Microplastics in wild Saccostrea cucullata oysters in Sri Lanka: Pollution status and risk assessment

Microplastics (MPs) have widely been reported in many marine organisms that cause significant environmental concern. Oysters are known to accumulate MPs through their filter-feeding mechanism yet studies focused on MPs pollution in oysters along with ecological risk assessment are scarce. In this study, we investigated MPs pollution in wild Saccostrea cucullata oysters and assessed the ecological risk of MPs pollution in oysters and their habitats along the southern and western coasts of Sri Lanka. Oyster MPs abundance varied from 0.63 to 2.20 particles g⁻¹ wet weight (ww), which showed a significant positive correlation with MPs abundances in surrounding surface seawater and surface sediment. The average MPs abundances in oysters, surface seawater and surface sediment showed significant spatial differences where high MPs abundances were reported in areas that had high anthropogenic activities. Size classification of MPs revealed that small size (100 μm-1 mm) blue fibres were dominant in oysters, surface seawater and surface sediment likely due to the high abundance of discarded fishing nets in studied areas. The abundance of various polymer types indicated that low-density polyethene polymers were most abundant (oysters, 45.74 %; surface seawater, 42.91 % and surface sediment, 39.62 %). Results of the ecological risk assessment indicated that MPs pollution in the environment was low (Level I). However, MPs pollution in oysters ranged from low to moderate risk levels (Level I-II), where moderate risk was reported in the areas with high MPs contamination. Therefore, our study highlights that mitigation of MPs pollution on the southern and western coast of Sri Lanka is important to alleviate the increasing ecological risk of MPs pollution in Saccostrea cucullata.