Fipronil in the Feed‐to‐Food Chain: Occurrence, Transfer Metrics, and Risk Implications

ABSTRACT Fipronil is a widely used insecticide/biocide with environmental dispersion, and the feed chain can represent a pathway for transfer of environmental contamination into animal‐derived foods. The 2017 fipronil crisis exposed systemic vulnerabilities in the safety of animal‐derived products, particularly eggs. We conducted a Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) 2020–guided systematic review to map fipronil occurrence in feed materials and synthesize carry‐over evidence in relation to regulatory benchmarks. A total of 707 records were identified (385 after duplicate removal) from Web of Science, Scopus, and PubMed (updated to November 2025); 104 peer‐reviewed studies were included using a Population, Exposure, Comparator, Outcome (PECO) framework. Internal validity was assessed across relevant bias domains, explicitly considering analytical reliability (limit of detection and limit of quantification reporting, recovery/precision, calibration/blanks, and matrix effects). Evidence identifies plant‐derived forages, industrial by‐products (including cane‐derived co‐products), and circular co‐products (e.g., distillers’ grains) as relevant entry vectors, although evidence strength differs across pathways. Fipronil‐sulfone consistently emerged as a marker of longer‐term exposure, and controlled laying‐hen evidence indicates that persistence in eggs and fat‐rich tissues can prolong depletion under chronic or extra‐label exposure scenarios. Evidence for ruminant transfer is more limited, and several emerging feed vectors remain exploratory. Overall, the findings support evidence‐proportionate surveillance at the environment–feed interface and monitoring strategies that combine validated confirmatory methods with rapid screening.