Cumulative Risk Assessment of Soil-Crop Potentially Toxic Elements Accumulation under Two Distinct Pollution Systems

Abstract

High geological background and human activities are the two major pollution sources for soil potentially toxic elements (PTEs) accumulation around the world. Mining is the prime human activity that poses a serious threat to the farmland’s ecosystem safety. This study assesses the farmland safety in the typical high geological background area and the superimposed area of high background-mining activity in eastern Yunnan in China by systematic analysis of the accumulation and risk characteristics of seven PTEs such as arsenic (As), mercury (Hg), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), and chromium (Cr). Furthermore, we used Cd as the characteristic element to establish a relationship model between crop PTEs accumulation and the physical and chemical characteristics of the soil. We find that in the farmland soil from the superimposed area, the accumulation point over-standard rate of seven PTEs is higher than in the typical high geological background area. The accumulation of Pb, Cd, Cu, and Zn is related to frequent man-made mining activities. The bioavailability relationship model, using Cd as the soil-crop characteristic element, reveals that only in the crops (cereals, vegetables) of the high geological background area; the Cd bio-concentration factor significantly correlate with the physical and chemical properties of the soil. This suggests that the PTEs contaminated farmland in high geological background areas can be concomitantly restored during usage by adjusting the soil’s physical and chemical properties, while in the superimposed area, the farmland area needs prior restoration by removing man-made mining activities.