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State Water Resources Control Board <br />Division of Water Quality <br />GAMA Program <br />OCCURRENCE <br />Anthropogenic Sources <br />Arsenic is widely distributed throughout the earth's crust, <br />most often as arsenic sulfide or as metal arsenates and <br />arsenides. Almost all of the arsenic used is obtained as a <br />by-product of smelting of ores of copper, lead, cobalt and <br />gold. Mining of these ores and the management of waste <br />materials associated with mining operations is a <br />significant source of arsenic released to the environment. <br />Commercial and industrial uses include alloying agents <br />in the manufacturing of transistors, lasers, <br />semiconductors, and solar cells. Other sources can <br />include processing of glass, ceramics, paints, pigments, <br />dyes and soaps, textiles, paper, metal adhesives, wood <br />preservatives, pyrotechnics, and ammunition. <br />Agricultural sources include pesticides, insecticides, <br />cattle and sheep dips, algaecides, and hide tanning. <br />Medicinal sources include antisyphilitic drugs. <br />Natural Sources <br />The primary source of arsenic in the environment is from <br />the weathering of arsenic -containing rocks. Naturally <br />occurring arsenic is found in a variety of solid phases, <br />including a component of volcanic glass in volcanic <br />rocks, adsorbed to and co -precipitated with metal oxides <br />(especially iron oxides), adsorbed to clay -mineral <br />surfaces, and associated with sulfide minerals and <br />organic carbon. The concentrations of arsenic in soil (0.1 <br />to 40 ppm) and sedimentary rocks (13 ppm) are <br />generally higher than the average (2 ppm) in the earth's <br />crust due to movement and accumulation of the arsenic <br />through weathering. Additionally, volcanic activity and <br />forest fires can release arsenic into the atmosphere <br />where it later falls to earth; however, precipitation in <br />unpolluted areas usually contains less than 1 ppb of <br />arsenic. <br />Arsenic is found in groundwater predominantly due to <br />History of Occurrence <br />natural sources. It may also be present in localized <br />environments in high concentrations as a result of <br />specific releases, such as from mine tailings and <br />chemical spills. <br />Contaminant Transport <br />In water, the most common valence states of arsenic are <br />Characteristics <br />As(V), or arsenate, which is more prevalent in well - <br />oxygenated (aerobic) surface waters, and As(III), or <br />arsenite, which is more likely to occur in anaerobic <br />Revised October 2017 <br />