AB prepress abstract  -  DOI: https://doi.org/10.3354/ab00711

Microplastics of different characteristics are incorporated into the larval cases of the freshwater caddisfly Lepidostoma basale

Sonja M. Ehlers*, Werner Manz, Jochen H. E. Koop

*Email: sehlers@uni-koblenz.de

ABSTRACT: Plastic pollution is present in aquatic systems worldwide. While numerous studies investigate microplastic interactions with marine organisms, microplastic effects on freshwater organisms, especially insects, are rarely studied. Moreover, microplastic studies mainly focus on microplastic dietary uptake. The presence of microplastics in animal constructions, as commonly known from macroplastics incorporated into birds' nests, is largely unknown. So far, microplastics have only been observed in the tubes of a marine polychaete species. In freshwater systems, common caddisfly (Trichoptera) larvae build cases by using larval silk and mineral grains from benthic sediments that are at the same time known as microplastic sinks. Therefore, we examined caddisfly cases for microplastic presence. We collected caddisfly cases in the field, disintegrated them using hydrogen peroxide, and determined microplastic polymer type through micro-Fourier-transform infrared spectroscopy (µFTIR). We found primary and secondary microplastics of different shapes, colors, sizes and chemical compositions (e.g., polypropylene, polyethylene, polyvinyl chloride). Therefore, this is the first study to show that microplastics are present in the biological construction of a freshwater organism. Larval stages are usually more vulnerable than adult individuals, and microplastics can transport persistent organic pollutants and emit toxic leachates. In the caddisfly larval case, those substances are in close proximity to the sensitive larval body which may be harmful for the larva and may eventually impede its development. Furthermore, we discuss the potential of caddisfly larval cases to act as microplastic bioindicators in freshwater habitats.