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.