Soil heavy metal sources analysis and risk evaluation of Zhundong coal mine in Xinjiang

Abstract: During the process of opencast and underground coal mining, a variety of rock types with different compositions are exposed to atmospheric conditions and undergo accelerated weathering. These materials are often deposited nearby as mine waste rocks and mine dust. Heavy metal pollution is the representative environmental pollution which is caused by heavy metals or their compounds. It has wide range, long duration, non-degradability, and some other features. The accumulation of heavy metals in soil will destroy the physical and chemical properties of soil, cause irreversible pollution of environment, and further threaten human health. For mining area, influenced by human exploitation, the top soil is thin and is easily affected by atmospheric dust fall. To study the origin of heavy metals in soils and ecological risk in Zhundong area, we analyzed heavy metal (As, Hg, Pb, Cr, Cu and Zn) content with 27 soil samples in three buffers (every 42 km from Zhundong Diggings to Fukang City was divided into a area, area A, area B and area C). The risk analysis of heavy metals was carried out by means of pollution index method, land accumulation index method and potential ecological risk index method. The results showed that: 1) In addition to the overall average value of Cr is 53.03 mg/kg, which is higher than the background value of soil (49.3 mg/kg) in Xinjiang, the contents of other heavy metals are lower than their background values. The figures of spatial distribution of soil heavy metals indicate that: High values of Cu and Hg content was distributed in the area C, high values of other heavy metal content appeared in soils near Zhundong mining area (area A), the heavy metal content in the three buffers are basically the same, the coefficient of variation decreased with the increasing of distance to the mining area. 2) Through the analysis of pollution sources, in Zhundong area, 89.31% of Hg comes from coal burning, 40.1% of Pb comes from transportation, 19.65% of As comes from atmospheric dust. The main source of Cu and Cr is coal dust and its contribution rates are 60.23% and 81.6% , respectively, 29.7% of Cu comes from the soil parent material, and 75.1% of Zn comes from the soil parent material. There are still unknown sources of heavy metals in soil except Zn. 3) The soil pollution risk in the study area was evaluated by means of pollution index method, land accumulation index method and potential ecological hazard index method. The pollution level of soil in Zhundong area is mild-moderate, single element pollution degree from high to low is Hg>As>Pb>Cr>Cu>Zn. The farther away from the mining area, the lighter the heavy metal pollution is. The rank of Regional ecological risks of As, Hg, Pb and Cr elements was A >B >C, the farther away from the mining area, the lower the ecological risk is. The potential ecological risk index is consistent with the order of single factor ecological risk of heavy metals. The mining of coal results in the pollution of heavy metals in the surrounding soil, which seriously affects people undefined cultivation and life, and also affects the ecological environmental system. Therefore, it is necessary to establish a system of environmental protection and strictly manage of mining in mining areas.