Effects of rearing substrate and larval stage on the contamination levels of chemicals in black soldier fly larvae

Abstract Possible risks associated with low value substrates used for sustainable and cost-effective rearing of the black soldier fly (BSF), Hermetia illucens , could be either biological or chemical. The aim of this study was to evaluate these risks specifically focusing on the bioaccumulation of commonly encountered chemicals. Firstly, bioaccumulation factors for BSF fifth instars and prepupae reared on biogas digestate were tested for the heavy metals As, Pb and Cd. In addition, for Cd substrate spiking was conducted in order to test potential bioaccumulation at different concentrations. Secondly, pesticide contamination of BSF reared on spiked chicken feed, biogas digestate and catering waste was assessed for a cocktail of 12 active substances commonly applied in arable crops, fruit and vegetable cultivation (2,4-D, azoxystrobin, bentazone, clopyralid, cymoxanil, difenoconazole, fenpropimorph, linuron, metalaxyl, pendimethalin, pyraclostrobin and tebuconazole; each at 5 mg/kg). Both 24 h and 2 weeks exposure of fifth instars and prepupae were assessed. Concerning heavy metals, only for Cd significant bioaccumulation was observed in fifth instars, but not in prepupae, starting from a substrate concentration of 2 mg/kg. In contrast, neither of the pesticides accumulated and no values were above the MRLs. The fungicide fenpropimorph and the herbicide pendimethalin were the most abundant in fifth instars across substrates. These active substances are both characterized by high log( K ow ) values (4.1 and 5.2, respectively) and a low water solubility. Prepupae contained substantially less of these pesticides than the corresponding fifth instars, indicating a substantial excretion rate. Fifth instars reared on digestate contained the highest concentrations.