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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Davis, J. W., Gonsior, S. J. and Marty, G. T. (2003b). Evaluation of aerobic and anaerobic transformation of Hexabromocyclododecane in aquatic sediment systems.Report no.: 021081. Report date: 2003-03-05.
Davis, J. W., Gonsior, S. J., Markham, D. A. and Marty, G. T. (2004). Investigation of the biodegradation of [14C]Hexabromocyclododecane in sludge, sediment and soil. Report no.: 031178. Report date: 2004-11-30.
Davis, J. W., Gonsior, S., Marty, G. and Ariano, J. (2005). The transformation of hexabromocyclododecane in aerobic and anaerobic soils and aquatic sediments. Water Research (2005) Vol. 39, pp. 1075-1084.
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.

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Additional information

In studies conducted according to OECD Guidelines 307 and 308 (aerobic and anaerobic transformation in soil and sediment respectively), HBCDD was tested at concentrations ranging from approximately 10 to 80 ng/g dry weight (Davis et al., 2005; 2003). Using LC-MS, HBCDD loss was observed in all with faster rates under anaerobic conditions. Biologically mediated transformation accelerated the rate loss of HBCDD compared to biologically inhibited (i.e. autoclaved) soils and sediments. Biotransformation half-lives were 63 and 6.9 days in the aerobic and anaerobic soils, respectively, and 11 to 32 days and 1.1 to 1.5 days in aerobic and anaerobic sediments. Brominated degradation products were not detected in any of the soils or sediments during the study. In the 2003 study only the γ-isomer could be analytically determined.

In a further investigation with 14C-HBCDD, the formation and identification of degradants were assessed in activated digester sludge, river sediment and surface soil under aerobic and anaerobic conditions. At concentrations of 3-5 mg/kg to generate sufficient products for identification (Davis et al., 2004; 2006 ES&T), HPLC with radiochemical detection, HPLC-APPI-MS and GC-EI-MS was utilised. Substantial biological transformation was observed in the anaerobic digester sludge and in aerobic and anaerobic freshwater sediment. No degradation was noted in aerobic soil. In sludge and sediment, degradation of each of the three diastereomers occurred with little difference in rates. Formation of the following three products was observed in the sludge and sediments: tetrabromocyclododecane, dibromocyclododecandiene and cyclododecatriene.

The EU Risk Assessment Report has used the Davis et al. (2004) sediment study to calculate half-lives which is not considered to be correct as the concentrations in this study were chosen at rates much higher than are adequate for a determination of degradation kinetics in order to be able to identify metabolites. The design of this study is not considered suitable for the determination of half-lives. Much longer half-lives are therefore likely due to the non-availability of HBCDD to the microorganisms in this study.