Microplastic pollution in two zooplankton groups on the southern coast of the Caspian Sea

The high volume of plastic waste, especially microplastics (MPs), has caused a global concern in the last decades. The present study aims to investigate the presence of MPs in two zooplankton groups in the southwest of the Caspian Sea due to the importance of zooplankton populations in the bottom levels of the marine food pyramid and the probability of their transfer to the human food chain. The samples were collected from four stations over one year (2020-2021) using 100 μm plankton nets. After separation and assessment of MP particles, fragments and fibers were the predominant forms of MPs. Analysis of 5123 Acartia tonsa and 1528 Pleopis polyphemoides, resulted in 38 (22 fragments and 16 fibers) and 28 (15 fragments and 11 fibers) MPs, respectively, and 42 MPs (24 fragments and 17 fibers) in the seawater. The average size of the ingested pieces in the zooplankton communities was in the range of 35-46.5 μm and 56.25 μm in the seawater in four stations. The most commonly observed colors in A. tonsa were orange and white, and black in P. polyphemoides and seawater. The samples were also inspected using FTIR-ATR method and confirmed the presence of polymeric compounds and the probable types of polyester, polyethylene, and polyethylene terephthalate in the zooplankton and seawater samples at all stations. Since seafood is an important source of nutrients in coastal areas, the polymers present in the zooplankton's bodies can transfer to higher trophic levels, including humans.