Influence of mesh selectivity on risk assessment of marine microplastics

In this study, environmental microplastic samples (>30 μm) were collected from surface seawater and the water column, characterized, and used to assess ecological risks. The influence of mesh selectivity on ecological risks was also evaluated through subsampling. Results show that surface microplastic concentrations (>30 μm) range from 92 to 3306 pieces/m³ along Japan's southwest coast, with significant increases at Stas. 2 and 1. Subsurface vertical concentration near Okinawa ranges from 991 to 1992 pieces/m³, with denser, more toxic polymers more frequently observed in deeper waters, suggesting that polymer types may be sorted by marine structure. Risk assessments revealed very high risks near main islands and populated regions, while remote regions had lower risks. Further analysis revealed that ecological risk estimates are significantly influenced by mesh selectivity, with variations in particle size distribution and polymer type composition resulting in changes of up to 100-fold at the same location when different mesh sizes were used, suggesting that current framework is not ideal for risk assessment of microplastics. This study is the first to demonstrate that samplers with different mesh sizes can lead to substantial differences in risk assessments, even at the same location. These findings underscore the critical impact of mesh selectivity on ecological risk estimates and highlight the need for standardized sampling protocols in microplastic research.