Hexabromocyclododecane: Current Understanding of Chemistry, Environmental Fate and Toxicology and Implications for Global Management

Abstract

Hexabromocyclododecane (HBCD) is a globally produced brominated flame retardant (BFR) used primarily as an additive FR in polystyrene and textile products and has been the subject of intensified research, monitoring and regulatory interest over the past decade. HBCD is currently being evaluated under the Stockholm Convention on Persistent Organic Pollutants. HBCD is hydrophobic (i.e., has low water solubility) and thus partitions to organic phases in the aquatic environment (e.g., lipids, suspended solids). It is ubiquitous in the global environment with monitoring data generally exhibiting the expected relationship between proximity to known sources and levels; however, temporal trends are not consistent. Estimated degradation half-lives, together with data in abiotic compartments and long-range transport potential indicate HBCD may be sufficiently persistent and distributed to be of global concern. The detection of HBCD in biota in the Arctic and in source regions and available bioaccumulation data also support the case for regulatory scrutiny. Toxicity testing has detected reproductive, developmental and behavioral effects in animals where exposures are sufficient. Recent toxicological advances include a better mechanistic understanding of how HBCD can interfere with the hypothalamic-pituitary-thyroid axis, affect normal development, and impact the central nervous system; however, levels in biota in remote locations are below known effects thresholds. For many regulatory criteria, there are substantial uncertainties that reduce confidence in evaluations and thereby confound management decision-making based on currently available information.

Hexabromocyclododecane (HBCD) and tetrabromobisphenol A (TBBPA) in riverine and estuarine sediments of the Pearl River Delta in southern China, with emphasis on spatial variability in diastereoisomer- and enantiomer-specific distribution of HBCD

“…The reported water solubility of TBBPA, varying from 0.17 to 4.2 mg/L at 25°C (due to transformation from nonionic to ionic forms) (Kuramochi et al, 2008), is much higher than those of the three HBCD diastereoisomers (0.002-0.05 mg/L) (Marvin et al, 2011), suggesting a preferred transport via aqueous phase for TBBPA. Whereas HBCD has vapor pressure 6.3 Â 10 À5 Pa at 21°C (Marvin et al, 2011), which is several order of magnitude higher than that of TBBPA (4.72 Â 10 À9 Pa at 25°C) (Kuramochi et al, 2008). Atmospheric transport and deposition may play a more important role in moving HBCD from sources to remote regions.…”

Hexabromocyclododecane and Hexachlorocyclohexane: How Lessons Learnt Have Led to Improved Regulation

“…On the basis of empirical data primarily, the half-life of HBCD in soil is ≥182 days (Environment Canada, 2011). Half-life in air >2 days 3.7 to 6.33 (Chen et al, 1984) 0.4 to 5.2 (Marvin et al, 2011) Half-life in water >60 days 3 to 300 days (Mackay et al, 1997) 60 to 130 days (Marvin et al, 2011) Half-life in aquatic sediments >180 days 90 days (WWFC, 1999) 0.9 to 12.6 years (Helm et al, 2002) 125-191 days (EC, 2008) Half-life in soil >180 days <180-1146<180- (IPCS, 1991 6.9 to 63 days (Davis et al, 2005) ≥182 days (Environment Canada, 2011) Half-life in biota (days/years) none 7 to 10 years (humans) (Zou and Matsumura, 2003) 23 to 219 days (humans) (Schecter et al, 2012) 1 to 17 days (mice) (Schecter et al, 2012) 53 to 136 days (fish) When released to the environment, HBCD isomers will adsorb onto solid particles of sediments and soil . Though there is a predominance (>90%) of γ-HCBD in the environment compared to α-and β-HBCD, α-HBCD often has the highest prevalence in biota, followed by β-HBCD (Birnbaum and Staskal, 2004).…”

Alteration of Diastereoisomeric and Enantiomeric Profiles of Hexabromocyclododecanes (HBCDs) in Adult Chicken Tissues, Eggs, and Hatchling Chickens

“…1 Commercial HBCD mixtures mainly consist of three racemic isomers (±) α-(6%), β-(10%), and γ-HBCDs (70%). 1,2 In the last few decades, HBCDs have been frequently detected in environmental matrices and biota samples. 1−3 HBCDs have been shown to be bioaccumulative in aquatic and terrestrial food webs 4,5 and were reported to exert toxic effects on the reproductive success and embryonic development of avian species, 6−8 which raise more environmental concern about HBCDs.…”