The presence of microplastics (MPs) in the aquatic environment has been intensely studied in recent years due to their potential threat to living organisms. Due to their small size and relatively large surface area, MPs act as carriers of other particles, adsorbing and transporting various pollutants such as heavy metal ions, organic micropollutants and pathogenic organisms. This study aimed to determine the abundance and characteristics of MPs in a peri-urban river that receives wastewater effluents. Samples were collected from upstream and downstream of the wastewater treatment plant. Particles isolated from the river were examined using an optical microscope (OLYMPUS BX 51 M, Olympus Corporation, Tokyo, Japan), operated with Olympus Stream Essential 1.9.3 software, using X100 magnification. The total number of MPs varied between 15 and 45 for upstream samples and between 16 and 26 for downstream samples. In both cases, most particles were detected in samples taken in winter, and the lowest abundance of particles was recorded in spring and summer in the case of upstream samples, and in summer in the case of downstream samples. Microscopic analysis revealed a prevalence of fibers (88.39% for upstream and 85.71% for downstream). Lower quantities were observed for the other types of MPs: 8.04% fragments and 3.57% films upstream, and 4.4% fragments and 9.89% films downstream. Moreover, an increased abundance of fibers was noted during autumn and winter for both sampling sources. The seasonal variations in MPs concentrations detected at both sampling points suggest that there is a direct influence of anthropogenic activity in the area. Moreover, the abundance of fibers highlights that one of the main sources of MPs is represented by water discharged from washing machines.

This research was funded by the Ministry of Education and Research, grant number OPTRONICA VII PN23 05 (11N/2023).