Effects of laundry-derived microplastic fibers on larval Japanese medaka (Oryzias latipes)

In recent years, laundry-derived microplastic fibers (LMFs) have been reported as one of the major sources of microplastics (MPs) released from wastewater treatment plants into the aquatic environment. Fish are considered to be among the types of aquatic biota most susceptible to ingested MPs; there is thus a need to assess the risk that LMFs pose to fish, although this remains largely unknown. Here, fluorescent LMFs were prepared using a washing machine, after which Oryzias latipes (Japanese medaka) larvae were exposed to them for 21 days to assess their toxicities. Upon exposure of the larvae to LMFs (0.2 and 2 mg/L), the typical yellow fluorescent signal of LMFs was observed mainly in the mouth, gastrointestinal tract, anus, and feces. No mortality was observed in larvae treated with either concentration of LMFs. However, decreases in body length and weight were observed upon the 2 mg/L treatment, which induced metabolites related to nucleotide metabolism. In addition, increased relative amounts of specific flora, Flavobacterium sp. and Burkholderiaceae, were observed in larvae exposed to 2 mg/L LMFs. Overall, 85.6 % of LMFs were ejected from LMF-treated medaka larvae after a 4-day depuration period; however, longer LMFs were more likely to remain in the larval gastrointestinal tract than shorter ones. These findings should deepen our understanding of the ecological effects of LMFs on freshwater fish.