Fractionation and risk assessment of potentially toxic elements in surface soil from northeast China mountains

Purpose The acceleration of industrialization and urbanization has increased the deposition of potentially toxic elements (PTEs) in the remote area of northeast (NE) China, which is facing rising environmental pressure. The objectives of this study are to characterize the PTEs pollution level, possible sources and the potential ecological risk in the mountain regions of NE China. Methods In this study, the BCR sequential extraction procedure was applied for partitioning the four fractions (acid soluble, reducible, oxidizable and residual) of 16 PTEs (As, Be, Ba, Cu, Co, Cd, Cr, Mn, Mo, Ni, Pb, Sr, Sb, Tl, V, and Zn) in 53 surface soils collected from the Great and Lesser Hinggan mountains. The geoaccumulation index (Igeo) and the Håkanson index (RI) were used to evaluate a regional pollution status and the potential ecological risk. The multivariate analysis was used to identify the PTEs potential sources. Results and discussion As, Be, Ba, Co, Mn, Ni, and Sr are mainly associated with reactive forms, which represent the metal bound to carbonates or sorbed/exchangeable phases, and the other metals like Pb, Zn, Cr, Cd, Sb, and Tl are mainly associated with the residual phase. The spatial pattern showed an increase of these PTEs contents in the soil environment from the southern Great Hinggan mountain to the Lesser Hinggan mountain, with an opposite trend for the potential risk of PTEs because of the altitude effect. The Cd, As and Pb pollution was significant with a high ecological risk, especially for Cd. PCA analysis suggested four potential sources for the PTEs accumulation in the soils: natural lithogenic sources, agricultural fertilizer, anthropogenic mining, and leaching migration. Conclusions Information from this study constitutes an estimation of PTEs pollution status and possible sources in the mountains’ surface soils. It represents a reference for future studies on soil monitoring and environmental protection in remote areas. The trend of soil pollution in remote mountainous areas makes us more alert to the global soil health problems and it is urgent to halt soil pollution and degradation for the realization of sustainable development goals.