THE EFFECTS OF REDOX ON MO, U, B, V, AND AS SOLUBILITY IN EVAPORATIONPOND 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. M uch 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 ev aluate the effects of redox status on the solubility of trace elements in saline sediments and soils from the San Joaquin valley. The elemen ts U and Mo were mobilized under oxidizing conditions, while Fe, Mn, N i, V, and As were more soluble under reducing conditions. Reduction an d precipitation of Mo, apparently as MoS2, Was observed from 1 to 10 d ays after flooding, but when reaerated the Mo resolubilized in less th an 1 day. The reductive dissolution of Fe- and Mn-oxyhydroxides releas ed adsorbed B, which resulted in an increased solution concentration o f B. Low redox conditions in drainwater ponds may reduce the solution concentrations of U, Mo, and Se, thereby reducing their chances of ent ering the food chain through algae uptake. However, low redox conditio ns favor the solubilization of As and V, which may pose an alternative threat to wildlife visiting the ponds.