Plastic ingestion by the Wels catfish (Silurus glanis L.): detailed chemical analysis and degradation state evaluation.

Plastic ingestion by various organisms within different trophic levels, including humans, is becoming a serious problem worldwide. Plastic waste samples are often found concentrated in an organism's digestive tract and can be degraded and further translocate to the surrounding tissue or circulatory systems and accumulate in food chains. In the present work, we report a detailed chemical analysis and degradation state evaluation of a relatively large piece of plastic waste found in the gastrointestinal tract of a Wels catfish (Silurus glanis L.) caught in the Bodrog River (Danube River basin), eastern Slovakia. Chemical analysis by surface-sensitive X-ray photoelectron spectroscopy (XPS) was performed to identify the surface composition of the digested plastic piece. Micro-Fourier transform infrared (µFTIR) spectroscopy showed that the plastic waste was oxidized low-density polyethylene (LDPE), with some nylon fibers adhered on the surface. Glyceraldehyde adhered onto LDPE was also detected, which might come from the carbohydrate metabolism of that fish. A morphology study by digital optical microscopy indicated solid inorganic particles attached to the surface of LDPE. A degradation study by differential scanning calorimetry (DSC) showed considerable oxidation of LDPE, leading to fragmentation and disintegration of the plastic waste material.