Arsenic Speciation and Sorption in Natural Environments

Aqueous arsenic speciation, or the chemical forms in which arsenic exists in water, is a challenging, interesting, and complicated aspect of environmental arsenic geochemistry. Arsenic has the ability to form a wide range of chemical bonds with carbon, oxygen, hydrogen, and sulfur, resulting in a large variety of compounds that exhibit a host of chemical and biochemical properties. Besides the intriguing chemical diversity, arsenic also has the rare capacity to capture our imaginations in a way that few elements can duplicate: it invokes images of foul play that range from sinister to comedic (e.g., “inheritance powder” and arsenic-spiked elderberry wine). However, the emergence of serious large-scale human health problems from chronic arsenic exposure in drinking water has placed a high priority on understanding environmental arsenic mobility, toxicity, and bioavailability, and chemical speciation is key to these important questions. Ultimately, the purpose of arsenic speciation research is to predict future occurrences, mitigate contamination, and provide successful management of water resources. Chemical speciation is fundamental to understanding mobility and toxicity. Speciation affects arsenic solubility and solid-phase associations, and thus the mobility, of arsenic in natural waters. It is also critical to designing treatment strategies, understanding human exposure routes, and even developing medical applications (e.g., as a treatment for acute promyelocytic leukemia; Antman 2001). As single- and multi-celled organisms are exposed to various forms of arsenic, they often alter its speciation to either utilize the arsenic for energy or to mitigate the detrimental effects of intracellular arsenic (detoxification). Some organisms can accumulate arsenic in cell material, which can be a concern if it accumulates in a human food product such as rice or seafood, but could be a potential remediation solution in hyper-accumulating plants (Ma et al. 2001). It is important to quantify speciation in addition to total amount of arsenic because …