Widespread occurrence of microplastics in marine bays with diverse drivers and environmental risk

Microplastic contamination in the sediment of marine bays has attracted widespread attention, whereas the distribution, sedimentation, morphology and risk of microplastics at regional scale remain poorly understood. By introducing a data mining framework into microplastic research, we compiled a microplastic dataset of 649 samples from 24 bays to enhance the understanding of geographical difference and drivers, transfer, composition profile and environmental risk of sedimental microplastics. Microplastic abundance varied from 0.72 to 1963.96 items/kg dry weight, with higher concentrations mainly occurring in East Asian bays. The spatial pattern in abundance was driven by the river plastic emissions, aquaculture production and hydrodynamic condition. A significantly positive correlation between microplastic abundance in water and sediment was found, and microplastic sedimentation was related to polymer density, hydrodynamic conditions and sediment properties. The dominant shape and polymer of sedimental microplastics were fiber and polypropylene, respectively, and the similarity of microplastic composition decreased with increasing geographical distance. The environmental risks of microplastics were partitioned into three classes (Rank II-Rank IV) with a two-dimensional assessment system considering the bioavailability and toxicity of microplastics, and Asian bays were identified as potential high-risk areas. To reduce the environmental risk of sedimental microplastics in bays, priority should be given to the removal of microfibers, and control measures depend on the risk classes and dominant polymers. Microplastic abundance and composition were significantly affected by methodological choices regarding sampling, pretreatment and identification, suggesting a unified methodology is essential to further enhance our knowledge on the distribution and risk of microplastics in marine bays.

Automated summary

Microplastic contamination in marine bays has been widely studied, but their distribution, sedimentation, morphology, and risk at a regional scale are not well understood. In this study, a microplastic dataset of 649 samples from 24 bays was compiled using a data mining framework. The study found that microplastic abundance varied across different bays, with higher concentrations in East Asian bays. The abundance was driven by river plastic emissions, aquaculture production, and hydrodynamic conditions. The dominant shape and polymer of microplastics in sediment were fiber and polypropylene, respectively. Environmental risk assessment identified Asian bays as potential high-risk areas. The study highlights the importance of a unified methodology for sampling, pretreatment, and identification to enhance our knowledge on microplastic distribution and risk in marine bays.