| Mercury is known as a toxic and unessential element. There are many large Hg mines worldwide abandoned recently because of more attentions to the toxicity of Hg and increasing environmental concerns. On the one hand, those abandoned Hg mines continue to impact local environments through mine-wastes, drainage, and elemental mercury vapor. On the other hand, different forms of inorganic Hg that released into the surroundings may, under certain conditions, be converted into MeHg, which is an organic Hg form and is more toxic than inorganic Hg. This organic Hg is readily accumulated by biota owning to its lipophilic and protein-binding properties and eventually enters the human body through food chains. Therefore, heavy Hg-contaminations from abandoned Hg mines pose increasing environmental concerns worldwide.Guizhou province located in a big natural circum-Pacific mercuriferous belt owns many large mercury mineral deposits, and as result, it is an important Hg production centre in China. The cinnabar deposits in Guizhou amount to about 88000 tons of metal Hg and consist of 80% of the total in whole China. The industrial scale of Hg production in Guizhou had been performed during last 630 years. Recently, large mercury mines in Guizhou, such as Wanshan, Wuchuan, Danzhai, Tongren and Lanmuchang, had been abandoned. In order to assess the environmental impacts and environmental geochemistry of those abandoned Hg mines, total Hg and MeHg in soils, plants, as well as different Hg species in stream-waters in Wanshan and Lanmuchang Hg mines were determined. Simultaneously, the risk assessment on exposure and human health of Hg was discussed.1. Mercury environmental geochemistry in typical Hg-mined areas in GuizhouOne of the most important mine wastes termed calcines, were formed during the retorting of the cinnabar ore at high temperatures. Because of the inefficient and incomplete process of retorting, calcines found at most Hg-mined sites enrich in mercury ranging from 5.7 to 4450 mg·kg-1, containing large quantities of secondary mercury phases, such as metacinnabar, polymorph of sulfide, corderoite, chloride, mercury sulfates, oxides, and elemental mercury. These secondary mercury phases aremore soluble than cinnabar and cause Hg deposits to contaminate the surroundings. Large quantities of water-soluble secondary mercury phases in calcines may also result in favorable conditions for methylation in calcines and surroundings. Therefore, huge quantities of mine-wastes calcines are the dominate Hg-sources related to the environmental Hg-contaminations and potential sources of MeHg-contamination in Hg-mined areas.Data show that total Hg and MeHg concentrations in surface soils from Hg-mined areas are elevated higher than those that obtained in soils from control sites, which greatly exceed the maximum Hg concentration of 1.5 mg-kg"1 recommended by the Chinese National Standard Agency for arable soils. Total Hg and MeHg concentrations measured in polluted soils range from 5.1 to 790 mg-kg"1 and from 0.13 to 15 jug-kg'1, respectively. Total Hg concentrations in soils from control sites range from 0.1 to 1.2 mg-kg"1, MeHg from 0.10 to 0.28 //g-kg"1. In Hg-mined areas, MeHg concentrations in different types of arable soils vary differently. MeHg concentrations in rice paddies as well as vegetable soils are generally higher than those that found in cornfields, suggesting conditions favorable for methylation in paddies. Analytical results show that variety of MeHg levels among different arable soils in Hg-mined areas may own to Hg sources, physical and chemical characters, and TOC in soils. The reclaim and rebuild wasteland to paddies in Hg-mined areas may accelerate the conversion of Hg methylations and the bioaccumulations of MeHg.Surface waters from Hg-mined areas are heavily impacted by mine-waste calcines. Total Hg concentrations in surface waters affected by calcines are elevated high, reaching up to jMg-L"1. Total Hg in water samples that obtained in the downstream especially in the tributaries isolated from Hg-mined areas are relatively low, less than 50 ng-L"1, which may be considered as a baseline value. High abilities of Hg methylation were also obtained in the Hg-contaminated aquatic systems owning to calcines. The peak values of different mercury species measured in surface water samples are: total Hg 9260 ng-L"1, particulate Hg 9210 ng-L"1, dissolved Hg 430 ng-L1, reactive Hg 400 ng-L'1, total MeHg 25 ng-L"1, particulate MeHg 7.3 ng-L"1, and dissolved MeHg 22 ng-L"1. Data of Hg species show that (1) a strong positive correlation between total Hg and particulate Hg form are displayed in the water samples collected from Hg-mined areas with the proportion higher than 80%;(2) highlevels of participate Hg always match high concentrations of TSS;(3) Concentrations of total Hg and paniculate Hg in water samples collected during the flood-flow season are higher than those that obtained in the base-flow season, whereas, concentrations of dissolved and reactive Hg are lower with the peak values observed in water samples collected in the base-flow season. Observations suggest that the dominate Hg species in waters is particulate form and suspended particles in surface waters would present as a primarily transport pathway in contaminated aquatic system. Reasons for the characters of Hg species in different seasons are (1) summer in Guizhou is, in general, always a rainy season, therefore, the rivers that have a strong hydrodynamic force can scour and carry large quantities of particles enriched in mercury, and as result, leading to the increasing of concentrations of particulate Hg and total Hg;(2) water-soluble Hg forms would be diluted by the increasing of flow-rate of rivers in summer season, resulting in the decreases.Atmospheric Hg concentrations in studied areas are strongly correlated with the mining activities. Total gaseous Hg concentrations near the abandoned smelting facilities or small retorts vary from 1220 to 15590 ng-m"3. Results for Hg fluxes between mine-waste calcines and air exhibit that calcines are an important Hg source for atmospheric Hg. The rate of Hg emission from calcines is strongly consistent with the solar radiation. A positive correlation between Hg flux and the solar radiation were obtained. Annual estimating Hg emissions from calcines in Wanshan range from 0.96 to 3.0 kg-yr"1. In addition, there is a positive relationship between Hg concentrations in mosses and the total gaseous Hg concentrations in the ambient air, indicating that the sources of Hg in naturally growing mosses in Hg-mined areas are primarily from the atmospheric Hg deposition, suggesting that the naturally growing moss is an effective bio-monitor of local air Hg pollution.Agricultural corps and vegetables collected from Hg-mined areas present highly elevated total Hg concentrations. Total Hg concentrations in vegetables range from 120 to 18000 jig-kg"1 and exceed the National Standard of 10 |
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