Potentially toxic elements contamination, risk and source analysis in sediments of Beiyun River supplied with reclaimed water, China

It is unknown the contribution rate of reclaimed water recharge to the accumulation of potentially toxic elements and the key factors affecting the speciation of potentially toxic elements in highly polluted urban river and lake sediments that have been replenished with reclaimed water. This study aims to clarify the contamination, risk and source analysis of potentially toxic elements pollution in the Beiyun River, (Beijing, China) which is a heavily polluted urban river. All eight potentially toxic elements have different degrees of ecological risk. Cr and Cu pose carcinogenic and non-carcinogenic risks to adults and children, whereas Ni poses carcinogenic risks to children only. Importantly, our proposed method based on meta-database construction combined with traditional analysis can effectively quantitatively evaluate the contribution rate of reclaimed water supply to potentially toxic elements in river sediments. The contribution of the reclaimed water supply project to potentially toxic elements was as high as 67%, followed by agricultural sources (26%), and atmospheric deposition (7%). Interestingly, we also used variation partitioning analysis combined with correlation analysis to identify key factors affecting the speciation of potentially toxic elements. The cations and microbial communities in the reclaimed water had the highest individual interpretation for the exchangeable fraction (29.4%) and reducible fraction (54%), respectively. The oxidizable fraction was affected by microbial communities, cations, and nutrient ions and had the strongest synergistic effect, with a co-influence of 37.5%. The residual fraction was the most stable, and the individual contribution of the microbial communities and their variance was high (42.7%). Therefore, disentangling the mechanism of potentially toxic elements enhances the management of pollutants in the urban rivers and lake recharged by reclaimed water.