MICROPLASTIC DYNAMICS IN SURFACE WATERS OF THE TOM RIVER (2021–2023)

Abstract

Rivers are important transport pathways for microplastics to reach the seas and oceans, as well as important sinks and reservoirs for plastic particles smaller than 5 mm along the longest axis. Three-year monitoring of microplastics in the 0.15–5 mm size range was conducted in surface waters of the Tom River (a first-order tributary of the Ob River) to assess seasonal and inter-annual dynamics. The analysis identified fibers as the most common shape and polyethylene terephthalate (PET) as the dominant polymer. However, particles of other shapes and diverse compositions were also detected. During the 2021–2023 observation period, the maximum absolute concentration of microplastics (up to 9.98 ± 2.47 items/m3) was recorded in the Tom River in 2022 during the winter low-water period. In terms of mass, the maximum average value (2.34 mg/m3) was observed in August 2022. The minimum absolute concentration of 0.35 ± 0.07 items/m3 was found in September 2023, and the minimum concentration of microplastics in mass units of 0.29 ± 0.18 μg/m3 – in April 2022. However, the total particle concentration in surface waters did not reliably depend on the hydrological regime. The average nominal microplastic concentration between years depends on the contribution of smaller particles, particularly spherical ones, as observed in 2021. Inter-annual differences in microplastic mass were insignificant. The concentration of microplastics in the form of spheres and films showed a reliable correlation with the water level and discharge rate (rs > 0.6, р < 0.01), which suggests that these particles are flushed from floodplain areas. The obtained data can be used to model microplastic transport in rivers and quantify individual links in the global plastic cycle.