Total mercury in wild fish in Guizhou reservoirs, China

The health hazard of mercury （Hg） compounds is internationally recognized, and the main pathways for methylmercury （MeHg） intake in humans are through consumption of food, especially fish. Given the large releases of Hg to the environment in China, combined with the fast development of hydropower, this issue deserves attention. Provided similar mobilization pathways of Hg in China as seen in reservoirs in North America and Europe one should expect increased Hg contamination in relation to future hydropower reservoir construction in this country. This study presents total Hg （THg） concentrations in wild fish from six Guizhou reservoirs, China. The THg concentrations in fish were generally low despite high background levels in the bedrock and depositions from local point sources. The over all mean ± SD concentration of THg was （0.066 ± 0.078） μg/g （n = 235）. After adjusting for among-reservoir variation in THg, there were significant differences in THg among functional groups of the fish, assumed to re？ect trophic levels. Predicted THg- concentration ratios, retrieved from a mixed linear model, between the functional groups were 9：4：4：1 for carnivorous, omnivorous, planktivorous and herbivorous fish. This result indicated that MeHg accumulation may prevail even under circumstances with short food chains as in this Chinese water system. No fish exceeded recommended maximum THg limit for human consumption set by World Health Organization and the Standardization Administration of China （0.5 μg/g fish wet weight （ww））. Only six fish （2.5%） exceeded the maximum THg limit set by US Environmental Protection Agency （0.3 μg/g fish ww）.

Transport and fate of mercury under different hydrologic regimes in polluted stream in mining area

Seepage from Hg mine wastes and calcines contains high concentrations of mercury （Hg）. Hg pollution is a major environmental problem in areas with abandoned mercury mines and retorting units. This study evaluates factors, especially the hydrological and sedimentary variables, governing temporal and spatial variation in levels and state of mercury in streams impacted by Hg contaminated runoff. Samples were taken during different flow regimes in the Wanshan Hg mining area in Guizhou Province, China. In its headwaters the sampled streams/rivers pass by several mine wastes and calcines with high concentration of Hg. Seepage causes serious Hg contamination to the downstream area. Concentrations of Hg in water samples showed significant seasonal variations. Periods of higher flow showed high concentrations of total Hg （THg） in water due to more particles being re-suspended and transported. The concentrations of major anions （e.g., Cl-, F-, NO3- and SO4^2-） were lower during higher flow due to dilution. Due to both sedimentation of particles and dilution from tributaries the concentration of THg decreased from 2100 ng/L to background levels （〈 50 ng/L） within 10 km distance downstream. Sedimentation is the main reason for the fast decrease of the concentration, it accounts for 69% and 60% for higher flow and lower flow regimes respectively in the upper part of the stream. Speciation calculation of the dissolved Hg fraction （DHg） （using Visual MINTEQ） showed that Hg（OH）2 associated with dissolved organic matter is the main form of Hg in dissolved phase in surface waters in Wanshan （over 95%）.