Size effect of polystyrene microplastics on the accumulation of anthracene for Java medaka (Oryzias javanicus).

Pollution by microplastics in aquatic ecosystems is a worldwide problem, and the role of microplastics as vectors of pollutants has been a concern. Although small microplastics are thought to have a greater effect than large microplastics as vectors of pollutants, the impact of the size of microplastics on their ability to serve as vectors of pollutants has not been quantified. In this study, we conducted the 14-day experiment (7 days of exposure and 7 days of depuration) with polystyrene microplastics (2-μm or 10-μm diameter) and anthracene. On the last day of the exposure period, the concentration of anthracene in the muscle of Java medaka exposed to both anthracene and 2-μm polystyrene microplastics was the highest (47.4 ± 15.2 μg/g-muscle) of any group, followed by the group exposed to both anthracene and 10-μm polystyrene microplastics (23.0 ± 4.2 μg/g-muscle) and the group exposed to only anthracene (11.2 ± 2.2 μg/g-muscle). These results demonstrated that the size of microplastics was a critical determinant of their ability to serve as vectors of anthracene. The concentrations of anthracene and fine microplastics in the environment are sufficiently low that the effect of microplastics as vectors of anthracene may be observed only under experimental conditions that are unlikely to occur in the present environment. However, because pollution by plastics is expected to become more serious in the future, careful thought and proactive action will be needed to ensure that the impact of microplastics as vectors of pollutants does not become demonstrable under future environmental conditions.