Characteristics and Seasonal Distribution of Microplastics in the Surface Waters of Southwest Coast of the Caspian Sea (Guilan Province, Iran)

The aim of this study was to investigate the occurrence, abundance and distribution of microplastics (MPs) in the southwest coast of the Caspian Sea in four seasons. Three stations were chosen and their surface waters were sampled between April 2019 and February 2020. The average number of MPs was 1.37 +/- 0.47 items/m(3) and the predominant frequency in different seasons were as follows: summer > autumn > spring > winter. MPs were dominated by fiber in shape. Black and blue were the most common colors respectively. The size was in the range of 0.3-5 mm with a mean of 1.44 +/- 1.08 mm. Due to Fourier-transform infrared spectroscopy equipped with attenuated total reflection (ATR-FTIR), four different polymers were identified dominating by polypropylene. The low MP concentrations detected in the present study can be related to lower sewage inlet and more MPs sedimentation in the investigated stations.

Automated summary

The study investigated the presence, abundance, and distribution of microplastics (MPs) in the southwest coast of the Caspian Sea. Results showed that MPs were predominantly fibers in shape, with sizes ranging from 0.3-5 mm and black and blue being the most common colors. Fourier-transform infrared spectroscopy identified polypropylene as the dominant polymer. The low concentrations of MPs detected were attributed to lower sewage input and increased sedimentation in the investigated stations.