Differences in Hexabromocyclododecane Isomers and Microbial Remediation: A Review
Hexabromocyclododecane (HBCD), a brominated flame retardant widely used in building insulation, plastics, and textiles, has been banned but persists in the environment and accumulates in biota. Its three main diastereomers (α-, β-, γ-HBCD) exhibit distinct physicochemical properties, leading to differences in half-life, toxicity, environmental distribution, and bioaccumulation. Microbial remediation offers advantages over chemical and physical methods, including fewer residues, cost-effectiveness, and shorter remediation cycles due to rapid microbial growth. Microorganisms degrade HBCD via debromination, hydroxylation, dehydrobromination, and combined pathways, with isomer transformation observed in environmental microbial communities. This review synthesizes current knowledge on HBCD isomer differences and microbial degradation mechanisms, emphasizing the importance of understanding these processes to mitigate environmental pollution and human health risks. Key findings include the predominance of γ-HBCD in technical mixtures, the higher bioaccumulation potential of α-HBCD, and the isolation of specific degrading strains such as Pseudomonas sp. and Citrobacter sp. Y3, which can mineralize HBCD under aerobic or anaerobic conditions. The paper also discusses the influence of environmental factors on degradation efficiency and the potential for bioremediation strategies in contaminated soils and sediments.