Co-occurrence of microplastics and heavy metals to urban river sediments: The vertical distribution characterization and comprehensive ecological risk assessment.

Microplastics (MPs) and heavy metals (HMs) are deemed to pose ecological risks in river ecosystems. The vertical distribution of these pollutants is more conducive to reflecting pollution status and monitoring trends in the sediment. This work analyzed the horizontal and vertical distribution, carried out a risk assessment of HMs and MPs in urban river sediment, and further optimized the two-dimensional comprehensive index (TPI) model for MPs-HMs combined pollution. The highest rates of contamination were for Zn, As, and Cd, and MP abundance in sediment ranged from 20.00 ± 8.82-1933.33 ± 141.42 items·kg, mainly characterized by PE and fragments. Moreover, the mean potential ecological risk index for MPs (PRI) at different depths of sediment were 197.21 ± 247.14, 176.79 ± 293.86, and 246.98 ± 538.38, respectively, indicating a moderate risk and the highest PRI value is at the bottom. The TPI exhibited that the average TPI at different depths is 324.10 ± 138.63, 368.30 ± 157.13, and 481.88 ± 296.05, indicating that the comprehensive pollution risk level belongs to considerable, the TPI increases with the depth of the sediment. The results further improved the objectivity and accuracy of the research on the ecotoxicity of compositive pollutants and provided an in-depth understanding of MPs and HMs in urban freshwater basins from a vertical perspective.