Mercury speciation in waters and sediments of Lake Murray, Papua New Guinea

Abstract

The speciation of mercury in Lake Murray, Papua New Guinea and nine surrounding rivers was investigated. Total mercury concentrations in waters (0.52-9.5 ng L^-1) and sediments (56-177 ng g^-1 dry mass) were similar to those found in other remote lake environments. Total methylmercury (MeHg) concentrations in waters and sediments were also low. Of the 50 water samples analysed during three surveys, only six samples had total MeHg concentrations between 0.1 and 0.64 ng L^-1 and 25 of the samples had total MeHg concentrations < 0.05 ng L^-1. Methylmercury concentrations were very variable and could not be linked with parameters known to affect mercury methylation such as pH, dissolved organic carbon and sulfate concentrations. A statistically significant and unexplained correlation was observed between filterable MeHg and filterable silicon. Intermittent inputs of turbid water from the Strickland River inject particulates and filterable MeHg into the southern end of Lake Murray. This has resulted in the formation of a depositional footprint that contains higher concentrations of particulate mercury and other elements compared with the rest of the lake.