ABSTRACT
Arsenic (As) occurs naturally as an impurity in metal ores (e.g. arseno-pyrite, copper, gold), in sulfide minerals (e.g. realgar = AsS, orpiment = As2S3, arsenopyrite = AsFeS), coal, shales, and in rock-phosphate, among others (Tamaki and Frankenberger, 1992; Williams, 2001; Carlson et al., 2002; O’Day, 2006). It has been released into the near-surface environment as a result of natural weathering phenomena, but more profoundly as a result of mining and other industrial operations. Although there is a fixed planetary As concentration, the concentration of As in the biosphere has and continues to increase! Arsenic in the solid phase is safer than in the aqueous and bio-available form, i.e. it is not readily accessible to biological receptors. Increased As concentrations in soils and soil solution have been responsible for yield decreases in and contamination of edible products (Woolson et al., 1971; Carbonell-Barrachina et al., 1995; Smith et al., 1998; Smith et al., 2009) and cause diseases such as bone marrow depression, liver diseases, and various forms of cancer in humans (Hall, 2002). The processes and factors that govern the transition from soluble to solid As phases are hence of great importance to many communities that suffer from elevated As levels in potable and irrigation waters. Of particular concern are regions in Bangladesh, India, and Vietnam.
