*Principal Investigator Biogeochemistry of Tungsten in California Soils

This project encompasses soil biogeochemical processes of tungsten (W) at scales ranging from regional to millimeter. A) Regional scale: Soil and alfalfa (Medicago sativa) specimens were sampled from the San Joaquin Valley, in order to assess the spatial distribution of geogenic W and Mo in agriculturally used soils. Additionally, soil, water and vegetation samples were taken at abandoned mine tailings in two areas in California. Various methods were tested to determine bioavailable W and Mo in these soils. B) Meso-scale studies: Adsorption experiments of tungstate and molybdate on soils were conducted to quantify the chemical processes affecting fate and transport. The factors affecting plant uptake of W, with potential interactions with Mo, were examined in hydroponic experiments. C) Micro-scale: The main parameters controlling weathering and dissolution of W-metal alloy shotgun pellets and tungsten carbide solids were studied in soil incubation studies reflecting environmentally relevant soil conditions. Samples from these experiments are scheduled for analysis on the Stanford synchrotron using x-ra