Master Thesis

Arsenic mobilization under sulfidic conditions from the Altenberg reservoir

Anja Schnell (07/2014-05/2016)

Support: Britta Planer-Friedrich, Jörg Schaller

Seasonal concentration changes of the carcinogenic metalloid arsenic were detected in the drinking water reservoir Altenberg, Germany, which coincided witch a change in arsenic speciation. The occurrence of methylated arsenic during summer maxima and thiolated arsenic during winter minima concentrations of total arsenic indicated a mechanistic link and were investigated in this study. Pore water and sediment of Altenberg reservoir were characterized by use of peepers and a five step sequential extraction from sediment core samples, respectively. The formation of thiolated and methylated arsenic was subsequently tested in anoxic batch experiments, with arsenic speciation measured by IC-ICP-MS. Sediment with large additions of acetate was required for realizing the complete sequence from iron and sulfate reduction to methanogenesis. Formation of thiolated (15 %) and methylated (2 %) arsenic was shown, but no influence on the mobility of arsenic could be proven. In contrast, the reductive dissolution of iron oxides and the competing effect of arsenic with sulfate and carbonate for sorption sites could be the main factor controlling the mobilization and immobilization of arsenic. Moreover, the potential of phytoplankton activity for the formation of methylated arsenic needs further investigations.