Microfibers are microplastic with a diameter of 5 mm or less, including polyester, nylon, rayon and acrylic. It has been reported that microfibers are the main cause of global marine pollution. Microfibers were found to be discharged into the soil, beaches and marine sediments without being eliminated in the domestic sewage treatment process. In this study, when zebrafish were exposed to microfibers using polyester, the residual potential of tissue in zebrafish was evaluated and the expression changes of antioxidant and stress-related genes were analyzed.
The zebrafish Danio rerio were exposed to polyester by feed and breeding water. The feed for exposure to polyester was prepared by adding 0.1% of polyester to the base of commercial feed. And 0.1% polyester was added to the fish tank to condition the microfibers to flow into the water for experiments in breeding water. The exposure experiments were carried out for 5 days, and sampling was performed after 5 days. The gills and intestine were collected and observed using a stereomicroscope. The gene expression levels of antioxidant-related genes such as sod, cat, and gsh were analyzed using liver. In the brain, tph involved in the synthesis of the neurotransmitter serotonin and the corticoid receptors gr and mr were analyzed by the Real-time PCR.
As a result of the evaluation of the microfiber residual in tissues by exposure to feed, it was confirmed that the amount of microfiber remaining in tissues increased as the number of times exposed to microfibers through the feeding process increased. Microfibers were detected in intestinal tissue and feces, even when exposed to polyester in breeding water. The expression levels of genes in the liver and brain were lower in the polyester-exposed groups than in the control group. Therefore, it is considered that polyester, which is a microplastic, can remain in the digestive tract through the feeding process and breeding water condition of fish, and has the potential to affect oxidative stress and inflammatory responses in the body. Microfibers alone can have a detrimental effect on fish, but they can also combine with toxic chemicals, such as heavy metals, present in the water. Therefore, it is estimated that the ingestion of microfibers by fish may cause problems such as gastrointestinal damage and endocrine disorders. Through the results of this study, it is possible to understand the toxic potential of microfibers on fish. In the future, we intend to investigate the effect of microfibers on the endocrine system of fish.