An in situ assessment of mercury contamination in the Sudbury River, Massachusetts, using transplanted freshwater mussels (Elliptio complanata)

Abstract

Freshwater mussels (Elliptio complanata) were transplanted into the Sudbury River, Massachusetts, to evaluate the bioavailability of total Hg and methyl mercury (MeHg) and the potential impacts to resident species. The principal Hg source is the Nyanza Superfund site, a former textile dye production facility. Mussels (initial tissue concentrations = 640 ng Hg·g dry weight-1 and 120 ng MeHg·g dry weight-1) were transplanted to eight locations in the Sudbury River watershed for 12 weeks. Tissue total Hg concentration increased significantly in mussels at the station closest to the Nyanza site (950 ng Hg·g dry weight-1). Mussel growth, which increased downstream with distance away from the site, was significantly negatively correlated with tissue concentrations of total Hg (r = -0.95) and positively correlated with average temperature (r = 0.85). Due to growth differences, uptake was best assessed by changes in content. Tissue total Hg and MeHg burdens were greatest in mussels at two stations closest to the Nyanza site, with less Hg accumulated in downstream mussels. However, the MeHg content in mussel tissue increased significantly at all Sudbury River stations, indicating that MeHg was bioavailable in all portions of the river evaluated.