Microplastics in Sediments of Southwest Caspian Sea: Characteristics, Distribution and Seasonal Variability

Microplastics (MPs) are recognized as an emerging contaminant posing a potential threat to the marine environments. Although marine MPs have been reported in different aquatic ecosystems of the world, research on the seasonal distribution of MPs is still relatively limited. Therefore, this study aimed to investigate MPs pollution in sediments of southwest coast of the Caspian Sea in different seasons between April 2019 and February 2020. Sediment samples were collected from three stations using Van Veen grab 20 × 20 cm, dried at air temperature, segregated by NaCl 1.2 g cm−3, filtered on filter paper and then observed under stereoscopic microscope. MPs were existed in all seasons and sampling sites. The average abundance of MPs was 397.7 ± 66.93 items/kg, and the highest concentration was detected at the Astara station by 996 ± 55.07 items/kg. Dominant frequency of MPs in different seasons were as follows: winter > summer > autumn > spring. MPs were dominated by class 1000–2000 µm in size, fiber in shape, polypropylene in polymer and red in color. High water level in winter followed by increasing MPs transmission from urban areas as well as fishing activity could be the main reasons for high MP concentrations in the studied areas.