Effects of microfiber exposure on medaka (Oryzias latipes): Oxidative stress, cell damage, and mortality

Fiber-type microplastics are major anthropogenic contaminants of marine environments. They are released mainly during cloth washing and are discharged from wastewater treatment plants into aquatic environments. This study aimed to evaluate whether microfiber exposure causes oxidative stress and cell damage in medaka (Oryzias latipes Temminck and Schlegel 1846). Fish were exposed to one of two different concentrations (500 and 1000 fibers/L) of a polyester-based microfiber (MF) for 21 days, and the degree of cell damage and changes in expression of antioxidant enzymes were investigated. Fish survival decreased with increasing concentrations of MF. The expression levels of superoxide dismutase (SOD) and catalase (CAT) increased in MF-exposed groups compared to those in the control. SOD activity increased compared to the control group, and MF exposure induced a significant increase in both SOD activity and mRNA expression over time. CAT mRNA expression increased from day 10 onwards following exposure. Plasma malondialdehyde content increased significantly on day 7 of exposure in the 1000 fiber/L group and on day 10 in the 500 fiber/L group. Caspase-3 mRNA expression significantly increased until day 10 of exposure. A terminal transferase dUTP nick end labeling assay confirmed increased apoptosis, and a comet assay demonstrated that higher DNA damage occurred in response to increased MF concentration and exposure time. In conclusion, we confirmed that MF exposure affects antioxidant reactions in fish, thus inducing oxidative stress, apoptosis, and DNA damage. In addition, a comprehensive understanding of MF pollution in aquatic systems is urgently required.