Dietary uptake, biodistribution, and depuration of microplastics in the freshwater diving beetle Cybister japonicus: Effects on predacious behavior

Microplastics (MPs) have adverse effects on aquatic organisms in marine environments; however, there is a lack of information on freshwater environments. This study investigated the dietary uptake, and biodistribution and depuration of MPs in the freshwater diving beetle Cybister japonicus (Coleoptera: Dytiscidae) after consumption of zebrafish (Danio rerio) exposed to MPs. The transfer of MPs in diving beetles after consumption of zebrafish was assessed to determine whether the presence of MPs affected diving beetle behavior and predation. We found that diving beetles that consumed MP-exposed fish had a significantly lower ingestion rate than the control. In addition, the trophic transfer rate of MPs was 13-18%. However, MPs were found only in the crop and proventriculus of the beetles, and all particles were depurated within 48 h, likely via regurgitation. As diving beetle is a top predator in freshwater ecosystems and could facilitate transfer from aquatic to terrestrial ecosystems via predation, its behavior towards indigestible MPs in its digestive organs (i.e., filtering and vomiting) could represent a meaningful phenomenon as a potential vector for MP transport. This is the first report of the trophic transfer of MPs from fish to dytiscid species, which helps clarify the effects and mechanisms of MPs in freshwater systems.