Heavy metals in centralized drinking water sources of the Yangtze River: A comprehensive study from a basin-wide perspective

Water quality in the Yangtze River Basin (YRB) has received considerable attention because it supplies water to 400 million people. However, the trends, sources, and risks associated with heavy metals (HMs) in water of centralized drinking water sources (CDWSs) in the YRB region are not well understood due to the lack of high-frequency, large-scale monitoring data. Moreover, research on the factors affecting the transportation of HMs in natural water are limited, all of which significantly reduce the effectiveness of CDWSs management. Therefore, this study utilized data on 11 HMs and water quality from 114 CDWSs, covering 71 prefecture-level cities (PLC) in 15 provinces (cities), to map unprecedented geospatial distribution of HMs in the YRB region and examine their concentrations in relation to water chemistry parameters. The findings revealed that the frequency of detection (FOD) of 11 HMs ranged from 28.59% (Hg) to 99.64% (Ba). The mean concentrations are ranked as follows: Ba (40.775 μg/L) > B (21.866 μg/L) > Zn (5.133 μg/L) > V (2.668 μg/L) > Cu (2.049 μg/L) > As (1.989 μg/L) > Mo (1.505 μg/L) > Ni (1.108 μg/L) > Sb (0.613 μg/L) > Pb (0.553 μg/L) > Hg (0.002 μg/L). Concentrations of Zn, As, Hg, Pb, Mo, Sb, Ni, and Ba exhibited decreasing trends from 2018 to 2022. Human activities, including industrial and agricultural production, have led to higher pollution levels in the midstream and downstream of the river than in its upstream. Additionally, the high concentrations of Ba and B are influenced by natural geological factors. Anion concentrations and nutrient levels, play a significant role in the transport of HMs in water. Probabilistic health risk assessment indicates that As, Ba, and Sb pose a potential carcinogenic risk. Additionally, non-carcinogenic risk to children under extreme conditions should also be considered. Ensuring the safety of drinking water is crucial for human health and sustainability. However, few systematic studies have examined the HMs in CDWSs on a large spatial-temporal scales. This study is the first to systematically investigate the occurrence, spatial-temporal trends, sources, and probabilistic risk of HMs in CWDSs across the YRB. It also preliminarily examined the response of HMs concentrations to water chemical parameters. The findings of this study will fill the knowledge gap regarding HMs in CDWSs and provide a scientific reference for managing hazardous substances in aquatic environments.