Environmental Pollution In Abandoned Mercury Mining Sites And Its Impact On The Surrounding Ecological Environment

Wanshan mercury(Hg)mine is considered as the “capital of Hg” in China.Although the mining activities were banned at the site due to the depletion of Hg resources and environmental protection,the abandoned mine site continues to release large amounts of Hg into the surrounding environment.However,the release pathways and the relative contribution of contamination remain unclear.In Hg mining areas,rice is the main exposure pathway for methylmercury to the local population.Identifying the sources of soil Hg contamination in paddy field is the basis for remediation and pollution control.In this study,the Yanwuping site of Wanshan Hg mine was selected to evaluate the impacts of the site on the surrounding atmosphere,water and soil.Sources and relative contributions of Hg in paddy soil were identified using Hg isotopes,Principal Component Analysis/Absolute Principal Component Scores(PCA/APCS)and Positive Matrix Factorization(PMF)receptor models.This study was also designed to compare the feasibility and limitations of various source analysis techniques for soil Hg contamination.From the above study,the following main conclusions were obtained:(1)The Hg concentrations in the exposed mine calcines at Yanwuping site were very high as compared to the restored part.This region was heavily contaminated with Hg and had the highest total gaseous Hg(TGM)concentrations in the study area.The Hg concentrations in the surface water of the Wengman River,which flows through the Yanwuping site,were highly variable.The most severe Hg contamination was found at the river source,which was as high as 1253 ng/L.The Hg isotopes binary mixing model revealed that the direct contribution of Hg mine waste to Hg contamination in the headwaters reached 89.3%.The relative contributions of mine waste total soluble Hg(TSHg)and particulate Hg(PHg)to dissolved Hg(DHg)and PHg in the headwater of the Wengman River were48.6% and 90.5%,respectively.This indicates that mine waste was the main source of Hg contamination in surface water.The Hg mine waste at the Yanwuping site continuously release Hg to the atmosphere and to surface water bodies through erosion and leaching.It was the main source of Hg contamination in the surrounding ecosystem,seriously endangering the local ecological environment and the health of local villagers.(2)The downstream paddy soil of Yanwuping site were heavily contaminated with Hg.The total Hg(THg)contents in the paddy soil were significantly correlated with the river water THg and TGM concentrations.It indicates that dry and wet deposition of atmospheric Hg and river water irrigation were the major sources of Hg contamination in paddy soil.The THg concentration in the first 5.5 km of paddy soil decreased continuously with increasing distance from Yanwuping site,but there was a significant increase in THg concentration after 5.5 km,and after that a continuous decrease was noticed with distance.(3)The contributions of river water,rainwater and geological background to soil Hg contamination in paddy fields were calculated using Hg isotope approach.The relative average contribution of the three sources was 46.3%,12.3% and 41.3%,respectively.The results show that the paddy soil before 5.5 km was mainly contaminated by river water from Hg mining waste.The results also show that the paddy soil after 5.5 km was mainly contaminated with domestic contamination.Both the PCA/APCS and PMF receptor models showed that the sources of Hg in paddy soil were Hg mine contamination,geological background,traffic and coal combustion.The contribution of Hg mine wastes by the two receptor models was 93.4% and 88.6%,respectively.The receptor models showed that Hg mine pollution is the main source of Hg in the paddy soil of the study area.In contrast,the contributions from geological background,traffic and coal combustion sources were relatively low.This study confirms the impact of Hg migration from the abandoned site of the Wanshan Hg mine on the surrounding environment,including atmospheric,water and soil Hg contamination.The pollution sources of Hg in paddy soil were evaluated based on Hg isotopes.This study demonstrated that the Hg isotopes can be used as an effective tool for tracing environmental Hg contamination in typical Hg polluted areas.Source control measures should focus on irrigation water contamination as the long-term use of irrigation water flowing through the mercurycontaminated site can significantly increase in Hg concentrations in paddy soil in the Hg mining area.It will reduce the bioaccumulation of Hg in crops in this area and the associated human health risks.