Contaminant Assessment and Sources Analysis of Heavy Metals in Soils from the Upper Reaches of the Wushui River

BACKGROUND Eco-functional areas play an important role in soil and water conservation and biodiversity conservation. The Wushui River is a watershed located in the Nanling ecological function area. However, study on the content and potential ecological risk of heavy metals in the soil of the upstream area of the watershed is scarce. OBJECTIVES To investigate the degree of heavy metals pollution and the potential ecological risk of soils in the upper reaches of the Wushui River. METHODS The soil samples of five land utilization types in the upper reaches of the Wushui River Basin, including mining, industrial, and cultivated land and forest, were collected to analyze the contents of seven heavy metals Cd, As, Cu, Hg, Ni, Pb and Zn in the soil. The Nemerow comprehensive pollution index was used to evaluate the degree of heavy metal pollution, and the Hakanson potential ecological risk index was used to evaluate the potential ecological risk of heavy metals in soil. Principal component analysis was used to investigate the source of heavy metal pollution. RESULTS The results show that the average concentrations of Cd, As, Cu, Hg, Ni, Pb and Zn in the upper reaches of the Wushui River were 1.28, 72.44, 54.62, 0.27, 68.32, 72.29 and 158.42mg/kg, respectively, which higher than the soil background values. The contents of the heavy metals, except mercury in mining land, were higher than those in other types of soils. The single factor pollution index of heavy metals in the mean state show that Cd and As were heavy pollution elements with factors of 5.07 and 3.25, respectively. In mining land, the Cd single factor pollution index reached 13.59. Heavy metal pollution in mining land was the most serious, followed by industrial land. Forest was in a safe state. Potential ecological hazard index evaluation results showed that Cd reached a very strong ecological hazard and As was a strong ecological hazard in mining land. Mining land and industrial land reached a strong ecological hazard, industrial land reached a moderate ecological hazard, and other types of soils were slightly ecologically harmful. The results showed that As, Cd, Cu and Zn came from industrial and mining activities, Ni and Hg mainly came from parent materials, and Pb came from transportation. CONCLUSIONS Heavy metal pollution of soil is relatively serious in the upstream area of the Wushui River Basin. Cd and As are the main risk factors in the area, mainly deriving from mining and industrial activities.