Risk Assessment and Influencing Factors Analysis of Heavy Metals in Soil of Non-Surface Coal Mines in Southern Hebei Province

Non-surface coal mining is an important means to obtain coal resources. It is crucial to study the influencing factors and ecological risks of soil heavy metal contents of non-surface coal mines for the protection and management of mine area ecosystems. The current study on soil heavy metals in the Fengfeng coal mine, a non-surface mine located in southern Hebei Province, primarily focuses on assessing local soil pollution levels and analyzing the linear effects of influencing factors, which makes it difficult to provide a scientific basis for the effective treatment of soil heavy metals in the entire region. To comprehensively evaluate the pollution level of soil heavy metal of the Fengfeng coal mine and deeply analyze the main influencing factors and their nonlinear mechanisms, 49 surface soil samples were collected and the contents of seven heavy metals (As, Cd, Cr, Cu, Ni, Pb, and Zn) were determined. The single pollution index method and potential ecological risk assessment method were employed to evaluate the soil heavy metal pollution level and potential ecological risks of the mine area, and the geographic detector was utilized to analyze the main influencing factors of the spatial distribution of soil heavy metal content. The results indicated that the soil heavy metal contents of seven types in the mine area exhibited certain spatial heterogeneity, with an overall distribution pattern of high in the north and low in the south. Only the average content of Cd in the samples exceeded the national natural background value. The comprehensive index of soil potential ecological risk was between 45.70 and 132.77, ranging from mild to moderate risk levels. The single heavy metal pollution indices were ranked as Cd (1.818)>Pb (0.744)>Cu (0.715)>Ni (0.714)>Cr (0.701)>Zn (0.684)>As (0.656). The spatial pattern of soil heavy metal content in the Fengfeng coal mine was influenced by human factors such as mining activities and gangue hills, as well as natural factors such as precipitation and soil moisture. Among them, enterprise distribution and transportation activities were the main influencing factors of the spatial differentiation of heavy metal Ni; mining activities were the main influencing factor of heavy metals Cu, Cd, Cr, Pb, and Zn; soil erosion and soil moisture were the main influencing factors of heavy metal As.