Arsenic toxicity, mobility, and bioavailability In sediment-water systems are highly depended on its oxidation states and chemical species. Arsenite (As(III)) and arsenate (As(V)) are two main species of arsenic in water ecosystem. As(III) is more toxic and mobile than As(V). In this research both wet chemistry and spectroscopic techniques were applied to study the adsorption and redox transformation of As(III) and As(V) on Fe and Mn iron minerals as well as on soil and sediment. The results indicate that the Fe mineral (goethite) can strongly adsorb both As(V) and As(III) while the Mn mineral Birnessite can effectively oxide As(III) to As(V) both in solution phase and on mineral surfaces. Mn and Fe are closely related in chemical properties and often occur together in soils and sediments. The interaction between of arsenite (As(III) and Mn-substituted goethite was investigated by both solution chemistry and XANES spectroscopy. This study suggests that the adsorption-oxidation system composed of Fe and Mn minerals may be significant in decreasing arsenic toxicity in terrestrial environments.

The adsorption-desorption and incubation-extraction of As(III) and As(V) on soil and sediment samples collected from Tulare Basin, San Joaquin Valley of California were investigated. Research indicates that the adsorption and redox transformation of arsenic oxyanions on different components of soils and sediments are the major processes for controlling the mobility and bioavailability of arsenic in the terrestrial ecosystem. Results from this study provided useful information for understanding these processes and potentially, possible techniques for arsenic contamination control.