Sources analysis and health risk assessment of heavy metals in agricultural soils of a mining town in Chongqing

Mining and processing activities significantly affect the environmental quality and human health. To understand the distribution characteristics and pollution sources of heavy metals in agricultural soil in a coal mining town in Chongqing, 216 surface soil samples were collected and analyzed for the content and spatial distribution of heavy metal(As, Cr, Pb, Cu, Zn, Ni, Cd, and Hg). Spatial distribution patterns and pollution sources were analyzed using Positive Matrix Factorization(PMF) model, and the health risks were assessed using Monte Carlo model. The results showed that the average content of Cr、Pb、Cu、Zn、Ni、As、Cd and Hg in the study area was 51.48、50.38、25.96、98.39、32.05、9.35、0.47 and 0.08 mg∙kg−1. Among these, the average value of Pb, Zn, As, Cd, and Hg exceeded the background values for Chongqing soil, with Cd emerging as the primary pollutant. Specifically, Cd content of 42.13% and 1.85% of the soil samples exceeding the screening and control values, respectively, as specified in the Interim Standard for Soil Pollution Risk Control(GB 15618-2018). Cu and Cd showed similar spatial trends, while Pb, Hg, Zn, and As exhibited similar patterns, with elevated concentrations predominantly concentrated in the northeastern part of the town, overlapping partially with the coal mining areas. The main sources of soil heavy metals were primarily attributed to traffic emissions and industrial discharges(33.5%), coal combustion(16.5%), parent material and agricultural activities(27.2%), coal mining and abandoned coal gangue piles(22.8%). Health risk assessment results indicated that the mean non-carcinogenic health risk indices for children and adults were 0.36 and 0.03, respectively, with As, Cr, and Pb being the main contributors. The mean carcinogenic health risk indices for children and adults were 8.24×10−6 and 2.99×10−6, respectively, with As and Cd identified as the primary carcinogenic risk elements.