Study of Environmental Contamination Through Accidental Ingestion of Microplastics by Amphibian Larvae

Environmental pollution by numerous microplastics is one of the serious problems for all living things. We are apt to regard microplastic pollution as a matter of oceanography, but many of the difficulties may also be common to freshwater environments. Aquatic amphibian larvae may be exposed to microplastics. Based on this standpoint, we aim to create a model system to evaluate the microplastic problem under laboratory conditions. First, we applied polystyrene microbeads to Xenopus laevis larvae, amphibian model organisms. Xenopus larvae earnestly ingested the microbeads and the developing guts were filled by the beads, and the larvae of other anuran species (Xenopus borealis and Japanese Dryophytes japonica, Microhyla okinavensis ) also frequently ingested the polystyrene microbeads. Xenopus larvae feeded on polypropylene beads, polyethylene beads, and glass beads, suggesting that, irrespective of the material of the microbeads, Xenopus larvae tend to eat them if they are of an appropriate size. In contrast, neither of the urodelan larvae of Pleurodeles waltl nor Tylototriton verrucosus ingested the polystyrene beads, suggesting a difference in the recognition of food particles between anuran and urodelan larvae. As a first step to promoting the conservation of anural larvae against microplastics, we administered cadaverine-coated beads to Xenopus larvae, because cadaverine is known to induce escape behavior in the presence of teleost model species, zebrafish. After administration, Xenopus larvae did not prefer the smell, but we could not succeed in stopping the ingestion of microbeads. Taken together, anuran larvae have a strong tendency to eat various microbeads, so we propose that we should continue protecting fragile amphibian larvae against microplastic pollution.