Bioavailability, Sorption, and Soil Redox Chemistry of Tungsten and Tungsten Metal-Alloys in Two California Soils.

An interest in tungsten in groundwater and soil environments has increased recently due to a possible link to childhood leukemia from naturally high levels of tungsten in drinking water at three sites in the western U.S. Anthropogenic sources of tungsten have increased from industrial use of tungsten carbide tools, military munitions, and recreational hunting (lead-shot replacement). Currently, tungsten metal-alloy shot (W-pellet) is an “environmentally friendly” alternative to lead metal-alloy shot for hunting waterfowl. W-pellets may enter the soil environment and be subjected to weathering conditions, locally increasing tungsten concentrations. Knowledge about the fate and transport of tungsten in soils is limited, especially in terms of bioavailability, adsorption/desorption, and redox chemistry. Two soils were used for this investigation: Boomer clay (mixed, superactive, mesic Ultic Haploxeralf) and Grangeville fine sandy loam (mixed, superactive, thermic Fluvaquentic Haploxeroll). Batch experiments were performed to assess the adsorption of tungsten in each soil, with and without the presence of competing anions (WO₄^-2, PO₄^-3, and MoO₄^-2) in solution. Aerobic and anaerobic soil environments were created to assess how redox conditions influence W-pellet oxidation. Five W-pellets (0.55 g to 0.72 g) from two different W-pellet types (one containing 50 % W and the other 95 % W) were incubated in 5 g of each soil under aerobic and anaerobic conditions for 12 weeks. The incubated soils were extracted in order to assess the bioavailable tungsten solubilized from the W-pellets. In addition, tungstate and molybdate uptake by alfalfa was assessed in a greenhouse trial.