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In situ mercury emission fluxes from soil in Lanmuchang Hg–Tl mining area, southwestern Guizhou, China, were measured using dynamic flux chamber (DFC) method in December 2002 and May 2003, respectively. Huge mercury emission fluxes from soil were obtained in the mining area, ranging from -623 to 10 544ngm2 h1 (n=92) with the maximal mean Hg flux of 2283±2434ngm2 h1. Meanwhile, highly elevated total gaseous mercury (TGM) concentrations in the ambient air observed during the sampling periods varied from 35.2±26.1ngm3 (7.9-353.8ngm3, n=532) in cold season to 111.2±91.8ngm3 (12:7-468.0ngm3, n=903) in the warm season, respectively. The correlations between mercury emission fluxes and environmental parameters, such as solar radiation, temperature, TGM concentration in air, relative humidity and soil Hg concentration are studied. The strong Hg emission fluxes resulted in the elevated TGM concentrations in the ambient air in the study area. We acquired a significant Log–Log correlation between the ratio of average Hg flux and average solar radiation and the soil Hg concentrations at all sampling sites in warm and cold seasons. Within the Langmuchang Hg–Tl mining area with a total area of ～2.9km2, the annual Hg emission rate is calculated to be ～3.54 kg Hg, which is a strong mercury emission source to the local ambient air.

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.

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.