Analysis of the Sources of Soil Heavy Metals in Geological High-Background Areas at a Large Spatial Scale

Determining the sources of heavy metals in soil on a large scale is of great significance for improving soil environmental management, especially in regions where the sources of soil heavy metals are complex. We analyzed the sources and correlations of soil heavy metals in southwestern China and counted the content of five typical heavy metal elements by collecting soil samples from 309 typical locations. The risk of soil heavy metal pollution in the study area is relatively high, with cadmium posing the highest risk. The risk of soil heavy metal pollution in areas with high and medium development levels of carbonate rocks is significantly higher than that in low development-level carbonate rock areas and non-carbonate regions. In medium-carbonate development regions, the intensity of human activities exceeds that in high-carbonate development regions, resulting in a more consistent risk of soil heavy metal pollution between the two zones. In high-carbonate regions, the main sources of heavy metals in soil are predominantly natural, while in moderate regions, there is a mixed influence of both anthropogenic and natural sources. In low regions, both sources are minimal. There are also notable differences within the non-carbonate region, with the southeastern area exhibiting much higher values than the other regions, which is related to the intensity of human activity being significantly greater than in other areas. Among these, polluting enterprises that discharge heavy metals are the most significant contributors. This provides support for understanding the spatial differences in soil heavy metals and their main influencing factors at the national or regional level.