Assessment of mercury distribution and bioavailability from informal coastal cinnabar mining - Risk to the marine environment

Coastal cinnabar mining commenced in 2010 around Luhu on Seram (Ceram) Island, Indonesia. This study investigates the ore characteristics and environmental distribution and bioavailability of mercury in coastal sediments from eight sites adjacent to, and north and south of the mining area. Sediment and ore samples were digested using 1:3 HNO3:HCl for total extractable metal determination and separate samples were extracted with 1.0 HCl for bioavailable metals (Hg, Cu, Zn, Cr, Ni and Pb). Analysis was completed using inductively coupled plasma-mass spectrometry. Ore defined by miners as 'first class ore' was around 50 % cinnabar. Mercury concentrations were extremely elevated in near coastal sediments (up to 2796 mg/kg) with bioavailable concentrations exceeding 450 mg/kg. Marine sediments elevated in mercury extend to the north and south of the coastal mine site and cover in excess of 14 km. Total organic carbon in marine sediments was relatively low (predominately <0.6 %) suggesting mercury methylation will likely be slow, however, inorganic mercury is a known toxicant. Other metals of environmental concern (Cu, Zn, Cr, Ni and Pb) in sediments were not strongly associated with the mining operations, rather were elevated around coastal villages, but not at concentrations that raise immediate concerns.