Microplastic Pollution in Mangrove-Adjacent Coastal Environments and Apparent Polymer Mass Loss in Mangrove Sediment Microcosms: A Case Study from Xiatanwei and Wuyuanwan

Microplastic pollution has emerged as a global environmental concern, with mangrove wetlands serving as both sinks and potential bioremediation sites for plastic debris. This study investigated microplastic contamination in water and sediment samples from Xiatanwei mangrove wetland and Wuyuanwan, China, and further examined the degradation of four types of microplastics—polyethylene (PE), polystyrene (PS), polyamide (PA), and fishing net fragments—in mangrove sediment microcosms over a 6-month incubation period. Across the three sediment zones sampled in Xiatanwei, the mean NaCl-recoverable microplastic abundance was approximately 483 items/kg, which was lower than the mean value of 935 items/kg previously reported for the Jiulong River estuary. Water samples from Wuyuanwan revealed a spatial distribution pattern with the highest abundance at the bay mouth (1661 items/m³), followed by the outer bay (1297 items/m³) and the inner bay (1056 items/m³), suggesting complex hydrodynamic influences on microplastic distribution in semi-enclosed bay systems. The 6-month incubation experiment demonstrated that PS exhibited the highest weight loss (6.02% ± 1.66%), followed by PE (3.07% ± 0.86%), while PA (0.56% ± 0.18%) and fishing net (0.52% ± 0.05%) showed minimal degradation. These findings confirm that mangrove sediments possess intrinsic microplastic-degrading capacity, though the extent varies significantly by polymer type. This study provides empirical evidence supporting the role of mangrove wetlands in microplastic trapping and degradation, with implications for coastal pollution management.