Arsenic contamination of natural origin in stream sediments of Lake Mulargia Reservoir, Southern Sardinia

High As contents have been detected in the stream sediments of Lake Mulargia and in the tributaries draining the basin which carry mineral matter mostly containing Fe, As and Sb sulphides. Systematic sampling has shown the presence of significant amounts of arsenic originating from natural sources alone, as it is supplied by the surrounding mineralised rocks.The seasonal water level fluctuations peculiar of this lake cause oxidation and remobilization of most metals. Arsenic is readly released in the acid waters, but the constantly high pH of the main body of water causes adsorption and co-precipitation of this element on the abundant newly formed Fe-hydroxides. These trap the As, as the negligible arsenic contents in the lake clearly demonstrate.