The effects of redox on Mo, U, B, V, and As solubility in evaporation pond soils

Soils and irrigation drainwaters from the west side of the San Joaquin Valley, California have elevated levels of Mo, U, B, V, As, and Se. Much of the drainwater is disposed of in evaporation ponds that may be periodically dried, resulting in cyclic changes in the redox status of the pond sediments. A laboratory incubation study was conducted to evaluate the effects of redox status on the solubility of trace elements in saline sediments and soils from the San Joaquin valley. The elements U and Mo were mobilized under oxidizing conditions, while Fe, Mn, Ni, V, and As were more soluble under reducing conditions. Reduction and precipitation of Mo, apparently as MoS[sub 2], was observed from 1 to 10 days after flooding, but when reaerated the Mo resolubilized in less than 1 day. The reductive dissolution of Fe- and Mn-oxyhydroxides released adsorbed B, which resulted in an increased solution concentration of B. Low redox conditions in drainwater ponds may reduce the solution concentrations of U, Mo, and Se, thereby reducing their chances of entering the food chain through algae uptake. However, low redox conditions favor the solubilization of As and V, which may pose an alternative threat to wildlife visitingmore » the ponds. 16 refs., 7 figs., 1 tab.« less