Quantifying Microplastic Contamination in the Río Bermejo (Argentina) Compared to the River Wear, Durham (UK)

Microplastics are defined as plastic particles <5 mm, with the lower size limit defined as the pore size of the sieve used during sample preparation. There have been increasing concerns on the ecological effect of microplastics, and therefore understanding the microplastic assemblage and the sources of microplastics can help inform microplastic contamination policies. Limited studies have looked at changes in microplastic concentration along the course of a river, to assess how different factors can affect microplastic contamination. This study quantifies and compares microplastic contamination along two rivers, the Rio Bermejo, Argentina, and the River Wear, UK, which serve two different societies. This will help to address how wastewater treatment plants (WWTPs), population and anthropogenic activity can affect microplastic contamination. Sediment samples were obtained from 8 locations in the River Wear, and 6 in the Rio Bermejo. Microplastics abundances were recorded and characterized by shape, size, and colour. Microplastics were observed in all study sites across the Rio Bermejo and the River Wear. Microplastic contamination changes along the course of both the River Wear and Rio Bermejo, and is influenced by WWTPs, population and land use. The River Wear contained a higher abundance of microplastics overall (208 microplastics/100 g) than the Rio Bermejo (35 microplastics/100 g and 22 microplastics/100 g in suspended sediment and riverbank sediment respectively) due to higher urbanisation and population density. High abundances of microplastic fibres in the River Wear (93.7%) and the Rio Bermejo (100% and 76.9% in suspended sediment and riverbank sediment respectively) suggests that WWTPs are the dominant input source of microplastics in both locations. Although generally, microplastic abundances are higher in more urban areas than rural, hydrodynamic forces must be understood to better understand its effects. The microplastic assemblage observed in this study are significant when considering ecological impacts.