Concentrations

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The toxicity of methylmercury (Me-Hg) has caused widespread public human concern as a result of several widely publicized disasters. Me-Hg is highly toxic, and the nervous system is its principal target tissue for humans. Although the general population is primarily exposed to Me-Hg through contaminated fish and marine mammals, in Hg mining areas a long history of mining activities can produce serious Hg pollution to the local environment. In a study of 98 persons from the Wanshan Hg mining area, hair Me-Hg levels indicated Me-Hg exposure. Rice, the staple food of the local znhabitants also showed high total Hg (T-Hg) and Me-Hg levels. The geometric mean concentration of T-Hg and mean concentration of Me-Hg in rice samples collected from 3 villages in Wanshan Hg mining area were 36.2 (ranging from 4.9 to 214.7), and 8.5 (ranging from 1.9 to 27.6) μg/kg, respectively, which were significantly elevatedcomparedto the rice samples collected fromareference area, where the mean T-Hg and Me-Hg concentrations were 7.0 (3.2-15.1) and 2.5 (0.8-4.3)μg/kg, respectively. Pork meat, vegetable, and drinking water samples collected in Wanshan Hg mining area contained highly elevated T-Hg, but very low levels of Me-Hg. The relationships between the estimated rice Me-Hg intake and hair Me-Hg levels (r) 0.65, p<0.001) confirmed rice with high Me-Hg levels indeed was the main route of Me-Hg exposure for the local residents in the Wanshan Hg mining area. From our study, we can conclude that the main human exposure to Me-Hg via food consumption is not restricted to fish, but in some cases in mining areas of China to frequent rice meals.

Elemental Hg–Au amalgamation mining practices are used widely in many developing countries resulting in significant Hg contamination of surrounding ecosystems. The authors examined for the first time Hg contamination in air, water, sediment, soil and crops in the Tongguan Au mining area, China, where elemental Hg has been used to extract Au for many years. Total gaseous Hg (TGM) concentrations in ambient air in the Tongguan area were significantly elevated compared to regional background concentrations. The average TGM concentrations in ambient air in a Au mill reached 18,000 ng m-3, which exceeds the maximum allowable occupational standard for TGM of 10,000 ng m-3 in China. Both total and methyl-Hg concentrations in stream water, stream sediment, and soil samples collected in the Tongguan area were elevated compared to methyl-Hg reported in artisanal Au mining areas in Suriname and the Amazon River basin. Total Hg concentrations in vegetable and wheat samples ranged from 42 to 640μg kg-1, all of which significantly exceed the Chinese guidance limit for vegetables (10μg kg-1) and foodstuffs other than fish (20μg kg-1). Fortunately, methyl-Hg was not significantly accumulated in the crops sampled in this study, where concentrations varied from 0.2 to 7.7μg kg-1.