Environmental behavior of microplastic - heavy metal synergistic contamination in a typical urban-rural river network

Microplastics (MPs) and heavy metals (HMs) in rivers pose a global threat to human health and the ecological environment. Given the differences in pollutant classes, the co-occurrence and interactions between MPs and HMs are still poorly understood. In this study, the co-occurrence of MPs and HMs across different seasons were investigated in the urban-rural rivers of a typical inland city, China. MPs and HMs were detected in all water samples at the wet and dry seasons, and the differences in the abundance of MPs and HMs between the two water periods were not significant. The abundance of MPs was higher in urban and industrial zones than that in agricultural zones. The predominant form and composition of MPs was granules (44.49 %) and polyethylene terephthalate (PET, 85.40 %), with the most common color being transparent (48.99 %). HMs (Mn, Cu, Cr, Zn, Cd, Pb) were detected in MPs, with the strongest adsorption capacity observed for Mn (K pw = 4.90). Based on the correlation analysis and structural equation model, the polymer type of MPs (path coefficient = 0.3798) and the content of HMs in water (path coefficient = 0.3391) were the significant influence drivers on the adsorption of HMs by MPs. The Hazard Index revealed a medium risk of MPs in the urban-rural rivers, while the Pollution Load Index indicated a low risk of the river water body. These findings suggest that synergistic pollution from MPs and HMs may increase the ecological risk in river water, and the results provide important data for understanding the characteristics of the urban-rural rivers. • Microplastics (MPs) and heavy metals (HMs) were found in the typical urban-rural river network. • Various HMs were absorbed on MPs, and the strongest adsorption capacity observed for Mn. • The polymer types and the HMs content in water were the main drivers for the adsorption of HMs by MPs. • MPs and MHs may cause ecological risk to the urban-rural rivers.