Traits and distribution of microplastics in stomach and intestinal tract of Pleuragramma antarcticum around the South Shetland Islands

Microplastic pollution in the ocean is a global environmental problem, and the microplastic pollution in the waters around Antarctica is a crucial part of it. However, there are few studies on microplastics in the Antarctic, most of which focus on the seawater and penguin excrement near the Antarctic. Studies on microplastics in the Antarctic fish are few, especially in Pleuragramma antarcticum. P. antarcticum is the most abundant pelagic fish living in the Antarctic continental shelf waters and plays a role of linkage in the Antarctic Marine ecosystem, so it is necessary for conserving this resource to explore microplastic pollution in P. antarcticum in the waters around South Shetland Islands, Antarctica. After thawing the samples from Antarctica and recording biological information, the gastrointestinal tract was extracted. At 60 °C, 10% KOH was used for digestion in a constant temperature shaker for more than 24 hours. After the solution was basically clarified, a 0.45 μm filter membrane was used for filtration. Suspected microplastics were picked out after filtration under a stereomicroscope, and then qualitatively detected by Fourier infrared spectrometer. Finally, the microplastic morphology was photographed by a Scanning Electron Microscope (SEM). The results showed that the average abundance of microplastics in P. antarcticum was (0.36±0.51) item/individual in the waters near South Shetland Islands. There was a positive correlation between the abundance of microplastics in the gastrointestinal contents and the body length of the fish. In general, the occurrence of microplastics in P. antarcticum was slightly higher in the northern Southern Shetland Islands than in the southern Bransfield Strait, but the overall pollution levels were relatively low. The microplastics in the P. antarcticum could be divided into fibrous and fragmentary types, and most of them were fibrous. The color of microplastics was mainly blue, followed by black, and red and transparent colors were less common. The average particle size of microplastics was (584.6±419.2) μm, 84.6% of which was less than 1 000 μm. Polyester microplastics accounted for nearly 80% of the microplastics in the P. antarcticum, most of which were polyethylene terephthalate (PET). Fishing nets and discharge of sewage from crew might be its main source. The surface characteristics of microplastics were analyzed by SEM which indicated that the fracture area of microplastics was rough and the specific surface area increased significantly. The SEM images of two kinds of fibrous microplastics illustrated the changes of microplastics in organisms. Due to the large specific surface area, it was easy to combine with other pollutants, carry toxic and harmful substances into the ecosystem, and then enter human life through the food chain. Therefore, it is still necessary to pay attention to the ecological effects caused by microplastics pollution. The results of this study enrich the basic data of microplastics research in Antarctic marine life and could be used as background data to provide a scientific basis for further research on microplastics in the Antarctic ecosystem.