Evidence of elevated microplastic accumulation in Pacific Island mangrove sediments

Although microplastics (MPs) in the environment are well-reported, there is a geographical research gap, particularly in Pacific Island Countries and Territories. Recognising the critical role mangroves play in regulating the exchange of sediment and pollutants between land and ocean, we conducted research in Fiji to compare levels of sediment MPs within mangroves with those in surrounding sediments, and to assess differences between urban and rural areas. MPs were found to be significantly higher in sediments collected inside the mangroves (13.79 ± 1.24 N kg^-1 dw) compared to the non-mangrove treatments (adjacent [1.42 ± 0.26 N kg^-1 dw] and seaward areas [2.14 ± 0.40 N kg^-1 dw]) (GLMM p = 6.82e-12). Findings were consistent between urban and rural areas (GLMM p > 0.137). The most prevalent form of MPs was fibre (84 %), and the predominant polymers were polyethylene terephthalate (30.7 %) and polypropylene (16.2 %). Comparisons made between MPs forms and polymer types suggest that MPs found along these coasts are closely linked to human activities in the respective areas. Conclusively, mangroves play an important role in entrapping MPs, thus containing the pollutants within the mangrove sediments rather than them being further distributed across the oceans.