Multivariate statistical analysis of potentially toxic elements in soils under different land uses: Spatial relationship, ecological risk assessment, and source identification

The Qinghai–Tibet Plateau is one of the most fragile and susceptible areas to climate change and human disturbances in the world. Here, a total of 48 soil samples were obtained from areas of different land uses within a typical basin in eastern Qinghai–Tibet, China. The selected potentially toxic elements (PTEs, including Cd, Cr, Cu, Pb, and Zn) contents were analyzed to explore their spatial patterns, ecological risks, and then the effects of land use types on these elements were assessed by self-organizing map (SOM) and random forest regression (RFR) models, and the main sources were revealed using positive matrix factorization (PMF) model. Results showed that mean concentrations of selected PTEs in surface soils were higher than local background values and those of subsurface soils. The low-degree ecological risk was obtained with comparatively high risks in the north and south of the study area. The results of the SOM and RFR models revealed that land use types affected the redistribution of PTEs in surface soil. The PMF model demonstrated that these PTEs were mainly derived from natural sources (46.7%), traffic emissions (31.2%), and industrial and agricultural inputs (22.1%). Natural sources were the essential contributors for these soil PTEs, especially for Cr. In addition to natural sources, traffic sources made great contributions for Cd, Pb, and Zn elements, while the enrichment of Cu was mainly related to industrial and agricultural activities.