Microplastics from the Danube River to the Black Sea: Transboundary Monitoring in the Lower Danube – Danube Delta – Black Sea

Abstract

Microplastic pollution is a major transboundary challenge for the Black Sea basin, with the Danube River collecting and transporting contaminants from the entire catchment towards the delta and the coastal zone. Within the Interreg NEXT Black Sea Basin project CARE SEA, transboundary microplastic monitoring was carried out along the Lower Danube – Danube Delta – North-Western Black Sea coastal area, with an emphasis on the Romania–Republic of Moldova comparison. Two sampling campaigns were conducted (May and October 2025) at nine monitoring sections, covering the Siret and Prut rivers, the Galati area, the Ceatal Chilia and Ceatal Sfântu Gheorghe bifurcations, and the discharge areas of the Chilia, Sulina, and Sfântu Gheorghe branches into the Black Sea. In the Danube Delta Biosphere Reserve, microplastic abundance ranged from 0.38 to 1.34 particles/m³ in the spring campaign and from 0.64 to 2.97 particles/m³ in the autumn campaign, with the maximum recorded at Ceatal Sfântu Gheorghe. At the branch mouths, concentrations were 1.70 particles/m³ (Sfântu Gheorghe), 1.38 particles/m³ (Sulina), and 1.34 particles/m³ (Chilia). On the Lower Prut River in the Republic of Moldova, abundance was lower (0.37 particles/m³ in spring; 0.27 particles/m³ in autumn). Polypropylene and polyethylene were the dominant polymers in Romania, and polypropylene and polystyrene in Moldova. Pollution was dominated by secondary irregular fragments and microfibres, attributed to local anthropic pressures such as wastewater discharges, poor waste management, fishing, navigation, and agricultural runoff. The results highlight the need for harmonized monitoring protocols, sustained surveillance of accumulation hotspots, and Romania–Republic of Moldova cross-border cooperation to reduce plastic inputs at the source and protect the Black Sea.