Pilot study on microplastics in the Suquía River basin: Impact of city run-off and wastewater treatment plant discharges in the mid-2010s

The presence of microplastics (MPs) in both water and sediment has been extensively reported in marine environments, with fewer works on their presence in rivers, particularly in rivers affected by semi-arid conditions. It is likely to expect a different behavior of MPs in the sea with respect to a river, mainly because of differences in the hydrology, salinity, etc. Thus, our main goal was evaluating the presence and behavior of MPs in a river belonging to a semi-arid region (Suquía River, Province of Córdoba, Argentina), looking to assess the main sources of MPs and verifying their changes along a river section that includes a big city and its wastewater treatment plant (WWTP). Sampling was performed in October 2016, with the river at its lower flow. Results show that MPs are present in high amount throughout the studied river basin, even upstream from the main city. The WWTP was identified as one of the main sources of MPs to the stream, but the city run-off was the responsible for the higher amount of MPs in sediments. Our results show qualitative and quantitative differences with other reports on MPs in water and sediment of rivers, having a range of MPs that exceeds most previous reports in rivers. Furthermore, among MPs found, fibers were more abundant than plastic fragments, triggering the need for a deep evaluation of probable negative effects of fibers on the aquatic biota.