Arsenic Fact Sheet

The presence of arsenic (As) in nature is due mainly to natural deposits of metalloids in the earth’s crust and usually in ancient rock formations. Arsenic enters ground water through erosion or from manmade sources such as wood preservative, petroleum production, semi-conductor manufacture or due to misuse of animal feed additives and arsenic-containing pesticides (e.g. Paris green). Since soluble arsenic is tasteless and colorless, a chemical water analysis is necessary to detect its presence. Higher levels of arsenic tend to be found more in ground water sources than in surface water sources (lakes and rivers) of drinking water. Compared to the rest of the United States, the western states have more water systems with arsenic levels greater than 10 micrograms per liter (µg/L, ppb).