Formation and environmental significance of aqueous contaminants at a wolframite-scheelite-hosted tungsten deposit

Environmental effects of tungsten (W) are under growing interest and scrutiny due to the increasing use of the metal for munitions and industrial applications. However, the mobility of W in stream and ground water, and its ecotoxicology to aquatic ecosystems is poorly constrained. The derelict Phoenix-Mt Charlested W mine in southeastern New South Wales hosts W in scheelite (CaWO4) and wolframite ((Fe,Mn)WO4). In order to understand how fast soil water flows through the site and interacts with the mineralogy, hydrological, chemical and ecotoxicological tests were carried out. Volumetric calculations of mine waste were used with measurements of saturated hydraulic conductivity (Ksat) to help understand the residence time of soil water. Research has identified that surface soil transmits water much faster than the subsoil. Surface soil saturated hydraulic conductivity increases as you move down slope from above the mine (702.4 cm.d⁻¹) to the upper tailings (1305.8 cm.d⁻¹) and into the lower tailings (1848.0 cm.d⁻¹). Ksat of the subsurface is much less variable and ranged between 0.28-17.7 cm.d⁻¹. Saturated hydraulic conductivity information was used in conjunction with leach tests to help predict to what extent solutes leach from the mine site. Environmental mobility of metal(loid)s was apparent in all samples analysed using ASLP 4439.3 leach tests. All 12 samples leached metals in quantities that exceeded either ANZECC (2000) trigger values for freshwater at the 95% species protection level or Russian Federation critical concentration values for tungsten for freshwater fishing lakes and rivers. Finally, a series of chronic toxicity tests using tungsten were conducted on multi-trophic aquatic plants and invertebrates. Aquatic animal and plant species were exposed to different levels of W and resistance was assessed based on first generation survival, length, weight, young produced and chlorosis. Tungsten had a toxicological effect on all four aquatic species; Duckweed (L. disperma), Water fleas (D. carinata), Freshwater snails (Lymnaea sp.) and Glass shrimp (P. australiensis). Sensitivity to tungsten based on these four aquatic species follows a hierarchy of Water fleas > Glass shrimp > Duckweed > Freshwater snails. Information from this research has increased the understanding of how W moves within groundwater and reacts with aquatic species in the environment.