Early diagenetic behavior of arsenic in the sediment of the hypersaline Maharlu Lake, southern Iran.

Arsenic (As) is a toxic element can experience phase and speciation changes during the early diagenesis of sediments across the sediment-water interface, affecting its mobility and toxicity. Maharlu Lake is a hypersaline lake in Southern Iran that today receives significant inflow from urban, industrial and agricultural wastewater. A 1-m core was sampled from the lake sediment in an area far away from the major inflows. We performed a semi-quantitative analysis of the elemental composition, and a quantitative analysis of the total As concentration, pH, loss on ignition, water content, salt content, and grain size distribution to characterize changes in sediment composition with depth and their influence on the variability of As partitioning and speciation. Nine characterized lithologies were selected for a sequential As extraction analysis to study the vertical variations in phase and speciation of As in the heterogenic lithologies. Total As concentrations range from 1.0 μg g to 13.6 μg g. As is present mostly in HNO and HCl extractable fractions with As being the predominant species. As was mostly found in phosphate and NHOH·HCl extractable fractions. The concentration of mobile As fractions generally decrease with depth. It seems that the As stored in volatile sulfides and very poorly crystalline Fe and Al hydr-oxides in the shallow sediment transforms to sulfides phases during burring. Our findings show that the mobility and toxicity of As decreases during early diagenetic processes in Maharlu lake. However, the As can be remobilized either via changes in the redox conditions in the lake.