Mercury (Hg) is a globally distributed toxic pollutant. In 1950’s, the disclosure of Minamata disease revealed that Monomethylmercury (MMHg) contamination in aquatic ecosystem would lead to the high Hg-accumulation in wildlife, which pose a threat to human health. MMHg is one of the toxic Hg forms that can bioaccumulate and biomagnify in food webs (Watras et al. 1998, Ullrich et al. 2001, Clarkson and Magos 2006, Fitzgerald et al. 2007). Humans and wildlife that are high in the food chain are subject to potential adverse health effects related to MMHg exposure via the consumption of fish and fish products (Clarkson and Magos 2006). The public health concerns of MMHg have prompted numerous studies on Hg biogeochemical cycling in aquatic systems.
Baihua Reservoir is located in Guizhou Province, Southwest China. During 1971 to 1997, this reservoir suffered serious mercury contamination from Guizhou organic chemical plant (GOCP), just like Minamata. But fortunately, neither Minamata disease nor high level methylmercury was found in fish samples although the total mercury concentration in sediment was up to 38.9 ppm in Baihua reservoir. Why? It was a scientific mystery. To solve the mystery, a collaborated project was conducted by Professor FENG Xinbin’s group from Institute of Geochemistry, Chinese Academy of Sciences (IGCAS) and Professor Janusz Dominik’ group from Institute F. -A. Forel, University of Geneva, Switzerland.
In their study, water, sediment, plankton, bentonic organism and fish samples were collected systematically in Baihua reservoir in 2009 and 2010. Mercury species and auxiliary parameters were measured in these samples by using mercury isotope and GC-ICP-MS technology, sediment-surface water analytical system method (SWISS 1.0). By analyzing large amounts of the data, the scientists discovered three clues to the above mystery: low rate of methylation in neutral-alkali waterbody, relatively simple food web structure, and reduced MMHg update by fish due to biodilution effect related to the eutrophic condition of the reservoir.
The above discoveries have been published in an article titled “Insights into low fish mercury bioaccumulation in a mercury-contaminated reservoir, Guizhou, China” (ENVIRONMENTAL POLLUTION, 160 109-117, JAN 2012). The scientists also suggested in the paper that the elimination of plankton should be conducted with remedy of mercury synchronously to avoid high mercury fish level happening in an oligotrophic reservoir.
(By YAN Haiyu)
