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SOURCES, FATE, AND USES Global production of arsenic is estimated to be 75,000 to 100,000 tons annually, of which the United States produces about 21,000 tons and uses about 44,000 tons; major quantities are imported from Sweden, the world's leading producer (NAS 1977; EPA 1980). Almost all (97%) of the arsenic made worldwide enters end-product manufacture in the form of arsenic trioxide (As 03 ), and the rest is used as additives in producing special lead and copper alloys (NAS 1977). More than 80% of the As 03 is used to manufacture products with agricultural application, suc? as insecticides, herbicides, fungicides, algicides, sheep dips, wood preservatives, dyestuffs, and the medicines for eradication of tapeworm in sheep and cattle (NAS 1977). The sole producer and refiner of As20 in the United States is a copper smelter in Tacoma, Washington (NAS 177). Arsenic naturally occurs as sulfides and as complex sulfides of iron, nickel, and cobalt (Woolson 1975). In one form or another, arsenic is present in rocks, soils, water, and living organisms at concentrations of parts per billion to parts per million (NAS 1977). Soil arsenic levels are normally elevated near arseniferous deposits, and in mineralized zones containing gold, silver, and sulfides of lead and zinc (Dudas 1984). Secondary iron oxides formed from the weathering of pyrite act as scavengers of arsenic (Dudas 1984). Pyrite is a known carrier of arsenic and may contain up to 5,600 mg/kg; for example, total arsenic is IOX above normal background levels in soils derived from pyritic shale (Dudas 1984). Natural weathering of rocks and soils adds about 40,000 tons of arsenic to the oceans yearly, accounting for <0.01 mg/l input to water on a global basis (NRCC 1978). Many species of marine plants and animals often contain naturally high concentrations of arsenic (NAS 1977), but it is usually present in a harmless organic form (Woolson 1975). Anthropogenic input of arsenic to the environment is substantial, and exceeds that contributed by natural weathering processes by a factor of about 3X (NRCC 1978). The most important concept with respect to arsenic cycling in the environment is constant change. Arsenic is ubiquitous in living tissue and is constantly being oxidized, reduced, or otherwise metabolized. In soils, insoluble or slightly soluble arsenic compounds are constantly being resolubilized, and the arsenic is being presented for plant uptake or reduction by organisms and chemical processes. Man reportedly has modified the 3