Exposure of black soldier fly larvae to microplastics of various sizes and shapes: Ingestion and egestion dynamics and kinetics

Black soldier fly (BSF, Hermetia illucens) larvae can valorize food waste into high-valuable products including animal feed. However, these wastes may contain microplastics originating from food packaging, potentially compromising larval growth and their safety as feed. This study investigates the impact of microplastic sizes and shapes on their ingestion and egestion by BSF larvae during waste bioconversion. BSF larvae were reared for 10 days on artificial food waste spiked with three size ranges of spherical or irregularly shaped fluorescent polyethylene microplastics. Daily, several larvae were dissected (n = 9 per treatment) to isolate their gut and to finally determine the number of particles in their alimentary canal using a fluorescence microscope. The microplastics had no impact on larval growth and no bioaccumulation of microplastics was observed in the larval gut (bioaccumulation factors < 0.3). However, there was a significant difference in the ingestion rate based on the different particle sizes. While almost no particles exceeding 100 µm were ingested by the larvae, a steady increase in microplastics was observed in the larval gut for the smaller particles. However, a three-day starvation period reduced the number of microplastics in the larval gut by over 90 %. No significant difference was observed between spherical and irregularly shaped microplastics in terms of larval bioaccumulation. We proposed a kinetic model for representing the temporal dynamics of microplastics accumulation and elimination with respect to particle distribution parameters, enabling the results obtained in this study to be extrapolated to other microplastic sizes.