Environmental Fate of Hexabromocyclododecane (HBCD) The Degradation Pathway

Introduction Hexabromocyclododecane (HBCD) is currently undergoing risk assessment in the EU (Existing Substances Regulations 793/93/EEC). During the risk assessment process, the environmental persistence of HBCD was investigated. In previous studies (Davis et al 2005, 2006a), the biodegradation of HBCD was reported to occur in freshwater aquatic sediments and digester sludge. Using C-labelled HBCD, it was demonstrated that HBCD was sequentially debrominated to t,t,t cyclododecatriene (t,t,t CDT). Moreover, the degradation rates of the three major diastereomers of HBCD (α, β, γ) were similar. The next step in elucidating the biodegradation pathway of HBCD was to investigate the fate of t,t,t CDT. Results from an initial experiment, based on a ready biodegradation test and conducted with t,t,t CDT, showed primary degradation of t,t,t CDT (Davis et al 2006b). However, due to the high background respiration (in relation to the low CDT concentrations of 1 mg to 10 mg/L), mineralization could not be verified. In the present study, the use of C radiolabeled t,t,t CDT enabled to determine both the extent of mineralization of t,t,t CDT and the metabolites formed during the degradation.