Air Pollution


Air pollution is a very big environmental challenge which is adversely dealing with global health. It has a deleterious impact on our health and wellbeing, especially, in urban areas where industrial activities and human population are on the rise. It is the introduction of chemicals, particulate matter, or biological materials into the atmosphere which can cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment. According to the World Health Organization, particulate matter, ground level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead are the six major air pollutants; and these pollutant particles which find their way into the atmosphere through man-made and natural sources have caused a lot of havoc in the human body systems, organs and tissues, causing different forms of diseases both acute and chronic which has resulted in systems and organs failures; and this will continue to happen until we find better sustainable solutions to mitigate against air pollution. Exposure to pollution from air pollutants diminishes the quality of the air we breathe. The importance of air to man is very tremendous because, it supports and sustains life in man; and without it, life will seize to exist on earth. In the light of this, the air we breathe should be of good quality; but unfortunately, due to some factors which have led to the pollution of the air in our environment, the quality of the air we breathe has been reduced; and this has led to so many health consequences to living organisms, especially, to man; and as such, reduce the quality of life. The government has a bigger role to play in tackling this problem of air pollution by making policies that bother about environmental protection; creation and adequate funding of a viable environmental protection agency whose duties should include and not limited to air quality monitoring and penalizing of offenders whose individual or industrial activities introduce hazardous materials into the atmosphere. Behavioural changes in individuals can be facilitated by vigorous awareness campaigns to inculcate to people the dangers of air pollution. Even though we are very much aware of the sources of pollution, a great deal of research is still continually needed to understand how it affects our health.

Understanding Air Pollution

Air pollution is a problem as old as history itself. It is the introduction of chemicals, particulate matter, or biological materials into the atmosphere which can cause harm or discomfort to humans or other living organisms, or cause damage to the natural environment or built environment. According to a media center article released by W.H.O in 2014, it was established that 7 million people die every year from air pollution-related diseases. Some of these diseases include stroke and heart diseases, respiratory illness and cancer. The article also noted that many health-harmful air pollutants also damage the climate. Fine particles of black carbon (soot) from diesel and biomass combustion and ground level ozone are leading examples; and reducing air pollution would save lives and help slow the pace of near-term climate change W.H.O. 2016).

The statistics above is a clear indication that air pollution is a very serious global problem which needs utmost attention because atmosphere contamination can also be regarded as global contamination. Solving the health problems associated with air pollution should be in a fast-track if actually we still want mankind survival on earth.

What is air pollution?

According to World Health Organization, air pollution is the contamination of the indoor or outdoor environment by any chemical, physical or biological agent that modifies the natural characteristics of the atmosphere. This implies that air pollution occurs when harmful, toxic or excessive quantities of substances, including gases, particles and biological molecules are introduced into earth’s atmosphere.

Air pollution can be of natural and anthropogenic origin. This is because human activities as well as natural occurrences or phenomena can make the air around us unfit for respiration. The natural phenomena which could cause air pollution include events such as wildfires, volcanic activity and dust/sand storms. Anthropogenic or man-made air pollution can be traced back to when humanity discovered how to make fire (Vhahangwele et al; 2018). While air pollution in those days was insignificant compared to the present time, burning biomass in enclosed spaces for space heating or for cooking purposes would have exposed humans to risk of respiratory diseases and injuries. As human populations proliferate and increasingly burned biomass and fossil fuels (such as coal) indoors, the exposure to air pollution and its negative consequences rose significantly (Guy, 2011).

The impacts of air pollution can be direct and indirect on humans. The direct impacts include poor health, damage of materials and the ecosystems, and poor visibility. Less direct impacts include ‘acid rain’ which results from mixture of rain and the chemicals being released into the atmosphere (Manisalidis et al; 2020). Changes in human behavior can occur as a result of air pollution. One of such behavioral change is the migration of inhabitants of heavily polluted urban areas or tourists staying away from polluted cities (Can et al; 2019). The main indirect impact is climate change. The biomass and fossil fuels that cause air pollution have also caused global warming resulting from the release of Greenhouse gases (GHGs). Air pollution has many and diverse impacts and it affects the quality of the air in our immediate environment (Jillian, 2016).

Air pollutants

Clean air is very vital and necessary to sustain the delicate balance of life on earth. However, the quality of air can be affected drastically by air pollution. Air pollution occurs when certain gases and particles build up in the atmosphere to levels such that they can cause harm to our health; causing breathing and respiratory problems, and even resulting in premature death, as well as damaging the environment around us (Ghorani et al; 2016).These gases and particles, known as pollutants tend to come from man-made sources, including the burning of fossil fuels such as coal, oil, petrol or diesel; but can also come from natural sources such as volcanic eruption and forest fires (Perera, 2017).Air pollutants can be in the form of solid particles, liquid droplets or gases; and these pollutants can be classified into primary and secondary pollutants.

Primary air pollutants

A primary pollutant is a pollutant which is emitted directly from the source or activities causing the pollution. Some of these sources include; airplanes, factories, wildfires, agriculture, vehicle exhausts, power generation and volcanoes. Examples of primary air pollutants include; carbon monoxide (CO), carbon dioxide (CO2), sulphur dioxide (SO2), nitric oxide (NO), ammonia (NH3), nitrogen dioxide (NO2), volatile organic compounds (VOCs), particulate matter (PM) (Donver et al; 2018).

Carbon monoxide (CO)

Carbon monoxide (CO) is a very poisonous gas. It is colourless and odourless in nature. It is formed as a by-product of incomplete combustion processes involving carbon based energy sources such as the burning of petrol, coal and wood. During the combustion process, if there is not enough oxygen available to create carbon dioxide as a by-product, then, carbon monoxide is created instead. The biggest sources of this dangerous carbon monoxide comes from vehicles, especially when they are moving slowly or when the engine is idle. (TRBNRC, 2002).

Carbon monoxide is very dangerous to humans. Once it is inhaled, it competes with oxygen by attaching on the hemoglobin to form carboxyhemoglobin in red blood cells and starving vital organs such as the brain, nervous system tissues and the heart of oxygen thereby reducing their ability to function properly (Chris, 2005).

Nitrogen oxide (NOx)

Nitrogen oxides species (NOx) represent one of the most threatening air pollutant due to their prevalence and harmful impact on environment and human health. The term NOx gather mainly nitric oxide (NO) and nitrogen dioxide (NO2), mostly produced by anthropogenic activities such as transport and industries (Depayras et al; 2018). Nitrogen oxides (NOx) can form secondary air pollutants and can result in environmental problems such as acidification and nitrogen enrichment (Lijun, 2020).

Sulphur dioxide (SO2)

The emission of sulphur in various forms into atmosphere poses a threat to human health and the environment. Within the atmosphere, sulphur forms sulphur oxides (SOX), which refers to many types of sulphur and oxygen containing compounds. The two major ones being sulphur dioxide (SO2) and sulphur trioxide (SO3). This emission has direct health effects on humans above certain atmospheric concentrations of SO2 and the potential for acid deposition which can have negative effects upon the environment (Chris, 2016).

Sulphur dioxide is the most important and common air pollutant produced in huge amounts in combustion of coal and other fuels in industrial and domestic use. It is also produced during smelting of sulphide ores. Sulphur dioxide concentrations in air have decreased in the past two decades, mainly because we use more non-sulphur-containing fuels for the generation of energy. Sulphur dioxide is a stinging gas and as a result it can cause breathing problems with humans. In moist environments, sulphur dioxide may be transferred to sulphuric acid. This acid causes acidification and winter smog (Iuliana and Barbu, 2011). Sulphur dioxide can cause breathing difficulties if inhaled into the body. It is also toxic to plants and can cause acid rain when it reacts with moisture in the atmosphere (Manisalidis et al; 2020).

Particulate Matter (PM)

Particulate matters (PM) include particles of solids, or liquids ranging in size from those that are visible such as soot and smoke, to those that are extremely tiny that they can be seen only through an electron microscope. Such particles can remain suspended for long period and can be carried great distance by winds (Charles and Blaise, 2015) Large particles – larger than 10µm (PM10), are generally filtered out of the body through the nose and throat. Particles that are 10µm or smaller can be inhaled into the deepest parts of the lungs and fine particles are smaller than 2.5µm (PM2.5) and are small enough to pass through the lungs into the blood system (Kim et al; 2015).

Ammonia (NH3)

Ammonia is an important environmental pollutant which has had a wide variety of impacts such as soil acidification, acid rainfall, and eutrophication of ecosystem. Also, when ammonia is released from the soil surface to atmosphere, it reacts with atmospheric gases such as sulfur dioxide or nitrogen oxides (in the presence of water) to form particulate matter less than 2.5 micrometers that is very harmful for human and animal health, and the environment (Bittman et al; 2014). The biggest source of ammonia release is from agriculture; including the intensive rearing of animals and crops. When ammonia and the ammonium pollutants fall to the ground, they add to the nitrogen enrichment effects, increasing the growth of some plants, including trees (Arkadiusz, 2020).

Secondary air pollutants

Secondary air pollutants are pollutants which are not emitted directly into the air but are formed in the atmosphere by chemical reactions between other pollutants and atmospheric gases. Examples of a secondary pollutant include ground level ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight; NO2, which is formed as NO combines with oxygen in the air; and acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water. (Stedman, 2000).

Ground level ozone (O3)

Ground level ozone is a colourlesas gas that is a major component of atmospheric smog. Ozone can cause irritation to the respiratory tract and eyes, causing chest tightness, coughing and wheezing, especially amongst those with respiratory and heart problems. Ozone also is a damaging air pollutant to plants, as it reduces growth and productivity, including food crops. Ozone (O3) also affects buildings and building materials (Donev et al; 2019).

Nitrogen Dioxide (NO2)

Nitrogen dioxide (NO2) is formed when fossil fuels are burned at high temperatures, but can also be formed naturally by lightning strikes. Most of the nitrogen dioxide (NO2) in urban areas comes from motor vehicle exhaust emissions. Other sources include; petrol and metal refining, electricity generation from coal-fired power stations, manufacturing industries and food processing. Nitrogen dioxide (NO2) can increase the likelihood of respiratory problems, as it inflames the lining of the lungs, and can reduce immunity to lung infections. This can cause health problems such as wheezing, coughing, colds, flu and bronchitis (Thurston, 2008).

Acid rain

Acid rain describes any form of precipitation that contains high levels of nitric and sulfuric acids. It can also occur in the form of snow, fog, and tiny bits of dry material that settle to Earth. Normal rain is slightly acidic, with a pH of 5.6, while acid rain generally has a pH between 4.2 and 4.4 (Chritina, 2019).

When the compounds fall to the ground, they can cause damage to plants, including trees. They can also increase the acidity levels of our soils, rivers, and streams, thereby affecting the delicate balance of ecosystems that live in these environments. Acidic rain also accelerates the decay of irreplaceable buildings, statues, and sculptures.

The pollutants that cause acidic rain – sulphur dioxide and nitrogen dioxide, can also be damaging to human health. As these gases interact in the atmosphere, they can form fine sulphate and nitrate water droplets which can irritate the air ways and cause irritation to eyes (Manisalidis et al; 2020).

Sources of air pollutants

Air pollutants can emanate from two different sources. These sources include: man-made sources and natural sources (European Environment Agency, 2019).

Man-made sources

Big and small scale industries, thermal power plants, and transport sectors are major sources of man-made air pollutants. Besides transport and industrial sectors, the domestic and commercial sectors also contribute to the overall pollution loads in urban areas. Other sources of air pollution include the use of generators, waste burning, construction activities, and roadside airborne dust due to vehicle movements. The following industries are among those that emit a great deal of pollutants into the air; thermal power plants, cement, steel, refineries, petrochemicals, and mines (Francisc and Ioana, 2010).

Today, fossil fuels combustion contributes significantly to air pollution with the release of soot (black carbon), sulphate, metals, fly-ash, carbon dioxide, carbon monoxide, toxic organic compounds, and nitrogen oxides. Sources and causes of air pollution include; sources of energy generation, transport, industry, house-holds, agricultural practices, land mining, earth-moving activity and quarrying, construction and repair works, burning of wastes and incinerators, and natural sources (Iuliana and Barbu, 2011).

Sources of energy generation

During energy generation, COx and SOx and water vapor are released into the atmosphere due to the combustion of large amount of coal, oil, L.P/ Natural gas, gasoline and bio-fuels (Sippy and Chauhan, 2011).


The transport industry is the leading source of CO. Combustion in engines is mainly fueled by Gas, petrol, diesel, and kerosene. Jet engines of sub sonic long range air craft are major source of NOx, (Masiol and Harrison, 2014).


Most of the industries are directly or indirectly dependent on fossil fuel, as they produce CO and CO2, sulfur hexafluoride and particle matters. Mainly cement industry releases large amount of particle matters in the environment. There is an array of hazardous volatile compounds that are released from paints, electronics, dry cleansing, decreasing agents. Furthermore, utilization of HFC, Oxides of Nitrogen, PFC and SF6 produces pollutants (Sivaramanan, 2014).


Carbon and soot emission during cooking by the use of fossil fuels can be considered here. Volatile toxicants such as Permethrine compounds release from insecticides could contaminate the air and even our food, resulting intoxication (Perera, 2017).

Agricultural practices

Agricultural activities such as use of natural fertilizer release greenhouse gases. Pesticides release persistent organic pollutants (POP). Enteric fermentation in cattle ranching produces green house gases mainly methane. Toxic chemicals found in pesticide and weedicide also reduces the quality of air inhaled (Gul, 2014).

Land mining, earth moving activity and quarrying

Process of mining large mineral deposits in the earth accompanied with emission of dust and other chemicals. Blasting, quarrying limestone in cement manufacturing produces dust particles (William, 2001).

Construction and repair works

Drilling, blasting, transportation, loading and unloading activities often causes dust generation. In addition, there are several non point anthropogenic sources related to dust generation such as welding, painting, auto mobile repairing, etc. (Sivaramanan, 2014).

Burning of wastes and incinerators

This is more severe threat to the environment as it contaminates the atmosphere with persistent organic pollutants (POP) such as dioxins, furans probably major sources are plastics and electronic wastes (Qingyuan et al; 2020). In addition, as in normal combustion carbon is emitted as oxides and soot. Wastes are in a vast array such as plastic, electronic wastes, cement dust, industrial chemicals, paper, glass, steel and various derivatives of soil minerals, biological and medicinal wastes, drugs and other chemicals. Incinerators destroys the hazardous effect of any gas or particle and the remaining dust emission could be as smalls as PM10 – PM2.5 or lesser, unless right particle filters are used it is also end up with adverse results (Akshey, 2020).

Natural sources

Air pollution also results from a variety of natural causes; not all of which are within human control. Dust storms in desert areas and smokes from forest and grass fires contribute to gaseous and particulate pollution of the air. The source of the pollution maybe in one country but the impact of the pollution may be felt elsewhere. Volcanic activity is another important natural source of air pollution. Acute volcano pours great amount of ash and toxic fumes into the atmosphere and lead to the deterioration of air quality (Majra, 2011).

Compounds released from volcanic activities such as black smoke, ash, metals, SOx, COx and release of methane form thawing of permafrost regions in the northern hemisphere, wetlands, sanitary landfills. Forest fires and bush fires, dust storm, sea spray and conversion of land use and release of isoprene and terpenes by forest (precursors of low level ozone) (Erika et al; 2015).

Air quality

Air quality has a significant impact on our health and on the environment. It significantly affects how we live and breathe. Just like the weather, it can change from day to day or even hour to hour. Air quality refers to the quality of the air around us; and if the quality of the air we breathe is poor (polluted), it significantly affects the quality of our health (Manisalidis, 2020). In recent times, outdoor and indoor air quality are always under serious problem due to the emissions of sulphur dioxide, particulate matter, nitrogen dioxide, nitrogen oxides, ozone, benzene and VOCs, and the corresponding high concentrations, which are referred to as air pollutants due to man’s activities. These pollutants are emitted by numerous sources; and these sources include: power generation activities, industrial processes, waste disposal, transportation (private and public vehicles), biomass burning, domestic fuel burning, landfill sites, waste water treatment and agriculture (Tran et al; 2020).
Air quality is divided into two; namely: indoor and outdoor (ambient) air quality.

Indoor air quality

Indoor air quality refers to the condition of the air within and around buildings and structures. The quality of indoor air affects the health, comfort and well-being of building occupants. Poor indoor air quality has been linked to sick-building syndrome, headaches, nausea, respiratory infection, lung cancer, etc. Indoor air quality has caused increasing concern due to the adverse effects that it may have on human health (Marios, 2011). Five factors contribute to indoor air pollution, namely: poor and inappropriate ventilation system; any horrible occupants’ activities such as smoking; bad personal habits such as unmanageable clothes, shoes or hair; any product being used in the building such as powder and fibre; and any processing method done such as heating, grinding, sawing or crushing (Rosmaini and Shahrul, 2006).

Indoor sources are the primary cause of indoor air quality problems in homes. Poor ventilation can increase indoor pollutant levels due to weak dilution of emissions from indoor sources. There are numerous sources of indoor air pollution; including combustion of domestic fuels such as coal, wood, paraffin, tobacco smoke, asbestos products, pesticides used in the home, and household cleaning products. Around 3 billion people still cook using solid fuels (such as wood, crop wastes, charcoal, coal and dung) and kerosene in open fires and inefficient stoves. Most of these people are poor, and live in low- and middle-income countries. These cooking practices are inefficient, and use fuels and technologies that produce high levels of household air pollution with a range of health-damaging pollutants, including small soot particles that penetrate deep into the lungs. In poorly ventilated dwellings, indoor smoke can be 100 times higher than acceptable levels for fine particles. Exposure is particularly high among women and young children, who spend the most time near the domestic hearth (W.H.O; 2018).

Indoor air pollution

Burning of solid fuels for household cooking, heating and lighting is a major cause of house-hold, or indoor air pollution. Indoor air pollution puts up to 3 billion people worldwide at risk of ill health and early death (WHO, 2016). Indoor pollutants include particulate matter (PM10 and PM2.5), mould, dust mites and bacteria, as well as chemicals and Volatile Organic Compounds (such as formaldehyde and benzene) from paints, personal care products and building materials (USEPA, 2015).

Ambient air quality

Ambient air quality refers to outdoor air quality and it is defined as the condition of the outdoor air in our surrounding environment; or is defined as the physical and chemical measure of pollutant concentrations in the ambient atmosphere to which the general population will be exposed to. In most developing countries, outdoor air pollution is a serious problem due to elevated concentrations of some pollutants which result in adverse health and environmental effects (Manisalidis, 2020).

Outdoor air pollution

Ambient air pollution is an ever-growing environmental problem. Recent studies indicate that urban outdoor air pollution has risen by 8 percent globally between 2008 and 2013 (WHO, 2016). Urbanization, which is often associated with rising air pollution, is increasing too; and by 2050, up to two thirds of the global population is expected to live in urban areas (UNDESA, 2014). Unless action is taken to control outdoor air pollution, studies show that outdoor air pollution will become the leading cause of environment-related child death by 2050 (OECD, 2012.

Health Consequences of air pollution

Air quality significantly affects the lives of people. People living in a pollution-free environment signify a better quality of life; but we need to understand how air pollution affects us and which parts of our body are damaged by each kind of Air pollution particle.

Seven million (7,000,000) deaths is caused by air pollution yearly (W.H.O. 2014). Growth and concentration of population in cities as well as the way in which we consume energy in urban areas through transport or heating and air-conditioning system among others results in the emission of huge quantities of gases that are harmful to our health.

Our physical and psychological well-being is affected differently by the kind of air pollution we are exposed to. There are many organs and bodily functions that can be harmed. The potential for harm from air pollution is related to both exposure (e.g., the concentration, dose and period of exposure, and the ability of the body to clear the pollutants) and toxicity of the pollutant (e.g., reactivity of the material, ability to access different biological compartments) (Kuan, et al; 2018).

The nervous system

Air pollution has been associated with diseases of the central nervous system (CNS), including stroke, Alzheimer’s disease, Parkinson’s disease, and neurodevelopmental disorders. It has been demonstrated that various components of air pollution, such as nanosized particles, can easily translocate to the CNS where they can activate innate immune responses. Furthermore, systemic inflammation arising from the pulmonary or cardiovascular system can affect CNS health. Despite intense studies on the health effects of ambient air pollution, the underlying molecular mechanisms of susceptibility and disease remain largely elusive. However, emerging evidence suggests that air pollution-induced neuroinflammation, oxidative stress, microglia activation, cerebrovascular dysfunction, and alterations in the blood-brain barrier contribute to CNS pathology (Genc et al; 2012).


Stroke is simply a damage caused to the brain due to interruption of its blood supply. It remains one of the leading causes of morbidity and mortality worldwide, accounting for over 118.6 million DALYs (DALYs – disability-adjusted life years) and 6.3 million deaths in 2015 (GBD; 2015).It is important to note that this burden of disease varies significantly across different parts of the world. Over the past 20 years, high income countries have experienced a significant decline in age-standardized mortality and DALY rates of approximately 20% to 40% (Nichols et al; 2014).Conversely, the vast majority of strokes (approximately 85%) now occur in LMICs (LMICs – Low and Medium Income Countries) where incidence, deaths and DALYs have increased significantly over this period. It is also in LMICs where air pollution is projected to increase significantly over the next few decades due to rapid industrialization (Lelieveld et al; 2015).

In regards to the ability of pollutants to access different biological compartments, the smaller the particle, the greater the potential for harm due to ability to penetrate deeper into the lung and larger reactive surface area available (for a given mass and composition). Consequently, association between PM2.5 and cardiovascular disease has been more marked and consistent than PM10 in epidemiological studies (Shah, et al; 2015).Smaller nanoparticles are able to penetrate the alveolar spaces of the lung and may even infiltrate the blood stream to reach systemic organs (Miller et al; 2017).The chemical composition of particles is another crucial factor in determining its biological effects once it has gained access into the human body. Combustion-derived particles have a vast cocktail of surface chemicals, including reactive transition metals and organic hydrocarbons, which are thought to be significant drivers of inflammation and oxidative stress and the biological mechanisms by which pollutants could pro¬mote stroke are complex, and remained to be fully elucidated (Kuan, et al; 2018).

Alzheimer’s disease

Alzheimer disease (AD) is characterized by a progressive decline in cognitive function. AD is substantially increased among people aged 65 years or more, with a progressive decline in memory, thinking, language and learning capacity. AD should be differentiated from normal age-related decline in cognitive function, which is more gradual and associated with less disability. Disease often starts with mild symptoms and ends with severe brain damage. People with dementia lose their abilities at different rate (Béatrice, 2013).
Air pollutants can cause Alzheimer’s disease because PM2.5 particles can remain airborne over a long period of time. These PM2.5 particles are easily inhaled. Long term exposure to PM2.5 means that they can accumulate in very large quantities in our body – including the brain. According to a research carried out by Diana Younan et al; published in BRAIN– A journal of Neurology in January, 2020 to examine if PM2.5 affects the episodic memory decline, and also explore the potential mediating role of increased neuroanatomic risk of Alzheimer’s disease associated with exposure; the authors/researchers points out a potential mechanism through which pollutants may affect the brain and as such, adds to the evidence that there is link between air pollution and Alzheimer’s disease (Diana, 2020).

Parkinson’s disease

Parkinson’s disease is a disorder of the central nervous system that affects movement, sometimes including tremors. Nerve cell damage in the brain causes dopamine levels to drop, thereby leading to the symptoms of Parkinson’s disease. This disease often starts with a tremor in one hand. Other symptoms include; slow movement, stiffness and loss of balance (DeMaagd, 2015).

Falls are one of the main concerns in people with Parkinson’s disease, leading to poor quality of life and increased mortality (Chiara et al; 2019).

Neurodevelopmental disorders

These are impairments of the growth and development of the brain and/or the central nervous system. Neurodevelopmental disorders are disabilities associated primarily with the functioning of the neurological system and brain. Neurodevelopmental disorders encompass a highly heterogeneous group of diseases characterized by impairments in cognition, communication, behaviour, and motor functioning as a result of atypical brain development (Moreno, 2013.

Examples of neurodevelopmental disorders in children include attention-deficit/hyperactivity disorder (ADHD), autism, learning disabilities, intellectual disability (also known as mental retardation), conduct disorders, cerebral palsy, and impairments in vision and hearing. Children with neurodevelopmental disorders can experience difficulties with language and speech, motor skills, behavior, memory, learning, or other neurological functions. While the symptoms and behaviors of neurodevelopmental disabilities often change or evolve as a child grows older, some disabilities are permanent. Diagnosis and treatment of these disorders can be difficult; treatment often involves a combination of professional therapy, pharmaceuticals, and home- and school-based programs (America’s Children and the Environment, 2015).

The impact of air pollution on the developing brain Air pollution potentially affects children’s brains through several mechanisms. First, particulate matter can cause neuro-inflammation by damaging the blood-brain barrier – a thin, delicate membrane that protects the brain from toxic substances (Garciduenas, et al; 2015). Ultrafine pollution particles (particulate matter that is equal to or less than 2.5 microns in diameter) pose an especially high risk because they can more easily enter the blood stream and travel through the body to the brain. In older people, the breakdown of the blood-brain barrier has been strongly linked with Alzheimer’s and Parkinson’s disease. The dosage of toxic chemicals required to damage the growing brain in the first stages of life is much lower than that which would cause damage to an adult brain (Grandjean et. al; 2006). Second, specific air pollution particles, such as magnetite, are so small that they can enter the body through the olfactory nerve and the gut. Magnetite is very common in urban outdoor air pollution, and a recent study found that it was considerably more present in brains of people living in areas where urban air pollution is high. Magnetite nanoparticles are highly toxic to the brain due to their magnetic charge and their ability to help create oxidative stress – which is often the cause of neurodegenerative diseases (Barbara, et al; 2016). Third, several studies also show that polycyclic aromatic hydrocarbons (PAHs), a specific class of pollutants formed from fossil fuel combustion and commonly found in areas of high automobile traffic, contribute to a loss of or damage to white matter in the brain (Peterson et al; 2015). White matter contains nerve fibers that are critical in helping neurons communicate across different parts of the brain. As children grow and experience the world around them, well-functioning neural connections provide the foundation for continued learning and development.

According to a press release by UNICEF on 6th December, 2017; almost 17 million babies under the age of one live in areas where air pollution is at least six times higher than international limits, causing them to breathe toxic air and potentially putting their brain development at risk.
There is every need to protect the children from air pollution problems. This is a very vital thing to do and it is not only beneficial to the children. It is also beneficial to the society at large (UNICEF, 2017).

The respiratory system

The negative impact by air pollutants on the respiratory system can be seen, especially, in individuals with pre-existing lung infections or other lung diseases because they are at great risk of contracting respiratory diseases; and also in children, simply because children have a relatively larger lung surface area and more outdoor physical activities with a greater chance to exposure to air pollutants (Saadeh and Klaunig 2015).

Respiratory diseases associated with air pollution include asthma and COPD (Chronic Obstructive Pulmonary Disease). Long-term exposure to indoor air pollution from second-hand cigarette smoke and biomass fuel is able to induce chronic inflammation that contribute to COPD (Gordon et al 2014) while exposure to PMs is linked to the acute exacerbation related hospitalization of COPD patients (Tsai et al; 2013). In general, more epidemiological associations have been reported to link the exposure to air pollutants with the development of asthmatic and chronic inflammation (Schiavoni et al 2017).

Several mechanisms have been suggested to explain the adverse effects of air pollutants. The most consistent and most widely accepted explanation is that, once in contact with the respiratory epithelium, high concentrations of oxidants and pro-oxidants in environmental pollutants such as PM of various sizes and compositions and in gases such as O3 and nitrogen oxides cause the formation of oxygen and nitrogen free radicals, which in turn induce oxidative stress in the airways. In other words, an increase in free radicals that are not neutralized by antioxidant defenses initiates an inflammatory response with release of inflammatory cells and mediators (cytokines, chemokines, and adhesion molecules) that reach the systemic circulation, leading to subclinical inflammation, which not only has a negative effect on the respiratory system but also causes systemic effects (W.H.O 2005).

PollutantsSourcesPenetration into the respiratory systemPathophysiology
TSPAnthropogenic sources: street dust, agricultural activities, and construction activities.

Natural sources: sea salt, pollen, spores, fungi, and volcanic ash.
Nose and throat.It impairs mucociliary and macrophage activity. It causes airway irritation. It induces oxidative stress and, consequently, pulmonary and systemic inflammation. Chronic exposure causes bronchial remodeling and COPD. It can be carcinogenic.
PM10Sources same as TSPTrachea, bronchi, and bronchioles.Pathophysiology same as TSP
PM2.5Burning of fossil fuels and biomass, thermoelectric power plants. AlveoliPathophysiology same as TSP
PM0.1Sources same as PM2.5Alveoli, lung tissue, and bloodstream.Pathophysiology same as TSP
O3It is not emitted directly into the atmosphere. It is produced by complex chemical reactions between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight. Sunlight and temperature stimulate such reactions, so that, on hot sunny days, O3 concentrations peak. The sources of VOCs and NOx emissions are vehicles, chemical industries, laundries, and activities that use solvents. Trachea, bronchi, bronchioles, and alveoli.It is a photochemical oxidant that is extremely irritating. It induces respiratory tract mucosal inflammation. At high concentrations, it irritates the eyes, the nasal mucosa, and the oropharynx. It causes cough and chest discomfort. Exposure for several hours produce damage to the epithelium lining the airways. It induces inflammation and airway obstruction in the presence of stimuli such as cold and exercise.

Anthropogenic sources: nitric acid, sulphuric acid, and combustion engine industries (major source), fuel burning at high temperatures, in thermal power plants that use gas or incineration. Natural sources: electrical discharge in the atmosphere. Trachea, bronchi, bronchioles, and alveoli.An irritant. It affects the mucosa of the eyes, nose, throat, and lower respiratory tract. It increases bronchial reactivity and increases susceptibility to infections and allergens. It is considered a good marker of vehicle pollution.
SO2Anthropogenic sources: petroleum refineries, diesel vehicles, furnaces, metallurgy, and papermaking. Natural sources: volcanic activities. Upper airways, trachea, bronchi, and bronchioles. An irritant. It affects the mucosa of the eyes, nose, throat, and respiratory causes cough and increases bronchial reactivity, facilitating bronchoconstriction.
COAnthropogenic sources: forest fires, incomplete combustion of fossil fuels or other organic materials, and road transportation. Urban areas with heavy traffic are the major contributing source of CO emissions.

Natural sources: volcanic eruptions, and chlorophyll decomposition.
Alveoli and bloodstream. It binds the hemoglobin, interfering with oxygen transport. It causes headache, nausea, and dizziness. It has a deleterious effect on the fetus. It is associated with low birth weight, neonates and fatal death.
Major air pollutants, their sources, their sites of action in the respiratory system, and their effects on human health. TSP: total suspended particles: PM: particulate matter; PM10: PM of less than 10 µm in diameter; PM2.5: PM of less than 2.5 µm in diameter; PM0.1: PM of less than 0.1 µm in diameter. Source: adapted from Künzli et al; 2010.

The cardiovascular system

Chronic and acute exposure to elevated PM2.5 levels is closely associated with elevated risks for ischemic heart disease, heart failure, and cerebrovascular disease. Air pollution aggravates existing heart conditions and appears to have a role in disease development (Hamanaka and Mutlu 2018). Harmful air pollutants lead to cardiovascular diseases such as artery blockages leading to heart attack (arterial occlusion) and death of heart tissue due to oxygen deprivation leading to permanent heart damage (infarct formation). The mechanism by which air pollution causes cardiovascular diseases are thought to be the same as those responsible for respiratory diseases pulmonary inflammation and oxidative stress (Lee, 2014).

Both long- and short-term studies have associated PM2.5 exposures with increased risk of fatal and non-fatal ischemic heart disease (Xie et al; 2015). Risk of myocardial infarction is also associated with PM2.5 exposures (Madrigano et al; 2013). The ACS study found increased risk of heart failure with PM2.5 exposures, although to a lesser degree than the association with ischemic heart disease. Additional studies and meta-analyses have associated both chronic and acute PM2.5 exposures with heart failure (Atkinson et al; 2013). Significant associations also exist between PM2.5 exposure and cerebrovascular disease (Stafoggia et al; 2014). Short-term studies have shown that elevations in pollution increase the risk of ischemic, but not hemorrhagic stroke (Wellenius et al; 2012).

Current evidence for the mechanisms by which particulate matter air pollution causes cardiovascular health effects: adapted from Hamanaka and Mutlu 2018.

Exposure Level: PM exposure is hypothesized to exert its effects on the cardiovascular system by three routes:

  1. PM induces an inflammatory response in the lung. PM acts on the cells of the lung, including alveolar macrophages, leading to mitochondrial reactive oxygen species (mROS)-dependent pro-inflammatory cytokine production.
  2. Inhaled PM acts on sensory receptors in the lung, promoting activation of the hypothalamic pituitary adrenal (HPA) axis and sympathetic pathway activation in the autonomic nervous system (ANS).
  3. Other effects of PM exposure may be mediated by translocation of particles into the circulatory system, or by particle ingestion, which may promote inflammation in the gut.

Signaling Level: Cytokines produced into the lung “spillover” into the circulation, leading to a systemic state of inflammation. Translocated particles as well as inflammation resulting from particle injection may also contribute to a general state of systemic inflammation. Sympathetic activation leads to elevated levels of circulating catecholamine.

Subclinical Level: Systemic inflammation and elevated catecholamine levels act on target cells leading to acute phase response, hypercoagulable state (activation of coagulation, and suppressed fibrinolysis), vasoconstriction, increased blood pressure, cardiac electrical changes, endothelial dysfunction, and increased adiposity and insulin resistance complicated by adipose tissue inflammation. Elevated catecholamine levels due to ANS imbalance further increase inflammation.
Sympathetic activation leads to increased catecholamine production, which increases heart rate and promotes vasoconstriction, endothelial dysfunction, and hypertension.

Clinical Level: The combined effects of systemic inflammation and sympathetic activation on their cellular targets lead to the clinical effects of PM on cardiovascular disease. These effects are seen at both the acute level (acute ischemic/thrombotic events, cardiac arrhythmias, or acute heart failure), or at the chronic level (atherosclerosis, hypertension, and chronic heart failure).

The musculoskeletal system

The musculoskeletal system is the internal framework of the body. It provides form, support, stability and movement to the body. It is made up of the muscular and skeletal systems. It also gives the body its shape, produces blood cells (in the bone marrow), provides protections for the organs and stores minerals. It is made up of bones and connective tissues including cartilages, tendons, and ligaments (Murphy, 2016). In essence, the musculoskeletal system, just like every other system in the human body, plays a vital role in our day-to-day activities, and if adversely affected, can cause deterioration of health, inhibit movement and expose other vital organs to mechanical damages.

Studies have shown that air pollution has negative health impact on the musculoskeletal system. Long term exposure to urban PM2.5 is associated with reduced skeletal muscle mass (Chi-Hsien et al; 2019), especially, in the elderly. Poor air quality is a possible risk factor for bone mineral density loss and fractures, in older people because, air particles might directly or indirectly, impact bone biology and increase bone mineral loss and osteoporosis (Prada, et al; 2017).

Air pollutants have high potential to cause systemic oxidative damage and inflammation, both of which are established mechanisms for bone mineral loss and osteoporosis. Cigarette smoke has several chemo-physical components found in PM and it causes bone demineralization and has also been associated with high risk of bone fractures and elevated loss of bone minerals in human studies. Parathyroid hormones; which hormones secreted by the parathyroid glands that regulates the serum calcium concentration through its effects on bone, kidney, and intestine; are also in very low amount in smokers and goes back to its normal concentration after the individual has stopped smoking (Prada, et al; 2017).

Osteoporosis is a progressive systemic skeletal disease characterized by reduced bone mass/density and micro-architectural deterioration of bone tissue (Ferdous et al; 2015).
Formation of bone exceeds bone resorption, but as an individual gets older, in his 30s, this activity reverses, leading to a net loss of bone mass; and results to elevated bone fragility and susceptibility to fragility. Fractures which result from mechanical forces that ordinarily would not lead to fracture are known as osteoporotic fractures and such fracture are linked to low bone mineral density (BMD). Examples include spine, hip, forearm and shoulder fractures.

The reproductive system

Some hypotheses have been put forward about air pollution and its effects on the reproductive system; i) it may cause placental inflammation, ii) it would affect placental development mainly in structures and mechanisms that are sensitive to oxygen tension and its exchange, and iii) it would affect trophaloblast development because of a deficit in potential vascularization (Veras et al; 2009). Any form of abnormalities in the placenta are a potential culprit in preterm labour malfunction or abortion; because toxic substances act on placental functions during pregnancy by altering hormones and enzymes production, gas exchange, nutrients, excreta and cell differentiation (Salines, 2018).

Human and animal epidemiological surveys support that air pollutants cause defects during gametogenesis leading to a drop in reproductive capabilities in exposed population (Carre et al; 2017). Air pollution has a negative impact on both male and female gametogenesis. These impacts not only influence the quality of gametes but also on their quality on a genetic and epigenetic level. These impacts, which include endocrine disruption, reactive oxygen species induction, cell DNA alteration and epigenetic modifications also alter the embryo development (Carre et al; 2017).

Risk of miscarriage, oocyte quality and menstrual cycle characteristics can equally be influenced by air pollution which may lead to fertility problems in women (Merklinger et al; 2017).

Female fertility and reproductive health respond in a special way to toxic exposure, especially to those with oestrogenic potential. This special way of response is mainly caused due to mimicking natural hormones activities and varying regulation and function of the endocrine system. Moreover, effect on reproduction and development are often the result of short-term exposure to PM during the vulnerable periods of ovulation or fetal organogenesis. Adverse effects of some toxicants may not become apparent for years because they accumulate in parental tissue and may be released many years later during pregnancy, lactation, or even post-natal development (Merklinger et al; 2017).

The main harm of air pollution to male fertility is the impact on semen quality because, long-term exposure to high concentrations of air pollutants can result in a decrease in semen quality (Fei et al; 2020). In vitro experiments have shown that exposure to air pollutants can activate multiple intercellular signaling pathways and initiate inflammatory response. The inflammation may cause the destruction of the integrity of the blood-testis barrier, which results in;

  1. Accelerating the apoptosis of spermatogenic cells, resulting in the decrease in the number of spermatogenic cells.
  2. Damaging the cell membrane, resulting in the decrease of sperm motility and fertilization ability.
  3. Causing DNA damage of sperm, affect the quality of the resulting embryo, resulting in miscarriage or genetic defects in the offspring (Silka et al; 2008).
    Reports have shown that some of the volatile organic compounds (VOCs) such as 1, 1, 1 – trichloroethane, 1, 1, 2, 2- tetrachloroethane, 1, 1-dichloroethylene, 1, 2-dichloroethane, 1, 2-dichloropropane, acrylonitrile, benzene and acetone has several negative effects on the human reproductive system (Alaee, S. 2018).

The renal/urinary system

The urinary or renal system consists of the kidneys, ureters, bladder and urethra. The job of this system is to remove wastes from the body, regulate blood volume and blood pressure, control levels of electrolytes and metabolites, and also regulate blood pH.

The Kidney

The detrimental effects of air pollution on the kidney have just begun to be acknowledged; and various pollutants, such as toxic metals, PM, cigarette smoke and gases, may harm the kidney (Afsar et. al, 2019)
Recent advances in nanomedicine enabled studies in rodents and humans, showing that inhaled gold nano-particles, when sufficiently small, permeates through the lung alveolar tissue and enter bloodstream where they interact with extra pulmonary organs, are filtered by the kidneys in a size-dependent manner, and ultimately excreted in the urine (Miller et al; 2017).

Several large epidemiological studies have since emerged suggesting that ambient fine particulate matter of <2.5µm in aerodynamic diameter (PM2.5) air pollution is associated with increased risk of incident Chronic Kidney Disease (CKD), CKD progression, and End-Stage Kidney Disease (ESKD) (Bowe et al; 2018 and Bragg et al; 2018); and recent studies also provided evidence that PM2.5 pollution is associated with increased risk of death due to kidney disease.

The kidney is particularly vulnerable to toxic effects of environmental pollutants owing to its filtration functions. Environmental and occupational exposures remain common causes of kidney diseases worldwide especially in developing countries (Xu et al; 2018).

Chronic kidney diseases

Fanconi syndrome and progressive loss of glomerular filtration rate (GFR) can be directly induced by cadmium exposure. Proteinuria, kidney stones, diabetes and hypertension which are risk factors for CKD have been associated with cadmium exposure (Boris et al; 2019). Cigarette smoke is also an air pollutant detrimental for kidney health.

Idiopathic nodular glomerulosclerosis, microalbuminuria or overt proteinuria, nephrosclerosis, glomerulonephritis, endothelial dysfunction, intimal hyperplasia, mesangial proliferation, glomerulosclerosis, tubuli interstitial fibrosis, renal cell reactive oxygen species (ROS) and apoptosis, together with albuminuria have all been associated with air pollution (Boris et al; 2019).

Fanconi syndrome

Fanconi syndrome, not to be confused with Fanconi anemia, is a defect of the proximal tubule that prevents the absorption of electrolytes and other substances that are normally absorbed by the proximal tubule (Keefe et al; 2020). This kidney tubule function disorder results in excess amount of glucose, bicarbonates, phosphates (phosphorus salts), uric acid, potassium and certain amino acids being excreted in the urine.

Progressive loss of glomerular filtration rate

The best overall indicator of the glomerular function is the glomerular filtration rate (GFR). GFR is the rate in milliliters per minute at which substances in plasma are filtered through the glomerulus; in other words, the clearance of a substance from the blood. The normal GFR for an adult male is 90 to 120 mL per minute (Gounden et al; 2020) Glomerular filtration rate GFR estimates how much blood passes through the glomeruli each minute. The glomeruli are tiny filters in the kidneys that filter wastes from the blood. This test is used to know how well the kidneys are functioning. The GFR decreases with age. As we get older, the GFR reduces. Long-term exposure to cadmium could result to the progressive loss of glomerular filtration rate (Glassock and Winearls, 2009).


This very condition can be a sign of the kidney damage. It is an increased level of protein in the urine. Proteins help to build muscles and bones; regulate the amount of fluids in the blood, combat infections and repair tissues; and as such, should not be found in the urine as wastes; rather, should remain in the blood. Normal total urine protein excretion is approximately <150 mg/day; and any value above this is considered proteinuria (D’Aguilar and Skandhan; 2020).

Kidney stone

This is also referred to as nephrolithiasis. Kidney stone disease is a crystal concretion formed usually within the kidneys. It is an increasing urological disorder of human health, affecting about 12% of the world population. It has been associated with an increased risk of end-stage renal failure (Alelign and Petros; 2018). Sometimes when there is too much of certain wastes and not enough fluid in the blood, these wastes can build up and bind together in the kidneys.


This refers to an abnormally increased excretion rate of the albumin in the uri6in the range of 30 – 299 mg/g creatinine (Toto, 2004). Albumin is a simple form of protein that is soluble in water and coagulate by heat, such as that found in egg white, milk, and (in particular) blood serum (oxford dictionary).


This is the hardening of the walls of the small arteries and arterioles (small arteries that convey blood from arteries to the smaller capillaries) of the kidney. This condition is caused by hypertension, which is a risk factor for chronic kidney disease (Meyrier, 2015).

Glomerulonephritis (GN)

This is the inflammation of the glomeruli, which are structures in the kidney that are made up of blood vessels. These knots of vessels help filter blood and remove excess fluids. If the glomeruli are damaged, the kidneys will stop functioning properly. Glomerulonephritis is an important cause of renal failure thought to be caused by autoimmune damage to the kidney. While each type of glomerulonephritis begins with a unique initiating stimulus, subsequent common inflammatory and fibrotic events lead to a final pathway of progressive renal damage (Vinen and Oliveira; 2003).

Endothelial dysfunction

This is a systemic pathological state of the endothelium. This occurs when there is damage to the vascular endothelium (the thin layer of cells that lines the blood vessels). Endothelial dysfunction is a term that refers to impaired functioning of the lining of the blood vessels. It is characterized by;
• Impaired vasodilatation
• Deficiency of nitric oxide
• An “activated” endothelium, that is in a state of inflammation, growth, and thrombosis (blood clotting).

Endothelial dysfunction precedes atherosclerosis and is an independent predictor of cardiovascular events (Giana A, 2015). Endothelial dysfunction occurs in chronic kidney disease and increases the risk of cardiovascular disease, this, results in progressive and irreversible loss of renal function (Martens et al; 2016).

Intimal hyperplasia

Intimal hyperplasia is the thickening of the innermost layer of the artery or vein (blood vessels), known as tunica intima, as a complication of a reconstruction procedure or endarterectomy (surgery removal of the part of the inner lining of an artery, together with any obstructive deposits (Wikipedia). Intimal hyperplasia is a common cause of vasculopathy due to direct endothelial damage (such as post-coronary revascularization) or indirect injury (such as chronic kidney disease (Chancharoenthana et al; 2017).


This is the scarring or hardening of the glomeruli — blood vessels located in the kidneys. The glomeruli filter the blood as it passes through the kidneys. They remove waste fluids that then leave the body as urine. Damaged glomeruli can’t perform their job adequately. As a result, large amounts of protein from the blood leak into the urine rather than remaining in the bloodstream. This leads to a condition called proteinuria. Glomerulosclerosis can affect children and adults. Men are slightly more likely to develop it. African-Americans are at higher risk than whites (Nayana, 2019).

The bladder

This is a muscular sac in the pelvis, just above and behind the pelvic bone. When the bladder is empty, it is about the size and shape of a roar. Urine is made in the kidneys and travels down two tubes called ureters to the bladder. It stores urine, allowing urination to be in and controlled (Matthew, 2020).

Cystitis, urinary incontinence, overactive bladder, interstitial cystitis and bladder cancer are some of the known bladder diseases, and only bladder cancer has been slightly associated with air pollution.

Bladder cancer

Few studies have suggested positive (even though, mostly non-significant) association between air pollution exposure and bladder cancer mortality and kidney cancer incidence. More studies and better confounding control and follow-ups are needed (Zare et al; 2020).

The immune/lymphatic system

Immune system is mainly composed of immune organs, tissues, cells, and molecules, all of which interact with each other to perform immune functions (Sun et al; 2017). The immune system is made up of special organs, cells and chemicals that fight infections (microbes). The main parts of the immune system are; white blood cells, antibodies, the complement system, the lymphatic system, the spleen, the thymus, and the bone marrow.

White blood cells

Inhaling dirty air can trigger the release of white-blood cells into the blood stream and can result in inflammation. The presence of PM triggers imbalance in the immune system; and molecules in the cells can start reacting when exposed to particulate matter and start change structures and activate toll like receptor 4 (TLR4); which duty is to identify the specific characteristics of pathogens and activates the white-blood cells (Kent, 2020). This is evident in a population-based study carried out to examine the relationship between the white blood cell series and short term ambient concentrations (within 8 days) of air pollutants in Kaohsiung, Taiwan. After adjusting the variables of age, gender, BMI, smoking, drinking, and betel quid use, it was revealed that short-term ambient concentrations of SO2 and NO2 are associated with white-blood cell count decrease and short-term ambient concentration of CO is associated with white-blood cell count increase. In vivo white-blood cells change, as well as neutrophils and monocytes may trigger or disturb immune systematic of chronic inflammatory process (Shih-Chiang et al; 2021).

The complement system

The complement system, which is also known as complement cascade, is a part of the immune system that enhances or complements the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen’s cell membrane (Wikipedia).

Studies have shown that PM air pollution can induce increase in the concentration of complement activation products in sera of individuals exposed to high levels of PM. Additionally, both cigarette smoke and diesel exhaust have been shown to activate complement through the alternative pathway; and interestingly, reactive oxygen species have also shown to activate complement, highlighting the possibility that PM may activate complement through induction of reactive oxygen species (Dianne et al; 2002).

Exposure to dirty air is linked to decreased function of the genes that appear to increase the severity of asthma in children; according to a joint study by researchers at Stanford University and the University of California, Berkeley. The researchers found out that air pollution exposure suppresses the immune system’s regulatory T cells (Treg), and that the decreased level of Treg function was linked to greater severity asthma symptoms and lower lung capacity. Treg cells are responsible for putting the brakes on the immune system so that it doesn’t react to non-pathogenic substances in the body that associated with allergy and asthma. When Treg function is low, the cells fail to block the inflammatory responses that are the hallmark of asthma symptoms (Sarah, 2010).

The endocrine system

The endocrine system is a chemical messenger system, comprising feedback loops of hormones released by internal glands of an organism directly into the circulatory system; the hypothalamus is the neural control center for all the endocrine system (Wikipedia).
These hormones released directly into the blood can travel to tissues and organs all over the body. They control many functions in the body, including; growth and development, metabolism and reproduction and even control mood.

Over the years, many environmental pollutants chemicals have been shown to possess the ability to interfere in the functioning of the endocrine system and have been termed Endocrine Disrupting Chemicals (EDCs). They exist in the air as volatile or semi-volatile compounds in the gas phase or attached to particulate matter (Darbre, 2018).

The endocrine disrupting chemicals (EDCs) are ubiquitous and are able to mimic hormones, to block hormones, or to modulate their synthesis, metabolism, transport, and action. The mechanism of damage can range from intracellular molecular alterations to disrupted multiorgan endocrine homeostasis and this disruption has resulted in insulin resistance, obesity, type 2 and type 1 diabetes, thyroid diseases, reproductive abnormalities and cancer (Di Ciaula and Portincasa, 2019).

The digestive system

The digestive system is a system of organs comprising of the gastrointestinal tract (GI), and its associated accessory organs that breakdown food into smaller components so that nutrients can be absorbed and assimilated (Ogobuiro et al; 2020).

The organs of the digestive system that make up the gastrointestinal tract include; the mouth, esophagus, stomach, small intestine, large intestine, and the anus; together with the liver, pancreas, and gallbladder (Minesh, 2020).

Epidemiological studies have revealed an association between exposure to air pollution and different gastrointestinal tract diseases, including inflammatory bowel diseases (IBD), appendicitis, irritable bowel syndrome (IBS), and enteric infections in infants (Saad et al; 2014).

Inflammatory bowel disease (IBD)

This is an umbrella term used to describe disorders that involve chronic inflammation of digestive tract.
Types of IBD include; ulcerative colitis and crohn’s disease.

Ulcerative colitis

This is a chronic, inflammatory bowel disease that causes inflammation and ulcers (sores) in the digestive tract. It affects the innermost lining of the large intestine (colon) and rectum. It usually begins in the rectum and lower colon, but may also spread continuously to involve the entire colon (Minesh, 2019).

Crohn’s diseases

This can affect any part of the GI tract, from the mouth to the anus. It most commonly affects the end of the small intestine (the ileum) where it joins the beginning of the colon. Crohn’s disease may appear in patches, affecting some areas of the GI tract while leaving other sections untouched completely. The inflammation may also extend through the entire thickness of the bowel wall (Noel, 2020).

Generally, air pollution exposure was not associated with the incidence of IBD. However, residential exposure to SO2 and NO2 may increase the risk of early – onset ulcerative colitis and crohn’s disease respectively (Gilaad et al; 2010).


Appendicitis is the inflammation of the vermiform appendix and is the commonest clinical differential diagnosis made in young adults presenting with acute abdominal and right iliac fossa pain. This is a condition in which the appendix becomes swollen and filled with pus, causing pain (Chandrasekaran and Natalie, 2014).

A study examined the possibility of the association between air contaminants level and frequency of hospital admissions for appendicitis in Taipei, Taiwan. Relative risk (RR) of hospital admission was determined using a case-crosssover approach, controlling for weather variables, day of the week, seasonality, and long-term time trends. In the single pollutant model, on warm days (>23Oc), number of appendicitis admissions was significantly associated with particulate matter (PM2.5), nitrogen dioxide (NO2), carbon monoxide (CO), and ozone (O3). On cool days (<23Oc), a significant rise in number of admissions for appendicitis was related to PM10, NO2, and O3 concentrations. In the two-pollutant models, on warm days, NO2 and O3 were significantly associated with increased number of admissions for appendicitis when combined with each of the pollutants. On cool days, NO2, O3 and PM10 remained significant for higher appendicitis admission cases in all two-pollutant models. At the end of the study, it was concluded that higher levels of ambient air pollutants may be associated with increase in the risk of hospital admissions for appendicitis in Taipei (Chih-Cheng and Chun-Yuh, 2018).

Irritable bowel syndrome

Some evidence suggests inhalation of fine particles, or air pollution from coal industry, may disrupt the immune system and trigger inflammation by increasing gut permeability and altering gut microbiota. The interplay between the gut microbiome and the immune system may influence the development of irritable bowel syndrome – IBD (Teck-King et al; 2018).

The liver

The liver is an organ consisting of the largest reticulo-endothelial cell network in the body and playing an important role in host defense against invading microorganisms. The organ is comprised of parenchymal cells and many different types of non-parenchymal cells, all of which play a significant role (Ishibashi et al; 2009).

The liver assists the digestive process and carries out many other essential functions. These essential functions include; producing bile to help break down food into energy; creating essential substances such as hormones; cleaning toxins from the blood; and controlling fat storage and cholesterol production and release (Ozougwu, 2017).

Together with other well-known harmful effects of air pollution, several animal models have provided strong evidence that air pollutants can induce liver toxicity and act to accelerate liver inflammation and steatosis (Kim et al; 2014); fibrosis, metabolic disease, liver cancer (Rachel, 2015), and cirrhosis (Orioli et al; 2020).

Liver inflammation

This is a reaction that occurs when liver cells are attacked by a disease-causing microbe or substance. The word hepatitis refers to liver inflammation. Chronic liver inflammation leads to fibrosis and cirrhosis (Koyama and Brenner, 2017).


This is the infiltration of liver cells with fat, associated with disturbance of the metabolism by, for example, alcoholism, malnutrition, pregnancy or drug therapy (Oxford medicine dictionary).
An increasing number of studies have proposed an association between environmental factors, namely, air pollution and fatty changes in the liver (Kelishadi and Poursafa, 2011).


This is the formation of an abnormally large amount of scar tissue in the liver. It occurs when the liver attempts to repair and replace damaged cells. Fibrosis develops when the liver is repeatedly or continuously damaged. After a single episode of injury, even if severe (as with acute hepatitis), the liver commonly repairs itself by making new liver cells and attaching them to the web of connective tissues (internal structures) that is left when liver cells die. However, if injury is repeated or continuous – as occurs in chronic hepatitis, liver cells attempt to repair the damages; but the attempt results in scar tissue – fibrosis (Jesse, 2019).

Acute exacerbations and worsening of idiopathic pulmonary fibrosis (IPF) have been associated with exposure to ozone O3, nitrogen dioxide NO2 and particulate matter PM, but chronic exposure to air pollution might also affect the incidence of IPF (Sera et al; 2017).


Cirrhosis is a late stage of scarring (fibrosis) of the liver caused by many forms of liver diseases and conditions, such as hepatitis and chronic alcoholism. Cirrhosis results from different mechanisms of injury that lead to necroinflammation and fibrogenesis (Haider et al; 2017).
Air pollution has been associated with a significant increase in the risk of cirrhosis. This suggests that it may act in addition to other main sources of chronic liver damages and promote the development of the disease (Orioli et al; 2020).

The pancreas

The pancreas is an organ located in the abdomen. It plays an essential role in converting the food we eat into fuel for the body’s cells. The organ pancreas has two main functions; an exocrine function that helps in digestion and an endocrine function that regulates blood sugar. The pancreas consists of two organs in one: exocrine and endocrine glands. The exocrine gland secretes enzymes into the digestive tract, whereas the endocrine gland secretes hormones into the bloodstream (Frantz et al; 2012).

Pancreatitis, pancreatic cancer and diabetes are some of the disorders that have been associated with air pollution. Exposure to ambient air pollutants adversely affects glucose tolerance, insulin sensitivity, and blood lipid concentrations; and recent studies suggest that air pollution plays a role in type 2 diabetes (T2D) and mortality (Chen et al; 2016).

As we know, it is no longer news that air pollution has been linked with lung cancer; a study suggests that pollution is also associated with increased risk of mortality for several other types of cancer, including breast cancer liver cancer and pancreatic cancer (Chit et al; 2016).

Gall bladder

The gall bladder is a small pouch that sits just under the liver. It stores bile produced by the liver. After meals, the gall bladder is empty and flat, like a deflated balloon. Before a meal, the gall bladder may be full of bile and about the size of a small pear. In response to signals, the gall bladder squeezes stored bile into the small intestine through the bile ducts. The secreted bile helps to digest fats (Mattew, 2019).

There is not enough evidence to show that gall bladder is impacted by air pollution even though heavy metals have been advocated as possible contributors to carcinogenesis but there is not much data on the level and rate of gall bladder cancer – GBD (Gondal et al; 2015).

The integumentary system

The integumentary system is an organ system consisting of the skin, hair, nails, and the exocrine glands. This system protects the body’s internal organs and tissues against invasion by infectious organisms, chemicals and other environmental factors; protects the body from dehydration; acting as sensory organ; modulating body temperature and electrolyte balance; and synthesizing vitamin D (Lawton, 2019).

Major air pollutants with effects on the skin include the solar Ultraviolet Radiation (UVR), polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), nitrogen oxides (NOx), particulate matter (PM), ozone (O3), and cigarette smoke. Considerable effects mediated by air pollutants on the skin may contribute to skin aging, atopic dermatitis, skin cancer, psoriasis, and acne. Oxides have been associated with increased prevalence of atopic dermatitis as well as exacerbation of the disease in children. VOCs, with the presence of sunlight and NOx, cause the formation of photochemical oxidant products – namely O3 at ground level, also called summer photochemical smog. Exposure to O3 has been associated with urticaria, eczema, contact dermatitis, and other non-specific eruptions. Exposure to PM contributes to extrinsic skin aging (wrinkles, pigmented macules or spots). Cigarette smoking has been associated with skin aging (wrinkles, skin dryness, skin dyschromias), and the combination of smoking and sun exposure may have a synergistic effect on skin aging. Furthermore, it has been associated with skin cancer (SCC, BCC), psoriasis and acne vulgaris. On the other hand, pollutants (O3, NO2, and SO2) and scattering particulates (cloud and soot) in the troposphere reduce the effects of shorter wavelength UVR and significant reductions in UV irradiance have been observed in polluted urban areas (Drakaki et al; 2014).


A lot of people, both in the rural and urban areas, do not really understand how most of their daily activities at home and at their place of work aid environmental air pollution. Ignorance is part of the reasons why most people suffer the negative impact of air pollution.

Awareness campaigns against air pollution should be done from time to time in the rural and urban areas. This will enable people to really understand the implications of their actions which introduce hazardous materials into the atmosphere. When this is in practice, over time, people will have a change of attitude and embrace more decent ways of living which reduces concentration of air pollutants in the atmosphere.

In conclusion, all hands, local, national and International, must be on deck to fight against air pollution. Governments have bigger role to play in tackling this problem of air pollution by making policies that bother about environmental protection; creation and adequate funding of a viable environmental protection agency whose duties should include and not limited to air quality monitoring and penalizing of offenders whose individual or industrial activities introduce hazardous materials into the atmosphere.


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