Assessment and modification of arsenic mobility in contaminated soil

Arsenic concentration in the seepage of contaminated soils of an old tannery site is assessed using batch and column experiments. The effect of reducing conditions, pH, and M ionic strength is also investigated. The iron oxide rich subsoil (C-horizon) is the main source of groundwater pollution with arsenic. In this horizon, mobilization can increase as a result of reducing conditions upon periodical water saturation. Therefore, the potentially mobile arsenic is determined by a reductive dissolution of the poorly crystalline iron oxide fraction using 0.1 M ascorbic acid. Arsenic concentration can be reduced from 100 mug/L to below 20 mug/L by an increase of ionic strength (e.g. by a 0.01 M CaCl2 solution). Arsenic contaminated soils should be limed regularly in order to maintain the highest possible calcium concentration in the soil solution.