ). Long-term effects from traffic, industrial air pollution, and combustion of fuels are the major factors for COPD risk ( 99 ).

Multiple cardiovascular effects have been observed after exposure to air pollutants ( 100 ). Changes occurred in blood cells after long-term exposure may affect cardiac functionality. Coronary arteriosclerosis was reported following long-term exposure to traffic emissions ( 101 ), while short-term exposure is related to hypertension, stroke, myocardial infracts, and heart insufficiency. Ventricle hypertrophy is reported to occur in humans after long-time exposure to nitrogen oxide (NO 2 ) ( 102 , 103 ).

Neurological effects have been observed in adults and children after extended-term exposure to air pollutants.

Psychological complications, autism, retinopathy, fetal growth, and low birth weight seem to be related to long-term air pollution ( 83 ). The etiologic agent of the neurodegenerative diseases (Alzheimer's and Parkinson's) is not yet known, although it is believed that extended exposure to air pollution seems to be a factor. Specifically, pesticides and metals are cited as etiological factors, together with diet. The mechanisms in the development of neurodegenerative disease include oxidative stress, protein aggregation, inflammation, and mitochondrial impairment in neurons ( 104 ) ( Figure 1 ).

Figure 1 . Impact of air pollutants on the brain.

Brain inflammation was observed in dogs living in a highly polluted area in Mexico for a long period ( 105 ). In human adults, markers of systemic inflammation (IL-6 and fibrinogen) were found to be increased as an immediate response to PNC on the IL-6 level, possibly leading to the production of acute-phase proteins ( 106 ). The progression of atherosclerosis and oxidative stress seem to be the mechanisms involved in the neurological disturbances caused by long-term air pollution. Inflammation comes secondary to the oxidative stress and seems to be involved in the impairment of developmental maturation, affecting multiple organs ( 105 , 107 ). Similarly, other factors seem to be involved in the developmental maturation, which define the vulnerability to long-term air pollution. These include birthweight, maternal smoking, genetic background and socioeconomic environment, as well as education level.

However, diet, starting from breast-feeding, is another determinant factor. Diet is the main source of antioxidants, which play a key role in our protection against air pollutants ( 108 ). Antioxidants are free radical scavengers and limit the interaction of free radicals in the brain ( 108 ). Similarly, genetic background may result in a differential susceptibility toward the oxidative stress pathway ( 60 ). For example, antioxidant supplementation with vitamins C and E appears to modulate the effect of ozone in asthmatic children homozygous for the GSTM1 null allele ( 61 ). Inflammatory cytokines released in the periphery (e.g., respiratory epithelia) upregulate the innate immune Toll-like receptor 2. Such activation and the subsequent events leading to neurodegeneration have recently been observed in lung lavage in mice exposed to ambient Los Angeles (CA, USA) particulate matter ( 61 ). In children, neurodevelopmental morbidities were observed after lead exposure. These children developed aggressive and delinquent behavior, reduced intelligence, learning difficulties, and hyperactivity ( 109 ). No level of lead exposure seems to be “safe,” and the scientific community has asked the Centers for Disease Control and Prevention (CDC) to reduce the current screening guideline of 10 μg/dl ( 109 ).

It is important to state that impact on the immune system, causing dysfunction and neuroinflammation ( 104 ), is related to poor air quality. Yet, increases in serum levels of immunoglobulins (IgA, IgM) and the complement component C3 are observed ( 106 ). Another issue is that antigen presentation is affected by air pollutants, as there is an upregulation of costimulatory molecules such as CD80 and CD86 on macrophages ( 110 ).

As is known, skin is our shield against ultraviolet radiation (UVR) and other pollutants, as it is the most exterior layer of our body. Traffic-related pollutants, such as PAHs, VOCs, oxides, and PM, may cause pigmented spots on our skin ( 111 ). On the one hand, as already stated, when pollutants penetrate through the skin or are inhaled, damage to the organs is observed, as some of these pollutants are mutagenic and carcinogenic, and, specifically, they affect the liver and lung. On the other hand, air pollutants (and those in the troposphere) reduce the adverse effects of ultraviolet radiation UVR in polluted urban areas ( 111 ). Air pollutants absorbed by the human skin may contribute to skin aging, psoriasis, acne, urticaria, eczema, and atopic dermatitis ( 111 ), usually caused by exposure to oxides and photochemical smoke ( 111 ). Exposure to PM and cigarette smoking act as skin-aging agents, causing spots, dyschromia, and wrinkles. Lastly, pollutants have been associated with skin cancer ( 111 ).

Higher morbidity is reported to fetuses and children when exposed to the above dangers. Impairment in fetal growth, low birth weight, and autism have been reported ( 112 ).

Another exterior organ that may be affected is the eye. Contamination usually comes from suspended pollutants and may result in asymptomatic eye outcomes, irritation ( 112 ), retinopathy, or dry eye syndrome ( 113 , 114 ).

Environmental Impact of Air Pollution

Air pollution is harming not only human health but also the environment ( 115 ) in which we live. The most important environmental effects are as follows.

Acid rain is wet (rain, fog, snow) or dry (particulates and gas) precipitation containing toxic amounts of nitric and sulfuric acids. They are able to acidify the water and soil environments, damage trees and plantations, and even damage buildings and outdoor sculptures, constructions, and statues.

Haze is produced when fine particles are dispersed in the air and reduce the transparency of the atmosphere. It is caused by gas emissions in the air coming from industrial facilities, power plants, automobiles, and trucks.

Ozone , as discussed previously, occurs both at ground level and in the upper level (stratosphere) of the Earth's atmosphere. Stratospheric ozone is protecting us from the Sun's harmful ultraviolet (UV) rays. In contrast, ground-level ozone is harmful to human health and is a pollutant. Unfortunately, stratospheric ozone is gradually damaged by ozone-depleting substances (i.e., chemicals, pesticides, and aerosols). If this protecting stratospheric ozone layer is thinned, then UV radiation can reach our Earth, with harmful effects for human life (skin cancer) ( 116 ) and crops ( 117 ). In plants, ozone penetrates through the stomata, inducing them to close, which blocks CO 2 transfer and induces a reduction in photosynthesis ( 118 ).

Global climate change is an important issue that concerns mankind. As is known, the “greenhouse effect” keeps the Earth's temperature stable. Unhappily, anthropogenic activities have destroyed this protecting temperature effect by producing large amounts of greenhouse gases, and global warming is mounting, with harmful effects on human health, animals, forests, wildlife, agriculture, and the water environment. A report states that global warming is adding to the health risks of poor people ( 119 ).

People living in poorly constructed buildings in warm-climate countries are at high risk for heat-related health problems as temperatures mount ( 119 ).

Wildlife is burdened by toxic pollutants coming from the air, soil, or the water ecosystem and, in this way, animals can develop health problems when exposed to high levels of pollutants. Reproductive failure and birth effects have been reported.

Eutrophication is occurring when elevated concentrations of nutrients (especially nitrogen) stimulate the blooming of aquatic algae, which can cause a disequilibration in the diversity of fish and their deaths.

Without a doubt, there is a critical concentration of pollution that an ecosystem can tolerate without being destroyed, which is associated with the ecosystem's capacity to neutralize acidity. The Canada Acid Rain Program established this load at 20 kg/ha/yr ( 120 ).

Hence, air pollution has deleterious effects on both soil and water ( 121 ). Concerning PM as an air pollutant, its impact on crop yield and food productivity has been reported. Its impact on watery bodies is associated with the survival of living organisms and fishes and their productivity potential ( 121 ).

An impairment in photosynthetic rhythm and metabolism is observed in plants exposed to the effects of ozone ( 121 ).

Sulfur and nitrogen oxides are involved in the formation of acid rain and are harmful to plants and marine organisms.

Last but not least, as mentioned above, the toxicity associated with lead and other metals is the main threat to our ecosystems (air, water, and soil) and living creatures ( 121 ).

In 2018, during the first WHO Global Conference on Air Pollution and Health, the WHO's General Director, Dr. Tedros Adhanom Ghebreyesus, called air pollution a “silent public health emergency” and “the new tobacco” ( 122 ).

Undoubtedly, children are particularly vulnerable to air pollution, especially during their development. Air pollution has adverse effects on our lives in many different respects.

Diseases associated with air pollution have not only an important economic impact but also a societal impact due to absences from productive work and school.

Despite the difficulty of eradicating the problem of anthropogenic environmental pollution, a successful solution could be envisaged as a tight collaboration of authorities, bodies, and doctors to regularize the situation. Governments should spread sufficient information and educate people and should involve professionals in these issues so as to control the emergence of the problem successfully.

Technologies to reduce air pollution at the source must be established and should be used in all industries and power plants. The Kyoto Protocol of 1997 set as a major target the reduction of GHG emissions to below 5% by 2012 ( 123 ). This was followed by the Copenhagen summit, 2009 ( 124 ), and then the Durban summit of 2011 ( 125 ), where it was decided to keep to the same line of action. The Kyoto protocol and the subsequent ones were ratified by many countries. Among the pioneers who adopted this important protocol for the world's environmental and climate “health” was China ( 3 ). As is known, China is a fast-developing economy and its GDP (Gross Domestic Product) is expected to be very high by 2050, which is defined as the year of dissolution of the protocol for the decrease in gas emissions.

A more recent international agreement of crucial importance for climate change is the Paris Agreement of 2015, issued by the UNFCCC (United Nations Climate Change Committee). This latest agreement was ratified by a plethora of UN (United Nations) countries as well as the countries of the European Union ( 126 ). In this vein, parties should promote actions and measures to enhance numerous aspects around the subject. Boosting education, training, public awareness, and public participation are some of the relevant actions for maximizing the opportunities to achieve the targets and goals on the crucial matter of climate change and environmental pollution ( 126 ). Without any doubt, technological improvements makes our world easier and it seems difficult to reduce the harmful impact caused by gas emissions, we could limit its use by seeking reliable approaches.

Synopsizing, a global prevention policy should be designed in order to combat anthropogenic air pollution as a complement to the correct handling of the adverse health effects associated with air pollution. Sustainable development practices should be applied, together with information coming from research in order to handle the problem effectively.

At this point, international cooperation in terms of research, development, administration policy, monitoring, and politics is vital for effective pollution control. Legislation concerning air pollution must be aligned and updated, and policy makers should propose the design of a powerful tool of environmental and health protection. As a result, the main proposal of this essay is that we should focus on fostering local structures to promote experience and practice and extrapolate these to the international level through developing effective policies for sustainable management of ecosystems.

Author Contributions

All authors listed have made a substantial, direct and intellectual contribution to the work, and approved it for publication.

Conflict of Interest

IM is employed by the company Delphis S.A.

The remaining authors declare that the present review paper was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

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Keywords: air pollution, environment, health, public health, gas emission, policy

Citation: Manisalidis I, Stavropoulou E, Stavropoulos A and Bezirtzoglou E (2020) Environmental and Health Impacts of Air Pollution: A Review. Front. Public Health 8:14. doi: 10.3389/fpubh.2020.00014

Received: 17 October 2019; Accepted: 17 January 2020; Published: 20 February 2020.

Reviewed by:

Copyright © 2020 Manisalidis, Stavropoulou, Stavropoulos and Bezirtzoglou. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Ioannis Manisalidis, giannismanisal@gmail.com ; Elisavet Stavropoulou, elisabeth.stavropoulou@gmail.com

† These authors have contributed equally to this work

Disclaimer: All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article or claim that may be made by its manufacturer is not guaranteed or endorsed by the publisher.

• Open access
• Published: 16 November 2011

The influence of environmental factors on the generalisability of public health research evidence: physical activity as a worked example

• Paul Watts 1 ,
• Gemma Phillips 1 ,
• Mark Petticrew 2 ,
• Angela Harden 1 &
• Adrian Renton 1  

International Journal of Behavioral Nutrition and Physical Activity volume  8 , Article number:  128 ( 2011 ) Cite this article

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It is rare that decisions about investing in public health interventions in a city, town or other location can be informed by research generated in that specific place. It is therefore necessary to base decisions on evidence generated elsewhere and to make inferences about the extent to which this evidence is generalisable to the place of interest. In this paper we discuss the issues involved in making such inferences, using physical activity as an example. We discuss the ways in which elements of the structural, physical, social and/or cultural environment (environmental factors [EFs]) can shape physical activity (PA) and also how EFs may influence the effectiveness of interventions that aim to promote PA. We then highlight the ways in which EFs may impact on the generalisability of different types of evidence.

We present a framework for thinking about the influence of EFs when assessing the generalisability of evidence from the location in which the evidence was generated (place A) to the location to which the evidence is to be applied (place B). The framework relates to similarities and differences between place A and place B with respect to: a) the distributions of EFs; b) the causal pathways through which EFs or interventions are thought to exert their effect on PA and c) the ways in which EFs interact with each other. We suggest, using examples, how this scheme can be used by public health professionals who are designing, executing, reporting and synthesising research on PA; or designing/implementing interventions.

Our analysis and scheme, although developed for physical activity, may potentially be adapted and applied to other evidence and interventions which are likely to be sensitive to influence by elements of the structural, physical, social and/or cultural environment such as the epidemiology of obesity and healthy weight promotion.

Introduction

It is widely advocated that decisions about investment in public health interventions should be based on the best available research evidence. This evidence will preferably include a high quality randomised controlled trial (RCT) of the intervention under consideration, carried out in the area targeted for public health action. If an RCT has not been conducted, information from observational studies conducted in that place may also provide useful information. However, this location-specific evidence is seldom available and therefore decisions must be based on evidence from studies that were conducted elsewhere [ 1 ]. Under these circumstances, it is necessary to make inferences about the generalisability of the research evidence from the location in which it was generated to the location of interest.

Regular physical activity is effective in reducing the risk of premature death and in preventing the development of many chronic diseases [ 2 ]. It is currently recommended that adults take some moderate or vigorous physical activity every day and a minimum of 150 minutes per week to accrue such health benefits [ 3 ]. However, less than half of adults in the UK meet these minimum recommended levels [ 4 ]. Traditionally, interventions for increasing physical activity levels have focused on individual behaviours, using "information, education and communication" approaches [ 5 ]. However, there is increasing recognition that structural (e.g. government policies), physical (e.g. the built environment), social and cultural factors may also influence individual physical activity level [ 6 ]. We will refer to the range of physical, social, cultural and political characteristics of a location as "environmental factors". There is now great interest in interventions that aim to directly modify environmental factors to provide supports for, or remove barriers to, groups of individuals increasing their physical activity levels. These interventions range from physical modifications of the urban environment to changes in policies on the pricing and provision of public transport or recreational facilities [ 7 ]. This broadening of the focus of public health action to include environmental and structural interventions is mirrored for other health behaviours and outcomes [ 8 ].

However, if environmental factors are important determinants of health behaviours, they may also moderate the effects of any interventions that are implemented. This is true whether the interventions seek to modify health behaviours through manipulation of environmental factors or through information, education and communication approaches directed at individuals. Given the very large variation in environmental factors between countries, regions or municipalities, an intervention that works well in one location could have a different effect, or no effect at all, when transferred to another location [ 9 ]. It is therefore essential to carefully consider the differences in environmental factors when deciding whether it is appropriate to generalise research evidence on the determinants of health behaviours, such as physical activity, and associated interventions to a new location.

In this paper we briefly review the discussion of the generalisability of public health research evidence in the peer-reviewed literature and describe how environmental factors fit into the broader issue of generalisability. We then describe the types of research evidence on physical activity determinants and interventions that particularly require consideration of environmental factors when making decisions on generalisability and the current state of guidance on how to make these decisions. Building on this brief review, we develop a causal model to describe how inter-setting variation in environmental factors, and the causal pathways through which environmental factors affect physical activity, could critically influence the generalisability of research evidence on physical activity determinants and interventions. Finally, we present a framework for considering environmental factors in the assessment of research evidence generalisability, based on the causal model, and outline the implications of this framework for: the interpretation of existing evidence; the design, execution, reporting and synthesis of research in this field; and the design and implementation of interventions to promote physical activity.

Generalisability in the peer-reviewed literature

There is a considerable body of literature addressing whether findings of a particular research study might be reproducible in other populations or settings, but the language and terminology used by epidemiologists, behaviour change experts, policy makers and social advocates varies greatly, both within and across disciplines. Wang and colleagues [ 1 ] reviewed this literature, finding that the terms 'applicability', 'generalisability' and 'transferability' are often used interchangeably, with no consensus over their meaning. They suggest that in most cases, these terms are used to describe the extent to which findings are generally useful beyond the original context in which they were generated. Wang and colleagues suggest a new definition of these terms where 'applicability' indicates whether the intervention could practically be implemented in the new setting, therefore focussing on the process of implementation, whilst 'transferability' indicates whether the intervention can be expected to have the same effect in the new setting, therefore focussing on the outcome of the intervention. In this taxonomy generalisability is a synonym for transferability.

There is more consistency in the use of the term 'external validity', which is used to denote the extent to which inferences about relationships and effects can be made beyond the range of settings, populations or time periods sampled in the original research study. The scheme presented by Shadish et al [ 10 ] can be extended to describe four levels at which inferences about the extrapolatability of evidence are commonly made in research studies (illustrated in Figure 1 ):

Levels of inference from research studies .

Level 1: from the study sample to the study population;

Level 2: from the study population to the target population under experimental conditions;

Level 3: from the target population under experimental conditions to the target population in 'real world' conditions;

Level 4: from one location or environment to another.

The problems associated with making extrapolations at levels 1, 2 and 3 have been discussed extensively in the literature regarding RCTs for individual-level medical interventions [ 11 ]. However, there has been far less discussion of level 4, the extrapolatability of evidence generated in one place or environment to another [ 12 ]. It is at this level, the transfer of interventions or evidence from one setting to another, that consideration of environmental factors is essential. In this paper we will address this inter-setting extrapolation of research evidence, which corresponds to external validity in relation to broader and different populations described by Shadish et al [ 10 ] and to 'transferability' described by Wang et al [ 1 ]. We reserve the term 'generalisability' to refer to confidence in making inter-setting/level 4 inferences from research findings.

Typology of research evidence on physical activity determinants and interventions

Evidence typology.

There are three main types of evidence relevant to the promotion of physical activity whose generalisability is likely, a priori , to be significantly affected by inter-setting variation in elements of the structural, physical, social and cultural environment.

Type 1 Evidence: Evidence on the influence of environmental factors on physical activity (observational studies).

Type 2 Evidence: Evidence of the effectiveness of interventions that seek to increase physical activity levels of individuals by providing information, education and/or communication approaches (IEC-based interventions).

Type 3 Evidence: Evidence of the effectiveness of interventions that seek to increase physical activity levels of individuals by modifying one or more elements of the structural, physical, social and cultural environment and which may incorporate information, education and/or communication components in a complex intervention (environment-based interventions).

Type 1 evidence: The influence of environmental factors on physical activity (observational studies)

Many public health bodies and officials have recognised the importance of environmental factors in influencing the physical activity levels of populations including the Chief Medical Officer for England and Wales [ 13 ], the Office for Science Foresight Report on Obesity [ 14 ], the National Institute for Health and Clinical Excellence (NICE) guidance [ 7 ] and the Strategic Review of Health Inequalities in England [ 15 ]. Over 400 studies, within disciplines that include transport studies, urban-design, public health and epidemiology, have described associations between different combinations of environmental factors and physical activity levels. Several comprehensive reviews of this evidence base have summarised the key relationships [ 6 , 16 – 18 ]. A summary of environmental factors consistently reported to be associated with physical activity is presented in Table 1 where environmental factors are categorised according to whether they pertain to structural, physical, social or cultural aspects of the environment. References to the reviews in which each association is reported have been provided. The majority of research to date has focused on physical environmental factors, therefore we have also included in Table 1 social and cultural environmental factors that have been under-researched [ 16 ] or excluded from reviews of the literature as published studies have used qualitative methods [ 19 – 22 ].

Type 2 and 3 evidence: Interventions to promote physical activity

A wide range of interventions to promote physical activity has been described [ 16 ]. These interventions aim to directly modify individual behavioural choices, or to modify the environmental factors that may condition these choices.

The majority of research into physical activity promotion has focused on policies and interventions that seek to increase physical activity levels of individuals or populations directly through information, education and communication approaches. Systematic reviews have demonstrated short-term effectiveness for some classes of information, education and communication interventions [ 23 , 24 ] and a range of these is recommended by NICE in the UK [ 25 ]. A small number of interventions which aim to increase the physical activity levels of populations through modifications to environmental factors have been shown to be effective [ 26 , 27 ]. NICE has recently conducted a review of such interventions and has endorsed the use of a range of environment-based interventions which have been shown to be effective [ 7 ].

Existing guidance for considering the inter-setting generalisability of evidence on physical activity determinants and interventions

In 2007 NICE conducted a synthesis of systematic reviews of observational studies investigating associations between environmental factors and physical activity [ 6 ] which highlighted the paucity of studies conducted in the UK. However, the authors did not discuss the generalisability of evidence from studies outside the UK to the UK context. It is likely that the authors' ability to comment on generalisability was limited by the absence of any in-depth discussion of generalisability in the systematic reviews they were synthesising and the primary studies contained in these reviews.

Type 2 evidence: Interventions to promote physical activity through information, education and communication

NICE has produced several sets of guidance informed by evaluations of the effectiveness of interventions employing information, education and communication approaches to increasing physical activity [ 25 , 28 ], which included assessment of the utility of reviewed evidence for public health decision-making in the UK. In this guidance, the term 'applicability' is used most often, but is used to indicate both the extent to which inferences can be made about both the generalisability of evidence of effectiveness generated outside the UK to the UK (analogous to 'transferability' as described by Wang et al [ 1 ] and our definition of generalisability) and the extent to which practical issues may act as barriers to implementing the intervention in the UK (analogous to 'applicability' as described by Wang et al [ 1 ]). It is often unclear which of these meanings is intended and there is no description of the methods used to make judgements about these issues.

NICE have since published an updated description of the methods used in developing their guidance [ 29 ], in which they clearly distinguish between the successful transfer of intervention processes and the replication of intervention outcomes. In relation to applying international evidence in the UK, they suggest that one should consider whether there are any 'demographic or geographic' factors that might influence generalisability. However, there is no guidance on assessing how this influence might be exerted or predicting in what ways generalisability might be affected. In relation to practical issues in implementation, NICE suggests that a range of structural, social, cultural and demographic factors (including some that we have presented in Table 1 ) should be considered. Examination of the 'geographical context' in which the intervention was originally implemented is recommended, but 'rural/urban' is the only operationalisation provided. The guidance also follows Bonell et al [ 12 ] who suggest that assessing the practical 'applicability' of an intervention requires consideration of 'feasibility', 'acceptability' and 'capacity' in both the place the intervention was originally delivered and alternative places the intervention might be implemented.

Type 3 evidence: Interventions to promote physical activity through modification of environmental factors

In 2008 NICE produced a review of evidence focussing on interventions in which environmental factors are modified in order to influence physical activity levels [ 7 ]. The resulting guidance again highlighted the predominance in the literature of research conducted outside the UK, and concluded that the range of participants included might not therefore reflect the sociodemographic diversity of some areas in the UK, and also that the distribution of environmental factors in the intervention trial sites (commonly suburban areas in the US and Australia) might not be comparable to the distribution of environmental factors found in the UK. Whilst the guidance does discuss generalisability, the methods used to assess it are not clearly described. As NICE guidance on environmental interventions [ 7 ] was produced before publication of the methodological guidance discussed above (under 'Type 2 evidence'), we sought clarification from the authors. We were informed by the lead analyst [ 30 ] that both the review team and the programme development group considered and discussed issues including the country in which the research was conducted, the date, cultural differences and urban/rural variation in population attribute and the environment. Judgements were made based on these discussions and the expertise within the programme development group.

As described in our evidence typology, complex environment-based interventions may incorporate information, education and communication components. The Medical Research Council guidance on developing and evaluating complex interventions [ 9 ], does not provide guidance on assessing generalisability, but does acknowledge that 'context is crucial' because interventions that are effective in one place may have a different or no effect in another. Rychetnik et al [ 31 ] produced a set of criteria for evaluating evidence on complex public health interventions in which they also highlight the importance of 'context', which they define as "the social, political and/or organisational setting in which an intervention was evaluated, or in which it is to be implemented" (p 119). These authors suggest that in assessing generalisability, information is needed on: the context of the intervention; the design and components of the intervention; and any potential interactions between the intervention and its context. They provide useful examples which illustrate why this information is important in assessing generalisability. This work was built upon by Wang et al [ 1 ] who further suggest that information is required regarding the prevalence of the health problem in question, the political and social environment, organisational structure and resources in the original research setting and the setting to which the evidence is to be generalised. Furthermore, Wang et al suggest that this information may be collected using Delphi studies involving professionals with diverse expertise, using consultations with people who have an in depth knowledge of the setting to which the evidence is to be generalised or using information gathered from systematic searches of the available literature.

Green and Glasgow [ 32 ], have provided a very useful summary of literature that has sought to address issues relating to the generalisability of public health research and have highlighted the importance of frameworks that consider generalisability between settings as well as between individuals. Following this summary, Green and Glasgow present criteria for the assessment of the generalisability of public health research. This includes the assessment of similarities and differences between the populations in which research has been conducted and the populations to which the evidence or intervention is to be applied (participation rates, target audiences, representativeness of participants, drop-out rates), similarities and differences in the implementation of the program (consistency of implementation, staff expertise, program adaptation, mechanisms through which the program exerted it's effect, sustainability and long term effects) and the quality of information provided in research reports regarding methods and outcomes (comparability of outcomes, adverse consequences, moderator effects, sensitivity and cost analysis).

In addition to these criteria, Green and Glasgow highlight the importance of comparing similarities and differences between settings; suggesting that the size, level of urbanity and availability of resources need to be considered when assessing generalisability. However, the authors also recommend development of these criteria and the formulisation of new criteria for making judgements about generalisability. In this paper, we aim to draw attention to factors influencing inter-setting generalisability that have not been discussed in any detail in the literature described above. This will include the comprehensive consideration of the ways in which the range of environmental factors presented in Table 1 may influence generalisability.

Despite repeated exhortations to consider issues of inter-setting generalisability in relation to observational studies and intervention studies in the field of physical activity, the above review highlights that there is little guidance in the literature to suggest how this might actually be achieved. In the following section we develop a causal model (Figure 2 ) that describes how environmental factors might interact to influence the findings of studies which generate evidence about physical activity determinants and interventions and then develop a framework for considering the influence of environmental factors in the assessment of the generalisability of this research evidence.

Model to show environmental factors and causal pathways for different types of evidence .

Development of a framework for assessing the inter-setting generalisability of evidence on physical activity determinants and interventions

Causal model for the interaction between environmental factors and research findings, type 1 evidence: observational studies.

The left panel of Figure 2 depicts the relationships between environmental factors and physical activity levels that have been identified in observational research studies. Environmental factors may exert direct mutual influence on each other as well as interacting in one or more causal pathways which directly influence physical activity levels. For example, observed associations between residential density (EF 1 ) and physical activity [ 33 ] are likely to be dependent on public transport accessibility levels (EF 2 ) and the thresholds for residential density that are used in many countries to trigger the introduction of bus services (EF 3 )[ 34 ]. These three environmental factors may vary greatly between settings, but the ways in which they influence each other may also vary. Residential density has an important influence on walkability which may be expected to directly influence physical activity levels [ 35 ]. However, bus services may influence physical activity by modifying perceptions of walkability (will I still consider 20 minutes to my friend's house walkable if I can do it by bus in 5 minutes?) or by another mechanism such as enabling easy access to facilities previously out of range[ 36 ]. Thus, observed associations between residential density and physical activity [ 7 ] from the USA (where 18 dwellings per hectare is enough to justify a local bus service), may not be consistent in a setting where this threshold is different (such as the UK where a density of 25 dwellings per hectare is considered too sparse to be able to maintain a bus service) [ 34 ].

Type 2 Evidence: Interventions to promote physical activity through information, education and communication

The centre panel shows the situation for studies of interventions which seek to modify behaviour by providing information, education or communication. Again, environmental factors may exert direct mutual influence on each other and interact in causal pathways to influence physical activity levels. For example, high levels of crime and vandalism (EF 1 ) will have a negative effect on the perceived aesthetic quality of the environment (EF 2 ) and the perceived safety of the environment (EF 3 ). In addition environmental factors may interact with the causal pathways through which information, education and communication activities either achieve changes in knowledge about, attitudes to or propensities for physical activity (CP A ), or the pathways through which changes in these are translated into changes in physical activity (CP B ). An example of how these pathways may influence the effect of an interviention is provided by Michael and Carlson [ 37 ] who measured the moderating effect of environmental factors on information-based walking interventions in Oregon, US, finding that perceived neighbourhood problems (gangs, graffiti, violent crime, vandalism, burglary, abandoned or boarded up buildings, or alcohol or drug use) appeared to suppress the effect of the intervention, while measures of social cohesion and neighbourhood walkability (physical-environment characteristics) were not significant moderators of the intervention effect. Therefore, an evaluation of the same intervention, implemented in a setting with different configurations of these environmental factors may produce a different outcome.

Type 3 Evidence: Interventions to promote physical activity through modification of environmental factors

The right panel depicts studies of interventions acting on environmental factors. In this case, the direct mutual influence of environmental factors on each other may constrain or enhance the ability of the intervention to secure the desired changes. For example, the effect of an intervention designed to create and maintain outdoor environments containing serviceable exercise equipment (EF 1 ) may be constrained by high levels of crime and vandalism in an area (EF 2 ) [ 38 ]. Further, other environmental factors (which are not the primary targets for the intervention) such as street connectivity (EF 3 ) [ 33 ] may influence the both the ability of individuals to access the exercise equipment provided and the levels of crime and vandalism in the area. Therefore, the outcome of an evaluation of the same intervention in a different setting may be different.

The studies cited above provide information about the evidence base for the proposed causal pathways. However, further research is required to generate evidence to support all causal pathways proposed in our model. This includes investigation of: (1) the under-researched environmental factors listed in Table 1 (predominantly social and cultural factors); (2) the ways in which environmental factors interact to influence physical activity; (3) the ways in which environmental factors influence each other independently of physical activity.

Framework for considering environmental factors in assessment of the generalisability of existing research evidence

Following from the causal model of environmental influences on physical activity determinants and interventions, we suggest that three principal considerations are necessary when generalising evidence generated in one location (place A) to another location (place B), independently of whether this evidence relates to observational studies, studies of the effect interventions. The three domains of the framework are;

1. The configuration of environmental factors in places A and B and the differences between these .

2. The actual or notional causal pathways through which environmental factors exert their effect on PA in place A and in place B and the differences between these .

3. The ways in which different environmental factors influence each other in place A and place B and the differences between these .

In what follows we now present some practical ways in which these three domains can be systematically considered.

In order to assess the configuration of environmental factors in places A and B and the differences between these, it is first necessary to decide which of the environmental factors listed in Table 1 are likely to influence physical activity and/or the processes of the intervention (if applicable) in places A and/or B. Secondly, appropriate sources of information about these environmental factors should be identified. In some cases, information about environmental factors in place A may be available from the published reports of the evidence to be generalised. If not, in the first instance we suggest contacting the authors of these reports as they are likely to be best placed to provide (or suggest sources of) this information. Alternatively, information about environmental factors in place A can be sought by accessing routinely available data sets where available.

Cummins et al [ 39 ] have provided an overview of the types of appropriate routine data that may be available and the ways in which it may be accessed and operationalised. Here, we will give an overview of how some of the factors listed in Table 1 may be evidenced from routine data. The following examples are from England and Wales, but similar data are available in many other countries, and the methods we describe can be applied in most countries. In England and Wales, routinely available data sets include those provided by the Office for National Statistics [ 40 ], and the large range of publically available data from diverse sources accessible through the single government data repository website [ 41 ]. These sources provide localised (census lower/middle super output areas) and local authority-level data on a wide range of socioeconomic factors as well as environmental factors including traffic, public transport accessibility, traffic safety, air/noise pollution, hilliness. Information regarding road and path networks and hilliness are available from Great Britain's national mapping agency, Ordnance Survey [ 42 ] and information about cycle lanes from UK charity Sustrans [ 43 ]. Measures such as street connectivity are not as readily available, but simple indicators of connectivity can be derived by counting the number of streets and street intersections and using one of several methods for calculating a connectivity index [ 44 ]. Resources for physical activity can be identified using Sport England's 'Active Living Database' [ 45 ]. Similarly, relevant, locally-specific health statistics from these sources such as obesity rates, healthy eating measures and rates of physical activity may help assessment of the extent to which the needs of people in place A and place B differ [ 31 ].

Beyond routine datasets, there is a range of robust quantitative assessment tools available that can be used to assess amenities that facilitate walking including the presence and quality of sidewalks. A selection (though mostly designed in relation to US neighbourhoods) can be found on the Active Living Research website [ 46 ]. Additionally, consultation with 'local experts' is likely to be valuable in order to gather information about the social and cultural factors listed in Table 1 where routine data sets are not available.

Once information about the configuration of environmental factors in place A and place B has been collated, a first step is to judge which environmental factors show potentially significant inter-setting differences in the light of the wider evidence base. Next, it is necessary to assess whether these differences are likely to influence generalisability. This can be approached by considering how each environmental factor showing potentially significant inter-setting differences might influence physical activity directly, or the processes of the intervention (if applicable). Then each environmental factor can be rated according to the extent of its likely influence on generalisability, to inform an overall judgement. In Table 2 we present an example of how this might be achieved. This is for illustration and is not proposed as a rigid framework. Each case is likely to be different and methods will need to be adapted. For example, it may be appropriate to differentially weight the ratings of some environmental factors if some are considered to be particularly important when making the overall judgement.

Our current understanding of the causal pathways through which environmental factors exert their effect on physical activity is largely based on commonsense narratives rather than evidence. Developing and evidencing models that conceptualise these causal pathways has recently been identified as a priority by a working group of leading researchers [ 47 ]. They suggest that the lack of models may be a key a barrier to moving forwards to produce strong evidence of associations between environmental factors and physical activity, and of the effectiveness of environment-based interventions to increase physical activity levels. We further propose that this deficit is also a key challenge in assessing the inter-setting generalisability of such evidence.

In the diagrams presented in Figure 2 and the examples used to illustrate these, we have suggested ways in which environmental factors may interact with each other and/or with environment-based and information, education and communication-based interventions to exert their influence on physical activity. In order to make inferences about the generalisability of the three types of evidence we describe, it is necessary to make a priori judgements about the causal pathways through which environmental factors exert their effect on physical activity in places A and B. To do this we can start by considering whether any causal pathways or models which are described or hypothesised to explain the evidence reported from place A are likely also to be applicable in place B. As process and qualitative evaluations are increasingly encouraged [ 9 ] alongside quantitative descriptive and experimental studies, such pathways and models are likely to become increasingly common in the intervention evaluation literature. Similarly, we can consider any causal pathways or models which are described in the wider literature to explain similar findings, and whether these are likely to be applicable in places A and B. In addition, we can list the environmental factors from Table 1 which are pertinent to place A and place B and use these lists to develop our own hypotheses about likely casual pathways through which environmental factors influence physical activity in each place and the likely differences in these pathways. In the case of environment-based and information, education and communication-based interventions, an additional model of the processes through which the interventions are thought to operate can be developed. This can be used to make judgements about how environmental factors might interact with these processes differently in place A and place B. In addition it may be possible to carry out primary qualitative studies in place A and place B to support people with expert knowledge of places A and B (especially residents), or with expert knowledge of the processes involved in the interventions to articulate notional causal pathways.

It is widely acknowledged that environmental factors will interact with each other in order to exert an effect on physical activity [ 48 ]. However, despite the numerous observational studies reporting associations between various combinations of environmental factors and physical activity, the ways in which environmental factors influence each other (independently of any effect on physical activity) have rarely been theorised, investigated or reported. We have proposed, giving examples, that these interactions and influences may differ between places. If this is the case then associations between environmental factors and physical activity reported in place A may not be generalisable to place B. Assessing the ways in which environmental factors influence each other in place A and place B might again involve making lists of pertinent environmental factors in each place and consulting local experts to propose which factors will influence each other in what way and in which combinations. In this case, interactions between environmental factors independent of physical activity are important, meaning that the involvement of experts from diverse disciplines such as sociology, geography, town planning and transport is likely to be useful. Similarly the application of concepts from these disciplines may illuminate the ways in which environmental factors exert influence on each other independently of physical activity. For example, the sociological 'broken windows theory' [ 49 ] describes the ways in which the aesthetic quality of the environment, crime levels, and perceived safety mutually influence each other.

Implications of the generalisability framework for researchers, policy makers and practitioners

The framework laid out above implies that, to support judgements of generalisability, the design and conduct of research should generate high quality information on the:

distributions of environmental factors in the research setting (place A);

causal pathways through which information, education and communication interventions or environmental factors are thought to exert an effect on physical activity;

ways in which different environmental factors influence each other in the settings where the research is carried out.

Conducting research on physical activity

We have identified a need for information about the configuration of environmental factors in place A. Therefore, it is therefore necessary to make the collection of this information an integral part of the research process. This is likely to require that researchers, and those who are providing research grants, agree to allocate sufficient resources to activities that will produce this information.

We have identified a need for conceptual models that describe the causal pathways through which environmental factors and information, education and communication interventions exert an effect on physical activity. In order to achieve this, detailed case studies of places may be required in order to build comprehensive pictures of the ways in which environmental factors influence each other and interact to influence physical activity. In addition, it has been suggested that alongside quantitative research, qualitative research involving consultations with residents and local experts may best illuminate these pathways [ 47 ].

Cross-disciplinary evidence gathering

While little is known about the ways in which environmental factors interact with each other to influence physical activity, interactions between environmental factors may have been studied extensively by other research disciplines, therefore collaboration is likely to be very valuable. For example, sociology and/or transport research may be able to inform us about the ways in which perceived safety interacts with public transport use. Or sociologists and/or environmental researchers may be able to tell us how crime rates interact with the aesthetic quality of an environment. Where information about these interactions is not available, primary research on interactions between environmental factors is likely to be desirable.

Designing new interventions and research into their effectiveness

We have described the ways in which environmental factors may influence the causal pathways through which interventions exert an effect on physical activity, however evaluations of information, education and communication-based physical activity interventions have seldom acknowledged a role played by environmental factors. Future studies may benefit from investigating how environment factors interact with interventions to influence physical activity. This may involve the systematic consideration of which environmental factors are relevant, as we describe in the above framework. Once pertinent environmental factors have been identified and the causal pathways through which they operate conceptualised, these theories can be tested in the design and implementation of interventions and evaluations of interventions. There are a few very recent examples of how this may be achieved, for example the study by Michael and Carlson [ 28 ], which is discussed earlier under Figure 2 .

Reporting research findings

In the reporting of research findings, information about environmental factors in the research setting needs to be summarised in sufficient detail to allow a third party to judge whether the findings are generalisable between place A and place B. Research reports seldom include information about the configuration of environmental factors, the way they feed into the causal pathways through which interventions are thought to work, or the ways in which they interact. There is a clear need to improve the reporting of such information in order to allow judgement regarding the generalisability of evidence. It may be necessary for publishers to provide alternative places to make this information available (e.g. online or as appendices).

Evidence synthesis

Systematic reviews present ideal opportunities to assess the generalisability of research. With regard to interventions, systematic reviews most often attempt to ask the question; 'does the intervention work?' and pay close attention to the internal validity of studies. However, it is becoming increasingly accepted that reviews are more useful when they also attempt to explain why interventions sometimes work and sometimes do not, the circumstances under which interventions work and the role played by environmental factors. Realist synthesis, for example integrates evidence from a number of studies to test and refine programme theory. The central principle to a realist approach to evaluation and synthesis is that the underlying assumptions about how an intervention works are made explicit and evidence is gathered systematically to test these assumptions [ 50 ]. For environment-based and information, education and communication-based interventions, an approach to synthesis that explicitly attempts to specify the role of environmental factors and incorporate theories about their role into the synthesis of evidence of the effectiveness of these interventions is likely to be extremely useful in assessing the extent to which interventions can be successfully transferred from place to place.

In this paper we have developed a causal model and framework for assessing the generalisability of public health research evidence. We have suggested that the extent to which the main types of research evidence on physical activity can be generalised relies heavily on three principle characteristics of environmental factors in the place in which the evidence was generated and the place to which the evidence is to be generalised. Below, we have summarised recommendations to help facilitate the systematic collection and consideration of information about environmental factors in public health research for researchers, journal editors and research funding bodies:

Authors of research reports make available, either in published reports or elsewhere:

Information about the distributions of EFs in the research setting.

Information about the causal pathways through which IEC-based interventions or environmental factors are thought to exert their effect on PA (where appropriate).

Information about the ways in which different environmental factors influence each other in the settings where the research is carried out.

Information about any other factors that may act as barriers to or facilitate the process of generalising the evidence to another location.

Editors of publications presenting research reports:

Require that the information about EFs in the research setting described above is included in research reports that are published.

To provide adequate space (either within a report, as appendices or online) for this information to be presented.

For bodies providing research grants:

To specify in invitations to tender that the collection of this information about EFs will be required.

To provide funds, where appropriate, for this information to be collected.

For those designing interventions:

To make explicit any assumptions regarding the role of EFs in the causal pathways through which the intervention is intended to exert its effect.

Our analysis and framework, although developed for physical activity, may potentially be adapted and used to consider other evidence and interventions which are likely to be sensitive to influence by elements of the structural, physical, social and/or cultural environment. These might include the epidemiology of obesity and weight management programmes. Such adaptation would require the systematic consideration of relevant environmental factors for each outcome and setting of interest, the causal pathways involved, and the typology of interventions used.

Abbreviations

Environmental factor associated with physical activity

Notional or real causal pathway through which physical activity may be influenced

Physical Activity.

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PW conceived the paper, its content and drafted the original manuscript. GP carried out significant editing and re-drafting to the final manuscript. AH provided edits to the whole paper and drafting of the discussion section. MP contributed considerably towards the conceptual content of the paper in its early stages and also provided comments on later drafts. AR contributed to the conceptual design of the paper, assisted in the development of the framework included, and carried out significant re-drafting of the manuscript. All authors read and approved the final manuscript.

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Watts, P., Phillips, G., Petticrew, M. et al. The influence of environmental factors on the generalisability of public health research evidence: physical activity as a worked example. Int J Behav Nutr Phys Act 8 , 128 (2011). https://doi.org/10.1186/1479-5868-8-128

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DOI : https://doi.org/10.1186/1479-5868-8-128

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Environmental drivers of demography and potential factors limiting the recovery of an endangered marine top predator

Understanding what drives changes in wildlife demography is fundamental to the conservation and management of depleted or declining populations, though making inference about the intrinsic and extrinsic factors that influence survival and reproduction remains challenging. Here we use mark–resight data from 2000 to 2018 to examine the effects of environmental variability on age-specific survival and natality for the endangered western distinct population segment (wDPS) of Steller sea lions (Eumetopias jubatus) in Alaska, USA. Though this population has been studied extensively over the last four decades, the causes of divergent abundance trends that have been observed across the wDPS range remain unknown. We developed a Bayesian multievent mark–resight model that accounts for female reproductive state uncertainty. Annual survival probabilities for male pups (0.44; 0.36–0.53), female yearlings (0.63; 0.49–0.73), and male yearlings (0.62; 0.51–0.71) born in the western portion of the wDPS range, estimated here for the first time, were lower than those in the eastern portion of the wDPS range, estimated as: male pups (0.69; 0.65–0.74), female yearlings (0.76; 0.71–0.81), and male yearlings (0.71; 0.65–0.78). There was a higher proportion of young female breeders in the western portion of the range, but overall natality was lower (0.69; 0.47–0.96) than in the eastern portion of the range (0.80; 0.74–0.84). Additionally, pup mass had a positive effect on pup survival in the eastern portion of the range and a negative effect in the western portion of the range, potentially due to earlier weaning of heavier pups. Local- and basin-scale oceanographic features such as the Aleutian Low, the Arctic Oscillation Index, the North Pacific Gyre Oscillation, chlorophyll concentration, upwelling, and wind in certain seasons were correlated with vital rates. However, drawing strong inferences from these correlations is challenging given that relationships between ocean conditions and an adaptive top predator in a dynamic ecosystem are exceedingly complex. This study provides the first demographic rate estimates for the western portion of the range where abundance estimates continue to decline. These results will advance efforts to identify factors driving regionally divergent abundance trends, with implications for population-level responses to future climate variability.

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Fossil fuels – coal, oil and gas – are by far the largest contributor to global climate change, accounting for over 75 per cent of global greenhouse gas emissions and nearly 90 per cent of all carbon dioxide emissions.

As greenhouse gas emissions blanket the Earth, they trap the sun’s heat. This leads to global warming and climate change. The world is now warming faster than at any point in recorded history. Warmer temperatures over time are changing weather patterns and disrupting the usual balance of nature. This poses many risks to human beings and all other forms of life on Earth.

Causes of Climate Change

Generating power

Generating electricity and heat by burning fossil fuels causes a large chunk of global emissions. Most electricity is still generated by burning coal, oil, or gas, which produces carbon dioxide and nitrous oxide – powerful greenhouse gases that blanket the Earth and trap the sun’s heat. Globally, a bit more than a quarter of electricity comes from wind, solar and other renewable sources which, as opposed to fossil fuels, emit little to no greenhouse gases or pollutants into the air.

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Using transportation

Most cars, trucks, ships, and planes run on fossil fuels. That makes transportation a major contributor of greenhouse gases, especially carbon-dioxide emissions. Road vehicles account for the largest part, due to the combustion of petroleum-based products, like gasoline, in internal combustion engines. But emissions from ships and planes continue to grow. Transport accounts for nearly one quarter of global energy-related carbon-dioxide emissions. And trends point to a significant increase in energy use for transport over the coming years.

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Producing food causes emissions of carbon dioxide, methane, and other greenhouse gases in various ways, including through deforestation and clearing of land for agriculture and grazing, digestion by cows and sheep, the production and use of fertilizers and manure for growing crops, and the use of energy to run farm equipment or fishing boats, usually with fossil fuels. All this makes food production a major contributor to climate change. And greenhouse gas emissions also come from packaging and distributing food.

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Consuming too much

Your home and use of power, how you move around, what you eat and how much you throw away all contribute to greenhouse gas emissions. So does the consumption of goods such as clothing, electronics, and plastics. A large chunk of global greenhouse gas emissions are linked to private households. Our lifestyles have a profound impact on our planet. The wealthiest bear the greatest responsibility: the richest 1 per cent of the global population combined account for more greenhouse gas emissions than the poorest 50 per cent.

Based on various UN sources

Effects of Climate Change

Hotter temperatures

As greenhouse gas concentrations rise, so does the global surface temperature. The last decade, 2011-2020, is the warmest on record. Since the 1980s, each decade has been warmer than the previous one. Nearly all land areas are seeing more hot days and heat waves. Higher temperatures increase heat-related illnesses and make working outdoors more difficult. Wildfires start more easily and spread more rapidly when conditions are hotter. Temperatures in the Arctic have warmed at least twice as fast as the global average.

More severe storms

Destructive storms have become more intense and more frequent in many regions. As temperatures rise, more moisture evaporates, which exacerbates extreme rainfall and flooding, causing more destructive storms. The frequency and extent of tropical storms is also affected by the warming ocean. Cyclones, hurricanes, and typhoons feed on warm waters at the ocean surface. Such storms often destroy homes and communities, causing deaths and huge economic losses.

Increased drought

Climate change is changing water availability, making it scarcer in more regions. Global warming exacerbates water shortages in already water-stressed regions and is leading to an increased risk of agricultural droughts affecting crops, and ecological droughts increasing the vulnerability of ecosystems. Droughts can also stir destructive sand and dust storms that can move billions of tons of sand across continents. Deserts are expanding, reducing land for growing food. Many people now face the threat of not having enough water on a regular basis.

A warming, rising ocean

The ocean soaks up most of the heat from global warming. The rate at which the ocean is warming strongly increased over the past two decades, across all depths of the ocean. As the ocean warms, its volume increases since water expands as it gets warmer. Melting ice sheets also cause sea levels to rise, threatening coastal and island communities. In addition, the ocean absorbs carbon dioxide, keeping it from the atmosphere. But more carbon dioxide makes the ocean more acidic, which endangers marine life and coral reefs.

Loss of species

Climate change poses risks to the survival of species on land and in the ocean. These risks increase as temperatures climb. Exacerbated by climate change, the world is losing species at a rate 1,000 times greater than at any other time in recorded human history. One million species are at risk of becoming extinct within the next few decades. Forest fires, extreme weather, and invasive pests and diseases are among many threats related to climate change. Some species will be able to relocate and survive, but others will not.

Not enough food

Changes in the climate and increases in extreme weather events are among the reasons behind a global rise in hunger and poor nutrition. Fisheries, crops, and livestock may be destroyed or become less productive. With the ocean becoming more acidic, marine resources that feed billions of people are at risk. Changes in snow and ice cover in many Arctic regions have disrupted food supplies from herding, hunting, and fishing. Heat stress can diminish water and grasslands for grazing, causing declining crop yields and affecting livestock.

More health risks

Climate change is the single biggest health threat facing humanity. Climate impacts are already harming health, through air pollution, disease, extreme weather events, forced displacement, pressures on mental health, and increased hunger and poor nutrition in places where people cannot grow or find sufficient food. Every year, environmental factors take the lives of around 13 million people. Changing weather patterns are expanding diseases, and extreme weather events increase deaths and make it difficult for health care systems to keep up.

Poverty and displacement

Climate change increases the factors that put and keep people in poverty. Floods may sweep away urban slums, destroying homes and livelihoods. Heat can make it difficult to work in outdoor jobs. Water scarcity may affect crops. Over the past decade (2010–2019), weather-related events displaced an estimated 23.1 million people on average each year, leaving many more vulnerable to poverty. Most refugees come from countries that are most vulnerable and least ready to adapt to the impacts of climate change.

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Development in Agricultural Ecosystems’ Carbon Emissions Research: A Visual Analysis Using CiteSpace

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Bibliometric analysis of research hotspots and trends in the field of volatile organic compound (VOC) emission accounting

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• Weiqiu Huang   ORCID: orcid.org/0000-0001-7233-3494 1 , 2 ,
• Yilan Xiao 1 , 2 ,
• Xufei Li 1 , 2 ,
• Chunyan Wu 1 , 2 ,
• Cheng Zhang 1 , 2 &
• Xinya Wang 1 , 3  

Abstract     

Volatile organic compounds (VOCs) have been extensively studied because of their significant roles as precursors of atmospheric ozone and secondary organic aerosol pollution. The research aims to comprehend the current advancements in domestic and international VOC emission accounting. The study utilized the CiteSpace software to represent the pertinent material from Web of Science visually. The hot spots and future development trends of VOC emission calculation are analyzed from the perspectives of thesis subject words, cooperative relationships, co-citation relationships, journals, and core papers. According to the statistics, the approaches most often employed in VOC accounting between 2013 and 2023 are source analysis and emission factor method. Atmospheric environment is the journal with the most publications in the area. The Chinese Academy of Sciences and the University of Colorado System are prominent institutions in VOC emission accounting research, both domestically and internationally. The primary research focuses on the realm of VOC emission accounting clusters, which are “emission factor,” “source analysis,” “model,” “air quality,” and “health.” A current trend in VOC emission accounting involves the construction of a VOC emission inventory using a novel model that combines emission factors and source analysis. This study reviews the progress made in calculating volatile organic compound (VOC) emissions over the past decade. It aims to provide researchers with a new perspective to promote the development of this field.

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This work is supported by the National Natural Science Foundation of China (No. 52174058), the Postgraduate Research & Practice Innovation Program of Jiangsu Province (KYCX23_3141), and the Jiangsu Key Laboratory of Oil–gas Storage and Transportation Technology (CDYQCY202301).

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Weiqiu Huang, Yilan Xiao, Xufei Li, Chunyan Wu, Cheng Zhang & Xinya Wang

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Weiqiu Huang contributed to the study’s conception and design. Ideas, research goals, and editing were formulated by Xufei Li. Data analysis and the first of the manuscript were written by Yilan Xiao. Chunyan Wu and Cheng Zhang authors commented on previous versions of the manuscript. Xingya Wang assisted in the submission process of the paper.

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Huang, W., Xiao, Y., Li, X. et al. Bibliometric analysis of research hotspots and trends in the field of volatile organic compound (VOC) emission accounting. Environ Sci Pollut Res (2024). https://doi.org/10.1007/s11356-024-33896-5

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Green microbe profile: rhizophagus intraradices —a review of benevolent fungi promoting plant health and sustainability.

1. Introduction

2. taxonomy and characteristics, 3. mycorrhizal symbiosis, 4. role of r. intraradices in promoting plant growth, 5. nutrient cycling and soil health, 6. environmental restoration and ecosystem resilience, 7. sustainable agriculture and organic farming, 8. agro-ecological relevance of glomeromycota and r. intraradices.

• (b) Mycorrhiza–plant interaction: yielding plant disease biocontrol
• (c) Mycorrhiza–microorganisms interaction
• (d) Mycorrhiza–soil interaction
• (e) Biogeochemical cycles and mycorrhiza

9. Genomic Research in Glomeromycota

10. negative effects of amf, 11. challenges and future perspectives, 12. conclusions, author contributions, institutional review board statement, data availability statement, conflicts of interest.

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Onyeaka, H.N.; Akinsemolu, A.A.; Siyanbola, K.F.; Adetunji, V.A. Green Microbe Profile: Rhizophagus intraradices —A Review of Benevolent Fungi Promoting Plant Health and Sustainability. Microbiol. Res. 2024 , 15 , 1028-1049. https://doi.org/10.3390/microbiolres15020068

Onyeaka HN, Akinsemolu AA, Siyanbola KF, Adetunji VA. Green Microbe Profile: Rhizophagus intraradices —A Review of Benevolent Fungi Promoting Plant Health and Sustainability. Microbiology Research . 2024; 15(2):1028-1049. https://doi.org/10.3390/microbiolres15020068

Onyeaka, Helen N., Adenike A. Akinsemolu, Kehinde Favour Siyanbola, and Victoria Ademide Adetunji. 2024. "Green Microbe Profile: Rhizophagus intraradices —A Review of Benevolent Fungi Promoting Plant Health and Sustainability" Microbiology Research 15, no. 2: 1028-1049. https://doi.org/10.3390/microbiolres15020068

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• Systematic Review
• Open access
• Published: 13 June 2024

Infant feeding experiences among Indigenous communities in Canada, the United States, Australia, and Aotearoa: a scoping review of the qualitative literature

• Hiliary Monteith 1 ,
• Carly Checholik 2 ,
• Tracey Galloway 2 ,
• Hosna Sahak 1 ,
• Amy Shawanda 3 ,
• Christina Liu 1 &
• Anthony J. G. Hanley 1 , 4 , 5  

BMC Public Health volume  24 , Article number:  1583 ( 2024 ) Cite this article

152 Accesses

Metrics details

Although exclusive breastfeeding is recommended for the first six months of life, research suggests that breastfeeding initiation rates and duration among Indigenous communities differ from this recommendation. Qualitative studies point to a variety of factors influencing infant feeding decisions; however, there has been no collective review of this literature published to date. Therefore, the objective of this scoping review was to identify and summarize the qualitative literature regarding Indigenous infant feeding experiences within Canada, the United States, Australia, and Aotearoa.

Using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses- Scoping Reviews and the Joanna Briggs Institute Guidelines, in October 2020, Medline, Embase, CINAHL, PsycINFO, and Scopus were searched for relevant papers focusing on Indigenous infant feeding experiences. Screening and full-text review was completed by two independent reviewers. A grey literature search was also conducted using country-specific Google searches and targeted website searching. The protocol is registered with the Open Science Framework and published in BMJ Open.

Forty-six papers from the five databases and grey literature searches were included in the final review and extraction. There were 18 papers from Canada, 11 papers in the US, 9 studies in Australia and 8 studies conducted in Aotearoa. We identified the following themes describing infant feeding experiences through qualitative analysis: colonization, culture and traditionality, social perceptions, family, professional influences, environment, cultural safety, survivance, establishing breastfeeding, autonomy, infant feeding knowledge , and milk substitutes , with family and culture having the most influence on infant feeding experiences based on frequency of themes.

Conclusions

This review highlights key influencers of Indigenous caregivers’ infant feeding experiences, which are often situated within complex social and environmental contexts with the role of family and culture as essential in supporting caregivers. There is a need for long-term follow-up studies that partner with communities to support sustainable policy and program changes that support infant and maternal health.

Peer Review reports

Introduction

Nutritional status is a key aspect of infant health with recommendations for exclusive breastfeeding for the first six months of life, which can also influence and be influenced by maternal health and wellbeing [ 1 , 2 ]. Breastfeeding has several benefits for the health and development of infants, including a reduced risk of ear and respiratory infections, obesity, asthma, skin conditions, childhood leukemia, and gastroenteritis [ 3 , 4 , 5 ]. It also supports bonding between the child and parent with improved intimacy [ 3 ]. Additionally, breastfeeding has several maternal physical and mental health benefits, including a reduced risk of breast and ovarian cancer, depression, and type 2 diabetes due to immunoprotective antibodies in breastmilk [ 3 ]. The World Health Organization (WHO) recommends exclusive breastfeeding for the first 6 months of life and initiation within the first hour after birth; however, less than half of infants 0–6 months old are exclusively breastfed worldwide [ 6 ]. Many countries are not meeting the WHO recommendations, with notable differences between low, middle, and high-income countries [ 2 ]. Differences in breastfeeding initiation rates and duration have been observed between Indigenous and non-Indigenous groups, with 6–10% lower breastfeeding initiation rates and shorter duration for Indigenous peoples [ 7 , 8 , 9 ].

Despite the many benefits of breastfeeding, bottle feeding with milk substitutes is a common form of infant nutrition and its common usage is related to a multi-dimensional set of factors influencing infant feeding decision-making. Breastfeeding is considered a traditional practice within many Indigenous cultures; however, disruptions to traditional lifeways through colonization have influenced intergenerational knowledge sharing, particularly within high-income, settler states like Canada, the US, Australia, and Aotearoa (New Zealand) [ 10 ]. Rollins et al. [ 1 ] summarize factors that influence the global breastfeeding environment including the sociocultural and market contexts, the healthcare system and services, family and community settings, employment, and individual determinants like the mother and infant attributes. However, these core breastfeeding environments for general populations overlook key considerations for Indigenous communities given the unique historical, cultural, and socio-economic contexts specific to Indigenous groups [ 11 ].

Many studies to date have focused on quantitative infant feeding data, incorporating structured questionnaires that have provided some insight into breastfeeding barriers and enablers for Indigenous caregivers [ 7 , 12 , 13 , 14 ]. However, these studies are informed by specific research questions and do not capture important nuances that caregivers experience related to infant feeding. Qualitative research can enhance our understanding of phenomena by providing flexible means for participants to engage in the research topic of interest without the constraints of structured instruments, and can even transform the research by highlighting community needs [ 15 , 16 ]. Qualitative research can also have synergy with Indigenous methodologies, supporting the use of qualitative research with Indigenous communities [ 17 ]. Given the value of qualitative inquiry and breastfeeding as traditional practice for many Indigenous cultures, disrupted by colonial influences and the burden of conditions that breastfeeding has been shown to mitigate [ 3 , 5 , 10 , 11 , 16 , 17 ], it is imperative that we consider Indigenous caregiver infant feeding experiences and perspectives to understand what needs exist as defined by communities and caregivers. Therefore, the overall aim of this scoping review was to identify and summarize the qualitative literature on infant nutrition experiences to inform needs as expressed qualitatively by Indigenous caregivers in Canada, the US, Australia, and Aotearoa. These regions are included given the shared colonial influences on Indigenous peoples with overlapping outcomes on health [ 10 , 18 ]. This review will also assess the qualitative methodologies used to understand what can be learned to inform Indigenous infant feeding services, policies, and research gaps.

Protocol and registration

This scoping review adheres to guidelines from Tricco and colleagues’ [ 19 ] Preferred Reporting Items for Systematic Reviews and Meta-Analyses ( PRISMA) extension for scoping reviews , the Joanna Briggs Institute’s Reviewer’s Manual Chap. 11 [ 20 ], as well as Arksey & O’Malley’s [ 21 ] foundational article on scoping studies. The protocol for the review is registered with the Open Science Framework ( https://doi.org/10.17605/OSF.IO/J8ZW2 ) and published with BMJ Open [ 22 ].

Eligibility criteria

Works included in this review must have focused on Indigenous populations in Canada, the United States, Australia, and/or Aotearoa. These four countries share commonalities in that they are colonial countries in which Indigenous peoples face inequitable health outcomes [ 10 , 18 , 23 ]. The topic of interest for this review was caregivers’ experiences of infant feeding within one or more of these regions. “Caregivers” refer to individuals in the infants’ immediate familial and social circles who are directly responsible for the regular care of the infant. A broad definition of those involved in caregiving was used, recognizing that within many Indigenous communities, traditional adoption practices occur, or biological parents may not be the primary caregivers in part related to complex socio-ecological challenges. The experiences of healthcare professionals were not included as they were not considered “caregivers” by this definition. Works that discussed breastfeeding, as well as alternative forms of infant feeding, such as formula and cow’s milk, were included. Works that only focused on the introduction of solid foods were excluded. To capture caregivers’ experiences of infant feeding, qualitative and mixed-method studies that discussed experiences, perspectives, and/or practices as described by caregivers were included. Studies that used exclusively quantitative methods or that only described an outsider perspective (e.g. health professional) were excluded. Peer-reviewed journal articles and grey literature were included if they met the above criteria, were published in the English language, and were published after 1969 [ 22 ].

Various types of grey literature such as government documents, dissertations, and research reports by academic and non-academic institutions, including Indigenous organizations, were included. Media reports (including videos, news, and blogs) were excluded from the grey literature as they did not follow a research design with results that could be considered alongside the studies included in the review, hindering our ability to compare and critically analyze the results. Similarly, publications that consisted of only an abstract were excluded from both grey and database publications during full-text review as not enough information was present for analysis.

Information sources

The search strategy was created with guidance from a research librarian at the Gerstein Science Information Centre, University of Toronto. The complete search strategy can be found as supplementary material in our published protocol [ 22 ]. Search terms primarily included broad terminology for Indigenous peoples (e.g. Native American) rather than specific Nation names (e.g. Ojibwe) as this would have significantly extended the search term list while not resulting in additional sources given how sources are indexed within Library systems. A database and grey literature search were conducted for this scoping review, completed independently from one another until final data extraction when the data were combined for analysis. For both searches, the reviewers followed a step-by-step process of title and abstract screening, followed by full-text screening, and then data extraction.

The database search planning and calibration occurred in August and September of 2020, and all data were exported in English on October 20, 21, and 22 of 2020. Exportation occurred over three days given feasibility of exporting the high number of citations and time capacity of the reviewers. A total of 16734 relevant sources available in the following databases were included: Medline, Embase, CINAHL, PsycINFO, and Scopus. These databases were selected to ensure a broad range of research given the multidisciplinary nature of research on this topic. The grey literature search consisted of a targeted search of a variety of Indigenous focused websites specific to the four countries and a thorough Google search with each of the country-specific Google versions (Google.com.au, Google.co.nz, Google.ca, and Google.com) where the first 10 pages of results were reviewed (Supplementary File 1 ). Lastly, Indigenous Studies Portal (I-Portal) was searched as part of the grey literature as this database uses a different indexing system than other research databases. The Canadian Agency for Drugs and Technologies in Health (CADTH)’s “Grey Matters” checklist [ 24 ] was used in the planning and tracking of grey literature searches and findings.

The results of the database search including 16734 citations were uploaded to Covidence (Veritas Health Innovation Ltd., Melbourne, Australia), a data management platform for systematic and scoping reviews, where 3928 duplicates were automatically removed. The 284 results of the grey literature search were recorded on Google Sheets (Alphabet Inc. California, USA) and 146 duplicates were manually removed by the reviewers. Due to the large number of results retrieved in the database and grey literature search, a hand-search of reference lists was not conducted.

A list of key words developed by HM were searched on each site and can be found in Supplementary File 1 . The grey literature search was completed by HM, CC, and HS with all reviewers assigned to search a Country-specific Google database for one of the included countries. Using a template created by Stapleton [ 25 ] at the University of Waterloo based on methods described by Godin et al. [ 26 ], the reviewers kept track of which search terms were searched on the websites, the number of results retrieved, and the number of items screened and saved for further full-text analysis. If a website did not have a search bar, relevant tabs were examined for research, resources, and other publications. I-Portal was originally searched on August 15th, 2021 (yielding 10 results), however the search was revised to remove Indigenous search terms as the database was already Indigenous-specific. The search was repeated on August 18th, 2021, and yielded 77 additional results. The grey literature search was completed between May 25, 2021 – August 18, 2021. No search limitations or filters were used for the grey literature search or the database search.

The database abstract screening was initially completed by HM and CC starting in October 2020. They were then joined by HS and CL in February 2021. To ensure all reviewers had a shared understanding of the eligibility criteria, two search results were screened together and each reviewer discussed their reasoning for inclusion or exclusion. HM also hosted an introductory meeting to review the screening process using Covidence Software [ 27 ] in detail. All 12806 database results were saved in Covidence [ 27 ].

Abstract and full-text screening was completed in Covidence by two independent reviewers. Any conflicts at the screening stage were resolved by AH after all the results had been screened by two reviewers. Full-text screening was completed by HM, AH, and CC, and when conflicts arose, the reviewers met to discuss the difference in opinion until a consensus was reached. A third reviewer joined to offer impartial opinions for full-text conflicts.

Grey literature results were not imported to Covidence. Instead, the team used Google Sheets to organize the publications. Similar to the database review process, each study was screened by two independent reviewers and conflicts were resolved by a third party and discussed for consensus. Full-text review of the grey literature was completed by HM, AH, CC, and HS.

Data extraction and analysis

HM compiled a list of variables to extract (Supplementary File 2 ), and the data extraction was completed by HM, AH, and CC in Covidence for database results and Google Sheets for the grey literature. The extraction template was reviewed and tested by all three reviewers using the same two articles. Discussion about any areas of confusion followed by minor edits to the data extraction template were completed prior to extraction.

Only one reviewer extracted data from most publications, however in circumstances where an article was complex or data extraction was not clear given the format of the article, two reviewers extracted data from the publication. An additional subset of five publications were also randomly double-reviewed by HM to ensure consistency in data extraction. There were an additional two articles that were excluded at this step after review and discussion by AH and HM.

Review findings using the extraction template (supplementary file 2 ) were exported into Microsoft Excel (Microsoft Corporation, Washington, USA) and reviewed by HM. HM compiled all data and completed summary figures for variables of interest. The primary analysis consisted of a qualitative review of the included papers’ results and recommendations using a thematic synthesis informed by grounded theory and meta-ethnography, where the included papers are synthesized together, and interpreted using descriptive and analytical themes [ 28 ]. Similar to grounded theory, this process was inductive and identifies themes through comparisons. HM reviewed all extracted data from the excel files, coding for overlapping themes and taking notes throughout. The full-text of the extracted papers were then revisited to identify overall concepts, followed by descriptive themes. Categorization of descriptive themes was completed based on the results and interpretations of included papers. Descriptive themes were refined through additional comparisons between papers. The same analytical process was used for both database and grey literature results, and final analysis involved the integration of themes from the database and grey literature papers. Supplementary file 3 provides a summary table of the included papers in this scoping review.

Characteristics of included articles

Of the final sample of 46 articles from which data was extracted (Fig.  1 ), there were studies from each of the four countries, with the most studies (39%) published from Canada. In addition, this qualitative literature on infant feeding included several Indigenous groups within the four countries. The studies retained in this review included authors who identified as either Indigenous or non-Indigenous, and several did not mention positionality (Fig.  2 ). 13% more grey literature studies discussed positionality and had Indigenous sole authorship compared to the database papers. Regarding methodologies utilized, several described Indigenous methodologies and used thematic analysis as an analytic tool (Figs.  3 and 4 ). However, a third of the studies did not describe their theoretical foundations for the qualitative inquiry. Over 60% of the studies were published in the fields of public health and/or nursing as per the authors stated fields of study and/or the Journal’s field, and although there were studies published from 1984 to 2019, 50% of the retained papers were published after 2010.

PRISMA flow diagram for studies identified, screened, and included in this review from both database and grey literature searches. Note that records not retrived are those in which the full-text was not accessible. This diagram was created from the PRISMA 2020 statement [ 29 ]

Author positionality as described in the retained papers

Summary of analytic tools used in the retained studies

Summary of theoretical foundations informing the retained studies’ methodologies

Analysis revealed a variety of important themes that aligned with Indigenous and public health perspectives on health, including the socioecological model. There were twelve final overarching themes including colonization, social perceptions, family, professional influences, culture and traditionality , environment (i.e. built environment) , autonomy, survivance, infant feeding knowledge, cultural safety , milk substitutes , and establishing breastfeeding with evidence of connections among these themes. These themes are shown in Fig.  5 in a circular pattern where the themes intersect with the infant and caregiver represented at the centre. This model is conceptually aligned with that of Dodgson et al. [ 30 ], who considered the “contextual influences within the social structures of family and community, Ojibwe culture, and mainstream culture.”

Scoping review research model of themes

The twelve final themes are shown as the main influences on infant feeding experiences. The themes are arranged in a circular pattern with the infant and caregiver represented at the centre, emphasizing the connection between all of the themes

Theme one: colonization

There were 14 papers that discussed colonization of Indigenous peoples as a key factor influencing infant feeding decisions and experiences (Fig.  6 ) [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 ]. Colonization has meant the dispossession of land and limited access to culturally safe healthcare, malnutrition, and loss of language through residential schools, loss of culture and traditional knowledge through assimilation and separation of families, disrupting breastfeeding practices and limiting income for infant formula. Eni et al. [ 36 ] described the policies leading to evacuation from communities to tertiary-care hospitals for birthing as the medicalization of birthing practices, which creates various challenges for First Nations women in Canada. One participant also shared about the impacts of intergenerational trauma related to colonization on breastfeeding, ‘‘You can’t teach about breastfeeding technique and think things will change. It’s the spirit that’s been affected, our experience with trauma. Our women need to relearn how to bond with their children.’’.

A qualitative study with Aboriginal Australian first-time mothers noted the disruptions to breastfeeding practices over time, providing a historical chart detailing how infant feeding practices changed as a result of colonial influences [ 38 ]. Brittany Luby [ 39 ] described how hydroelectric flooding from 1900 to 1975 in Northwestern Ontario reduced breastfeeding practices for Anishinabek mothers and their infants. Although not all studies specifically discussed history and colonization, those that considered the broader historical context highlighted how important this issue is in understanding the factors that lead to infant feeding decisions, particularly those that do not align with breastfeeding as a traditional feeding practice.

Frequency of identified themes in the database papers and the grey literature

Theme two: culture and traditionality

Culture , including traditionality, was the second most described theme throughout all papers, identified both directly and indirectly in 31 papers (Fig.  6 ) [ 30 , 31 , 32 , 34 , 35 , 37 , 38 , 39 , 40 , 41 , 42 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 ]. The Navajo Infant Feeding Project focused on cultural beliefs influencing infant feeding practices within three Navajo communities in the United States [ 48 ] and emphasized breastfeeding’s significance for nutritional, physical, and psychological health where mothers not only pass along physical health benefits, but also their wellbeing to their children. The Baby Teeth Talk Study in Cree communities in Northern Manitoba, Canada, has identified breastfeeding as a cultural intervention for the prevention of early childhood caries [ 52 ]. Several studies included a variety of generations in data collection, contributing to rich discussion of how breastfeeding rates and connection to traditionality has changed in some communities [ 48 , 57 , 64 , 65 ]. For example, grandmothers living on the Fort Peck Reservation in Montana, US, were interviewed about their perspectives on infant feeding [ 65 ]. In one of the ethnographic studies, there was a specific focus on the Ojibwe culture relating to infant feeding practices from the perspective of mothers, professionals who were also community members, and Elders [ 35 ]. This study emphasized the holistic and collective worldview of the community, influencing women’s roles within the family and how teachings were passed on from generation to generation [ 35 ]. This was considered to be important in influencing effective and culturally safe breastfeeding promotion. Within the Northwest Territories, Canada, Moffitt and Dickinson [ 53 ] supported breastfeeding knowledge translation tools for Tłı̨chǫ women with one of the themes focused on factors that “pull to breastfeeding,” including breastfeeding as a traditional feeding method. In general, Indigenous communities described breastfeeding as a cultural practice; however, how this is supported and the traditional knowledge surrounding this practice may differ from community to community. Therefore, health providers must be aware of community-specific protocols and support these within programs and recommendations.

Theme three: social perceptions

Societal influences are often considered alongside cultural perspectives of infant feeding; therefore, this theme was also commonly discussed in the papers retained in this scoping review (Fig.  6 ) [ 30 , 32 , 33 , 36 , 37 , 38 , 40 , 42 , 49 , 50 , 52 , 54 , 57 , 58 , 59 , 61 , 64 , 66 , 67 , 68 , 69 , 70 , 71 ]. In New South Wales, Australia, Aboriginal mothers and key informants noted the need for “a safe place to feed,” including concerns about the social acceptability to breastfeed in public [ 32 ]. Broader social “norms” are also discussed as influencing maternal behavior [ 68 ], and respondents in some studies expressed concern about judgements from others [ 32 , 36 ]. Tapera et al. [ 40 ] described concerns about social pressures and a lack of support with one grandparent sharing, “well here in New Zealand, I know we have a problem with this [breast-feeding], especially when mothers go out and they breast-feed their babies in public. There’s a lot of people that moan and groan about this.” Similarly, regarding social norms, a grandmother living in the US shared,

“a long time ago that, it [breastfeeding] was acceptable and nobody had any qualms about it but today, I mean you read continually about, people, mother’s tryin’ ta breastfeed and they’re being chased out a places or stores or people are rude about it […]. Society’s changed, you know, it’s […] society, has come to the point where it’s […] trying to tell us what’s the right way ta live what’s the right way ta raise our kids” [ 65 ].

Dodgson et al. [ 30 ] described how in an Ojibwe community in Minnesota, US, participants noted the dominant societal influences in contrast to community traditions, with women making an effort to engage in traditional practices. The sexualization of breasts in mainstream society sometimes influenced Indigenous mothers’ infant feeding experiences [ 36 ], although Ojibwe caregivers in Minnesota attributed shyness with breastfeeding to traditional value opposed to sexualization of breasts [ 30 ]. Eni et al. [ 36 ] included sexual objectification of the feminine body as a subtheme in their study, describing how this social perception damages maternal mental health, creating a barrier to breastfeeding. While shifting social norms is a significant challenge, breastfeeding supports can address concerns about the sexual objectification of breasts by creating safe spaces for parents to talk about the challenges and ensure that parents have access to mental health resources.

Theme four: family

Dodgson et al. [ 30 ] described family as a pattern that influences breastfeeding intersecting with the social structures of the community, culture, and the broader society. There were 33 other papers that described the influence of family on infant feeding practices making this the most discussed theme (Fig.  6 ) [ 30 , 31 , 32 , 33 , 36 , 38 , 39 , 40 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 53 , 54 , 55 , 57 , 58 , 59 , 60 , 61 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ]. Native American mothers living in six communities highlighted the importance of family as a key theme [ 47 ]. One mother shared, “For me, it’s my mom definitely [whose advice is most important] because she has had three kids and I lived with her or near her for all of my kids. So I’ve always gone to her first for advice.” This was echoed by many other participants with a paraprofessional adding, “family [advice is most important], because they are around their family most. And they always hear from their aunties, or from grandma, baby’s fussing, baby must be hungry, baby needs this and baby needs that.” The Baby Basket Program in Cape York, Australia identified that empowering families was the foundation of the program to ensure that mothers and their partners were equipped for the arrival of their babies [ 50 ]. Family often plays an integral role in supporting mothers in infant feeding practices. Bauer and Wright [ 45 ] note that even when mothers don’t have other supports or conditions in place to support breastfeeding, they may still choose to breastfeed if their family is supportive. However, when this support is lacking, mothers find it challenging to breastfeed [ 31 , 36 ]. Some studies identified the significance of family in the study design, integrating family caregiver perspectives in data collection [ 64 , 65 ]. Therefore, health programs and research studies should consider the role and experience of non-primary caregivers within family networks for infant and maternal health and nutrition.

Theme five: professional influences

This theme represents the influence of formal systems including healthcare professionals, health and social programs, child services, and the legal system. In total, there were 26 papers that referenced professional influences on infant feeding experiences (Fig.  6 ) [ 30 , 31 , 33 , 38 , 41 , 42 , 43 , 45 , 47 , 48 , 50 , 51 , 52 , 54 , 58 , 59 , 61 , 62 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 ]. Some studies incorporate health workers as participants in data collection [ 47 , 50 , 65 ]. One health paraprofessional shares about some of the pressures experienced by mothers to formula feed, “sometimes hospitals and doctors want to push formula in bottles on moms [ 47 ].” One of the main themes in a study with Sioux and Assiniboine Nations in the US was the ‘ Overburdened Healthcare System’ , describing a lack of resources and infrastructure to support breastfeeding, including a subtheme of mistrust in the healthcare system due to previous negative experiences such as forced sterilization of Indigenous women [ 65 ]. However, some caregivers also expressed positive healthcare supports, “when I was at home, [clinic midwife] and [lactation consultant made home visits] … they encouraged me … And then it started getting a little bit better, but it was still a bit hard. Now he feeds pretty all right [ 73 ].” Professional influences on infant feeding are nuanced and may differ significantly within various contexts and individuals; therefore, tailored interventions are needed.

Theme six: environment

This theme represents the external variables within the built environment that influence decision making including work, school, remoteness, and cost of formula. Eighteen papers addressed this theme [ 30 , 31 , 44 , 45 , 46 , 47 , 48 , 49 , 51 , 53 , 58 , 59 , 66 , 67 , 68 , 70 , 71 , 72 ]. Wright et al. [ 74 ] specifically considered the challenge of breastfeeding with maternal employment among the Navajo population in the US. In Bauer and Wright’s [ 45 ] study that explored infant feeding decision models, they identified that work and school are part of the decision-making process on whether to breastfeeding or to use formula, but even when these environmental challenges are present they can be further influenced by other factors, like family . For example, a mother may choose to breastfeed and use a breast pump to navigate work/school schedules, but family members may recommend that they can incorporate formula; decision-making is not only about the main caregiver’s desires but can involve various decision-makers.

Theme seven: autonomy

This theme describes parents’ freedom to make infant feeding decisions that fit for them and their priorities. Maternal desire to breast- or bottle-feed was discussed in select papers in this review [ 45 , 51 ]. In addition, other papers describe parents’ freedom to do activities outside of infant feeding in the early months of baby’s life with discussion of time required to breastfeed or prepare bottles for feeding [ 31 , 58 , 72 , 74 ]. A key informant in a study with an Aboriginal community in Northern New South Wales, Australia, shares, “they want to breastfeed, but then it comes down to when they want to go out, or keep up with their man [ 32 ].” Some parents report that they experienced judgements from others or feel forced into making a specific decision on infant feeding method, highlighting a desire to have support and freedom to make their own decisions [ 36 , 56 ].

Theme eight: infant feeding knowledge

Several studies emphasize the importance of knowledge on infant feeding experiences, highlighting the value of infant feeding education, both within the overall healthcare system and from traditional teachings [ 30 , 32 , 35 , 40 , 42 , 43 , 47 , 52 , 57 , 58 , 62 , 64 , 66 , 67 , 68 , 69 , 70 , 71 , 72 ]. Within the theme of addressing feeding challenges in one study [ 66 ], a caregiver shared how knowledge helped her to work through a challenge,

“He did start fussing at about 6 weeks and that was kind of hard because I thought, ‘No, I have got this perfect now, and he has started to muck up’. But then I read, because I had those booklets and I read that sometimes they — at a certain point — they get a bit fussy and you just have to work through it. [Ml7]” [ 66 ].

Traditional breastfeeding knowledge is important for many communities; one Anishinaabe community knowledge keeper shared that “breast milk is a gift and a medicine a mother gives her child” [ 35 ]. This study also discusses feeding patterns as shared by Elders and traditional teachers. Traditional knowledge considers holistic perspectives of health where caregivers are also focused on the baby’s spiritual wellbeing [ 48 , 56 ].

Theme nine: milk substitutes

Bottle feeding (formula or canned milk) and solid foods are described in several papers as alternatives or complements to breastfeeding [ 31 , 33 , 34 , 37 , 39 , 47 , 48 , 49 , 51 , 52 , 53 , 58 , 66 , 67 , 74 , 75 ]. In Neander and Morse’s [ 37 ] study with a Cree community in Alberta, Canada, bottle feedings were offered particularly when mothers felt that they were not producing adequate milk supply to meet the baby’s nutritional needs. Insufficient milk supply is echoed as a concern in several other papers resulting in complementary bottle feeding or weaning [ 48 , 51 , 56 , 66 , 67 ]. A Māori father shares,

“about the second week, baby just wanted more food. She (partner) would end her day and baby was just hungry. We had to [give her] the bottle and then she would be finally satisfied. It wasn’t that she made a choice. Baby was actually demanding more and more and she couldn’t produce it. (First-time father, mid 20’s) [ 56 ].”

This theme particularly overlaps with autonomy as parents balance infant feeding decisions with breastmilk supply, work, school, and other personal commitments.

Theme ten: cultural safety

Indigenous caregivers interact with a variety of health services postnatally; however, there is a need to address cultural safety within the healthcare system. Twelve retained papers highlighted this theme either directly as one of their themes or as part of another theme (Fig.  6 ) [ 30 , 31 , 44 , 47 , 50 , 64 , 66 , 67 , 69 , 71 , 73 , 74 ]. One health worker in Victoria, Australia, shared,

“I can’t say often enough or long enough, loud enough the ideal for children 0–8 is to have access to maternal and child health. You might say ‘oh yes, they’ve got access to mainstream and they’re culturally going to put up a few Indigenous prints in their rooms’ It’s not the same. Our families are telling us with their feet it’s not the same.”

Mothers expressed a desire for more traditional infant feeding knowledge within services and culturally relevant supports [ 47 , 64 ]. A study that focused on a baby basket program to support families in a Murri (Local Australian Aboriginal Group) Way identified how important culturally safe language and relationships are for families,

“…the nurse is also learning what the best way is to approach a family and what the wording has to be, what the languaging is around things, what the traditional words are for Indigenous language and are appropriate for use in certain circumstances” [ 50 ].

Theme eleven: survivance

Indigenous caregivers experience a variety of hardships; however, through resistance and survival, they practice cultural revitalization [ 76 ]. This theme is discussed in 15 papers and is often described through a lens of maternal mental health (Fig.  6 ) [ 30 , 31 , 33 , 43 , 53 , 54 , 57 , 58 , 59 , 63 , 64 , 66 , 68 , 36 , 74 ]. Some parents express feelings of guilt for the challenges they encounter, which can further contribute to negative emotions [ 58 ]. Maternal mental and emotional health can impact infant feeding experiences,

“…sometimes people’s psychological health, mental health is more of a risk factor, you know if you’re not sleeping and you’re bordering on depression and you’re not coping well and you can’t get the baby to latch and you’re constantly feeling like a failure and you can’t get out of that rut, is it worth it?…People have to decide that for themselves. (Key Informant #5)” [ 33 ].

A grandmother in the Northwest Territories of Canada noted the disembodiment caused by residential schools as expressed as a disconnection between physical experiences and relationships,

“You know in those days, I mean residential school. In those days, they never did talk about their body parts because I think they were too ashamed [of your body] to say to your kids. I never did hear it [breastfeeding] from my sisters or nobody in the family. They were so private (L151-156)” [ 57 ].

Traumatic experiences, like residential schools, can have a lasting impact on how caregivers navigate motherhood and infant feeding, and the support they receive from family members.

Theme twelve: establishing breastfeeding

There are several practical challenges that mothers encounter while breastfeeding like pain, latching issues, and low milk supply, discussed in 11 of the studies (Fig.  6 ) [ 48 , 51 , 54 , 56 , 58 , 61 , 66 , 68 , 71 , 72 ]. A mother shared,

“He wouldn’t latch on all the time, like, the nurses and stuff tried to help me but then it would be all frustrating…. He didn’t really know what to do. He tried and then they gave him formula. He really loved it. [MI5]” [ 66 ].

Although these challenges are most discussed at the beginning of breastfeeding, sometimes concerns arise when babies are older.

“Yeah it was 8 or 9 months after she was born. After a while there was too much pressure on me. She was getting up all through the night and she would eat and eat and eat and not get full…” [ 33 ].

Overall, many caregivers reported that breastfeeding is difficult; therefore, supports that consider the variety of challenges that can arise are needed.

Study recommendations

The studies included in this review were published over three decades starting in 1984 until 2019 and were completed with various Indigenous communities in four countries. We anticipated that earlier work would demonstrate markedly different infant feeding recommendations than more recent research; however, this was not necessarily the case. For example, cultural safety is a more recent discussion within the health literature; however, although we see some discussion of this in more recent studies, studies in the 80’s and 90’s also highlight the importance of incorporating traditional teaching and consulting community members [ 37 , 48 ]. Therefore, supporting Indigenous self-determination where health professionals provide culturally appropriate care is essential.

In addition to topics related to cultural safety, various studies highlight a need for community-driven and local knowledge to inform programs and policies related to infant nutrition [ 31 , 47 , 57 , 64 , 75 ]. Several studies also focus on infant feeding specific programs and behavioral changes in their recommendations [ 47 , 50 , 65 ]; however, many of these studies also highlight the need to expand beyond the individual’s role in decision making and address the broader social and environmental factors such as the workplace, healthcare infrastructure, social perceptions, among others, that influence infant feeding decisions. For example, Eni et al. [ 36 ] note that there are a complexity of factors resulting in various breastfeeding environments. These structural, social and cultural contexts are discussed throughout several of the grey literature texts as well [ 32 , 33 ]. It is also important to note that in the most recently published database paper, maternal mental health is directly addressed in the recommendations and this is the only paper with this focus for next steps [ 65 ]. Interventions that target socio-ecological factors based on the included papers’ recommendations for infant feeding are summarized in Fig.  7 .

(Adapted from Rollins et al. 2016)

The components of Indigenous infant feeding environments informed by community-based interventions

This scoping review presents and summarizes the findings reporting Indigenous infant feeding experiences within the qualitative literature in Canada, the US, Australia, and Aotearoa. Twelve themes were identified which summarize the literature including culture and traditionality , colonization, family, environment, social perceptions, professional influences, milk substitutes, breastfeeding initiation, cultural safety, survivance, infant feeding knowledge, and autonomy. The most prevalent themes discussed by caregivers and researchers in the included papers were family and culture/traditionality . The frequency of these two themes highlight the significant impact of family and culture/traditionality on infant nutrition decision-making for Indigenous caregivers and overlaps with components of the socio-ecological model [ 77 ]. This focus on family and culture/traditionality also emphasizes the importance of familial relationships and a collective mentality within traditional life ways for many Indigenous communities in these regions on infant nutrition and care practices.

In their informative global breastfeeding paper, Rollins and colleagues’ [ 1 ] conceptualize the components that contribute to the breastfeeding environment at multiple levels, overlapping with the social determinants of health. In this review, we observed that caregivers report similar components of the breastfeeding environment; however, these components seem to be described collectively, rather than as separate contexts. This is evident in the recommendations proposed by authors with a large focus on local and community-specific leadership, multidisciplinary interventions, and cultural safety in response to historical traumas, particularly within the healthcare system (Fig.  7 ). This aligns with Indigenous epistemology with an emphasis on the collective and interconnectedness of all things where power is manifested together, not over one another, and is based in local land-based knowledge [ 78 , 79 ].

A primary recommendation echoed within many of these studies was the need for community engagement in program and policy development [ 34 , 47 , 50 , 64 ]. This may need to be expanded upon to support Indigenous self-determination of policy and programs related to infant feeding where community members are not only engaged but leading the way forward in maternal and infant health. It is important to note that there have been changes over time in how these recommendations and perspectives are discussed and the role of the health professional, particularly related to cultural safety. For example, although similar concepts are discussed in Neander and Morse’s paper published in 1989, ‘cultural safety’ is not used as the terminology, which has been expanded upon in recent years by Indigenous and non-Indigenous scholars [ 37 , 80 , 81 ].

Related to this focus on health professionals and cultural safety, it’s important to distinguish that in many of the positive experiences expressed by participants in the studies, these interactions seemed to be primarily with professionals interacting closely with families. For example, midwives, who make home visits, were often included as part of positive experiences. In the literature, there is an emphasis on including practitioners who can build strong relationships with families through home visits and regular community engagement in routine services, which supports cultural safety within the healthcare system [ 82 , 83 ]. Health professional regulatory bodies should consider implementing practice competencies that support professionals to build and navigate strong and ethical relationships with clients/patients. Similarly, healthcare settings that serve Indigenous peoples should consider processes and therefore, facility infrastructures that enable close family-client-professional interactions. An example of this implementation with positive client experiences is the Toronto Birthing Centre, which uses an Indigenous framework and has birthing rooms with space for family [ 84 ].

The studies in this review are written within various fields of research; therefore, there were differences in methodological reporting. Future qualitative work should be thorough in reporting theoretical foundations to provide clarity of how the analyses and overall projects are approached (Fig.  4 ) [ 85 ]. Given the limited studies that report author/researcher positionality (Fig.  2 ), this may be an important addition in forthcoming work as a means of respecting Indigenous and qualitative literature conventions where we recognize that positionality influences ontological origins [ 86 ]. We challenge the academy to recognize that Indigenous and local knowledges are required within Indigenous health research and dissemination practices, while acknowledging our own limitation in this review of a single country authorship team.

This systematic scoping review utilized a rigorous search strategy that limited the possibility of missing relevant publications; however, it was time intensive. PRISMA-ScR guidelines were followed with two independent reviewers at each stage, enabling reproducibility of this review. The inclusion of the grey literature is a strength in this study as it captured important papers that were not published in peer-reviewed journals, often from Indigenous authors and communities (many of which were graduate dissertations), which was a priority in this review. A possible limitation is the exclusion of work that only discussed the introduction to solid foods; it is possible that this excluded an important conversation about the differences of introducing solids, like traditional foods from an Indigenous group’s perspective. In addition, the topic of this review is multidisciplinary; therefore, it is possible that although effort was made to include a broad range of research field databases in the search, relevant sources may have been missed.

In conclusion, this scoping review highlights important considerations for infant feeding environments within Indigenous communities with a focus on family and culture. Based on caregiver experiences, Indigenous breastfeeding supports must be community led with a focus on local capacity and traditional teachings. An emphasis on an intergenerational perspective that considers structural and systems approaches including cultural safety within healthcare, addressing maternal mental health, and consideration of sustainability over time is encouraged. Future work should focus on these key areas through strength-based research approaches, grounded in strong relationships and long-term follow-up.

Data availability

All data generated or analysed during this study are available from the corresponding author on reasonable request.

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Acknowledgements

We wish to acknowledge the important contribution of Halima Abubakar in the review process. Given the knowledge specific to Indigenous communities discussed in this scoping review and out of respect for Indigenous research conventions, the authors position themselves within the research to explain the lens from which they approach and understand the research process. TG and AH are non-Indigenous scholars and faculty members based at the University of Toronto, which rests on lands that are the traditional home of the Huron-Wendat, the Seneca, and the Mississaugas of the Credit. All other authors have had student or supporting roles throughout this work and situate themselves as follows: HM is a settler of Scottish, Irish, French, German, and English ancestry residing in Haudenosaunee and Anishinaabe territory, which is part of the dish with one spoon agreement; CC is a settler living in Treaty 7 Territory, with ancestral roots in Germany, Scotland, and the Ukraine; AS is an Odawa Kwe from Wikwemikong, Manitoulin Island, Ontario. Currently, residing in the Tiohtià:ke in Kanien’kéha unceded territory; and HS is living in Treaty 13 territory with ancestral roots in Afghanistan. The remaining co-authors identify as non-Indigenous scholars.

This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.

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As the first author, HM conceptualized this work and provided leadership throughout. She participated in every aspect of this review, wrote the initial manuscript, and completed revisions. CC contributed to the screening and full text review of this work. She also contributed to the analysis, and the writing and review of the manuscript. TG supported the protocol of this review and provided guidance throughout analysis. She also contributed to the final manuscript. HS supported screening and full text review. She also provided edits for the manuscript. AS provided feedback on the analysis for this review and contributed to the writing of the manuscript. CL supported screening of papers and provided edits to the final manuscript. AH provided guidance throughout the duration of this review, supported decision making, and provided edits on the manuscript. All authors approved the final manuscript.

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Monteith, H., Checholik, C., Galloway, T. et al. Infant feeding experiences among Indigenous communities in Canada, the United States, Australia, and Aotearoa: a scoping review of the qualitative literature. BMC Public Health 24 , 1583 (2024). https://doi.org/10.1186/s12889-024-19060-1

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DOI : https://doi.org/10.1186/s12889-024-19060-1

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• Published: 05 June 2024

The urgent need for designing greener drugs

• Tomas Brodin   ORCID: orcid.org/0000-0003-1086-7567 1   na1 ,
• Michael G. Bertram   ORCID: orcid.org/0000-0001-5320-8444 1 , 2 , 3   na1 ,
• Kathryn E. Arnold   ORCID: orcid.org/0000-0002-6485-6065 4 ,
• Alistair B. A. Boxall 4 ,
• Bryan W. Brooks   ORCID: orcid.org/0000-0002-6277-9852 5 ,
• Daniel Cerveny   ORCID: orcid.org/0000-0003-1491-309X 1 , 6 ,
• Manuela Jörg   ORCID: orcid.org/0000-0002-3116-373X 7 , 8 ,
• Karen A. Kidd   ORCID: orcid.org/0000-0002-5619-1358 9 ,
• Unax Lertxundi   ORCID: orcid.org/0000-0002-9575-1602 10 ,
• Jake M. Martin 1 , 2 ,
• Lauren T. May   ORCID: orcid.org/0000-0002-4412-1707 11 ,
• Erin S. McCallum 1 ,
• Marcus Michelangeli   ORCID: orcid.org/0000-0002-0053-6759 1 , 3 , 12 ,
• Charles R. Tyler 13 ,
• Bob B. M. Wong   ORCID: orcid.org/0000-0001-9352-6500 3 ,
• Klaus Kümmerer   ORCID: orcid.org/0000-0003-2027-6488 14 , 15   na2 &
• Gorka Orive 16 , 17 , 18   na2  

Nature Sustainability ( 2024 ) Cite this article

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• Drug regulation
• Environmental impact

The pervasive contamination of ecosystems with active pharmaceutical ingredients poses a serious threat to biodiversity, ecosystem services and public health. Urgent action is needed to design greener drugs that maintain efficacy but also minimize environmental impact.

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Acknowledgements

We acknowledge funding support from the Swedish Research Council Formas (2018-00828 to T.B., 2020-02293 to M.G.B., 2020-00981 to E.S.M., 2020-01052 to D.C., 2022-00503 to M.M. and 2022-02796/2023-01253 to J.M.M.), the Kempe Foundations (SMK-1954, SMK21-0069 and JCSMK23-0078 to M.G.B.), the Swedish Research Council VR (2022-03368 to E.S.M.), the European Union’s Horizon 2020 Research and Innovation Programme under the Marie Skłodowska-Curie grant agreement (101061889 to M.M.), Research England (131911 to M.J.), the Spanish Ministry of Economy, Industry and Competitiveness (PID2022-139746OB-I00/AEI/10.13039/501100011033 to G.O.), the Australian Research Council (FT190100014 and DP220100245 to B.B.M.W.), the Jarislowsky Foundation (to K.A.K.), a Royal Society of New Zealand Catalyst Leaders Fellowship (ILF-CAW2201 to B.W.B.) and the National Institute of Environmental Health Sciences of the National Institutes of Health (1P01ES028942 to B.W.B.). The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Institutes of Health.

Author information

These authors contributed equally: Tomas Brodin, Michael G. Bertram.

These authors jointly supervised this work: Klaus Kümmerer, Gorka Orive.

Authors and Affiliations

Department of Wildlife, Fish, and Environmental Studies, Swedish University of Agricultural Sciences, Umeå, Sweden

Tomas Brodin, Michael G. Bertram, Daniel Cerveny, Jake M. Martin, Erin S. McCallum & Marcus Michelangeli

Department of Zoology, Stockholm University, Stockholm, Sweden

Michael G. Bertram & Jake M. Martin

School of Biological Sciences, Monash University, Melbourne, Victoria, Australia

Michael G. Bertram, Marcus Michelangeli & Bob B. M. Wong

Department of Environment and Geography, University of York, York, UK

Kathryn E. Arnold & Alistair B. A. Boxall

Department of Environmental Science, Baylor University, Waco, TX, USA

Bryan W. Brooks

Faculty of Fisheries and Protection of Waters, University of South Bohemia in České Budějovice, Vodňany, Czech Republic

Daniel Cerveny

Medicinal Chemistry Theme, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia

Manuela Jörg

Centre for Cancer, Chemistry – School of Natural and Environmental Sciences, Newcastle University, Newcastle Upon Tyne, UK

Department of Biology, McMaster University, Hamilton, Ontario, Canada

Karen A. Kidd

Bioaraba Health Research Institute, Osakidetza Basque Health Service, Araba Mental Health Network, Araba Psychiatric Hospital, Pharmacy Service, Vitoria-Gasteiz, Spain

Unax Lertxundi

Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University, Parkville, Victoria, Australia

Lauren T. May

School of Environment and Science, Griffith University, Nathan, Queensland, Australia

Marcus Michelangeli

Biosciences, Faculty of Health and Life Sciences, University of Exeter, Exeter, UK

Charles R. Tyler

Institute of Sustainable Chemistry, Leuphana University Lüneburg, Lüneburg, Germany

Klaus Kümmerer

International Sustainable Chemistry Collaborative Centre (ISC3), Bonn, Germany

Laboratory of Pharmaceutics, School of Pharmacy, University of the Basque Country, Vitoria-Gasteiz, Spain

Gorka Orive

Biomedical Research Networking Centre in Bioengineering, Biomaterials and Nanomedicine, Vitoria-Gasteiz, Spain

Bioaraba, NanoBioCel Research Group, Vitoria-Gasteiz, Spain

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Corresponding authors

Correspondence to Tomas Brodin , Michael G. Bertram or Gorka Orive .

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Nature Sustainability thanks Lydia Niemi, Terrence Collins and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Brodin, T., Bertram, M.G., Arnold, K.E. et al. The urgent need for designing greener drugs. Nat Sustain (2024). https://doi.org/10.1038/s41893-024-01374-y

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