Mercury (Hg) is a global pollutant and poses a worldwide concern due to its high toxicity. Guizhou province is recognized as a heavily Hg-polluted area in China due to both the special geochemical background and human activities. Here an integrated overview of current knowledge on the behavior of Hg in environments, as well as human health risk with respect to Hg contaminations in Guizhou was presented. Two key anthropogenic Hg emission sources in Guizhou were coal combustion and metals smelting, which dominantly contributed to the high levels of Hg in local ecosystems and high fluxes of Hg deposition. The annual Hg emission from anthropogenic sources ranged between 22.6 and 55.5 t, which was about 6.3-10.3% of current total Hg emissions in China. Meanwhile, Hg Hg-enriched soil in the province serves an important natural Hg emission source to the ambient air. The local environment of Hg mining and zinc smelting areas are seriously contaminated with Hg. It is demonstrated that rice growing in Hg Hg-contaminated soil can accumulate methylmercury (MeHg) to a level to pose health threat to local inhabitants whose staple food is rice. Local inhabitants in Hg mining areas are exposed to Hg through inhalation of Hg vapor and consumption of rice with high level of MeHg. Rice intake is indeed the main MeHg exposure pathway to local inhabitants in Hg mining areas in Guizhou, which is contrary to the general point of view that fish and fish products are the main pathway of MeHg exposure to humans.

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.

[1] Total gaseous mercury (TGM) exchange fluxes between air and water surface were measured using a dynamic flux chamber (DFC) coupled with a gaseous mercury analyzer at two sampling sites of Hongfeng reservoir in cloudy and rainy weather conditions. The concentrations of dissolved gaseous mercury (DGM) in water were also measured and indicated that DGM was supersaturated at most time during the sampling periods, which implied that the water body acted primarily as a source of mercury to the atmosphere. In general, TGM fluxes displayed a consistent diurnal pattern with peak fluxes at noon and minimum levels at early morning or night. However, this diurnal pattern was not clear when the weather was heavily cloudy and rainy with the maximum solar radiation of less than 140 W m 2. At this specific weather condition, a significantly positive correlation between TGM flux and relative humidity was observed. The behaviors of TGM flux over Hongfeng reservoir observed at cloudy weather conditions were some what different from those observed during mostly sunny weather conditions in Northern America and Europe. The empirical model developed based on the correlation between TGM flux and solar radiation during sunny days in Northern America was not applicable for estimation of TGM flux at cloudy and rainy weather conditions.

Wuchuan Hg mine, located in the Circum-Pacific Global Mercuriferous Belt, is one of the important Hg production centers in Guizhou province, China. Soil Hg concentrations in this area are elevated by 2–4 orders of magnitude compared to the national background value in soil which is 0.038 μgg1. In situ air Hg concentrations and air/soil Hg fluxes were measured at five sampling sites in Wuchuan Hg mining area (WMMA) from 19 to 26 December 2003 and from 18 to 25 December 2004. The results showed that air Hg concentrations were 2–4 orders of magnitude higher than those observed in background areas in Europe and North America due to a large amount of Hg emission from artisanal Hg smelting activities. The average in situ Hg fluxes at site Laohugou, Jiaoyan, Luoxi, Sankeng and Huanglong were -5493, 124, -924, -13 and 140 ngm2 h1, respectively. Diurnal pattern of Hg flux was not found and a number of negative Hg fluxes were observed in our sampling campaigns. The correlations between Hg fluxes and meteorological parameters such as solar irradiation, air temperature, soil temperature and relative humidity and air Hg concentrations were investigated. The commonly observed significant correlations between Hg fluxes and meteorological parameters observed in many previous studies were not obtained in WMMA. However, significantly negative correlations between Hg flux and air Hg concentration were observed at all sites. Our study demonstrated that highly elevated air Hg concentrations could suppress Hg emission processes even from Hg-enriched soil. At specific conditions in WMMA, air Hg concentrations play a dominant role in controlling Hg emission from soil.

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.