The competition of heavy metals between hyporheic sediments and microplastics of driving factors in the Beiluo River Basin

Both sediments and microplastics (MPs) are medias of heavy metals (HMs) in river ecosystems. This study investigated HMs (Mn, Cr, V, As, Cu, Co, Cd, Pb, and Ni) concentration and driving factors for competitive enrichment between hyporheic sediments versus MPs. The medias basic characteristics indicated that the sediments were mostly sand and rich in Fe2O3; three polymer types were identified, with blue, fragment, less than 500μm being the main types of MPs. The results have shown that the average content of extracted HMs in MPs was much higher than that of the same metals accumulated in sediments. HMs in sediments and MPs reached heavily polluted at some points, among which As and Cd were ecological risks. Electrostatic adsorption and surface complexation, and biofilm-mediated and organic matter complexation were the interaction mechanism of HMs with sediments and MPs. Further, the driving factors affecting the distribution of HMs in the two carriers were analyzed by multivariate statistical analysis. The results demonstrated that carrier characteristics, hydrochemical factors, and the inherent metal load of MPs were the main causes of the high HMs content. These findings improved our understanding of HMs fate and environmental risks across multiple medias. Owing to large specific surface area and hydrophobicity, microplastics adsorb heavy metals (HMs) from the surrounding environment, aggravating potential ecological hazards and posing a threat to aquatic organisms. Many laboratory experiments have confirmed the compound effect of the two, but the attribution of HMs in natural rivers under the influence of multiple factors remains to be studied. This study investigated the distribution of HMs concentrations in different media, assessed HMs pollution in sediments and microplastics, and explained the drivers of uneven HMs concentrations. The finding provides new insights for further understanding of the fate of HMs in ecosystems.