Exploring potential uses of insect frass for agricultural production considering its nutrients, and chemical and microbiological safety

Insect rearing for food and feed has seen a sharp increase in Europe and is expected to grow further. Exploring the potential use of insect by-products like frass is crucial to improving the economic feasibility and circularity of the insect industry. This review study explores the potential uses of frass in agricultural applications by considering frass contents (nitrogen (N), phosphorus (P), potassium (K), and other compounds that have the potential to improve plant health) as well as chemical and microbiological safety. To this end, literature has been reviewed, and frass samples have been analysed. Our results showed that from the available data on frass contents, frass has fertilizing product potentials, such as fertilizer and biostimulants. Data on the occurrence of chemical and microbiological contaminants in frass are limited. However, the available data suggest that contamination depends on the feed substrates, type of contaminants, and insect species. These potential food safety hazards include mycotoxins, dioxins, heavy metals, pesticide residues, veterinary drugs and human food-borne pathogens (e.g. Clostridium perfringens, Bacillus cereus, Listeria monocytogenes, Salmonella spp.). Therefore, frass application in agricultural activities raises a concern whether such hazards will transfer and accumulate in crops and the environment (e.g. soil, water); studies on this topic are still limited. Considering this possible safety risk, it is important to establish proper mitigation strategies. Further research is needed to fill data gaps for hazard prioritisation and risk assessment, e.g. on the occurrence of hazards in frass (of different species reared on various feed substrates) and the fate of these hazards in crops and the environment following frass application. Finally, studies on frass valorisation will benefit from a holistic approach covering multiple topics, including safety, economic, and environmental impacts.