Microplastics in different tissues of some commercially important fish species from Anzali Wetland in the Southwest Caspian Sea, Northern Iran

Highlights: • This is the first study on microplastic pollution in different tissues, especially gonads of fish from Anzali Wetland. • More particles were found in omnivorous than in carnivorous fish. • PE and PP were the most dominant polymers in MPs found in fish tissues. The aim of this study was to investigate the occurrence of microplastics (MPs) in the gastrointestinal (GI) tract, muscle and gonads of 193 individuals of nine commercially-important fish species from Anzali Wetland between May and July 2018. Tissues were removed, digested by 10% KOH for 24 h at 60 °C, filtered on cellulose nitrate filter and then dried. MPs were found in all tissues. There were significant differences between the numbers of isolated particles from GI tract and control groups (procedural blank containing Milli Q water without tissue), while their abundance in the muscle and gonads did not display significant differences with control groups. Higher abundances of MPs were recorded in omnivorous fish (2.26 ± 2.93 items/individual) than carnivorous species (1.10 ± 1.10 items/individual) (P < 0.05). MPs were ranged from 20 to 4800 μm in size and were dominated by fiber-like in shape, polyethylene in polymer and black in color.