Bioremediation of dioxin-contaminated soils: Microbial approaches, field perspectives, and analytical challenges

Polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDD/Fs) remain among the most challenging legacy soil contaminants because their extreme hydrophobicity and congener-specific toxicity combine with multi-decadal persistence and strong sequestration in aged matrices. Over the past decades, bioremediation has been explored as a lower-impact alternative to disruptive physicochemical treatments, but translation from laboratory success to field performance remains limited by the bioaccessibility bottleneck, heterogeneous redox conditions, and the difficulty of demonstrating durable risk reduction. This review synthesizes bacterial, fungal, and bio-hybrid strategies for PCDD/F transformation in soils, emphasizing the process logic that underpins most concepts: anaerobic reductive dechlorination of highly chlorinated congeners (often associated with organohalide-respiring taxa such as Dehalococcoides) followed by aerobic oxidative steps that become feasible once substitution is reduced (e.g., dioxygenase-driven pathways in sphingomonads and actinobacteria). In parallel, ligninolytic fungi expand the treatable congener space through extracellular oxidoreductases (laccases and peroxidases) that can access sorbed substrates and generate more polar intermediates, supporting hybrid schemes that distribute functions across communities or treatment stages. A central message is that congener disappearance or toxic equivalency (TEQ) decline alone is not sufficient evidence of detoxification: biotransformation can produce intermediate products and non-monotonic toxicity trajectories, while many transformation products remain poorly characterized in terms of persistence, mobility, and bioactivity. We therefore discuss analytical and experimental design requirements for regulatorily robust evaluation, highlighting the continued role of chemical analysis for congener-resolved quantification and the complementary value of bioassays and untargeted screening workflows to capture emerging by-products and unexpected activity. By linking mechanistic pathways, biosafety constraints, and monitoring resolution, this review identifies key limitations and research priorities for environmentally robust and regulatorily acceptable bioremediation of PCDD/F-contaminated soils.