Hydro-sedimentary conditions shape the microplastic occurrence in sediments of the Pearl River Estuary (China)

Currently, research on the link between hydro-sedimentary conditions and microplastic prevalence in estuarine sediments remains scarce. This study focused on influencing mechanisms of microplastics in surface sediments of the Pearl River Estuary (PRE; South China), based on the field investigation. The results show that microplastics abundance in sediments spanned from 4 to 220 particles per kilogram (n/kg), with an average of 62 n/kg, and exhibited a distinct spatial gradient-higher in nearshore zones and lower offshore. In terms of morphology, microplastics were dominated by fragments (53 %) and fibers (46.3 %); in terms of color, white and black were primary; most microplastics were <2 mm in size; and polymer types were polypropylene (51.8 %) and polyethylene (18.5 %). Bottom-water hydrodynamics and sedimentary environments have significantly influenced the distribution of microplastics. Pearson correlation analysis revealed that median particle size (Md) of sediments and BOD were negatively correlated with the microplastics abundance, while petroleum was positively correlated, highlighting key factors directly linked to distribution. Principal component analysis (PCA) clarified distinct factor groupings between microplastics and environmental factors at the shoals and troughs of the PRE, with their different hydrodynamics and sedimentary environments. Structural equation modeling (SEM) further quantified specific pathways and intensities of these factors on microplastics, identifying hydro-sedimentary conditions as the dominant driver, and providing critical insights for understanding the environmental behavior of microplastics in estuarine sediments. Collectively, these findings not only deepen understanding of microplastics environmental behavior in estuarine sediments but also provide a scientific basis for targeted monitoring of microplastics pollution in estuaries.