Integrated quantitative and qualitative analysis of microplastics in fish from the Danube River in Belgrade (Serbia)

Microplastics (MPs) are an emerging environmental concern due to their persistence, ability to act as carriers of contaminants and microorganisms, and potential impacts on aquatic ecosystems and human health. This study presents the first comprehensive assessment of MPs in common bream (Abramis brama; Linnaeus, 1758) from the Danube River that integrates both visual characterization and qualitative polymer identification using μFTIR. The presence, abundance, morphology, size, color, and polymer composition of MPs were investigated in the gastrointestinal tract of common bream collected from the Danube River in Belgrade, a river section exposed to pronounced anthropogenic pressure. Particles were detected in all analyzed specimens. In total, 88 particles were extracted from 15 fish, corresponding to a mean abundance of 5.87 ± 3.29 particles per individual (range: 2-15). Particle lengths ranged from 39 to 10,223 μm, with an average length of 1146 ± 1499 μm. Morphological analysis revealed a strong dominance of fibers (97.70%), while only two fragments were recorded. Most fibers were smaller than 2000 μm and were predominantly blue, brown, and grey in color. Chemical characterization was performed on 37 particles (∼42% of the total) using μFTIR. Cellulosic fibers represented 40.50% of identified particles, followed by polyester (27.00%) and acrylic (10.80%), while nylon, polyvinyl chloride and polypropylene were detected less frequently. These results indicate that urban river sections are important MPs hotspots, with common bream representing a species that can effectively reflect contamination in these areas. Future studies should extend spatial coverage along the Danube River and apply harmonized methodologies to improve comparability of results and strengthen assessments of MPs distribution across different riverine conditions, alongside integration of data from other biotic and abiotic compartments for a more comprehensive evaluation of riverine pollution.