Fate of arsenicals in different environmental substrates.

The current knowledge of arsenic (As) transformations in the environment, as well as some gaps in this knowledge, are reviewed. These transformations involve As chemical and biochemical transformations in air, waters, sediments, and soils. Arsenic moves in a dispersive manner through air and water and is in physical and chemical equilibrium in many substrates. It is oxidized, reduced, methylated, volatilized, incorporated into biotic tissues, excreted, adsorbed, and desorbed. Oceanic sediments become the eventual sink for As. The rates of As movement and transformation vary with environmental conditions. Besides inorganic As, various methylated arsenicals are found naturally at environmentally sensitive equilibrium concentrations, which are probably maintained biotically. An As-transformation model has been constructed from rate constants derived from field observations. The environmental factors affecting these rate constants are discussed.