Biodegradation mechanisms of PBDE − 209: enzymatic, microbial, and omics-driven insights

Abstract Decabromodiphenyl ether (PBDE − 209) is the most extensively produced and environmentally persistent congener among polybrominated diphenyl ethers (PBDEs) and remains widely detected in soils, sediments, sludge, dust, and biota despite global regulatory restrictions. Its extreme bromination, strong hydrophobicity, and resistance to physicochemical degradation limit natural attenuation and complicate remediation efforts. Although biological processes are increasingly recognized as key drivers of BDE − 209 transformation, current knowledge remains fragmented across microbial, enzymatic, and molecular scales, hindering predictive understanding and effective remediation strategies. Unlike previous PBDE reviews that examine microbial taxa or degradation reactions in isolation, this review provides a systems-level synthesis that integrates microbial ecology, enzyme catalysis, metabolic bottlenecks, and multi-omics evidence to explain why PBDE − 209 biodegradation frequently remains incomplete in both natural and engineered systems. Reductive debromination, oxidative transformation, and stepwise formation of lower-brominated intermediates are critically examined alongside with their environmental relevance and toxicity implications. Recent advances in metagenomic, transcriptomics, proteomics, and metabolomics are integrated to identify key functional genes, active enzymes, metabolic constraints, and cooperative microbial interactions governing degradation efficiency. The review further evaluates emerging biotechnological strategies, such as bioaugmentation, biostimulation, engineered microbial systems, immobilized enzymes, synthetic consortia, rhizoremediation, and advanced bioreactor configurations, with emphasis on overcoming bioavailability limitations and minimizing accumulation of toxic intermediate. By consolidating mechanistic insights across biological scales, this review establishes a comprehensive systems-level framework to advance predictive understanding and guide the development of effective, field-applicable remediation strategies for BDE − 209 contaminated environment.