Geochemical controls on mobilization and transport of tungsten in sediments from Fallon, Nevada: The importance of a possible anthropogenic tungsten source

Abstract:

Elevated tungsten (W) levels in human body fluids have been linked to a childhood leukemia cluster in Fallon, Nevada. We studied the occurrence and speciation of W in sediments from Fallon, NV in order to understand mobilization of W in the environment. Sedimentary W concentration was measured by total and sequential extraction followed by high resolution inductively coupled plasma mass spectrometer (HR-ICP-MS) analysis, whereas the speciation was determined by μ-XANES. The water extractable fraction of sedimentary W was determined by HR-ICP-MS and the aqueous species of W were identified by size exclusion chromatography. Our results indicate that sedimentary W concentrations ranged between 37 and 25,908 mg/kg at Fallon, NV, of which 20 – 50% occurred as metallic W⁰ and the rest occurred as oxide (W^VIO₃) based on μ-XANES analysis. Only 0.21-1.36% of the sedimentary W was extractable with water at neutral pH (i.e. 0.1–352 µg/L) and it primarily occurred as the tungstate oxyanion (WO₄^2-). These findings are consistent with earlier studies that reported mobilization of up to 1,070 µg/L W from contaminated soil with deionized water (Bednar et al., 2008) as well as studies that reported groundwater W concentrations in the range of 0.27-742 µg/L (Seiler et al., 2005; Cutler, 2011; Mohajerin et al., 2014) and 3 – 610 µg/L (Walker and Fosbury, 2009). These findings suggest that that metallic W⁰ particles from currently unknown but local anthropogenic source(s) are deposited onto surface sediments and are oxidized by meteoric water to form W^VIO₃. Oxidized W forms soluble tungstate oxyanions that are transported along the groundwater flow path. Polymeric species of dissolved W appear to be more mobile, whereas monomeric W species sorbs onto the sediments during the transport. Our study (Hobson et al., 2020) proposes a model to illustrate mobilization of W from sediments to groundwater, which is important to constrain the link between environmental W levels and human health.