Sources analysis and ecological risk assessment of soil heavy metals and metalloids in Yao'an area of central Yunnan

A suite of 428 surface soil samples were collected in the Yao'an area of central Yunnan area to evaluate the pollution characteristics, sources, and ecological risks associated with the heavy metals and metalloids such as As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. The concentrations and spatial distribution characteristics of these heavy metal elements are illustrated through statistical data analysis and geochemical maps. The sources of heavy metals and metalloids were explored using correlation analysis, principal component analysis, and cluster analysis methods. The degree of heavy metal pollution and potential ecological risks were evaluated by the geo-accumulation index method, the enrichment factor method, and the potential ecological risk index method. The results show that As, Cu, Pb and Zn are influenced by the natural background and mineral mining. Cr and Ni mainly reflect soil parent materials; Cd enrichment is associated with mineral mining and agricultural fertilizer use. Hg is affected by surrounding factory emissions and coal combustion. The analysis of the Geo-accumulation Index and Enrichment Factor showed that the pollution degree in the study area was generally not high; however, there was local enrichment of the heavy metals such as Cd and Hg. The potential ecological risk index method also showed that Cd and Hg are the most important risk elements in the study area, but they are mainly mild and moderate ecological hazards. The distribution area of strong ecological hazards is small, and the overall ecological risk in the study area is low and controllable. Our study provides a current assessment of soil heavy metal and metalloid pollution in the study area that can be used to guide future land-using plan in central Yunnan.