The Assessment of Heavy Metal Accumulation and Risks in Urban Rivers and Sediments of China’s Nine Major River Systems: A Meta-Analysis

Abstract

The objective of this study is to analyze the spatial–temporal patterns, identify risk zones and explore the co-occurrence correlation of eight heavy metals (HMs) in urban rivers in nine river systems of China using a meta-analysis. A spatial–temporal analysis was conducted to analyze the variation trend of publications and HMs. Health risk and ecological risk assessment models were used to identify risk zones in river water and sediment, respectively. A co-occurrence network analysis was conducted to determine the co-occurrence correlation of HMs. The results demonstrated that cadmium (Cd), chromium (Cr) and mercury (Hg) in river water in the Huaihe (region 5) and Haihe River systems were 20–40 times higher than the environmental quality standards; Hg, Cd, copper (Cu) and zinc (Zn) were heavily accumulated in sediments in the Songliao (region 1), Yellow River (region 3) and Southeast Drainage (region 9) systems. Cr in river water in region 5 posed carcinogenic risks to urban residents through ingestion and dermal contact, while Cd and Cu posed high ecological risks in the sediments in regions 1, 3, 5 and 9. Multiple HMs exhibited significant co-occurrence correlations. In river water, the average clustering coefficients among lead (Pb), Cu, Zn, Cd, Cr and nickel ranged from 0.51 to 0.76. In sediments, eight HMs exhibited even more significant correlations, ranging from 0.34 to 0.81 (p < 0.05). The coexistence and strong correlation of HMs in urban river systems may exacerbate their potential risks.