Tungsten Speciation and Solubility in Munitions-Impacted Soils.

Tungsten contamination from industrial sources and munitions has contaminated a large number of soil environments.  Despite the potential toxicity of tungsten, little information is known about the chemical form of tungsten in these soils, or the solubility of tungsten in the environment. Most contamination sources contain metallic tungsten; however, the persistence of tungsten metal in the environment, and the prevalence of secondary tungstate minerals, or adsorbed tungsten is not well established. Here, we examine the chemical speciation of tungsten in a variety of soils contaminated with tungsten munitions using a combination of X-ray absorption spectroscopy (XAS) and microprobe X–ray fluorescence. Despite the fact that tungsten munitions were actively used on the range within one year of sample collection and analysis, nearly all of the tungsten had oxidized to tungsten(VI). Adsorbed tungstate and polytungstates comprised much of the tungsten in the system. These adsorbed forms of tungstate was only weakly retained by soil minerals; aqueous concentrations of tungstate in soil pore waters exceeded 1 g/L and thus tungstate may be highly mobile in these soil solutions.