Polychlorinated biphenyls (PCBs), hexabromocyclododecanes (HBCDDs) and degradation products in topsoil from Australia and the United Kingdom

Hexabromocyclododecane (HBCDD) is listed under the Stockholm Convention on persistent organic pollutants, yet very few data are available on HBCDD concentrations in soil. Median concentrations of total hexabromocyclododecanes (ΣHBCDDs) from soils from the UK (n = 24) were 0.73 ng g⁻¹ dry weight (range <0.01–430 ng g⁻¹) and exceed significantly (p = 0.002) those in Australian soils (n = 17, median = 0.10 ng g⁻¹, range <0.0002–5.6 ng g⁻¹). Concentrations of polychlorinated biphenyls (PCBs) (average = 4.7 ng ΣPCBs g⁻¹, range = 0.39–21 ng g⁻¹) were determined in 19 UK samples and found to be statistically indistinguishable (p > 0.05) from those of HBCDDs; thereby underlining the extent to which HBCDDs have migrated into the UK environment. Moreover, PCB concentrations in this study are not markedly lower than those recorded in UK soils sampled in the mid-1980s indicating that the initial rapid decline in UK contamination with PCBs following bans on their manufacture and use, has not been maintained. Degradation products of HBCDD: pentabromocyclododecenes (PBCDs) and tetrabromocyclododecadienes (TBCDs) were detected in some UK soil samples with semi-quantitative concentrations ranging between 0.01 and 7.3 ng g⁻¹ for ΣPBCDs and 0.01–1.3 ng g⁻¹ for ΣTBCDs. In Australian soils only ΣTBCDs were detected at concentrations ranging from 0.0023 to 0.45 ng g⁻¹. Chiral signatures of HBCDDs were racemic or non-racemic in all samples indicating minimal edaphic enantioselective degradation. A horizontal transect at the most contaminated UK location (a suburban garden) revealed a marked decrease in concentrations of HBCDDs with increasing distance from buildings.