Analyzing topsoil heavy metal pollution sources and ecological risks around antimony mine waste sites by a joint methodology

Studies on soil contamination caused by waste sites near antimony mining areas are scarce. For environmental protection, it is critical to investigate the contamination levels, spatial distribution, and ecological risk assessment of heavy metals (HMs) in the surface soils of different land use types around waste sites and to identify related potential sources. In this study, the pollution status, spatial distribution, sources and ecological risks of Hg, Pb, Cd, Cr, As and Sb in the surface soils of built-up areas, woodlands and croplands around the waste sites of antimony mining areas were resolved for the first time by combining self-organizing maps (SOM), K-means clustering, geographic information systems (GIS) and positive matrix factorization (PMF). According to the analysis results of soil samples, the average abundance order of HMs is: Sb > As > Cd > Pb > Cr > Hg. The cumulative geological index defines Sb as a severe pollution level. The pollution index shows that Sb and Cd in all samples are above the severe pollution level. The pollution load index shows that 67.7% of soil samples are heavily polluted. SOM and K-means divided the studied elements into three clusters and were combined with GIS analysis to from Cd as cluster 1, Sb and As as cluster 2, and Pb, Hg and Cr as cluster 3. The PMF analysis yielded three potential sources of heavy metals: natural sources dominated by Hg, Pb and Cr (48.6%), direct sources caused by the accumulation of waste sites represented by Sb and As (32.9%) and mixed sources caused by human activities and transportation represented by Cd (18.5%). Ecological risk shows that the risk of construction area is prominent, and Sb is the main contribution element of high risk. This study combines multiple methods to investigate the current status of heavy metal pollution in the soil environment around antimony mine slag sites, providing a theoretical basis for better research on the pollution of heavy metals in the soil around antimony mine slag sites and source control, and contributing to the scarcity of antimony mine slag site pollution research.