Differences in Hexabromocyclododecane Isomers and Microbial Remediation: A Review

• • HBCD technical mixtures contain three main diastereomers (α, β, γ) with γ-HBCD comprising the highest proportion (typically >70%), but α-HBCD shows higher bioaccumulation potential in biota, necessitating isomer-specific risk assessment. • • Microbial degradation of HBCD proceeds via debromination, hydroxylation, and dehydrobromination pathways; Pseudomonas sp. strain HB01 degrades γ-HBCD under aerobic conditions, while anaerobic consortia can debrominate HBCD, with Citrobacter sp. Y3 mineralizing HBCD via novel gene HBCD-hd-1. • • Bioremediation efficiency is influenced by redox conditions: aerobic degradation is faster for some isomers, but anaerobic processes are effective for highly brominated compounds; studies report up to 90% degradation of γ-HBCD within 14 days using specific strains. • • Isomer transformation during microbial activity (e.g., γ- to α-HBCD) complicates remediation, as it may increase toxicity; therefore, monitoring isomer profiles is critical for evaluating remediation success.