| 其他摘要 | Guizhou province is an important mercury (Hg) production centre in China and it owns many large Hg mineral deposits. The cinnabar deposits in Guizhou amount to about 88000 tons of metal Hg and consist of 80% of the total in whole China. It has a long history of Hg mining activities and large Hg mines had been abandoned recently. However, the illegal artisanal mining activities are extensively existed in Hg mining areas because of its remote position, backward economy and the markup of Hg. The artisanal Hg mining activities together with the long history large scales Hg mining activities have resulted in serious Hg contaminations to local environment in these Hg mining areas. Because the simple mining processes are without any environmental protection measures, a large amount of Hg vapor was released to the ambient air during the mining process and the workers might be seriously exposed to Hg vapor. The Hg that released into the surroundings may, under certain conditions, be converted into Methyl Hg (MeHg), which is an organic form and is more toxic and bio-available than inorganic Hg. This organic Hg is readily accumulated by biota owning to its lipophilic and protein-binding properties and eventually poses a threat to the local residents’ health through the food chains.
In order to evaluate the biogeochemistry cycle of Hg in typical artisanal Hg mining areas in Guizhou Province, the Hg emission from the artisanal Hg mining, the Hg pollution investigation, the human exposure and risk assessment were carried out in Wuchuan, Wanshan Hg mining areas and Gouxi, Laowuchang areas in Tongren District.
1. The artisanal Hg mining was the most important anthropogenic Hg emission sources in Wuchuan and Gouxi areas. The average emission factor was 18.2% (ranging from 6.9 to 32.1%) and 9.8% (ranging from 6.6 to 14.5%) for the artisanal Hg mining in Wuchuan and Gouxi area, respectively, and the annual Hg emission was 3.7-9.6 and 1.3-2.7 metric tons in the two areas, respectively.
2. The artisanal Hg mining activities together with the long history large scales Hg mining in Wuchuan Hg mining area and the artisanal Hg mining activities in Gouxi and Laowuchang areas have resulted in serious Hg contaminations to local air, surface water and soil, the extent of Hg contamination depended strongly on the history and the scale of artisanal Hg mining activities. Total gaseous Hg in the ambient air in Wuchuan Hg mining area ranged from 7 to 40000 ng•m-3, the concentration of total gaseous Hg were significantly elevated in the serious affected area by the mining activities; average concentrations of total gaseous Hg in the ambient air were 15000, 120 and 24 ng•m-3 in the high polluted area, the median polluted area and control site, respectively. Hg concentrations in the surface water ranged from 43 to 2100 ng•L-1 for the Total Hg (THg) and from 0.30 to 1.1 ng•L-1 for the total MeHg in Wuchuan area. Hg concentrations in the surface water ranged from 92 to 2300 ng•L-1 for the THg and from 2.6 to 7.9 ng•L-1 for the total MeHg in Gouxi and Laowuchang area, which indicated high methlation abilities in the surface water. The particulate phase was the main route of Hg transportation, but the MeHg was mainly in dissolved phase. THg in the soil ranged from 1.3 to 360 mg•kg-1 and from 0.18 to 47.5 mg•kg-1 for Wuchuan and Gouxi, Laowuchang area, respectively. T-Hg distribution patterns in soil profiles showed that top soil is contaminated with Hg, which was derived from atmospheric deposition. Soil pH, organic matter concentration and the land-using types might play important roles in control of Hg concentrations and transport in the soil.
3. The mean of urinary Hg (UHg) was 1060 g•g-1 Creatinine (g•g-1 Cr), 347 g•g-1 Cr and 917 g•g-1 Cr for the artisanal mining workers in Wuchuan Hg mining area, Gouxi area and Laowuchang area, respectively, which were obviously exceeded the value (50 g•g-1 Cr) for the occupational exposure recommended by WHO. It indicated serious Hg vapor exposure for the artisanal mining workers. Several workers already manifested some clinical symptoms of lightly chronic Hg poisoning and the data showed a serious adverse effect on renal system for the workers. The mean of UHg was 40.0, 66.2 and 56.9 g•g-1 Cr for the residents in Gouxi area, Laowuchang area, and Dashuixi Village, Wanshan Hg mining area, respectively, which also indicated the Hg vapor exposure to the residents. The mean of UHg was2.5 and 1.30 g•g-1 Cr for the residents in Changshun (control site) and Xiachangxi Village, Wanshan Hg mining area, respectively, which indicated a background level.
4. Rice with high Me-Hg levels was the main route of Me-Hg exposure for the local residents in the Hg mining area. The mean of hair THg concentration was 7.3、1.9 and 2.3 g•g-1 for the residents in Dashuixi (DSX), Xiachangxi (XCX) and Baoxi (BX) Village in Wanshan Hg mining area, respectively, and the mean of hair MeHg concentration was 2.8、1.3 and 1.5 g•g-1, correspondingly. The data indicated that the population from Wanshan Hg mining area was exposed to Hg in a certain level. The mean of THg concentration was 58.5、21.3 and 33.1 ng•g-1 for the rice collected from the 3 villages, respectively, and the mean MeHg concentration was 14.6、5.7 and 4.0 ng•g-1, correspondingly. Pork meat, vegetable, and drinking water samples collected in Wanshan Hg mining area also contained highly elevated T-Hg concentrations, but with very low MeHg levels. Rice intake constituted 97.5%, 94.1%, and 93.5% of the total Me-Hg exposure to participants in DSX, XCX, and BX, on average, respectively. The significant relationship between the estimated rice Me-Hg intake and hair Me-Hg levels (r=0.65, p<0.01) 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.
5. The mean of hair MeHg concentration was 5.05 g•g-1（ranging from 2.35 to 10.6 g•g-1）and 5.63 g•g-1（ranging from 2.54 to 9.55 g•g-1）for artisanal mining workers in GX and LWC area, respectively, and 3.53 g•g-1（ranging from 1.87 to 5.65 g•g-1）, 4.01 g•g-1（ranging from 2.29 to 9.23 g•g-1）for the residents. The mean of hair MeHg concentration was 2.8、1.3 and 1.5 g•g-1 for the residents in Dashuixi (DSX), Xiachangxi (XCX) and Baoxi (BX) Village in Wanshan Hg mining area, respectively. The MeHg concentration for the artisanal Hg mining workers and residents in Wuchuan Hg mining area ranged from 0.47 to 5.69 μg•g-1. The mean of hair MeHg concentration was 0.65 g•g-1(ranging from 0.26 ¬to 1.38 g•g-1). The risk assessment indicated the daily MeHg intake through rice consumption for some residents in Gouxi and Laowuchang area were exceeded the WHO recommended value of 0.23 g•d-1•kg-1 and the daily MeHg intake for major residents in Hg mining area were exceeded the USEPA recommended value of 0.10 g•d-1•kg-1. So the residents in Gouxi and Laowuchang area were at a health risk of MeHg exposure and the residents in other Hg mining areas also were at a potential risk of MeHg exposure through rice intake. |
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