Mounting evidence suggests that our environment contains many carcinogens. The air we breathe, the water we drink, and the power lines that supply us with energy may pose threats to your health. It is important for you to understand what the dangers are so that you can work to modify them. As with many carcinogens, the time be-tween exposure to the carcinogen and actual development of cancer may be quite long. Because of this, the cause of a cancer initiated by trace amounts of either airborne or waterborne carcinogens years before may be attributed to an unrelated or unknown cause at time of diagnosis. This is why we must detect and clean our environment of as many carcinogens as possible.
The American Lung Association estimates that air pollution costs the nation $40 billion to $60 billion a year. Since the mid-1950s, it has been shown that the air in large urbanized areas is a risk factor for lung cancer. (1-3) Collectively, the studies suggest that the increased incidence of cancer in cities is due to three factors: 1) more cigarette smoking by the people who live in cities; 2) increased exposure of nonsmokers to side-stream or passive smoke from lighted cigarettes; and 3) occupational exposures.
The following occupations, involved with ambient air pollutants, are risk factors for certain cancers. Gas production workers have a greater risk of getting lung cancer than those who rarely work in the gas production area, especially if they are exposed to the products of coal carbonization. Men working at coke ovens in United States steel factories have an excess of lung cancer compared to men working in other parts of the steel industry. This is directly related to the exposure to the emissions from the ovens. Roofers who work with hot pitch are exposed to large amounts of benzo(a)pyrene (BaP). They, too, have a higher risk of getting lung cancer. So the concentration of BaP is a significant factor in heavily polluted cities and contributes to the excess of cancer.
The numerous atmospheric contaminants are found in one of two forms: particulate form, in which the carcinogen adheres to small particles in the air, or vapor form, in which the carcinogen is in a gas form. A city's atmosphere contains more contaminants than the atmosphere of a suburb or rural area. Many of these contaminants have been shown to be carcinogenic in various animals. The carcinogens found in particulate form are more important than those in vapor form because they can remain in the air from four to forty days and consequently travel very long distances. Carcinogens in particulate form originate mainly from the burning of fuels. Contaminants in vapor form are derived from the release of aerosols from industrial activities, from car exhaust, and from natural sources.
City air pollution is derived from many sources. A large amount of the particulate carcinogens comes from the burning of any material containing carbon and hydrogen, including petroleum, gasoline, and diesel fuel. A list of more than 100 different particulates containing detected carcinogens has been compiled. (4) A great many more exist, but detection of additional carcinogens in low concentrations is difficult because existing instruments are incapable of doing so.
In order to have a means of discussing carcinogenic air pollution in a standard fashion, one chemical compound, benzo(a)pyrene (BaP) was chosen as the indicator because it is a very potent carcinogen. The problem with choosing this one substance as an indicator is that there is no correlation between the level of BaP in the air and the level of other known detectable carcinogens. For instance, car emissions (gasoline or diesel fuel), coal-fired electric power plants, and oil-fired residential furnaces have low levels of BaP. But forest fires, residential fireplaces, refuse burning and coal burning in older furnaces, and motorcycle emissions produce high levels of BaP. With the new laws from the U.S. Environmental Protection Agency, the level of BaP in cities has dropped dramatically, but permitted levels of other carcinogens have risen. Since the level of BaP does not correlate with other atmospheric carcinogens, a new standard should be devised. This new standard or index should be composed of some number of different carcinogens that would more accurately reflect the total atmospheric carcinogen level. This atmospheric carcinogen index would be much like the pollen count or the Dow Jones Average which is composed of a number of different pollens or stocks, respectively. No accurate statement can be made correlating the number of lung cancer victims and the level of BaP (currently used as the atmospheric carcinogen standard) because BaP levels have decreased while lung cancer cases have increased.
The carcinogens found in the vapor phase include benzene, carbon tetrachloride, chloroform, and vinyl chloride, among others. Vapor phase carcinogens are derived from car emissions, industrial activity, burning of solid waste, forest fires, and evaporation of solvents. (6)
Asbestos, a potent carcinogen, can also be found airborne. Persons working with the following may inhale high concentrations of asbestos: asbestos roofing and flooring, car brakes and clutches, dry walls, home heating and plumbing. Family members of persons who work with asbestos or asbestos products are exposed to very high levels of asbestos also. High levels of asbestos are found near asbestos waste dumps; near asbestos mines, mills, and manufacturing plants; near braking vehicles; at demolition areas; and in buildings that were sprayed with asbestos.
Asbestos as a risk factor for lung cancer is well established for those who work with asbestos and for their family members. However, cigarette smoking acts synergistically with asbestos to greatly enhance the risk of lung cancer.
In many parts of the world, rain can no longer be regarded as a beneficial occurrence; rather it is thought to be a deadly acidic agent. Acid rain results when sulfur dioxide and nitrogen oxide are released into the atmosphere and converted into sulfuric acid and nitric acid. The evidence shows that fossil fuel combustion and power plant emissions contribute significantly to the production of acid rain. (7)
Next to carbon dioxide, acid rain ranks second as the most serious global pollution problem in modern time. Many natural habitats in the United States, Norway, Sweden, Scotland, and Canada, and some areas of the Netherlands, Denmark, and Belgium, have been reported to be severely hurt by acid rain. Acid rain has also decreased the amount of fir, spruce, and beech trees in the forests of central Europe.
Normal rain water is slightly acidic. But it is the higher acid content of acid rain that is devastating to human, animal, and plant life. During the past thirty years there has been a substantial increase in the amount of acid precipitation. Three important changes that have enhanced the production of acid rain are: 1) higher chimneys, 2) control of particulate discharge, and 3) a change from seasonal to year-round emission. Two of these were designed by environmentalists to control pollution. The tall chimneys allow the oxides of sulfur and nitrogen to stay longer in the atmosphere and thereby convert more efficiently to the acid.
Because of the increased acid in the atmosphere, there has been a decrease in the fish population and also other forms of animal life and vegetation in the lake areas of Canada, Eastern United States, Sweden, and Norway. (8) Vegetation and some animal forms are affected first; later fish suffer the harmful effects of acid increases.
The lethal effects of acid rain are due not only to the acidity but also to the aluminum and other toxic metals that are mobilized from the soil by the acid. Aluminum is toxic to fish and other life forms. (9) Zinc, nickel, lead, manganese, and cadmium are also increased in water after acid precipitation. Zinc, nickel, and mercury are toxic to aquatic forms of life. The direct toxic effects to man are still being reviewed. Aluminum poisoning is recognized in patients with impaired renal function and in patients with certain neurological diseases like Alzheimer's and amyotrophic lateral sclerosis in Guam. (10,11) Amyotrophic lateral sclerosis is prevalent in areas of Guam, where there is a high acid rain content. Consequently, there is a high aluminum concentration and low calcium level in the drinking water in Guam. Low calcium levels in the body lead to increased absorption of aluminum, which then gets deposited in the brain, causing the neurological disorder. The addition of calcium to the diet can help reverse this problem of increased aluminum absorption.
Another heavy metal of major concern is lead. Most of the lead that enters our bodies comes from food, dust, and air. Combustion of petroleum products is a main source of lead in the air and dust. Acid rain is also a culprit, leaching lead from the soil and putting it in our drinking water. Also mobilized by acid rain is mercury, which is consumed by fish that we in turn consume. And finally, acid rain reduces selenium, leading to selenium deficiencies, which is important in cancer prevention.
Acid rain may also be deposited on the human skin, but there have been no harmful consequences from this. However, people can inhale the sulfuric acid and nitric acid, which inhibit normal functioning of the lungs.
Findings of the United States National Acid Precipitation Assessment Program confirm the following:
- Acid rain adversely affects aquatic life in about 10 percent of Eastern lakes and streams.
- Acid rain decreases the number of red spruce at high elevations.
- Acid rain contributes to the corrosion of buildings and materials.
- Acid rain and other pollutants, especially fine sulfate particles, reduce visibility in the Northeastern states and in parts of the West.
There seems to be no direct correlation between acid rain and the etiology of cancer in humans; however, studies are ongoing. To control acid rain we should remove the sulfuric and nitric acids at their source by switching to fossil fuel with a low sulfur content. The key regions in the United States affected by acid rain are the Northeast, Midwest, and West. Lakes in the Northeast are being acidified by acid rain produced by the high-sulfur coal burned in the large power plants of the industrial Midwest. Low-sulfur fuel can almost completely obviate the production of acid rain, eliminating it as a risk factor for many illnesses.
Diesel Exhaust Exposure
Animal studies in rats and mice show a link between exposure of whole diesel exhaust and lung cancer. The lung cancer is associated with diesel exhaust particulates and diesel exhaust gas.
Several human studies have also been done and show an increased risk of death from lung cancer in workers who have been exposed to diesel engine emissions. (12) This, too, is another controllable risk factor, especially emissions from vehicles that are obviously polluting the air.
Depletion of Natural Upper Atmospheric Ozone
The naturally occurring upper atmospheric ozone layer is crucial to the protection of living organisms because it absorbs harmful ultraviolet radiation. About 3 percent of the sun's electromagnetic output is emitted as ultraviolet radiation, but only a fraction of this reaches the surface of the Earth. Wavelengths of 240-290 are eliminated, and only a portion of the wavelengths at 290-320 penetrate to the Earth. The lower-range ultraviolet light wavelengths destroy DNA, which is the genetic material of all life forms.
Chlorofluorocarbons, commonly known as CFCs, are chemical compounds that have been shown to damage the protective ozone layer. What is of major concern now is the appearance of an actual hole in the ozone layer over Antarctica. (13) The concern here is obvious: what happens if there is a hole in the ozone layer in more densely populated areas of the globe?
Ultraviolet exposure is highly associated with melanoma, basal cell carcinoma, and squamous cell carcinoma of the skin. People with fair skin, blond hair, and blue eyes who also sunburn easily are at highest risk for the development of these skin cancers. Not only does ultraviolet exposure cause cancer, but in most people it causes severe skin damage and ages the skin dramatically. The U.S. Environmental Protection Agency calculates that a 1 percent decrease in the ozone concentration will increase the incidence of most skin cancers by 3-5 percent. The EPA further calculates that for every 2.5 percent increase per year of chlorofluorocarbon, an additional one million skin cancers and 20,000 deaths will occur over the lifetime of the existing United States population. In fact, in 1990 the incidence of skin cancer increased markedly: squamous cell carcinoma rose 3.1 times in women and 2.6 times in men; and melanoma rose 4.6 times in women and 3.5 times in men. By the year 2000, 1 in 75 will develop melanoma.