Varying levels of microplastics in benthic sediments within a shallow coastal embayment

Microplastics are pervasive items in the environment and it has been suggested that subtidal sediments are a potential sink and hotspot areas for these pollutants. Due to logistic limitations, this environmental compartment is not routinely sampled, which is evident in the limited number of studies conducted in subtidal zones, compared to intertidal zones and open waters. In order to fill part of the knowledge gap, this study aims to determine the abundance of microplastics in subtidal sediments in a shallow coastal embayment. Sediment samples were collected using the Reineck box corer from the RV Celtic Voyager. Microplastics were extracted by density separation using sodium tungstate dihydrate (Na₂WO₄·2H₂O)). Subsequently, a subsample of fibres were confirmed as having a synthetic origin by μ-FTIR spectroscopic analysis. A relatively low abundance of microplastics was recorded, c. 73 MP/kg d.w. of sediment, with a variable range across and within stations e.g. 0.3–15.4/100 g d.w. All identified microplastics were secondary (i.e. fibres (99%), fragments (1%)), with the majority identified as polystyrene, polyester, and polyethylene terephthalate. The data in this study illustrates the need for replicates and monitoring marine sediments for microplastics.