Biotransformation and toxicity attenuation of 2,6-Dichlorobenzoquinone in simulated human gastrointestinal conditions: Insights from a systematic in vitro study

2,6-Dichlorobenzoquinone (2,6-DCBQ), a highly toxic and currently unregulated disinfection byproduct (DBP), is frequently detected in drinking water. However, its metabolic fate and toxicity following ingestion remain poorly understood. This study employed an in vitro gastrointestinal model—including simulated gastric fluid, small intestinal fluid, and colonic microbiota—to investigate its biotransformation, metabolite profiles, and associated toxicity alterations. 2,6-DCBQ remained stable in gastric fluid but underwent rapid degradation (99 % within 4 h) in small intestinal fluid, producing amino acid-conjugated metabolites (M1–M3), primarily M1 (53.9 %) and M2 (45.4 %). In contrast, the colonic microbiota achieved 70–83 % degradation over 24 h and generated a broader spectrum of metabolites (M4–M12) through amino acid conjugation, dehalogenation, sulfation, and phosphorylation. QSAR predictions and bioassays (Salmonella typhimurium TA100 and Caco-2 cells) confirmed reduced acute and genotoxic effects for both small intestinal and colonic metabolites. However, detoxification was notably less efficient in the colon, and certain metabolites (e.g., M5 and M6) retained mutagenic potential. These findings highlight region-specific metabolic differences and underscore the pivotal role of small intestinal metabolism in detoxification. This study provides the first comprehensive insight into the gastrointestinal transformation and toxicity modulation of 2,6-DCBQ, laying a foundation for its health risk assessment and mitigation strategies. Copyright © 2025 Elsevier B.V.