Towards Safer Insect-Based Feed and Food: Toxicokinetics of Cadmium, Arsenic and Lead in the Black Soldier Fly Larvae

Insects are rich in protein, lipids, and other nutrients, and they possess an exceptionally efficient bioconversion capacity. Besides these benefits, a significant advantage, particularly within the context of a circular bioeconomy, is their ability to utilize a wide range of food sources in rearing facilities, including residual biomass, thereby avoiding competition with key food commodities (e.g., wheat and soybean). However, before utilizing alternative feedstocks such as bio-waste, it is crucial to ensure the safety of these insects as food and feed. This study aimed to assess the uptake and elimination of common contaminants—cadmium (Cd), arsenic (As), and lead (Pb)—by the larvae of black soldier fly (Hermetia illucens) from feed substrates. A two-phase bioaccumulation study was conducted: a 5-day uptake phase where larvae were fed a contaminated substrate, followed by a 5-day elimination phase with a clean substrate. The substrate used was the Gainesville diet, spiked with cadmium chloride (CdCl2), sodium arsenite (NaAsO2), and lead nitrate (Pb(NO3)2) at concentrations of 2 mg/kg for Cd and As, and 10 mg/kg for Pb, based on EU regulatory limits for feed. The control group consisted of organisms exposed to clean substrate during the 10-day experiment. A 16-hour light/8-hour dark photoperiod and a temperature of 25±2°C were maintained during the exposure. Daily sampling was carried out, followed by a 12-hour depuration time, and lyophilization. Inductively coupled plasma mass spectrometry was used for metal quantification. Data from both the uptake and elimination phases were used for toxicokinetic modelling. The kinetic bioaccumulation factors were 1.21 for As, 1.45 for Pb, and 6.13 for Cd. Results indicated that the larvae accumulated these metals at concentrations exceeding the permissible levels (2 and/or 10 mg/kg dry substrate). The highest uptake rate was for Cd, followed by As and Pb. However, larvae reached safe internal concentrations for use as food for other animals after being moved to a clean substrate during: 2 days for As, 4 days for Pb, and 5 days for Cd. Fromt the obtained results, we recommend implementing this depuration period after exposure to bio-waste, although the duration should be adapted depending on the particular contaminants involved. Toxicokinetic studies are valuable for assessing the safety of insects for feed and food, and they can be useful tools to define the conditions that will assure sustainable use of insects in bio-waste management.