Transformation/dissolution characterization of tungsten and tungsten compounds for aquatic hazard classification

The transformation/dissolution protocol (T/DP) for metals and sparingly soluble metal compounds was applied to determine the transformation/dissolution (T/D) characteristics of yellow tungsten trioxide, WO₃ ; blue tungsten oxide, WOx, x taken as 2.9; tungsten disulphide, WS₂ ; tungsten metal, W; 3 samples of tungsten carbide, WC; sodium tungstate, Na₂ WO₄ · 2H₂ O; ammonium paratungstate (APT), (NH₄ )₁₀ (H₂ W₁₂ O₄₂ ) · 4H₂ O; and ammonium metatungstate (AMT) (NH₄ )₆ (H₂ W₁₂ O₄₀ ) · 3H₂ O. The T/D data were used to derive aquatic hazard classification outcomes under the United Nations Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS) and European Union Classification, Labelling and Packaging of Substances and Mixtures (EU CLP) schemes by comparing the data with selected acute and chronic ecotoxicity reference values (ERVs) of 31 and 3.37 mg W/L, respectively. In addition to the concentration of total dissolved tungsten (W), the T/D solutions were analyzed for the concentration of the tungstate anion, because speciation can be an important factor in establishing the ecotoxicity of dissolved metals. Results show that the tungstate anion was the predominant W-bearing species in solution for all substances examined at pH 6 and 8.5. It was found that the 100 mg/L loadings of both the yellow WO₃ and the blue WOx exceeded the 31 mg/L acute ERV, so they would classify as Acute 3-Chronic 3 under the UN GHS scheme but they would not classify under the EU CLP. An effect of pH on the reactivity of the W metal was observed with 3% and 16% W dissolution at pH 6 and 8.5, respectively. Tungsten metal would not classify under either the UN GHS or EU CLP schemes nor would the WS₂ . The WCs were the least reactive in terms of the 1% or less dissolution of the contained W at pH 6. A critical surface area for WC was calculated. The sodium tungstate, APT and the AMT all yielded, at pH 8.5, total dissolved W concentrations that would result in UN GHS Acute 3-Chronic 3 classifications. Integr Environ Assess Manag 2018;14:498-508. © 2018 Her Majesty the Queen in Right of Canada. Integrated Environmental Assessment and Management © 2018 SETAC.