Microplastic accumulation in a mixed species seagrass bed in the Tamar Estuary, Torpoint, Cornwall, UK

Microplastic pollution is a major threat to UK seagrass habitats, which provide essential ecosystem services by supporting biodiversity and economically valuable fish species. Seagrass beds, acting as long-term ‘sinks’ for microplastics due to their dense canopies face a high risk of degradation. This study investigated microplastic accumulation in the sediment of a mixed species (Zostera marina and Nanozostera noltei) seagrass bed in the Tamar Estuary, Southwest England, considering the effect of sediment particle size. Microplastics were extracted by density separation using Sodium Bromide (NaBr) and sediment particle size analysis was used to investigate the seagrass bed sediment. FT-IR analysis was used to identify polymers, and microscopy was used to quantify plastic particles. Microplastics were found in all samples ranging from 33.34kg-1 to 1033kg-1 of dry sediment, with blue fibres (45%) proving the most common. ANCOVA revealed a positive relationship between seagrass bed density and microplastic accumulation (p<0.005). FT-IR results indicate microplastic particles originate from a range of anthropogenic sources mostly associated with land, which highlight the need to investigate the transport routes of microplastics into water bodies. These findings highlight the urgency to assess microplastic pollution in the Tamar Estuary’s seagrass habitats to inform conservation strategies and protect at-risk organisms from habitat degradation and bioaccumulation, this includes identifying potential sources of microplastic pollution and the need for ongoing monitoring and research.