Arsenic cycling in the Earth's crust and hydrosphere: interaction between naturally occurring arsenic and human activities

Field-based research on naturally occurring arsenic contamination of surface waters and groundwaters and the mechanisms of contamination are reviewed. The distribution of arsenic is strongly related to areas of active plate tectonics, magmatism and associated hydrothermal activity, and high rates of erosion. Sources of arsenic contamination are mainly hydrothermal water, sulfide and arsenide minerals, volcanic ash, and iron oxyhydroxide/oxide as weathering products. The promotion of the reduction and oxidation of arsenic source minerals by in situ microbial activity is an important secondary mechanism that often determines arsenic levels in groundwater. Anthropogenic activities, such as geothermal and mining operations, as well as excess pumping of shallow groundwaters, disperse arsenic in the environment, thereby expanding areas of arsenic contamination.