The distribution of total mercury and methyl mercury in a shallow hypereutrophic lake (Lake Taihu) in two seasons

Abstract

Abstract To understand the geochemical cycle of Hg in hypereutrophic freshwater lake, two sampling campaigns were conducted in Lake Taihu in China during May and September of 2009. The concentrations of unfiltered total Hg (unfTHg) were in the range of 6.8–83 ng L −1 (28 ± 18 ng L −1 ) in the lake water and total Hg in the sediment was 12–470 ng g −1 , both of which are higher than in other background lakes. The concentration of unfTHg in ∼11% of the lake water samples exceeded the second class of the Chinese environmental standards for surface water of 50 ng L −1 (GB 3838-2002), indicating that a high ecological risk is posed by the Hg in Lake Taihu. However, the concentrations of unfiltered total MeHg (unfMeHg) were relatively low in the lake water (0.14 ± 0.05 ng L −1 , excluding two samples with 0.81 and 1.0 ng L −1 ). Lake sediment MeHg varied from 0.2–0.96 ng g −1 , with generally low ratios of MeHg/THg of