Microplastics pollution alters bacterial community in hyporheic sediments: A case study from the Beiluo River Basin

Microplastics (MPs), as emerging contaminants, are widely present in rivers and accumulate in hyporheic zone sediments through processes such as aggregation and sedimentation. They pose ecological and biological risks, significantly influencing bacterial communities. However, research on the impact of MPs on bacterial communities in riverine hyporheic zone sediments remains relatively limited. This study investigated the distribution characteristics of MPs in the sediments of the Beiluo River hyporheic zone and explored the relationships between environmental factors, bacterial communities, and MPs based on the field investigation. The results showed that the average abundance of MPs was 18.41 ± 18.94 items·g^-1, exhibiting moderate pollution. The dominant polymer type of MPs was Polyethylene terephthalate (PET, 44%), with particles smaller than 30 μm (52%) constituting the majority. The properties of MPs, particularly polymer types and particle size (<30 μm), are key drivers of bacterial community structure in the hyporheic zone. Bacterial responses to MPs exhibit clear polymer specificity. Acidobacteriota and Methylomirabilota show positive correlations with PET but negative correlations with Polypropylene (PP) and Polytetrafluoroethylene (PTFE). Furthermore, MP diversity is significantly negatively correlated with bacterial α-diversity. Partial least squares path modeling further indicates that sediment properties indirectly influence bacterial communities by regulating MP diversity and polymer composition, while MP diversity significantly suppresses both the structure and diversity of these communities. This study provides critical insights into the ecological risk assessment of MPs in the hyporheic zone sediments of the Beiluo River and reveals the potential impacts of MPs on bacterial communities.