Arsenic and mercury biogeochemistry in relation to revegetation treatments at the Sulphur Bank Mercury Mine, Clear Lake, California

The Sulphur Bank Mercury Mine (SBMM) is an abandoned open pit mine located on the eastern shore of Clear Lake, California where mining operations resulted in deposits of waste material (overburden, tailings) stockpiled along the shoreline. Because of Hg pollution of Clear Lake, SBMM is listed as an Environmental Protection Agency (EPA) Superfund site.; A survey was conducted at SBMM to examine mercury (Hg) and arsenic (As) concentrations in plants and sods. Compared to native soil, the waste materials had elevated concentrations of Hg and As. Soils on the bare areas of the overburden material had much higher Hg and As concentrations compared to vegetated areas. However, tissue concentrations of Hg and As in oak and annual grasses were lower than levels considered to cause toxicity in many species.; A greenhouse study examined interacting effects of lime, fertilizer and organic matter (OM) additions on soil solution chemistry and As and Hg uptake by Zorro fescue (Vulpia myuros L.). Fescue was grown on three mine-soils from SBMM containing high (164 mg/kg) (S-H), medium (123 mg/kg) (S-M) and low (31 mg/kg) (S-L) As. Mercury in these sods ranged between 1700–3000 mg/kg. Lime and OM additions were negatively correlated with soluble Hg and Hg tissue concentration. Mercury uptake was more strongly related to root length density (RLD) than to soluble Hg indicating that plant root characteristics are an important factor affecting uptake. Compared to total As, extractable As decreased in the order: total-As > oxalate-As > dithionite-As > mixed acid-As > water soluble-As. Oxalate extractable Fe correlated well with total As and As extracted by oxalate, dithionite and mixed acid methods. Soluble As was strongly correlated with soluble P and DOC for the sods. The effect of soluble P on soluble As was much greater in S-H than in S-M or S-L; while the effect of DOC on soluble As was similar in S-H and S-M but considerably lower than in S-L Since the solution phase was undersaturated with respect to possible solid phase As containing solids, adsorption/desorption reactions appear to control solution As in these soils.