Bioaccumulation and reproductive effects of fluorescent microplastics in medaka fish

This study was performed to elucidate the uptake and bioaccumulation of polystyrene microplastics (PS-MPs) in Japanese medaka (freshwater fish) and Java medaka (marine fish), and to assess its impacts on the survival, reproduction, and gene expression of Japanese medaka. Both species were exposed to 2-μm fluorescent PS-MPs (10⁷ beads/L) for 3 weeks. The bioaccumulation factor of PS-MPs for Java medaka was calculated at about 4 × 10², higher than that for Japanese medaka (about 1 × 10²). The exposure had no significant effects on the survival and reproduction of Japanese medaka. The mRNA sequencing analysis showed that the expression of a few genes involved in the cell adhesion, xenobiotic metabolic process, brain development, and other functions in medaka intestines significantly changed after exposure. These results suggest that virgin PS-MPs can potentially accumulate in medaka intestines, but has limited toxicity to Japanese medaka at the concentration up to 10⁷ beads/L.