Ecological risk assessment and priority control factor analysis of heavy metals in farmland soil around mining areas based on specific source allocation

To explore the distribution of heavy metal pollution in the farmland surrounding a coal mine area in Pingxiang City and to apportion ecological risks based on specific sources, surface soil samples were collected from the farmland to determine the concentrations of heavy metals (Cd, Hg, As, Pb, Cr, Cu, Ni, and Zn). The geo-accumulation index method, the modified Nemerow index method, and the Positive Matrix Factorization (PMF) model were employed, coupled with a comprehensive ecological risk index approach, to study the pollution characteristics and sources of heavy metals in the farmland soil near the mine area. This methodology was also used to quantitatively analyze the contribution rate of each pollution source to the ecological risk and to determine the priority control pollution factors. The results showed that, except for As, the mean concentrations of Cd, Hg, Pb, Cr, Cu, Ni, and Zn were all higher than the background values of Jiangxi Province, with Cd and Ni having sample points exceeding the risk screening values for farmland soils, with exceedance rates of 64.86% and 51.35%, respectively. The pollution assessment results indicated that the soil is generally at a moderately polluted level, with Cd and Ni being the main pollutants, showing moderately severe and moderate pollution, respectively. The PMF model analysis revealed that the soil in the study area is mainly influenced by a composite source of mining and agricultural activities, industrial sources, natural sources, and traffic sources, with contribution rates of 33.30%, 21.68%, 19.20%, and 25.82%, respectively. The specific source-comprehensive ecological risk index indicated that Cd and Ni are the priority control pollution elements in the soil of the study area, with the composite source being identified as the priority control pollution source. These research outcomes provide a reference for the pollution prevention and control of heavy metals in the farmland soil surrounding the coal mines in Pingxiang City.