Ingestion and excretion dynamics of microplastics by black soldier fly larvae and correlation with mouth opening size

Black soldier fly (BSF) larvae (Hermetia illucens) are voracious feeders that can be reared on food waste streams originating from the food industry and retailers. Because these food waste streams are automatically being unpacked in substantial amounts, they can contain microplastics, potentially jeopardising the larvae's chemical safety when applied as compound feed ingredients. During this study, the dynamics of ingestion and excretion of microplastics by BSF larvae reared on substrates containing different contents (w_MP = 0.00, 0.01, 0.10, 0.50, 1.00, 3.00%) of fluorescent blue-labelled microplastics (median size, Dv(50) = 61.5 µm) were monitored. To correlate the particle size with their uptake, larval mouth opening dimensions were measured during the rearing process. In conclusion, it appeared that ingestion of microplastics by BSF larvae depends on initial particle load, mouth size, and consequently also age. The larvae took up between 131 (w_MP = 0.01%) and 4866 (w_MP = 3.00%) particles leading to bioaccumulation factors (BAF) between 0.12 (w_MP = 3.00%) and 1.07 (w_MP = 0.01%). Larvae also appeared to excrete the microplastics, lowering the BAFs to values between 0.01 (w_MP = 3.00%) and 0.54 (w_MP = 0.01%).