Distribution and ecological risk assessment of heavy metals in soils in the Yuanzhou District of Guyuan City, Ningxia

This paper is the result of environmental geological survey engineering.

Objective This study investigated the contents and spatial distributions of heavy metals in surface soils in Yuanzhou District, Guyuan City, Ningxia, evaluating heavy metal accumulation and its associated ecological risk.

Methods A total of 12988 soil samples were collected and the levels of eight heavy metals, namely, As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn, were measured. The single−factor index, Nemerow comprehensive pollution index, and potential ecological hazard index were used to estimate the ecological risks associated with heavy metal contamination in soils.

Results Compared to the background values of the Ningxia Autonomous Region, the average enrichment coefficients of As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn were 1.01, 1.42, 1.04, 0.99, 1.03, 0.81, 1.01, and 1.07, respectively. Similar distributions of the eight heavy metals, with high concentrations, were observed in areas characterized by high human activity, such as the east and west sides of Liupan Mountain, as well as Guyuan City, Zhangyi Town, and Huangduobao Town. In contrast, low concentrations were observed in Tanshan Township and Zhaike Township in the northeast Quaternary areas with loess−covered soil. Single−factor index evaluation revealed that the soil was "clean" in the Yuanzhou area. Evaluation using the Nemerow comprehensive pollution index indicated that the soil pollution index of all heavy metals was less than 0.7, which is considered "clean." While the single−element potential hazard index of Cd and Hg showed a level of moderate risk, the comprehensive potential ecological hazard index of the heavy metals showed slight risk levels.

Conclusions The soil quality in Yuanzhou District, Guyuan City, is in good condition, although slight enrichment of heavy metals was seen in the topsoil due to human activities in some areas.