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Environmental fate & pathways

Biodegradation in water: screening tests

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Link to relevant study record(s)

Description of key information

Schafer, E. C. and Haberlein, D. (1996). Hexabromocyclododecane (HBCD): Closed Bottle Test. Report no.: 439E-102.
Davis, J. W., Gonsior, S. J., Markham, D. A. and Marty, G. T. (2004a). Investigation of the biodegradation of [14C]Hexabromocyclododecane in sludge, sediment and soil. Report no.: 031178.
Davis, J. W., Gonsior, S. J., Markham, D. A., Friedrich, U., Hunziker, R. W. and Ariano, J. M. (2006). Biodegradation and Product Identification of [14C]Hexabromocyclododecane in Wastewater Sludge and Freshwater Aquatic Sediment. Environ. Sci. Technol. (2006) Vol. 40, pp. 5395-5401.
Gerecke, A. C., Giger, W., Hartmann, P. C., Heeb, N. V., Kohler, H. -P. E., Schmid, P., Zennegg, M. and Kohler, M. (2006). Anaerobic degradation of brominated flame retardants in sewage sludge. Chemosphere (2006), Vol. 64, pp.311-317.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

HBCDD is not readily biodegradable in a 28 day aerobic degradation sewage sludge test (Schafer and Haberlein, 1996). However, inherent biodegradation was observed in aerobic and anaerobic digester sludge (Davis et al., 2004; 2006 (Chemosphere); 2006 (Environ. Sci. Technol.)). Within 28 days HBCDD had decreased to approximately 10% of the starting value while a 50% loss occurred by day 15. Abiotic degradation processes appeared to play an important role. All three diastereomers were degraded. Gerecke et al. (2006) reported a much shorter half-life of 0.66 days in anaerobic sewage sludge. The difference in half-lives (15 days versus 0.66 days) was attributed to the 90-fold higher HBCDD concentration used by Davis et al. At higher concentrations for poorly soluble substances such as HBCDD, biodegradation rates are more dependent on mass transfer limitations than on true biodegradation kinetics. Environmentally relevant concentrations should be used to generate meaningful kinetic data.

Davis et al. (2006) reported three degradants: tetrabromocyclododecane, dibromocyclododecadiene and cyclodecatriene. The authors proposed that HBCDD was sequentially debrominated via dihaloelimination where at each step there is the loss of two bromines from vicinal carbons with the subsequent formation of a double bond between the adjacent carbon atoms. The conclusion was that microorganisms naturally occurring in anaerobic digester sludge mediate complete debromination of HBCDD.