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.

Acid mine drainage (AMD) is one of the major environmental problems impacting aquatic ecosystems globally. We studied changes in the community composition of macroinvertebrates and amino acid (AA) profiles of dominant taxa along an AMD contamination gradient within the Dee River, Queensland, Australia to understand how AMD can affect the biomolecular composition of macroinvertebrates. Taxa richness and community composition of macroinvertebrates changed widely along the AMD gradient with significantly lower taxa richness recorded at the polluted sites compared to upstream and downstream sites. The Dipteran families: Chironomidae and Ceratopogonidae, the Odonata family Gomphidae, and the Coleoptera family Dytiscidae were the only families found at all sampling sites and were used here for AA analysis. There were significant variations in the AA profiles among the studied taxa. The AA profile of each taxon also varied among upstream, polluted and downstream sites suggesting that contamination of a river system with acid mine drainage not only alters the overall macroinvertebrate community composition but also significantly influences the AA profile of organisms that are tolerant to AMD. This study highlights the potential of using AA profiling to study the response of aquatic organisms to contamination gradients such as those associated with AMD.