Nitrates and nitrites

Nitrates and nitrites are families of chemical compounds containing atoms of nitrogen and oxygen. Occurring naturally, nitrates and nitrites are critical to the continuation of life on the earth, since they are one of the main sources from which plants obtain the element nitrogen. This element is required for the production of amino acids which, in turn, are used in the manufacture of proteins in both plants and animals.

One of the great transformations of agriculture over the past century has been the expanded use of synthetic chemical fertilizers. Ammonium nitrate is one of the most important of these fertilizers. In recent years, this compound has ranked in the top fifteen among synthetic chemicals produced in the United States.

The increased use of nitrates as fertilizer has led to some serious environmental problems. All nitrates are soluble, so whatever amount is not taken up by plants in a field is washed away into groundwater and, eventually, into rivers, streams, ponds, and lakes. In these bodies of water, the nitrates become sources of food for algae and other plant life, resulting in the formation of algal blooms. Such blooms are usually the first step in the eutrophication of a pond or lake. As a result of eutrophication, a pond or lake slowly evolves into a marsh or swamp, then into a bog, and finally into a meadow.

Nitrates and nitrites present a second, quite different kind of environmental issue. These compounds have long been used in the preservation of red meats. They are attractive to industry not only because they protect meat from spoiling, but also because they give meat the bright red color that consumers expect.

The use of nitrates and nitrites in meats has been the subject of controversy, however, for at least twenty years. Some critics argue that the compounds are not really effective as preservatives. They claim that preservation is really effected by the table salt that is usually used along with nitrates and nitrites. Furthermore, some scientists believe that nitrates and nitrites may themselves be carcinogens or may be converted in the body to a class of compounds known as the nitrosamines, compounds that are known to be carcinogens.

In the 1970s, the Food and Drug Administration (FDA) responded to these concerns by dramatically cutting back on the quantity of nitrates and nitrites that could be added to foods. By 1981, however, a thorough study of the issue by the National Academy of Sciences showed that nitrates and nitrites are only a minor source of nitrosamine compared to smoking, drinking water, cosmetics, and industrial chemicals. Based on this study, the FDA finally decided in January 1983 that nitrates and nitrites are safe to use in foods.

See also Agricultural revolution; Cancer; Cigarette smoke; Denitrification; Drinking-water supply; Fertilizer runoff; Nitrification; Nitrogen cycle; Nitrogen waste

[David E. Newton ]

RESOURCES

BOOKS

Canter, L. W. Nitrates in Ground Water. Chelsea, MI: Lewis, 1992.

Cassens, R. G. Nitrate-Cured Meat: A Food Safety Issue in Perspective. Trumbull, CT: Food and Nutrition Press, 1990.

Selinger, B. Chemistry in the Marketplace. 4th ed. Sydney, Australia: Harcourt Brace Jovanovich, 1989.

PERIODICALS

"Clearest Lake Clouding Up." Environment 30 (January-February 1988): 22–3.

Raloff, J. "New Acid Rain Threat Identified." Science News 133 (30 April 1988): 276.