Distribution Characteristics of Microplastics in Wild Fish near Changshan Islands

Plastic products are widely used in human daily life, while facilitating human life, plastics have also produced many negative effects due to the lack of effective recovery measures, plastic pollution has become an important environmental issue of global concern. Marine plastics can be degraded into smaller microplastics (MPs) through various ways under the influence of environmental factors. They can be ingested by marine organisms mixed with food sources, and then accumulated in the body, causing serious negative effects on marine lifes and marine ecology. Recently, it has been proved that the Changshan Islands sediments contain a certain amount of MPs, the content reached 133.14 to 499.82 n/kg. Changshan Islands is one of the eight major islands in China. It is located at the confluence of the Yellow Sea and the Bohai Sea, and has a unique geographical location. The fish community between the islands is rich in species, especially in many migratory species, and high in species diversity. The seasonal change of fish species composition and dominant species is obvious. It has been proved MPs can cause a certain degree of harm to marine organisms. Therefore, the distribution of MPs in organisms in the Changshan Islands sea area deserves to be studied. In this study, the MPs in the gastrointestinal tracts and muscles of wild fish were digested and separated after collecting them from the marine culture zone of Changshan Islands. The results showed that MPs were detected existing in the gastrointestinal tracts of all fish, but not in muscle tissues. The reason may be that MPs are too large to be endocytosed by intestinal epithelial cells, and thus can not participate in the blood circulation of fish. The abundance of MPs in the gastrointestinal tracts of seven species of marine wild fish ranged from 0.19 to 3.79 items/individual. The abundance of MPs in Coilia nasus is the highest among all fish, this phenomenon may be related to the living environment and predation habits of C. nasus, which living in the bottom of the sea. The MPs in sediments will undergo a cyclic process of suspension, sedimentation and resuspension under the flow of seawater, thus greatly increasing the exposure and intake risk of MPs by bottom organisms, such as C. nasus. The shape of MPs was dominated by the fiber, and the color was mostly transparent, which size is mainly less than 300 μm. The reason may be that the individual size of fish collected in this survey is small, and larger-sized MPs cannot enter into the gastrointestinal tract of fish through feeding. Large plastics in the environment are broken under the photooxidation, wave action, physical wear and alternating freeze-thaw. The different shapes of MPs detected in this study may be derived from the decomposition of these large plastics. Fibers are the predominant form of MPs encountered in global wildlife studies. It could also be because fibrous MPs are the most abundant in the marine environment. Additionally, MPs Fibers can be bended or intertwined with food, possibly due to long-term accumulation for the slower fibers excretion, increasing the chance of being ingested by organisms. The types of polymers detected were cellophane, cellulose and polyethylene, among which cellophane had the highest content. Cellophane is an organic cellulose-based polymer that has been used in food packaging and cigarette packaging. It is also used as a release agent in the manufacture of glass fiber and rubber products, or as a coating in combination with synthetic polymers. There was no obvious toxic effect on cellulose and cellulite. The polymer hazard index (PHI) is an important criterion for risk assessment of MPs, and is based primarily on the percentage content of a given polymer and the polymer's hazard fraction for ecological and health risk assessment. The potential risk of MPs to humans can be estimated by the polymer hazard index. The higher the polymer hazard index, the higher the ecological risk in the sea area. The toxicity coefficient of polyethylene is 10, the toxicity grade is grade II, the hazard index is low, and it belongs to the low risk polymer. Moreover, people usually discard the gastrointestinal tract of fish before eating, thus the MPs in the fishes of Changshan Islands, and the safety factor of fish products in Changshan Islands is higher. In this study, through the collection of wild fish in Changshan Islands, the MPs in gastrointestinal tract and muscle tissue were extracted, and the abundance and type of MPs were analyzed. The pollution status of MPs in fish in the adjacent waters of Changshan Islands was clarified, which provided basic data for exploring the impact of MPs on the ecological environment safety of Changshan Islands ecosystem. Further research on the distribution of MPs in other wild organisms, such as shellfish, and in other economically viable locations should be considered, which can provide a scientific basis for the analysis of MP pollution levels and the formulation of prevention and control strategies in the marine environment.