The distribution and abundance of microplastics in the waters and organisms of the River Thames, UK.

A ubiquitous contaminant across the globe, microplastic contamination is a growing issue of which the effects and consequences in the environment are relatively unknown. Freshwater systems, specifically rivers, are important in the translocation of microplastics from terrestrial sources to the marine environment. This makes it vital to understand the abundance and distribution of plastics within them and any potential effects on freshwater organisms. The River Thames is the second largest river in the UK and has multiple anthropogenic stressors and pathways of potential microplastic contamination along its trajectory. This study aims to determine the distribution and abundance of microplastics in the waters and benthic organisms that inhabit the River Thames. It will explore how location and proximity to sites of potential contamination, and feeding type influence the ingestion of microplastics in organisms. Water samples were collected from the river in May 2019 along with benthic dwelling organisms from 3 sites of suspected microplastic contamination. Initial findings reveal a high abundance of microplastics in water samples from the River Thames (average 3.55 mp/m³) and abundance increases along the trajectory of the river (1.05 mp/m³ at the highest sampling site increasing to 5.72 mp/m³ at the lowest sampling site). In all sites sampled, fragments and fibres were the most dominant particle shapes. Filter feeders ingested the highest abundance of microplastic fibres whilst grazers had the highest abundance of ingested fragments. The abundance of particles ingested by invertebrates differed across study sites showing varying levels of contamination. The presence of microplastics in a range of benthic taxa aligned with differences in dominant particle shapes in species with distinct feeding modes indicates widespread contamination with potential ecological impacts of microplastics in freshwater species of the River Thames.