(See the section on the chemical industry in Chapter 2, “Air Quality (Outdoor [Ambient] and Indoor)”

There is a complex interaction between human genetics, the environment, and environmental pollutants. In some situations, the same level of environmental pollutants will cause different levels of disease in different people because of their genetic disposition.

Humans are exposed to a variety of environmental pollutants, biological, chemical, physical, and radiological, either continuously, intermittently, repeatedly, or sporadically. These environmental stress factors can have an acute or chronic effect on the human body. They may affect the genetic, immune, and endocrine systems as well as all other systems of the body, causing fatal flaws, which can then in turn lead to cancer, as well as other potential diseases. Environmental chemicals modify gene expression and cause excessive stress and inflammation within the human body and the human brain. Endocrine disruptors also have inflammatory and metabolic effects.

Compounding the problem is the nature of the individual. The individual’s age, sex, weight, genetic predisposition, previous illnesses, existing physical condition, level of nutrition, and exposure to various concentrations of pollutants contribute to the potential for acute and chronic illness caused by environmental pollutants. Further, the potential for disease and injury is complicated by ambient temperature and weather conditions.

Past exposure may have resulted in tissue damage or heightened the susceptibility of the individual to disease processes from the contaminant which has been retained in the human body or the damage done by previous exposures. The length of time of the exposures and the concentration of the exposures are very important. The exposures may be through inhaled air, ingestion of water and food, absorption through the skin, or a combination of these routes of entry into the body. Bioconcentration of chemicals may occur in the food chain when a higher form of life consumes a contaminated lower form of life, and then this food source may cause disease when ingested by people. Further, multiple contaminants may interact with each other to become more toxic to the individual. The human body may alter the contaminants and make them more toxic during the metabolic process. The liver and kidneys become special potential problem areas when the substances are processed and secreted.

Complicating the understanding of the severity of exposure to environmental stresses such as chemicals is the potential alteration of the chemicals in the environment when they are transported from the point of origin to the point of contact with people. Chemicals are deposited in the air, on the land, in the water, and taken up by plants and animal food sources. The original chemical may stay the same or may be transformed through the previous processes. In any case, the chemicals can be the direct or indirect cause of acute or chronic illness and potential physical injury. The chemicals may be precursors for cancer, create latent cancer cells, be direct carcinogens, alter, depress or enhance the action of enzymes, bind to cellular DNA, damage DNA, be direct toxins, or enhance the action of other chemicals in a negative manner for the human body.

Chemicals are rarely released in the pure form, but are rather a mixture of several different chemicals as well as the degradation stages of the original chemical and the mixture of chemicals. This makes it more difficult to remove the chemical from the source of pollution. Also, a chemical which is very useful for one type of pollution, such as methyl tert-butyl ether (MTBE) used as a gasoline additive to reduce air pollution, can cause another type of pollution, groundwater contamination. MTBE is often found together with other gasoline contaminants such as benzene, toluene, ethyl benzene, and xylenes.

Chemicals may contribute to increased levels of chronic disease. In a study in California, it was shown that children with type I diabetes were exposed to higher levels of ozone in the air than healthy children. These children were also exposed to higher levels of sulfate air pollution than the healthy children control group. In Montreal, Canada, a study of individuals with the autoimmune disease systemic lupus erythematosus had increased autoantibody levels when air particles in the 0.1-2.5 pm range increased beyond normal. Apparently these particles triggered an autoimmune response in these individuals. (See endnote 15.) Diesel exhaust particles have been shown to affect the development of the thymus during pregnancy and in early life, thereby affecting the development of the immune system.

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