Surface-Water Microplastics in the Pearl River Estuary and Beibu Gulf: 2024–2025 Observations in a Long-Term Monitoring Context

Microplastic pollution in marine ecosystems poses significant ecological and public health risks. However, long-term monitoring datasets remain scarce, limiting our understanding of the temporal variability in coastal microplastic pollution. Here, surface-water microplastics were investigated in the Pearl River Estuary (PRE) and the Beibu Gulf (BBG) during the August surveys of 2024 and 2025 and compared with previously published observations from 2019–2023, providing a broader temporal perspective on microplastic pollution in the northern South China Sea. Temporal changes in microplastic abundance, spatial distribution, physical characteristics and polymer composition were evaluated. Microplastic abundance was higher in the PRE than in the BBG in August 2024, whereas comparable levels were observed between the two regions in August 2025. In contrast, physical characteristics varied among survey years, with the available observations suggesting increasing proportions of fragments and films, accompanied by variations in particle size distribution. Polymer composition remained dominated by polyethylene terephthalate, polypropylene, polyethylene and polyamide, while a broader range of polymer types, including engineering polymers (e.g., polyether urethane and alkyd resin), was detected in the August 2025 survey. Overall, different microplastic characteristics exhibited distinct temporal and regional patterns, indicating that abundance alone does not fully characterize the variability in coastal microplastic pollution. Integrating abundance, physical characteristics and polymer composition into sustained monitoring can provide a more comprehensive basis for evaluating temporal and spatial patterns of coastal microplastic pollution.