Compartment-specific patterns of microplastic pollution across clams and the water-sediment interface along the Chinese coast: Implications for bioindicator-based monitoring

Microplastic (MP) pollution is pervasive in coastal marine ecosystems, where MP particles are dynamically exchanged among seawater, sediments, and biota. Bioindicators, particularly bivalves, have been widely proposed by the scientific community for monitoring environmental MP pollution. In this context, understanding the relationship of MP pollution across these interconnected compartments is essential for accurate and robust bioindicator-based environmental monitoring and risk assessment. Therefore, in this study, large-scale sampling was conducted along the Chinese coastline to investigate MP abundance, community characteristics, and associated ecological risks in a widely distributed clam species ( Ruditapes philippinarum ) and at the seawater–sediment interface. The results showed no significant correlations in MP abundances between clams and seawater or sediment. MP community composition also differed significantly between clams and surrounding environment, with higher integrated MP community diversity observed in seawater and sediment, which exhibited broadly similar community compositions. By integrating MP pollution load, particle-specific ecological toxicity (polymer type, size, shape, and color), and co-occurring chemical pollutant risks, a multidimensional risk assessment demonstrated that environmental risk scores reflected by clams generally underestimated the actual environmental risks, with no significant concordance in overall risk patterns between clams and environmental compartments. Collectively, these findings revealed complex and dynamic interactions between MP pollution in environmental matrices and its bioaccumulation in clams. This study underscores the necessity of adopting a holistic perspective to understand the linkages between MP pollution in biota and environmental matrices and provides valuable reference for the selection of appropriate bioindicators in environmental MP monitoring programs.