Introduction
Air pollution is the most important and dangerous environmental risk factor in the world. The harmful substances released into the environment due to air pollution cause various diseases. The fine particulate matter (PM) present in the air penetrates the lung during respiration and reaches the blood. Exposure to fine dust over a long period results in the dysfunction of the immune system. It increases the risk of cardiovascular and respiratory diseases such as colds, asthma, bronchitis, and some skin conditions. In addition, recent studies regarding the effect of air pollution show evidence of central nervous system (CNS) damage.
What Is Air Pollution?
Air pollution occurs due to the contamination of air by harmful gasses, dust, and smoke which affects plants, animals, and humans. Pollutants like Sulfur-dioxide emitted from factories directly cause air pollution as a primary pollutant. The pollutants formed by mixing up and reacting to primary pollutants are known as secondary pollutants. For example, smog is formed by the mixing up of smoke and fog, which is a secondary pollutant. Air pollution causes several respiratory disorders and heart diseases among humans. Studies show that air pollution also increases the incidence of central nervous system disorders, including stroke, Alzheimer's disease, neurodevelopmental disorders, and Parkinson's disease.
What Are the Causes of Air Pollution?
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Factories and Industries - Polluted air from factories and industries contains carbon monoxide, hydrocarbons, organic compounds, and chemicals. These pollutants are released into the air, degrading the air quality.
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Burning of Fossil Fuels - The combustion of fossil fuels emits a large amount of sulfur dioxide. Carbon monoxide is released due to incomplete combustion of fossil fuels resulting in air pollution.
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Automobiles - Gasses emitted from vehicles such as jeeps, trucks, cars, and buses pollute the environment.
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Mining Activities - Dust and chemicals released during mining pollute the air and cause damage to the overall health of the workers and other people around the area.
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Domestic Sources - Household cleaning products and paints contain toxic chemicals released into the atmosphere. As a result, they pollute the atmospheric air and cause breathing problems.
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Agricultural Activities - Ammonia is the most hazardous gas emitted from agricultural practices. The pesticides, herbicides, insecticides, and fertilizers used in agriculture release harmful chemical substances into the atmosphere and contaminate it.
What Is Traffic-Related Air Pollution (TRAP)?
Traffic-related air pollution (TRAP) is a complex mixture of pollutants like tailpipe emissions from internal combustion engines, such as particulate matter (PM), gasses (carbon monoxide, nitrogen oxides or NOx, and benzene), as well as evaporative emissions from vehicles that interact with chemicals in the air to form hazardous substances, such as ozone and NO2. Pulmonary disease (asthma, lung cancer, and reduced lung capacity), cardiovascular disease (myocardial infarction, hypertension), and neurological disorders are associated with traffic-related air pollution (TRAP).
How Does Air Pollution Affect the Brain?
Fine dust present in polluted air causes harmful effects on the body and environment. Research on the impact of traffic-related air pollution (TRAP)on the human body shows that they result in neurological disorders. Air pollution can cause neurotoxicity and central nervous system (CNS) damage. Inflammation of the central nervous system (CNS), oxidative stress, activation of microglial cells, protein condensation, and cerebral vascular disorders due to air pollution results in brain damage. Air pollution is associated with diseases affecting the central nervous system (CNS), like stroke, Parkinson's disease, Alzheimer's disease, and neurodevelopmental disorders. Fine dust causes neurological damage, especially in fetuses and infants, resulting in permanent brain damage or developmental neurological disorders.
What Are the Neurological Diseases Associated With Air Pollution?
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Neurodevelopmental Disorders - Fine particulate matter (PM) present in the air contains toxic substances such as lead, methylmercury, arsenic, polychlorinated biphenyls, and toluene. These substances have neurotoxic activity and are thought to affect nerve development. Therefore, continuous exposure to high levels of polluted air during pregnancy can negatively affect the fetus's brain development. Brain development is established during fetal life, and exposure to toxic substances inutero can lead to permanent brain damage or cognitive impairment in old age.
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Dementia and Cognitive Disorders - Exposure to contaminated external air promotes brain aging. Epidemiological studies show an increased risk of dementia and Alzheimer's in people exposed to fine particulate matter (PM < 2.5 μm). In addition, air pollution will lead to metabolic disorders, the development of oxidative stress in the brain, and dysfunction of the insulin signaling system, resulting in reduced cognitive function and increased risk of dementia.
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Stroke - Scientific studies indicate that people exposed to polluted air are associated with an increased risk of developing stroke and acute coronary syndromes like myocardial infarction. Nitrogen dioxide (NO2), the major component of air pollution, is one of the main causes of stroke. In addition, these toxic components present in the polluted air are associated with increased heart rate, frequency of heart block, and atrial fibrillation.
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Depression - Long-term exposure to particulate matter ( PM2.5) and short-term exposure to particulate matter (PM10), NO2, SO2, and carbon monoxide (CO), increase the risk of depression. The brain is highly sensitive to stress hormones such as cortisol, which plays an important role in cognition and depression. Stress response starts in the central nervous system (CNS) and acts through the hypothalamus and pituitary gland, increasing the secretion of cortisol from the adrenal cortex. NO2, PM2.5, and PM10 present in the polluted air increase cortisol levels and activate the genes responsible for inflammatory reactions, metabolism, apoptosis, and impaired neurogenesis, neurotoxicity, and glial cell reactivity and eventually leading to cognitive decline, dementia, and depression.
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Multiple sclerosis - It is a chronic disease caused by inflammatory reactions and neurodegeneration. Several studies have been done to find the correlation between multiple sclerosis and air pollution. When the particulate matter is absorbed into the lungs through the respiratory tract, pulmonary or systemic inflammation is induced, and the T cells are activated, which then secrete proinflammatory cytokines in the brain.
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Schizophrenia - It is a mental disorder affecting more than 21 million people worldwide. Increased mental illness among urban residents is due to exposure to pollutants present in the air.
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Attention Deficit Hyperactivity Disorder (ADHD) - Air pollution has a negative impact on a child's brain development. It triggers the receptors for attention deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD).
How Does Organosulfates Cause Neurological Diseases?
Organosulfates(OSs) are organic sulfate esters present in atmospheric aerosol particles. The concentrations of airborne organosulfates are much higher in vehicle emissions and traffic-related air pollution (TRAP). Particulate matter in the air is classified according to particle size, and particle sizes with diameters less than 2.5 micrometers (PM2.5) or equal to 2.5 micrometers cause health concerns. Organosulfates make up 4 % to 30 % of the overall PM2.5 mass. Organosulfates associated with particulate matter (PM2.5) present in polluted air may cause neurotoxicity. When inhaled, PM2.5 readily crosses cell membranes, reaches blood vessels, and accesses all body organs, including the brain.
Conclusion:
Air pollution has a deleterious effect on respiratory, cardiovascular, and neurological disorders. Particulate matter in polluted air enters the body through respiration and causes harmful health conditions. Several studies have shown an increase in neurological diseases like depression, dementia, attention deficit hyperactivity disorder, and developmental neurological diseases in polluted urban areas than in less polluted rural ones.
