Advances in thioarsenic in groundwater systems

Thioarsenic has been proved to be predominant species in sulfidic groundwaters, and is taken as threat to human health and the environment. Since our understanding of this species is far from comprehensive, based on survey of current research results in this field, this paper is focused on hydrologic-biological-environmental geochemical processes, sample preservation, separation and detection techniques of thioarsenic species, to demonstrate the latest advances in the thioarsenic studies. The results show that pH, Eh, concentration of sulfide and microorganism activities are key factors for the thioarsenic stability and speciation in groundwater. Iron-bearing minerals can form coordination bonds with thioarsenic to adsorb them, however, the capacity of adsorption are generally lower than those with arsenite and arsenate, making thioarsenic species easier to transport in groundwater systems. Filtration, quick-freezing and short time anaerobic cryopreservation can be used on natural water samples for thioarsenic analyses, in order to slow down the transformation or even disappear of thio species. IC-ICP-MS can be used in quantitative analyses of thioarsenic in natural water samples, and Ultraviolet-Visible Spectrophotometry and X-ray Absorption Spectrometry can be capable of quantitative characterization analysis of thioarsenic in different scenarios. Thioarsenic can be encountered in both shallow groundwater and geothermal water. Due to the unavoidable transformation of thioarsenic in water samples, it is difficult for indoor analyses to accurately reflect the geochemical processes. Thus, the update of field sample preservation technology and field detection method may have more research potential in the future.