Microplastics in commercial marine fish species in the UK – A case study in the River Thames and the River Stour (East Anglia) estuaries

The aim of this study was to assess the abundance of microplastics in the gastro-intestinal tracts of three commercially important fish species in the UK, to determine whether catch location, feeding habits and fish size influence the amount of microplastics within fish. Fish were collected from two rivers in the UK: the River Thames and the River Stour (East Anglia). Fish were collected from two sites in the River Thames and one site in the River Stour. Species selected were European flounder (Platichthys flesus), whiting (Merlangius merlangus), and Atlantic herring (Clupea harengus), and were chosen to represent benthic and pelagic feeding habits. Across all locations, 41.5 % of fish had ingested at least one microplastic particle (37.5 % of European flounder, 52.2 % of whiting, and 28.6 % of Atlantic herring). The average number by species was 1.98 (±3.50) microplastics/fish in European flounder, 2.46 (±3.10) microplastics/fish in whiting and 1.47 (±3.17) microplastics/fish in herring. There were no significant differences in the number or mass of microplastics in fish based on river, site, species or habitat. However, the number and mass of microplastics within benthic fish (European flounder) in the River Stour were significantly higher than in benthic fish from the River Thames. By number of microplastics, larger and heavier fish were more highly contaminated. This study enhances our understanding of microplastics in commercially important fish but highlights that fish contamination is not easily predicted by feeding habits or catch location alone. Exposure and uptake is likely to vary with changing environmental conditions. Fish size tends to be a good predictor of contamination, with larger fish generally containing more microplastics. This is the first study to directly compare concentrations of microplastics in fish from different UK rivers and the first evidence of microplastics in the River Stour.