Trace Element (Se, As, Mo, B) Contamination of Evaporites in Hypersaline Agricultural Evaporation Ponds

Abstract

Disposal of saline drainage waters containing elevated concentrations of the trace elements Se, As, B, and Mo poses a severe environmental hazard in the western part of the San Joaquin Valley of California. This study investigated the partitioning of these trace elements into evaporite minerals formed in agricultural evaporation ponds to determine trace element behavior during the evaporite formation stage and to provide information for development of management strategies to minimize environmental hazards. The trace elements were largely excluded from the evaporite minerals (∼100 times depleted relative to the solution phase), resulting in comparatively low trace element concentrations in these minerals. The affinity of trace element partitioning to the solid phase follows: Se B > As Mo. No differences in trace element partitioning were evident between summer and winter seasons, the type of evaporite formed, or whether the evaporites were collected wet or dry. Since trace elements accumulate in the solution phase, highly evapoconcentrated waters may exceed threshold levels for hazardous waste classification. Isolating these trace element-rich solutions during the latter stages of evapoconcentration into specialized treatment and handling facilities may provide an effective management strategy that minimizes both exposure to waterfowl and the amount of hazardous solid waste generated.