Characteristics and health risk assessment of heavy metal pollution in soil around Shanhu Mining Area in Guangxi

To summarize the patterns of heavy metal pollution in soil around tin mining areas and the associated health risks, we investigated 244 surface soil samples collected around typical quartz-vein-type tin deposits in Guangxi. A systematic evaluation was conducted using the single pollution index method, Nemerow comprehensive pollution index method, principal component analysis (PCA), Pb isotope analysis, and human health risk assessment model. The results showed that the average contents of heavy metals in the soil around Shanhu Tin Mining Area followed the order of As > Zn > Cr > Pb > Cu > Ni > Cd > Hg from highest to lowest. Among these heavy metals, the contents of Pb, Zn, Cr, and As exceeded the soil environmental background values of the Guangxi Zhuang Autonomous Region. The heavy metal pollution assessment indicated that As was the most severely polluting element in the study area, followed by Cd, while the remaining elements were mainly characterized by no pollution or mild pollution. The Nemerow comprehensive pollution index of all samples ranged from 0.53 to 340.35, with most samples falling into the categories of "warning level" and "mild pollution", and severely polluted samples accounting for 26.2% of the total. These results confirmed the existence of certain heavy metal pollution in the study area. Pb isotope analysis and source identification revealed that the pollution of Cu, Pb, Zn, Ni, Cd, and As in the soil was mainly derived from the weathering of mineralized bodies, while the contribution of mining activities was negligible. Cr and Hg represented background values and were of natural origin. The health risk assessment indicated that As in the soil was the primary risk factor, oral ingestion was the dominant exposure pathway, and children were more vulnerable to the threats of heavy metal pollution. In conclusion, the heavy metal pollution in the soil around Shanhu Mining Area was generally controlled by natural processes. It was therefore recommended to strengthen the monitoring of As and Cd to prevent adverse effects on residents' health.