Trophic transfer of mercury and methylmercury in an aquatic ecosystem impacted by municipal sewage effluents in Beijing, China.

Gaobeidian Lake, located in Beijing, China, serves as a recipient lake for effluents from a large municipal sewage treatment plant (MSTP). In order to evaluate the effects of discharging MSTP effluent on the mercury contamination of the local aquatic ecosystem, sediment cores, water, plankton, fish, and turtle samples were collected from Gaobeidian Lake for mercury speciation analysis. High concentrations of total mercury (T-Hg) were detected in sediment cores (5.24-17.0 microg/g dry weight (dw), average: 10.1 microg/g). The ratio of methylmercury (MeHg) to T-Hg was less than 0.3% in sediments and ranged from 35% to 76% in biota samples. The highest level of T-Hg and MeHg were found in aquatic bryophyte and crucian carp (3673 and 437 ng/g dw, respectively). The relative contents of MeHg were significantly correlated with trophic levels (R2 = 0.5506, p < 0.001), which confirmed that MeHg can be bio-transferred and biomagnified via food chain in this aquatic ecosystem.