Influence of Feeding Substrates on the Presence of Toxic Metals (Cd, Pb, Ni, As, Hg) in Larvae of Tenebrio molitor: Risk Assessment for Human Consumption

Abstract

Larvae of Tenebrio molitor L. (Coleoptera: Tenebrionidae) are particularly suitable as novel food for the human consumption; nevertheless, there are some potential safety risks linked with insect consumption. In this study we investigated the presence of Cd, Pb, Ni, As, Hg in new feeding substrates coming from solid residues generated by olive fruits processing, called olive-pomace, and their influence on the metal content in larvae of T. molitor. Morover, bioaccumulation factor and the mercury-selenium balance were evaluated. Analyses were carried out via graphite furnace atomic absorption spectrophotometry for Cd, Pb, Ni, As and Se, and via Direct Mercury Analyzer for Hg. All metal concentrations found in feeding substrates were below the legal limit of undesirable substances in animal feed (2002/32/EC). Concentrations in larvae were in the range (mg kg−1 wet weight): Cd 0.008–0.016, Pb 0.063–0.079, Ni 0.03–0.63, As 0.021–0.023, Hg 0.12 × 10−3–0.49 × 10−3, and Se 0.057–0.085. Statistically significant correlation between metal content in feeding substrates and in larvae was evidenced only for Hg, which bioaccumulates. Se protects from mercury toxicity, with a Selenium Health Benefit Value (HVBSe) of > 0. Overall, our results indicate that the risk of exposure to metals from consumption of mealworm larvae is relatively low and in compliance with European Union regulations.

A Chemically Safe Way to Produce Insect Biomass for Possible Application in Feed and Food Production

“…Data are consistent or lower with respect to literature results about HI reared on different natural growth substrates [25,32,52]. Compared with other insect species, the Cd content found in the HI prepupae was higher than that recorded in Tenebrio molitor reared on substrates made up of organic wheat milling and olive processing by-products [24], or in edible grasshoppers (Oxya Chinensis Formosana) from Korea [54]. Referring to the EC limit 2002/32/EC [53] on undesirable substances in animal feed, HI prepupae showed Cd concentrations within the limit (Table S1).…”

“…Analyses were carried out on three aliquots per sample. For the determination of Cd, Pb, Ni, and As, samples were digested in a high-quality (65% w/v) nitric acid HNO 3 and 30% v/v H 2 O 2 (Merk) mixture in a Microwave-Accelerated Reaction System, MARS-X, 1500 W (CEM, Mathews, NC, USA) and the operational parameters were as in Truzzi et al (2019) [24].…”

“…Quantitative determinations of Cd, Pb, Ni, and As were made with an Agilent DUO 240FS atomic absorption spectrometer (Agilent, Santa Clara, CA 95051, USA) equipped with a graphite furnace (GTA120 Graphite Tube Atomizer) and a Zeeman-effect background corrector. The analytical methodology and instrumental parameters were described earlier [24]. Atomic absorption spectrometry standard solutions for Cd, Pb, As, and Ni (Titrisol grades from Merk) were used to build up the calibration curves.…”

“…The homogenized samples were weighed directly into quartz containers. The optimized reading conditions for mercury determination in feed and in insects were as in Truzzi et al (2019) [24]. It was not possible to perform frass analysis with DMA-1, as the catalytic tube was rapidly destroyed during the analysis.…”

“…PTEs eventually present in growth substrates can be transferred to the insect larvae, and therefore enter the feed/food chain. It has been demonstrated that larvae of mealworm (Tenebrio molitor, Coleoptera Tenebrionidae) reared on olive fruits processing by-products can accumulate Pb and Hg [24], whereas Biancarosa et al (2018) [25] evidenced that HI grown on seaweed-enriched media accumulated significant amounts of PTEs such as Cd, Pb, and Hg. However, knowledge on chemical hazards associated to insects as potential ingredients for feed and food is scarce [9], but the interest about this topic is increasing [2,3,6,12,26,27].…”