Sources and hotspots of microplastics of the rivers ending to the southern Caspian Sea

The occurrence of microplastics (MPs) in beach sediments of the southern Caspian Sea was well documented, however, there are still many unknowns about the abundances and distributions of MPs in the rivers ending to the Caspian Sea. Here, bank sediments of 26 sites in the thirteen rivers were surveyed in two seasons. However, there was not any significant difference (p > 0.05) between the concentrations of MPs during the two seasons. MPs were detected in all samples with mean concentrations of 214.08 +/- 14.35 MPs/kg. The most common size, shape, color, and polymer types of MPs were L < 300 mu m, fragment/film, white/transparent, and polystyrene (PS), respectively. In all rivers, positive MP gradients from upstream to downstream were observed. Maximum concentrations of MPs were found in the downstream parts of Chalus, Haraz, and Safarud rivers. Recreational-tourism and fishing activities had significant positive relationships (p < 0.05) with concentration of MPs in the rivers.

Automated summary

The presence of microplastics (MPs) in beach sediments of the southern Caspian Sea has been confirmed, but there are still uncertainties regarding the abundance and distribution of MPs in the rivers that flow into the Caspian Sea. This study surveyed the bank sediments of 26 sites in thirteen rivers during two seasons, and found no significant difference in MPs concentrations between the seasons. MPs were detected in all samples, with an average concentration of 214.08 +/- 14.35 MPs/kg. The most common characteristics of MPs were size L < 300 μm, shape fragment/film, color white/transparent, and polymer type polystyrene (PS). Positive gradients of MP concentrations from upstream to downstream were observed in all rivers, with the highest concentrations found in the downstream parts of Chalus, Haraz, and Safarud rivers. Recreational-tourism and fishing activities were significantly associated with MPs concentrations in the rivers.