Unraveling the Plastic Pollution in the Aquatic Environment of the Croatian Krk Island

The assessment of plastic pollution due to microplastics (MPs) and nanoparticles (NPs) was performed for the first time on water samples from four natural sites located near the beaches of Krk Island, Croatia, namely Melska, Črnika, rt Šilo, and Zala. MP and NP occurrence was investigated for the water samples collected during December 2022 and June 2023, using the bulk water method followed by filtration using stainless-steel sieves and the digestion process. Factor analysis and Spearman’s correlation revealed that the percentage of MP fragments correlated well with salinity (ρ = 0.76, p < 0.05) and the percentage of filaments correlated well with brown MPs (ρ = 0.80, p < 0.05). The monitoring of MPs throughout the sampling periods generally showed a decrease in abundance as the size increased. The presence of filaments indicated potential contributions from wastewater outlets, particularly from household washing machines, either directly from residents or tourists and abandoned fishing nets. The increased concentration of NPs over time could signify the continuous fragmentation of MPs in water due to natural degradation and biofilm formation on their surface. These findings could potentially be explained by the implemented plastic waste measures along the coast of Krk Island, which on 30 October 2024 was officially declared a zero-waste island.