Temporal variation in microplastic abundance in sediment, fish and shrimp: a case study in the Thames Estuary, UK

Microplastics are abundant in marine and terrestrial habitats, with rivers transporting particles to the sea. The River Thames catchment, UK, encompasses 15 million residents and many pollution sources. Temporal trends in microplastic abundance are sparse, with ad hoc studies in the estuary demonstrating great variability in concentrations. Taking a seasonal approach to time-series data collection, sediment and biota were sampled every three months over 2 yr. To account for the heterogeneity of microplastics in sediment, three grab samples were collected per survey. On average, 1000 ± 1100 (s.d.) plastic items kg^-1 were recovered from sediment, with significantly more from samples in July (summer) and September (autumn) 2020. The recorded concentrations were comparable with studies worldwide. Biota in the estuary are exposed to this plastic. Fish (<i>Osmerus eperlanus, Platichthys flesus, Solea solea</i>) and shrimp (<i>Crangon crangon</i>) contained on average 1.59 ± 2.62 items per individuals and 0.39 ± 0.95 items per individual, respectively. The greatest proportion of contaminated individuals was in December 2018 (winter; 75%) followed by March and June 2019 (spring; 42% and summer; 43%, respectively). Seasonal factors, such as rainfall, can affect plastic accumulation in an estuarine system, but these microplastics are not always bioavailable. Understanding the drivers of this variability is key in designing mitigation strategies and managing risk.This article is part of the Theo Murphy meeting issue 'Sedimentology of plastics: state of the art and future directions'.