Arsenic

Abstract

Arsenic is relatively abundant in the biosphere owing to contamination from a variety of anthropogenic sources in addition to its natural occurrence in minerals. Since the industrial revolution, arsenic has been discharged into waterways as a waste product of sulfuric acid manufacturing, sprayed onto soils as a pesticide, dispersed into the air during ore smelting, and distributed over the Earth through mining activities. Although human activities are estimated to release 50,000 tons of arsenic per year, simple weathering of igneous and sedimentary rocks (including coal) naturally releases nearly an equal amount of arsenic into the environment. The geochemical cycle of arsenic is controlled by a variety of chemical reactions, including oxidation-reduction, precipitation-dissolution, adsorption-desorption, and methylation. Strong evidence exists that microorganisms play an important role in these reactions. This article will focus primarily on the microbial contributions to the cycling of inorganic arsenic.