A first comprehensive quantification of microplastic contamination in the gastrointestinal tract of endangered caspian seals (Pusa caspica) from the Caspian Sea

Microplastics (MPs) are considered a serious threat to the Caspian seal (Pusa caspica), an endangered species, apex predator, and bioindicator in the Caspian Sea. The first assessment of MP ingestion in Caspian seals is presented in this work. For this purpose, the gastrointestinal tracts (GITs) of 17 Caspian seal carcasses along the southern Caspian Sea coast were examined. Alkaline digestion and density separation methods were used to extract MPs. The morphology, size, and color of particles larger than 50 μm were visually detected and categorized, and Fourier-transform infrared (FT-IR) spectroscopy was utilized to confirm the polymer composition. A total of 174 MPs were found in the GITs of all seals, with a mean of 10.2 ± 5.1 MPs/GIT and 0.87 MPs/g of dry content. There was no significant difference in MP levels in the GIT between males and females. The stomach had the highest particle density (0.93 ± 0.11 MPs/g), while the large intestine had the highest total number of MPs (104 particles). In terms of morphology, fibers predominated (52.3 %), followed by fragments (31.6 %) and films (16.1 %). The majority of MPs were tiny, with 85 % of them being between 0 and 2 mm. Polyethylene and polyester have been determined to be the most abundant polymers, containing more than 58 % of the MPs. The most present particle color (43.7 %, n = 76) was black. This study shows that MPs are widely and diversely present in Caspian seals, which is a serious warning for the survival of this vulnerable species.