Distribution, Risk Assessment, and Source Identification of Potentially Toxic Elements in the Sediments of the Upper Reaches of Zhanghe River, Haihe Basin

The Beijing-Tianjin-Hebei region is mostly located in the Haihe Basin. Studying the distribution and sources of potentially toxic elements (PTEs) and heavy metals in the upper reaches of Zhanghe River, the largest tributary of Haihe runoff, is of great significance to the water security of Beijing-Tianjin-Hebei region, a world-class urban agglomeration. In this study, 32 sediment samples were collected in the upper reaches of Zhanghe River, and the concentrations of eight PTEs were analyzed. The results show that the concentrations of PTEs in sediments ranked are as follows: Mn > Cr > Zn > Cu > Pb > Co > As > Cd. Cr, Cu, Zn, and Cd show a random spatial variation trend; Mn, As, and Pb are mainly distributed in the headwaters of the Zhuozhang River. Ninety percent of samples of Cr, Cu, Zn, Cd, and Pb are under the threshold effect level, and 16% of the Cr samples are above the probable effect level. PTEs in the study area have low to moderate pollution as the enrichment factor and geo-accumulation index showed, and the contribution of anthropogenic sources to the enhancement of PTEs in sediment samples is still at a preliminary stage. Potential ecological risk results indicate that 96% of the upper reaches of Zhanghe River have a low risk level. The three evaluation methods all point out that Cr is the main pollutant in the upper reaches of Zhanghe River, and the Southern Headwater of Zhuozhang River is the main polluted area. Cr, Mn, Co, and Pb originate from mining activities and road dust, while Cu, Zn, As, and Cd originate from agricultural activities.