The influence of microplastic polymer characteristics on estuarine phosphorus dynamics through microbial mediation: A...

Microplastic pollution poses significant threats to estuarine ecosystem. However, the mediating role of microbial communities in linking polymer characteristics to nutrient dynamics remains poorly understood. This study investigates how microplastic characteristics, rather than abundance alone, influence nutrient dynamics via microbial mediation in an anthropogenically impacted estuary, the Pearl River Estuary (PRE). Comprehensive spatial surveys revealed heterogeneous microplastic distribution (0-3.20 items/L), dominated by polyethylene (PE), polybutene (PB), and poly(vinylidene chloride-co-acrylonitrile) (PVDC-AN), with blue and black as the most prevalent colors. The observed spatial patterns of polymer type and color correlate with known industrial zones and urban centers, whereas morphology and size patterns reflected hydrodynamic and topographic constraints. Critically, microplastic abundance exhibited negative correlations with water quality parameters, particularly total phosphorus (TP). High-throughput 16S rRNA sequencing showed that polymer type and color were key factors structuring these specialized communities, selecting for the distinct bacterial taxa. Specifically, PVDC-AN enriched Cyanobiaceae and Rhodococcus degraders, while PB favored hydrophobic colonizers like Flavobacteriaceae. Blue microplastics also modulated communities through bacterial photoreception pathways. Through partial least-squares-path modeling, we suggested that microplastics may indirectly affect TP through polymer-specific microbial mediation, with additional influence from physicochemical variables. This work provides the first field-based evidence suggesting that specific microplastics may act as selective microhabitats within the estuary, potentially contributing to nutrient cycling even at low over abundance. Our findings underscore the need for polymer-specific risk assessments and highlight microbial mediation as an essential pathway through which microplastics influence eutrophication in urbanized coastal systems.