Chemical Contaminants

13. Chemical Contaminants

In the past 10 years, the production of synthetic organic chemicals has expanded by 255 percent; relatively few of the new compounds have been studied for their cancer-causing potential. Because of the typical development period of 15 to 40 years for cancer, we must assume that much of the cancer from recent industrial development is not yet observable.

The majority of known environmental carcinogens are encountered at the workplace. In fact, the link between cancer and chemicals was first detected among workers; in 1775, soot was singled out as a causative agent in chimney sweeps cancer, cancer of the scrotum. Above-normal incidences of cancer are found in workers having contact with known or suspected carcinogenic substances such as asbestos, arsenic, benzopyrene, benzidine, bis-chloromethyl-ether, coal tar, carbon black, and vinyl chloride.

One such agent is benzidine, of which many million pounds are produced annually in the United States for use in making dyes. An excess of bladder tumors among workers in the industry was first reported in the early 1930s. But because benzidine was just one of a number of compounds to which these workers were exposed, a specific causative agent could not be identified at that time.

Later studies of populations of workers exposed only to benzidine firmly established a cause-and-effect relationship. One retrospective study of a coal-tar dye plant conducted in 1965 showed that 17 of 76 (21%) of workmen, exposed only to benzidine developed bladder tumors. This incidence rate greatly exceeds that of bladder cancer in general U.S. population—13.2 cases per 100,000 population.

Association of occupational exposure to asbestos with increased lung cancer was first reported in the 1950s. The, diagnosis of mesothelioma, an otherwise rare type of cancer, in some asbestos workers provided conclusive evidence that asbestos is a cancer hazard. In the past decade, mesothelioma has suddenly become more common: where environmental data exist, most cancer sufferers may be traced to potential or actual asbestos exposure. This exposure often occurred in the workplace, but not infrequently it was associated only with residence in the vicinity of an asbestos processor or in the household of an asbestos worker. Asbestos products—fabrics, housing insulation, ceiling tile, brake lining—are an additional source of exposure.

Until recently, vinyl chloride, a gas used primarily in the manufacture of polyvinyl chloride plastic, was also used as a propellant for aerosol sprays. In 1974, the discovery of four cases of angiosarcoma of the liver among vinyl chloride workers in a plant in Louisville suggested that vinyl chloride is a carcinogen. Workers exposed to vinyl chloride were later discovered to have a significant excess not only of angiosarcoma but also of more common cancers of the respiratory system, brain and the lymphatic system.

Chlorinated hydrocarbons and arsenical pesticides that have been used in homes and gardens are known carcinogens. Commercially-processed foods have also been found to contain residues of pesticides known to be carcinogenic and other chemicals suspected of being so. Foods may also contain naturally-occurring carcinogens such as aflatoxins produced by particular mold contaminants. Drugs and cosmetics have been reported as carcinogenic. Estrogen as well as synthetic drugs developed for treating chronic conditions such as diabetes, arthritis and anemia have been implicated in helping to produce a variety of malignant tumors.

Combustion products released from industrial smokestacks as well as from chimneys of office buildings, apartment buildings, hospitals, and government and municipal buildings may contain a variety of carcinogenic materials. In 1975, the Environmental Protection Agency found cancer-producing agents in low concentrations in the drinking water of all 80 cities whose water supplies it investigated.