Linking human activity to spatial accumulation of microplastics along mangrove coasts

Microplastics (MP) in mangrove coasts are threating ecological health and seafood safety. However, quantitative evidence on the effects of different coastal human activities on microplastic accumulation in mangrove sediments is lacking, thereby impeding the policy development of evidence-based waste management. In this study, continuous geographical sampling (N = 50) was applied to collect sediments from the largest mangrove coast, namely the Leizhou Peninsula in China. Similar worldwide research data (16 mangrove coasts) were collected from the Science Citation Index Expanded (SCIE) database of the Web of Science. The connections between human drivers and microplastic accumulation were evaluated by spatial comparison, multi-correspondence analysis, and multiple differences analysis. The microplastic abundance fluctuated widely along the mangrove coasts (average value was 51.24, ranged from 6.40 to 255.57 items·kg^-1 dry weight; coefficient of variation = 97%) with a globally lower-middle concentration in sediments of the Leizhou Peninsula. Densely populated urban residents and the floating population of tourists largely contributed to the high abundance of microplastics in mangrove sediments, of which large-sized (1-5 mm) white foams were the dominant type. Although suburbs had less crowds, both onshore and offshore fishery production could cause high accumulation of microplastics in neighboring mangrove coasts, which were characterized by small-sized (<1 mm) fragments with fresh color. Small microplastics (80%) with fresh color (44%) were dominant. Weathering may break down more toxic particles in urban areas neighboring mangrove coasts. Larger mangrove patches could partly block ocean-based microplastics; however, coasts surrounded by more geographical barriers had intensified pollutant accumulation. It was suggested that foam packaging of commodities for urban residents and tourists in popular tourism areas should be reduced and restrictions of fishery waste plastics are needed along shores with mangroves, especially in coasts surrounded by more geographic barriers.