Distribution, risk evaluation, and source analysis of the heavy metals in the sediment deposition of the lower Shichuanhe River, Shaanxi, China

In this study, 30 sediment samples were collected from the lower reaches of the Shichuanhe River in Xi'an, Shaanxi Province, China, to test the distribution of heavy metal elements in this area and for an analysis of the pollution levels of this area, hope to provide guidance on agricultural production activities in this region. The results show that the heavy metal elements in this area are mainly concentrated at the Qinghe River and Shichuanhe River confluences. Furthermore, the element contents are higher than that of the background levels of the continental crust (UCC) and close to the background levels of the soil from Shaanxi Province; the two most enriched elements are Cd and As, with contents of 0.79 and 22.7 mg·kg−1, respectively, and their contents are 3.8 and 1.72 times higher than that of the background values. Herein, the heavy metal pollution assessment methods applied indicated that Cd and As are the two most abundant pollutant elements in the area’s soils. As has a peak geo-accumulation index value of 3, and the pollution level is high, while Cd exhibits high potential ecological risks due to its high toxicity (potential risk index of 143) and an active fraction of more than 64%. In addition, a principal component analysis and hierarchical cluster analysis study showed that there are two sources of the heavy metals in this area. The Zn, As, Ni, Cu, Pb, and Cr are mainly from natural sources, and the Cd likely comes from a discharge of untreated agricultural wastewater in the region. The Cd which poses a high potential risk and mainly results from human activities, needs to be further monitored.