Microplastic content of Kutum fish, Rutilus frisii kutum in the southern Caspian Sea

Highlights: • Microplastics were ingested by 80% of investigated Kutum fish. • Ingested MPs were mainly fibers followed by fragments and synthetic microbeads. • More than half of MPs were less than 500 μm and possessed light colors. • Strong carbon and oxygen peaks confirmed them as synthetic polymers. • MP surfaces revealed various degrees of erosions upon environmental exposure. The occurrence of microplastics (MPs) in the digestive tract of commercial Kutum fish, Rutilus frisii kutum was investigated. Fish samples, ranging from 33 to 48.5 cm fork length which sold for human consumption, were collected from local fish markets in Bandar-e Torkaman (the south-eastern of Caspian Sea) on November 2017, and March 2018. The MPs were characterized using optical microscopy, NR staining, and SEM-EDS for number, shape, color, surface morphology, and elemental composition. On average, 11.4 MP items per fish (0.015 items per 1 g fish wet weight) were found in Kutum's stomach at an individual detection rate of 80%. Around 66% of all identified MP items were < 500 μm, and 53% possessed light colors. Morphological researches indicated that fish ingested the degradation fragments from larger plastic pieces, fibers, and manufactured microbeads. Microfibers are the most dominant items accounting for over 75% of all MPs. The SEM images indicated the various degrees of erosions upon environmental exposure. Some MPs had surface cracks, broken margins, scaly appearances, and obvious pores. Considering the commercial importance which the Kutum plays for Iran's fishery, the potential effect of MPs on the trophic food web, particularly for human consumption and health, should be urgently investigated.