Microplastic occurrence in coastal waters and aquatic faunas of the Western Black Sea 

The Danube River, an important pathway connecting the western, central, and eastern Europe, serves as a route for various pollutants that ultimately accumulate in the Danube Delta and the broader Black Sea basin. These historically pristine regions now face escalating pressures from extensive tourism, intense fishing activities, regional conflicts, and inadequate waste disposal across the whole Danube basin. The imbalance in sediment flow, mainly caused by numerous upstream hydropower plants, aside the abovementioned anthropogenic factors, poses a severe threat to the deltaic and coastal ecosystems.Among the emerging pollutants, litter stands out prominently, with anthropic macro-objects pervading natural environments. Microplastics (MPs) constitute a category of the litter, characterized by solid, petroleum-based items sized between 1 µm and 5 mm. These particles are either preformed within these dimensions or result from the fragmentation of larger plastic debris due to natural weathering. Known for their fast spreading across diverse environments, MPs possess a porous texture that might absorb substantial amounts of various pollutants, significantly impacting the entire food chain, particularly aquatic species.Given the limited data on MPs pollution in Black Sea coastal areas, the precise impact on the natural environment remains largely uncertain. Furthermore, the correlation between MPs pollution in aquatic environments and the concentration of MPs within mussels and fish has yet to be established. To address these knowledge gaps, our study investigated the abundance of MPs in the water surface layer (average concentration of 0.63 MPs/m³) and in two distinct species: (i) the mackerel - Alosa immaculata – a pelagic fish captured at the Saint Geoge branch mouth of the Danube Delta during inland migration for reproduction, with an average concentration of 11.8 MPs/individual, and (ii) Mytilus galloprovincialis – a filter feeder mollusc collected near the Constanța harbour – with an average concentration of 6.05 MPs/individual.Our findings indicate that fibers represent the predominant morphology of MPs found in both species, while fragments dominate the surface water layer. Notably, before the tourist season, the distribution of MPs types differs, suggesting potential influences from coastal natural factors such as wind, waves, and currents on the variety of MPs encountered. This research underscores the urgency of further investigations to comprehend the intricate dynamics of MPs pollution in these vital ecosystems and the cascading effects on marine life.