Toxicity and Enrichment of As in Surface Soils near An Active Mine Site, Victoria, Australia.
Ryan Noble1, Robert M. Hough1, and Ronald T. Watkins2. (1) CSIRO, CSIRO Exploration and Mining/CRC LEME, PO Box 1130, Bentley, Western Australi 6102, AUSTRALIA, (2) Curtin University of Technology, 1 Turner Avenue, Brodie Hall Building, Bentley, Australia
The Stawell Gold Mine (SGM) operation in NW Victoria, Australia, mines Au from As-rich sulfides. Dispersion and enrichment of As around the mine site has been investigated, and the minimum human exposure required to exhibit As toxicity estimated. Forty surface soil samples from within 3 km of SGM, as well as 10 background samples within 15 km, were collected and analyzed by ICP-MS/OES following extraction using a bioavailable (stomach acid analogue) and a near-total four-acid leach. Soils near SGM show greater concentrations of As (up to 946 mg/kg) than regional background (up to 16.5 mg/kg), which is attributed to a natural geochemical halo associated with mineralization, and anthropogenic enrichment due to mining, agriculture and other human activities. X-ray diffraction, SEM and microprobe analysis was used to assess the soil mineralogy and the in-situ siting of As. Dispersion from the current mine ore processing is < 500 m, with the most enriched soils closer to the town and unrelated to SGM’s activities. The highest concentrations are suspected to be sites of older, small mine workings from the gold rush in the 1850s - 70s. The bioavailable As concentrations (5.6 mg/kg maximum), soil ingestion rates and Risk Reference Doses were used to estimate health risks. The maximum bioavailable As soils would pose a risk at average human ingestion rates. Soil-eating disorders would exceed the safe daily consumption limits for As, and potentially other toxic elements such as Cr and Pb. Small children are not typically exposed to the highest As concentration soils everyday, few have soil eating disorders, and therefore the health risk from the soils around the mine site is minimal.