Agricultural By-Products as Secondary Risk Matrices: Hazard Occurrence, Contaminant Fate, Mitigation Strategies, and Regulatory Considerations in Food Systems.

Agricultural by-products are increasingly valorized as food ingredients within circular food systems. However, their safety cannot be directly inferred from their corresponding primary commodities. Moreover, agricultural by-products serve as secondary risk matrices by acting as reservoirs or accumulation points for microbiological hazards, mycotoxins, pesticide residues, heavy metals, process-related contaminants, other organic contaminants, including PAHs and mineral oil hydrocarbons, and allergenic compounds. This occurs during field exposure, processing-driven redistribution, and storage. Hence, the safety and sustainability of by-product-derived ingredients require matrix-specific evaluation. Therefore, this study aims to provide a comprehensive and structured assessment of agricultural by-products as food-relevant matrices. Accordingly, this review integrated evidence using a two-tier literature approach that combined broad literature mapping of agricultural by-product valorization with a targeted safety-focused analysis of peer-reviewed studies. The primary focus was hazard occurrence, contaminant fate during processing, mitigation strategies, and regulatory considerations governing the use of agricultural by-products in food systems. Particular emphasis was placed on the processing-driven redistribution of contaminants, matrix-dependent variability, multi-contaminant co-occurrence, and limitations of regulatory frameworks originally developed for primary commodities. This review highlights that addressing current gaps in exposure assessment, mitigation validation, and regulatory alignment is critical for the safe integration of these by-products into circular food systems.