Quantification and composition analysis of plastic pollution in riverine beaches of the lower Paraná River, Argentina.

Plastic pollution and the numerous consequences it has on aquatic life have become a huge concern in recent years. While many studies have been conducted in marine environments, studies in freshwater ecosystems are scarce and insufficient. The Paraná River is the most important water course in the La Plata River basin and the fifth in the world with a mean annual discharge of 18,000 m3 per second. Currently available studies show the presence of plastic in river shores and fish gut, but more research should be carried out in order to know the extension and origin of plastic contamination. Therefore, the aim of this study was to quantify and characterize macro-, meso-, and microplastics found in the riverine beaches next to Rosario city, the most populated city standing by the lower Paraná River coast in Argentina. The results show that plastic pollution is ubiquitous, but the city shores are significantly more polluted than the wetland shore with a mean of 30,780 and 6375 microplastics per square meter respectively (p = 0.024). The food and beverage industry packaging combined were the most frequent macroplastics found. Also, 3 out of 4 meso- and microplastics were white/transparent, the color that is most likely to be ingested by fish and invertebrates. Finally, all micro- and mesoplastics found were secondary and, in the case of microplastics, they were mainly fibers (93.4%) which highlight its ecological relevance. As a whole, plastic contamination is a serious issue in the Rosario area, specially single-use plastics and short-lived products. The anthropic effect of the cities and how it contributes to plastic pollution are evident.

First DNA Barcode Reference Library for the Identification of South American Freshwater Fish from the Lower Paraná River.

Valid fish species identification is essential for biodiversity conservation and fisheries management. Here, we provide a sequence reference library based on mitochondrial cytochrome c oxidase subunit I for a valid identification of 79 freshwater fish species from the Lower Paraná River. Neighbour-joining analysis based on K2P genetic distances formed non-overlapping clusters for almost all species with a ≥99% bootstrap support each. Identification was successful for 97.8% of species as the minimum genetic distance to the nearest neighbour exceeded the maximum intraspecific distance in all these cases. A barcoding gap of 2.5% was apparent for the whole data set with the exception of four cases. Within-species distances ranged from 0.00% to 7.59%, while interspecific distances varied between 4.06% and 19.98%, without considering Odontesthes species with a minimum genetic distance of 0%. Sequence library validation was performed by applying BOLDs BIN analysis tool, Poisson Tree Processes model and Automatic Barcode Gap Discovery, along with a reliable taxonomic assignment by experts. Exhaustive revision of vouchers was performed when a conflicting assignment was detected after sequence analysis and BIN discordance evaluation. Thus, the sequence library presented here can be confidently used as a benchmark for identification of half of the fish species recorded for the Lower Paraná River.