The accumulation of heavy metals in feeder insects and their impact on animal production

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Insects have emerged as a novel feed protein source that could help to produce enough food to feed the growing global population. Good-quality protein content, minerals and bioactive compounds are the main reasons for the use of insects in livestock. Nonetheless, insects should be proven to be safe for use before being used as feeder insects for livestock. The accumulation of heavy metals in the feedstuff is becoming a major food safety concern, as this poses a serious problem to animal health and threatens human health through the transmission of toxic substances into the human food chain. It has been shown that feeder insects grown from agricultural waste materials contain chemical contaminants such as pesticides and veterinary drug residues. Current research mostly focuses on the safety evaluation of undesirable substances in edible insects for human consumption, but rarely indicates if these insects are safe to use in livestock feeds, particularly for avian species. Therefore, owing to the potential risks of heavy metal in animal production, heavy metal residues in feeder insects have received scientific attention. Hence, this review article is intended to evaluate and discuss selected heavy metals in insects, comparing them with toxicity limits for feedstuff of animal origin, and their potential risks of exposure. A literature search on metal elements present in insects was conducted using electronic databases. In addition, the citations included in articles were used to find other relevant articles or documents on this topic. Identified published articles were grouped and evaluated according to the insect species, growth stage and substrate from which the insects were grown. It was observed that the accumulation of heavy metals in insects is mainly associated with agricultural waste materials fed to insects. Furthermore, metal toxicity in animals varies according to animal species and age, metal type, concentration, and chemical form.