Characteristics, sources, and distribution of microplastics in sediments and their potential ecological risks: A case study in a typical urban river of China

Sediments serve as habitats for benthic organisms and also harbor a significant amount of microplastics. Studies on the distribution of microplastics and their interactions with benthic communities contribute to the understandings on microplastic pollution. Here, we investigated the characteristics of microplastics in the sediments of an urban river located in Guizhou Province, China, and their correlations with benthic communities to unravel their distribution patterns and their possible environmental risks. The results demonstrated that microplastics were detected in all sampled regions, with an average abundance of 2740 items/kg. The dominant polymers were polyethylene (PE) and polyvinyl chloride (PVC) and their main sources were the wear of terrestrial plastic products and the waste discharges from human activities. Regions with landscape functions and wastewater discharge contained higher abundances of microplastics and the Spearman's correlation demonstrated positively correlation between populations/GDP and microplastic abundances, indicating a regional specificity of microplastics distribution. Based on the safety thresholds of microplastics, we found that the exposure concentration of microplastics in the study area posed no theoretically risk to benthic communities. Results of network analysis, however, showed that communities of microalgae and bacteria had stronger associations with microplastics, with degree values of 4.7 and 2.1, respectively, suggesting the risk transmission of microplastic through the food chain. Further RDA results showed that in macrophyte communities, the dominant species Stuckenia pectinata and Potamogeton wrightii were significantly positively correlated with the PE abundance. The same pattern was observed between benthic invertebrate groups and PVC abundance, which might be ascribed to the species-specific' responses to microplastics, with tolerant invertebrate species being more competitive and therefore higher abundance. In all, microplastic exposure in urban rivers poses potential threats to the composition of benthic communities and might affect humans through various food chain pathways. Recommendations on policy and research were also proposed for better remediation on microplastic contaminants in urban rivers.