Due to the increasing global consumption, more and more packaging and other plastics are ending up
as waste. This breaks down to microplastics, entering the natural cycle and food chain, and is often
transported by rivers to the sea. Research on microplastics transport requires understanding of
spreading and dispersion of such particles due to currents, simulated using mathematical models. One
of the methods applied is the particle tracking method. By using relevant data on velocity fields in
various meteorological conditions, we can simulate particle motion in advance. We applied the model
NAFTA3d, upgraded for neutrally buoyant and negative bouyant particles. We observed motion and
concentration of discrete particles due to circulation. In simulations without meteorological extremes,
pollution moves due to the circulation throughout the Gulf of Trieste and can reach Croatia's Istria and
the Slovenian sea. In detail, we observed motion of the floating particles inflow with the Soča River
into the Gulf of Trieste in extreme wind conditions. Positively buoyant particles were mainly
transported towards the south along the Italian coast. Graphic depiction of simulation results enabled
us to illustrate motion of discrete particles. Further research on circulation in semi-closed and closed
seas is important for understanding possible contamination pathways, as well as in terms of safety and
rapid response in case of hazardous discharges and accidents.
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