Distribution, sources, contamination, and risks of toxic metals in Zijiang River, a typical tributary of the midstream of the Yangtze River in China

Abstract

Excessive concentrations of toxic metals are a global threat to aquatic systems. Taking a typical tributary (Zijiang River, ZR) of the midstream of the Yangtze River as the research area, the concentration distribution and chemical fractions occurrence characteristics of five toxic metals (Cd, Cr, Cu, Pb, and Zn) were analyzed, their potential sources were explored, and their contamination and ecological risk was assessed. In the surface waters and sediments, there were high concentrations of Zn, a low concentration of Cd, and small spatial differences in concentration among the upstream, midstream, and downstream. In terms of speciation, Cd mainly existed in the acid-soluble fraction, Pb mainly existed in the reducible fraction, and Cr, Cu, and Zn mainly existed in the residue fraction. The potential sources in surface waters and sediments were determined to be industrial emissions and agricultural non-point sources through the absolute principal component scores–multiple linear regression model (APCS–MLR). Based on the assessment results of total concentration and speciation, Cd was the typical contamination element in ZR sediments. In addition, the secondary phase enrichment factor (SPEF) based on speciation underestimates the degree of Pb contamination, and the ecological risk of Zn assessed by the ratio of secondary phase and primary phase (RSP) and the risk assessment code (RAC) was higher than that of Cr, which was inconsistent with the results based on total concentrations. SOM and Al/Fe/Mn cycles in sediments influenced the geochemical behavior of toxic metals.