Distribution characteristics and ecological risk assessment of soil heavy metal in Yuanzhou District of Guyuan City, Ningxia

Objective Through studying the content and spatial distribution characteristics of heavy metals in the surface soil of Yuanzhou District, Guyuan City, Ningxia, the ecological risk of this area was evaluated, and the accumulation of heavy metals in the surface soil of Yuanzhou District was clarified. Methods A total of 12,988 soil samples were collected and tested for the concentration of eight heavy metals, namely As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn. The single-factor index, Nemerow comprehensive pollution index, and potential ecological hazard index methods were employed to estimate the ecological risks associated with heavy metal contamination in soils. Results Compared to the background values of 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. We observed similar distributions of the eight heavy metals, with high concentration values primarily found in areas with frequent human activities, such as the east and west sides of Liupan Mountain, Guyuan City, Zhangyi Town, and Huangduobao Town. In contrast, low concentration values were observed in Tanshan Township and Zhaike Township in the northeast Quaternary areas with loess-covered soil. The single-factor index evaluation revealed that the soil was "clean" in the Yuanzhou area. The Nemerow comprehensive pollution index evaluation 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 reached moderate risk levels, the comprehensive potential ecological hazard index of heavy metals was at a slight risk level.Conclusion Overall, the soil quality in Yuanzhou District, Guyuan City is in good condition, but heavy metals were slightly enriched in the topsoil due to human activities in some areas.