Bioaccumulation and trophic transfer of mercury in a food web from a large, shallow, hypereutrophic lake (Lake Taihu) in China

PURPOSE: Due to the fast development of industry and the overuse of agrichemicals in past decades, Lake Taihu, an important source of aquatic products for Eastern China, has simultaneously suffered mercury (Hg) contamination and eutrophication. The objectives of this study are to understand Hg transfer in the food web in this eutrophic, shallow lake and to evaluate the exposure risk of Hg through fish consumption. METHODS: Biota samples including macrophytes, sestons, benthic animals, and fish were collected from Lake Taihu in the fall of 2009. The total mercury (THg), methyl mercury (MeHg), δ¹³C and δ¹⁵N in the samples were measured. RESULTS AND DISCUSSION: The signature for δ¹⁵N increased with the trophic levels. Along with a diet composed of fish, the significant relationship between the δ¹³C and δ¹⁵N indicated that a pelagic foraging habitat is the dominant pathway for energy transfer in Lake Taihu. The concentrations of THg and MeHg in the organisms varied dramatically by ∼3 orders of magnitude from primary producers (macrophytes and sestons) to piscivorous fish. The highest concentrations of both THg (100 ng g⁻¹) and MeHg (66 ng g⁻¹), however, were lower than the guideline of 200 ng g⁻¹ of MeHg for vulnerable populations that is recommended by the World Health Organization (WHO). The daily intake of THg and MeHg of 92 and 56 ng day⁻¹ kg⁻¹ body weight, respectively, was generally lower than the tolerable intake of 230 ng day⁻¹ kg⁻¹ body weight for children recommended by the Joint FAO/WHO Expert Committee on Food Additives. Significant relationships between the δ¹⁵N and the logarithm of THg and MeHg showed an obvious biomagnification of Hg along the food web. The logarithmic bioaccumulation factor of MeHg in the fish (up to 5.7) from Lake Taihu, however, was relatively low compared to that of other aquatic ecosystems. CONCLUSION: Health risk of exposure to Hg by consumption of fish for local residents is relatively low in the Lake Taihu area. Dilution of Hg levels in the phytoplankton induced by eutrophication is a possible factor inhibiting accumulation of MeHg in fish in eutrophic Lake Taihu.