Air pollution is one of the most serious issues in the modern world, posing significant toxicological effects on human health and the environment. This article analyzes the sources of air pollution, key pollutants (particulate matter, ozone, carbon monoxide, sulfur dioxide, nitrogen oxides, and lead), and their impact on human health, including respiratory diseases, cardiovascular conditions, and cancer risks. Additionally, it examines ecological damage such as acid rain, climate change, and threats to biodiversity. The article highlights the Pollutant Standard Index (PSI) used to assess air quality and its significance. Based on WHO data, air pollution causes millions of deaths annually, posing a major risk, particularly in the Asian region. The article also discusses preventive measures and strategies to mitigate the effects of air pollution.

Keywords: toxicology, ground-level ozone, carbon monoxide, carboxyhemoglobin, sulfur dioxide, nitrogen oxide.

Air pollution has become one of the major issues of recent decades, exerting serious toxicological effects on human health and the environment. Pollution sources range from small-scale natural contributors, such as cigarette smoke and volcanic activity, to large-scale emissions from vehicle engines and industrial operations. The long-term impact of air pollution is widely recognized as a leading cause of respiratory infections, inflammation, cardiovascular dysfunctions, and cancer, resulting in millions of deaths worldwide each year.

In developing countries, industrial activities contribute significantly to air pollution, while poorly regulated transportation systems further increase emission levels. Approximately 4.3 million people die annually due to household air pollution, and 3.7 million from outdoor air pollution—most of whom (around 3.3 and 2.6 million, respectively) reside in Asia. Air pollution is defined as the harmful effects of various sources contributing to atmospheric contamination and ecosystem degradation. It arises due to human intervention and natural events and consists of pollutants present in solid, liquid, and gas phases.The Pollutant Standard Index (PSI) is a numerical value used to assess pollution risk, facilitating easy evaluation. The PSI ranges from 0 to 500 and serves as a guideline for air quality reporting. First introduced in 1974 by Thom and Ott, the index remains an essential tool for monitoring pollution levels.Thus, it provides a method for comparing the relative contribution of each pollutant to overall risk. PSI calculation is based on the concentration levels of five major air pollutants: particulate matter (PM), sulfur dioxide (SO ₂ ), nitrogen dioxide (NO ₂ ), carbon monoxide (CO), and ozone (O ₃ ).Havo ifloslanishining toksikologiyasi .

The impact of air pollutants on living organisms extends beyond human and animal health, affecting the entire environment. Various geographical conditions, global climate change, and environmental shifts influence both human health and wildlife. Environmental damage: From an ecological perspective, air pollution can severely contaminate groundwater, soil, and air, posing a significant threat to biodiversity. Research on the relationship between air pollution and species decline has clearly demonstrated the harmful effects of environmental pollutants on the extinction of both animal and plant species. Suspended toxins in the air can also impact animal reproduction. Key ecological consequences of air pollution include acid rain, temperature inversion, and global climate change, primarily caused by greenhouse gas emissions into the atmosphere.

Air Pollutants and Their Toxic Effects: Any substance present in the air that negatively impacts human health or significantly affects the environment is classified as an air pollutant. According to the World Health Organization (WHO), six major air pollutants known to harm human health and ecosystems include particulate matter (PM), ground-level ozone (O ₃ ), carbon monoxide (CO), sulfur oxides (SO ₂ ), nitrogen oxides (NO ₂ ), and lead (Pb). The atmosphere contains a wide range of suspended pollutants, such as dust, vapor, smoke, fog, gaseous contaminants, hydrocarbons, volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH), and halogenated substances. In high concentrations, these pollutants contribute to various diseases, including an increased susceptibility to different types of cancer. Below is a brief overview of the most significant air pollutants, their toxic effects on different organs in the human body, and associated diseases.Particulate Pollutants Particulate pollutants are among the most significant components of air pollution. Simply defined, they are a mixture of particles found in the air. Pollution caused by particulate matter (PM) is strongly linked to respiratory and cardiovascular diseases, contributing to the majority of illness and mortality associated with air pollution. These particles typically range in size from 2.5 to 10 micrometers (PM2.5 to PM10).

The size of particulate pollutants is directly related to the development and progression of lung and heart diseases. Smaller particles can reach deeper into the respiratory system, increasing the likelihood of triggering health complications. Scientific studies indicate that fine particulate pollutants contribute to premature death in individuals suffering from heart or lung diseases, including heart arrhythmias, nonfatal heart attacks, aggravated asthma, and reduced lung function. Depending on exposure levels, particulate pollutants may cause both mild and severe illnesses. Common clinical symptoms of respiratory diseases due to air pollution include wheezing, coughing, dry mouth, and limited physical activity. Long-term exposure to current environmental PM concentrations may significantly reduce life expectancy. Increased mortality due to cardiopulmonary diseases and lung cancer is a primary cause of reduced lifespan. Additionally, decreased lung function in both children and adults—leading to conditions such as asthmatic bronchitis and chronic obstructive pulmonary disease (COPD)—can negatively impact quality of life and shorten life expectancy. Strong evidence from cohort studies supports the link between prolonged exposure to PM and increased cardiovascular and cardiopulmonary mortality. Ground-Level Ozone (GLO): Ozone (O ₃ ) is a colorless gas with the chemical formula O ₃ , which is a fundamental component of the atmosphere. It exists both at ground level and in the upper layers of the atmosphere, specifically in the troposphere. Ground-level ozone (GLO) is formed through chemical reactions between nitrogen oxides (NO ₂ ) and volatile organic compounds (VOC) emitted from natural sources and human activities. GLO is strongly associated with an increased risk of respiratory diseases, particularly asthma. As a powerful oxidant, ozone readily accepts electrons from other molecules. In the surface fluid lining of respiratory tract cells, polyunsaturated fatty acids are highly concentrated. The double bonds within these fatty acids are unstable, making them susceptible to oxidative attack by ozone.

Ozone reacts with unpaired electrons, leading to the formation of ozonides that transition through unstable zwitterions or trioxolanes (depending on water presence). Ultimately, these reactions result in the production of lipohydroperoxides, aldehydes, and hydrogen peroxide, initiating lipid radical propagation and oxidative damage to cell membranes and macromolecules. Additionally, ozone exposure can increase DNA damage in epidermal keratinocytes, disrupting cell function. At concentrations frequently observed in urban areas, ozone induces various toxic effects in humans and experimental animals, causing morphological, functional, immunological, and biochemical changes. Due to its low water solubility, inhaled ozone penetrates deeply into the lungs. However, its reactivity allows approximately 17 % clearance by the nasopharynx in rats and 40 % in humans during resting states. Environmental Impact: Ecologically, ozone can reduce carbon assimilation in trees, which may significantly affect global food security with long-term exposure.

Carbon Monoxide (CO): Carbon monoxide (CO) is a colorless and odorless gas produced by the incomplete combustion of fossil fuels, such as coal and wood. Its affinity for hemoglobin, the oxygen carrier in the body, is approximately 250 times stronger than oxygen, meaning it readily replaces oxygen in the blood, leading to toxic effects. The severity of CO poisoning depends on concentration levels and exposure duration. Symptoms can range from mild (headache, dizziness, weakness, nausea, and vomiting) to severe (loss of consciousness and even death). These symptoms often mimic those of food poisoning or viral infections, making diagnosis challenging. Carboxyhemoglobin (COHb) levels below 2 % typically do not affect human health, but concentrations exceeding 40 % can be fatal. CO toxicity is primarily caused by hypoxia, apoptosis, and ischemia, which result from CO's competitive binding to hemoglobin's heme groups, reducing oxygen transport. Cardiovascular effects have also been observed with COHb levels exceeding 5 %, leading to complications like angina pectoris. In the early 1990s, the Health Effects Institute conducted studies to assess angina risk in individuals exposed to COHb levels between 2–6 %, revealing an increased likelihood of early angina—though the exact risk of ventricular arrhythmias remained uncertain.

Sulfur Dioxide (SO₂): Sulfur dioxide (SO₂) is a colorless, highly reactive gas considered a major air pollutant. It is primarily emitted from fossil fuel combustion, natural volcanic activity, and industrial processes. SO₂ poses severe risks to plant life, animal health, and human well-being. Individuals with lung diseases, children, the elderly, and those exposed to SO₂ regularly have a higher risk of skin and respiratory illnesses. Exposure to high concentrations of SO₂ can lead to respiratory irritation and dysfunction, as well as worsening pre-existing cardiovascular conditions. SO₂ is mostly absorbed in the upper airways, where it acts as an irritant, potentially causing bronchospasms and increased mucus secretion. In polluted environments, low SO₂ concentrations (<1 ppm) may still cause chronic bronchitis in industrialized regions.SO₂ enters the lungs more significantly through mouth breathing compared to nasal breathing. Increased airflow from deep and rapid breathing allows more SO₂ to penetrate deep into the lungs, making physical activity in polluted air more hazardous. Once inside the respiratory tract, SO₂ dissolves into surface fluids, forming compounds like sulfite and bisulfite, which can easily spread throughout the body. Sulfite interacts with airway receptors, triggering bronchoconstriction through local and central mechanisms.

Nitrogen Oxides (NO ₂ ): Nitrogen oxides are major air pollutants that can increase the risk of respiratory infections. They are primarily emitted from motor vehicle engines, making them a transport-related air pollutant. When inhaled at high levels, they act as deep lung irritants, potentially causing pulmonary edema. Although generally less toxic than ozone (O₃), nitrogen dioxide (NO₂) can lead to significant toxicological issues. Exposure to 2.0–5.0 ppm of NO₂ has been shown to affect T-lymphocytes, particularly CD8+ cells and natural killer cells, which play crucial roles in host defense against viruses. While these levels can be high, epidemiological studies suggest that NO₂ increases the risk of respiratory infections in children. Common symptoms of nitrogen oxide toxicity include coughing and wheezing, but may also involve eye, nose, or throat irritation, headaches, shortness of breath, chest pain, excessive sweating, fever, bronchospasms, and pulmonary edema. One report suggests that NOx levels between 0.2–0.6 ppm are not harmful to the general population, though prolonged exposure to higher concentrations may pose health risks.

Conclusion

Air pollution is a serious toxicological threat to human health and the environment, emerging as a key concern in contemporary civilization. It originates from various emission sources, with motor vehicles and industrial processes being the largest contributors. According to the World Health Organization (WHO), six primary air pollutants include particulate matter, ground-level ozone, carbon monoxide, sulfur oxides, nitrogen oxides, and lead. Both short-term and long-term exposure to airborne toxins can result in multiple health complications, including respiratory disorders, cardiovascular diseases, neuropsychiatric complications, eye irritation, skin diseases, and chronic conditions like cancer. Several studies have established a direct link between poor air quality and rising morbidity and mortality rates, primarily due to cardiovascular and respiratory illnesses. Furthermore, air pollution is recognized as a major environmental risk factor contributing to asthma, lung cancer, ventricular hypertrophy, Alzheimer’s and Parkinson’s diseases, psychological disorders, autism, retinopathy, fetal growth complications, and low birth weight.

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