Examples of air pollutants and their human health effects
Air pollution can cause mainly respiratory ailments like bronchitis, asthma, tuberculosis, pneumonia and lung cancer as well as skin lesions, death, etc. For example, the exhaust of diesel engines is considered a human carcinogen by the International Agency for Research on Cancer (IARC):
Therefore, illnesses from air pollution may result from chemical irritation of the respiratory tract, with certain sensitive subpopulations being more affected:
- Very young children, whose respiratory and circulatory systems are poorly developed;
- The elderly, whose cardiorespiratory systems function poorly;
- People with cardiorespiratory diseases such as emphysema, asthma, and heart disease.
Heavy smokers are also affected more adversely by air pollutants. In most cases, human health problems are attributed to the combined action of particulates and sulphur dioxides (SO2).
Examples of air pollutants:
Lead - One of the most familiar particulates in air pollutants is lead, with foetuses and young children being the most susceptible. Lead can impair renal function, interfere with the development of red blood cells, impair the nervous system, leading to mental retardation and even blindness, and also cause problems in liver, etc. The two most common routes of exposure to lead are ingestion and inhalation. It is estimated that approximately 20% of the total body burden of lead comes from inhalation.
More information on human health effects caused by lead can be found in the following links:
http://www2.epa.gov/lead/learn-about-lead#effects
http://www.who.int/mediacentre/factsheets/fs379/en/
Carbon Monoxide - Combines readily with hemoglobin (Hb) to form carboxyhemoglobin (COHb), thereby preventing the transfer of oxygen to tissues. The affinity of hemoglobin for CO is approximately 210 times its affinity for oxygen. A blood concentration of 5% COHb, equivalent to equilibration at approximately 45 ppm CO, is associated with cardiovascular effects. Concentrations of 100 ppm can cause dizziness, headaches, nausea, and breathing difficulties. An acute concentration of 1000 ppm is invariably fatal. Carbon monoxide levels during acute traffic congestion have been known to be as high as 400 ppm. Additionally, people who smoke increase their total body burden of CO as compared with nonsmokers. The effects of low concentrations of CO over a long period are not known, but it is possible that heart and respiratory disorders are exacerbated.
The following review article discusses how the carbon monoxide poisoning affects the central nervous system:
Sulphur Oxides - Sulphur dioxide is a common component of polluted air that results primarily from the industrial combustion of coal, with soft coal containing the highest levels of sulphur. The sulphur oxides tend to adhere to air particles and enter the inner respiratory tract, where they are not effectively removed. In the respiratory tract, SO2 combines readily with water to form sulphurous acid, resulting in bronchial constriction and irritation of mucous membranes. This irritation in turn increases the sensitivity of the airway to other airborne toxicants.
Nitrogen Oxides - Nitrogen dioxide (NO2), a gas found in photochemical smog, is also a pulmonary irritant and is known to lead to pulmonary oedema and haemorrhage. The main issue of concern is its contribution to the formation of photochemical smog and ozone. However, nitrogen oxides also contribute to acid deposition. In addition to the respiratory disorders, acid rain (see fig. 1) also causes skin disorders.
For more information on human health effects of acid rain see the following link:
http://www.epa.gov/acidrain/effects/health.html
Photochemical smog:
a type of air pollution formed through solar radiation reacting with airborne pollutants, such as nitrogen oxides and volatile organic compounds.
Ozone - A highly irritating and oxidizing gas is formed by photochemical action of ultraviolet (UV) light on nitrogen dioxide in smog. The resulting ozone can produce oedema, pulmonary congestion, and haemorrhage.
NO2 + UV light → NO + O-
O- + O2 → O3
Tropospheric ozone occurs from 0 to 10 mi above the earth's surface, and is harmful. However, the stratospheric ozone, located about 30 mi above the earth's surface, is responsible for filtering out incoming UV radiation and hence is beneficial. It is estimated that a 1% decrease in stratospheric ozone will increase the amount of potentially harmful solar UV radiation reaching the earth's surface by 2% and will cause a 10% increase in skin cancer. Therefore, it is the decrease in the stratospheric ozone layer that has been of much concern recently. Major contributors to damage the stratospheric ozone are thought to be the CFCs (chlorofluorocarbons). Chlorine is removed from the CFC compounds in the upper atmosphere by reaction with UV light and is then able to destroy the stratospheric ozone through self-perpetuating free radical reactions.
Cl + O3 → ClO + O2
ClO + O → Cl + O2
Before being inactivated by nitrogen dioxide or methane, each chlorine atom can destroy up to 10,000 molecules of ozone. The use of CFC compounds is now phased out and banned by international agreements.
Hydrocarbons or Volatile Organic Compounds (VOCs) - These are derived primarily from two sources:
- Approximately 50% are derived from trees as a result of the respiration process (biogenic);
- The other 45-50% comes from the combustion of fuel and from vapour from gasoline. Many gasoline pumps now have VOC recovery devices to reduce pollution.
Additional information on human health effects caused by VOCs can be found in the following link:
http://www.epa.gov/iaq/voc.html
Solid Particles - Dust and fibers from coal, asbestos, glass, clay, and minerals, can lead to scarring or fibrosis of the lung lining. Pneumoconiosis, a condition common among coal miners that breathe coal dust, silicosis caused by breathing silica-containing dusts, and asbestosis from asbestos fibers are all well-known industrial air pollution diseases.
An example of a pollution incident that occurred in the United States relates to workers involved in the manufacture of asbestos. In the late 1960s, asbestos use soared based on its insulation properties. Uses during this time included components of rocket engines used in the space program, paper and cement products, and components of gaskets. Asbestos can be naturally found in certain rock types (e.g. serpentinite), being extracted from the rock and manufactured in indoor factories. A large amount of dust containing asbestos was released into the indoor air environment during the process. Several years after people starting working in the factories, cases of a new type of lung cancer called mesothelioma began appearing in these workers. Soon it was determined that the asbestos fibers released into the air and inhaled caused this type of lung cancer.
Because many years can elapse between asbestos exposure and cancer, most of these cases are probably related to when asbestos was still manufactured, rather than recent exposure cases. Asbestos-related toxicity is still prevalent in other countries where asbestos is mined, manufactured, and used without regulatory restrictions (e.g. South Africa).
Asbestos: a broad mineralogical term applied to numerous fibrous silicates composed of silicon, oxygen, hydrogen, and metallic ions like sodium, magnesium, calcium, and iron. At least six forms of asbestos occur naturally.
Therefore, the airborne asbestos can result from natural processes (e.g. rock weathering) but also human activities (e.g. mining, milling, automotive industry, demolition of asbestos-containing buildings).
