Heavy Metals And Toxic Substances

In 1970, Barry Commoner (Commoner 1970) and other scientists alerted the nation to the growing problem of mercury contamination of lakes, streams, and marine waters. The manufacture of chlorine and lye from brine, called the chlor-alkali process, was identified as a major source of mercury contamination. Elemental mercury is methylated by aquatic organisms (usually anaerobic bacteria), and methylated mercury finds its way into fish and shellfish and thus into the human food chain. Methylmercury is a powerful neurological poison. Methylmercury poisoning was first identified in Japan in the 1950s as "Minamata disease." Mercury-containing effluent from the Minamata Chemical Company was found to be the source of mercury in food fish. Mercury contamination in oceanic fishes is currently widespread, and of sufficient concern that the U.S. Food and Drug Administration issued a consumer alert on March 9, 2001, advising that pregnant women, women of childbearing age, nursing mothers, and young children should avoid eating shark, swordfish, king mackerel, and tilefish. Many states in the United States have issued similar warnings about potentially hazardous levels of mercury or other bioaccumulated toxins in freshwater sport fish.

Arsenic, copper, lead, and cadmium are often deposited in lakes and streams from the air near emitting facilities. These substances may also enter waterways from runoff from slag piles, mine drainage, and industrial effluent. Effluents from electroplating contain a number of heavy metal constituents. Heavy metals, copper in particular, may be toxic to aquatic species as well as harmful to human health.

In the past quarter century, a considerable number of incidents of surface water contamination by hazardous and carcinogenic organic compounds were reported in the United States. The sources of these include effluent from petrochemical industries and agricultural runoff, which contains both pesticide and fertilizer residues. Trace quantities of chlorinated hydrocarbon compounds in drinking water may also be attributed to the chlorination of organic residues by chlorine added as a disinfectant. The production of these disinfection by-products is difficult to eliminate in the drinking water treatment process, but maintaining clean, unpolluted, source water is the first step.

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