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Environmental fate & pathways

Biodegradation in soil

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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. (2004a). 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. and Perala, A. W. (2010). HBCD: Investigation of the aerobic transformation of the three major diastereomers (α, β, γ) of Hexabromocyclododecane in soils. Report no.: 081105. Report date: 2010-04-12.

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Additional information

In studies conducted 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 Water Research; 2003). Using LC-MS, HBCDD was observed in all with faster rates under anaerobic conditions. Biologically mediated transformation accelerated the rate loss of all 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 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). HPLC with radiochemical detection, HPLC-APPI-MS and GC-ELMS were 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, dibromocycloedodecandiene and cyclodecatriene.

The primary degradation and mineralisation of the three major HBCDD diastereomers (alpha, beta and gamma) was further characterised in two aerobic soils (Davis et al., 2010). Soil microcosms (25-85 ng/g) were prepared and incubated for up to 221 days, extracted and analysed at intervals using HPLC-ESI with MS operating in the MRM mode. The concentrations of the three diastereomers decreased in both soil types in both the viable and biologically inhibited microcosms. Each diastereomer behaved differently in the two solid and degradation was a function of the specific diastereomer and soil type. The half-lives of alpha, beta and gamma in the sandy clay loam viable soil microcosms were 441, 64 and 126 days respectively while in the viable loamy soil, half-lives were 162, 147 and 201 days respectively. Loss of all three was also observed in the biologically inhibited microcosms, however, greater biological loss was noted for all the beta and gamma diastereomers. Loss in the inhibited microcosms could be attributed to biodegradation resulting from slow recovery and growth of the microbial populations. Mineralisation to CO2 was observed in the aerobic soils (27%-16% after 218 days). 5-10% of the 14C-activity could not be extracted from the soils ands was 6-fold higher in the viable soils demonstrating the importance of the biological processes in transformation of HBCDD in aerobic soils.

Thus, biodegradation of HBCDD in anaerobic soils is rapid with a half-life of approximately 7 days. Slower biodegradation was observed in aerobic soils with an overall half-life of 63 days for HBCDD and half-lives of 162 or 441, 64 or 147 and 126 or 201 days for the alpha, beta and gamma diastereomers, respectively, depending on soil type.