The particulate and gaseous contaminants in polluted air may irritate the eyes and respiratory system or damage the clearance mechanism of the lungs, thereby increasing susceptibility to upper respiratory diseases and aggravating existing chronic illnesses. Diseases mentioned as also being associated with air pollution include bronchial asthma (restriction of the smaller airways or bronchioles and increase in mucous secretions), chronic bronchitis (excessive mucus and frequent cough), pulmonary emphysema (shortness of breath), lung cancer, heart diseases, and conjunctivitis (inflammation of the lids and coatings of the eyeballs) (also with lead and carbon monoxide poisoning as previously discussed). In an example of the built environment influencing health, one study found the higher prevalence of asthma in poor neighborhoods of Hartford, Connecticut, to be due in large part to a heavy burden of dust laden with cockroach antigen.73
A direct single cause-and-effect relationship is often difficult to prove because of the many other causative factors and variables usually involved. Nevertheless, the higher morbidity and mortality associated with higher levels of air pollution and reported episodes are believed to show a positive relationship.
Certain air contaminants, depending on the body burden, may produce systemic effects. These include arsenic, asbestos, cadmium, beryllium compounds, mercury, manganese compounds, carbon monoxide, fluorides, hydrocarbons, mercaptans, inorganic particulates, lead, radioactive isotopes, carcinogens, and insecticides. They require attention and are being given consideration in the development of air quality criteria.
Bronchial asthma affects susceptible sensitive individuals exposed to irritant air contaminants and aeroallergens. The aeroallergens include pollens, spores, rusts, and smuts. There also appears to be a good correlation between asthmatic attacks in children and adults and air pollution levels.
Chronic bronchitis has many contributing factors, including a low socioeconomic status, occupational exposure, and population density; smoking is a major factor. Air pollution resulting in smoke, particulates, and sulfur dioxide is an additional factor.
Emphysema mortality rates in U.S. urban areas are approximately twice the rural rates, indicating an association with air pollution levels (sulfur oxides). Asthma and bronchitis often precede emphysema.
Lung cancer rates are reported to be higher among the urban populations than the rural. The dominant factor in lung cancer is smoking. Air pollution plays a small but continuous role.
Some generalized effects of common air pollutants and their possible relationship to these diseases are of interest. Sulfur dioxide and sulfuric acid in low concentrations irritate the lungs, nose, and throat. This can cause the membrane lining of the bronchial tubes to become swollen and eroded, with resultant clotting in the small arteries and veins. Children are more susceptible to coughs, colds, asthma, bronchitis, and croup. Carbon monoxide can affect the cardiovascular system; in high concentrations, the heart, brain, and physical activity can be impaired. It can reach dangerous levels where there is heavy auto traffic and little wind. Smokers are at greater risk. Acute carbon monoxide poisoning causes a lowered concentration of oxygen in the blood and body tissues. (See the discussion on carbon monoxide poisoning earlier in this chapter.) Ozone and other organic oxidants, known as photochemical oxidants, are produced by the reaction of hydrocarbons and nitrogen oxides in sunlight. Ozone is believed to be responsible for a large portion of the health problems associated with photochemical oxidants.74 Ozone and other chemicals formed in smog irritate the eyes and air passages, causing chest pain, coughing, shortness of breath, and nausea. Ozone can cause aging and severe damage to the lung tissues and interference with normal functioning of the lungs at levels of 0.12 ppm to greater than 0.20 ppm. Nitrogen dioxide in high concentrations can result in acute obstruction of the air passages and inflammation of the smaller bronchi. Nitrogen dioxide at low levels causes eye and bronchial irritation. In the presence of strong sunlight, nitrogen dioxide breaks down into nitric oxide and atomic oxygen, and this then combines with molecular oxygen in air to form ozone. Particulate matter can cause eye and throat irritation, bronchitis, lung damage, and impaired visibility.
Benzopyrene and related compounds are known to cause some types of cancer under laboratory conditions and have been incriminated as carcinogens. Olefins have an injurious effect on certain body cells and are apt to cause eye irritation. Beryllium concern relates primarily to lung disease, although it also affects the liver, spleen, kidneys, and lymph glands. Vinyl chloride is related to lung and liver cancer. Mercury may affect several areas of the brain as well as the kidneys and bowels. Lead is associated with retardation and brain damage, especially in children (see separate discussion earlier). The EPA National Emission Standards for Hazardous Air Pollutants identify vinyl chloride, lead, benzene, asbestos, beryllium, and mercury as hazardous. Considerable evidence has been assembled linking air pollution with adverse health effects.225, 226
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