Hexabromocyclododecane

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Hexabromocyclododecane
Hexabromocyclododecane.svg
Identifiers
Abbreviations HBCDD
HBCD
CAS number [1] 3194-55-6[1] N
Jmol-3D images Image 1
Properties
Molecular formula C12H18Br6
Molar mass 641.7 g/mol
Melting point 186 °C (175–195 °C, depending upon isomer)
Solubility in water 3.4 µg/L in water
Hazards
EU classification SVHC
R-phrases R43
S-phrases S24
NFPA 704
Flammability code 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g., canola oil Health code 2: Intense or continued but not chronic exposure could cause temporary incapacitation or possible residual injury. E.g., chloroform Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
Except where noted otherwise, data are given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
 N (verify) (what is: YesY/N?)
Infobox references

Hexabromocyclododecane (HBCD or HBCDD) is a brominated flame retardant. It consists of twelve carbon, eighteen hydrogen, and six bromine atoms tied to the ring. Its primary application is in extruded (XPS) and expanded (EPS) polystyrene foam that is used as thermal insulation in the building industry. HBCD is highly efficient in this application so that very low levels are required to reach the desired flame retardancy. Typical HBCD levels in EPS are 0.7% and in XPS 2.5%. At present, according to BSEF, the brominated flame retardant industry panel, HBCD is the only suitable flame retardant for these applications. Any other flame retardant would likely need higher load levels in the polystyrene foam. Other uses are upholstered furniture, automobile interior textiles, car cushions and insulation blocks in trucks, packaging material, video cassette recorder housing and electric and electronic equipment. According to UNEP, “HBCD is produced in China, Europe, Japan, and the USA. The known current annual production is approximately 28,000 tonnes per year. The main share of the market volume is used in Europe and China”.[2]

HBCD's toxicity and its harm to the environment are currently discussed. HBCD can be found in environmental samples such as birds, mammals, fish and other aquatic organisms as well as soil and sediment.[3] On this basis, on 28 October 2008 the European Chemicals Agency decided to include HBCD in the SVHC list,[4] Substances of Very High Concern, within the Registration, Evaluation, Authorisation and Restriction of Chemicals framework. HBCD has been found widely present in biological samples from remote areas and supporting evidences for its classification as Persistent, Bioaccumulative and Toxic (PBT) and undergoes long-range environmental transportation.[5] In July 2012, an EU harmonised classification and labelling for HBCD entered into force. HBCD has been classified as a category 2 for reproductive toxicity.[6] Since August 2010 hexabromocyclododecanes are included in the EPA's List of Chemicals of Concern.[7] On 19 October 2012 the Persistent Organic Pollutants Review Committee, a subsidiary body of the Stockholm Convention on Persistent Organic Pollutants (POPs), adopted a recommendation to include HBCD in the Convention’s Annex A for elimination, with specific exemptions for expanded and extruded polystyrene needed to give countries time to phase-in safer substitutes. A final decision for the adoption was taken in May 2013.[8]

Because HBCD has 16 possible stereo-isomers with different biological activities, the substance poses a difficult problem for manufacture and regulation.[9] The HBCD commercial mixture is composed of three main diastereomers denoted as alpha (α-HBCD), beta (β-HBCD) and gamma (γ-HBCD) with traces of others. A series of four published in vivo mice studies were conducted between several federal and academic institutions to characterize the toxicokinetic profiles of individual HBCD stereoisomers. The predominant diastereomer in the HBCD mixture, γ-HBCD, undergoes rapid hepatic metabolism, fecal and urinary elimination, and biological conversion to other diastereomers with a short biological half-life of 1-4 days. After oral exposure to the γ-HBCD diastereomer, β-HBCD was detected in the liver and brain, and α-HBCD and β-HBCD was detected in the fat and feces [10] with multiple novel metabolites identified - monohydroxy-pentabromocyclododecane, monohydroxy-pentabromocyclododecene, dihydroxy-pentabromocyclododecene, and dihydroxy-pentabromocyclododecadiene. [11] In contrast, α-HBCD is more biologically persistent, resistant to metabolism, bioaccumulates in lipid-rich tissues after a 10 day repeated exposure study, and has a longer biological half-life of up to 21 days; only α-HBCD was detected in the liver, brain, fat and feces with no stereoisomerization to γ-HBCD or β-HBCD and low trace levels of four different hydroxylated metabolites were identified. [12] Developing mice had higher HBCD tissue levels than adult mice after exposure to either α-HBCD or γ-HBCD indicating the potential for increased susceptibility of the developing young to HBCD effects.[13] The reported toxicokinetic differences of individual HBCD diastereoisomers have important implications for the extrapolation of toxicological studies of the commercial HBCD mixture to the assessment of human risk.

Structures of the six (out of 16 possible) hexabromocyclododecane isomers that are present in the technical product at > 1 %

Environmental Concerns[edit]

Due to its persistence, toxicity, and ecotoxicity, a ban on HBCD production has been agreed under the framework of the Stockholm Convention on Persistent Organic Pollutants, with a time-limited exemption for use in building materials. After the time-limited exemption period has passed, global production will be limited to countries that have not ratified the Stockholm Convention, of which USA is the only major HBCD producer. There is a large and still increasing stock of HBCD in the anthroposphere, mainly in EPS and XPS insulation boards.[14]

References[edit]

  1. ^ https://treaties.un.org/doc/Publication/CN/2013/CN.934.2013-Eng.pdf
  2. ^ ^ UNEP Stockholm Convention HBCD Risk management evaluation http://chm.pops.int/Convention/POPsReviewCommittee/Chemicals/tabid/243/Default.aspx
  3. ^ Covaci, A; Gerecke, AC; Law, RJ; Voorspoels, S; Kohler, M; Heeb, NV; Leslie, H; Allchin, CR; De Boer, J (2006). "Hexabromocyclododecanes (HBCDs) in the environment and humans: A review". Environmental Science & Technology 40 (12): 3679–88. doi:10.1021/es0602492. PMID 16830527. 
  4. ^ "ECHA SVHC Official List". Echa.europa.eu. 2011-12-19. Retrieved 2012-06-20. 
  5. ^ "ECHA HBCD SVHC Supporting Documentation". Echa.europa.eu. Retrieved 2012-06-20. 
  6. ^ 5. Commission Regulation (EU) No 618/2012 of 10 July 2012 amending, for the purposes of its adaptation to technical and scientific progress, Regulation (EC) No 1272/2008 of the European Parliament and of the Council on classification, labelling and packaging of substances and mixtures.http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:179:0003:0010:EN:PDF
  7. ^ "EPA action details on HBCD". Epa.gov. Retrieved 2012-06-20. 
  8. ^ "Stockholm Convention Conference of Parties, decision SC-6/13 Listing of hexabromocyclododecane". Retrieved 2014-08-26. 
  9. ^ "Hexabromocyclododecane Challenges Scientists and Regulators". Retrieved 2012-06-20. 
  10. ^ Szabo DT, Diliberto JJ, Hakk H, Huwe JK, Birnbaum LS; Diliberto; Hakk; Huwe; Birnbaum (2010). "Toxicokinetics of the flame retardant hexabromocyclododecane gamma: effect of dose, timing, route, repeated exposure, and metabolism". Toxicological Sciences 117 (2): 282–93. doi:10.1093/toxsci/kfq183. PMID 20562218. 
  11. ^ Hakk H, Szabo DT, Huwe J, Diliberto J, Birnbaum LS; Szabo; Huwe; Diliberto; Birnbaum (2012). "Novel and distinct metabolites identified following a single oral dose of α- or γ-hexabromocyclododecane in mice". Environmental Science and Technology 46 (24): 13494–503. doi:10.1021/es303209g. PMC 3608416. PMID 23171393. 
  12. ^ Szabo DT, Diliberto JJ, Hakk H, Huwe JK, Birnbaum LS; Diliberto; Hakk; Huwe; Birnbaum (2011). "Toxicokinetics of the flame retardant hexabromocyclododecane alpha: effect of dose, timing, route, repeated exposure, and metabolism". Toxicological Sciences 121 (2): 234–44. doi:10.1093/toxsci/kfr059. PMID 21441408. 
  13. ^ Szabo DT, Diliberto JJ, Huwe JK, Birnbaum LS; Diliberto; Huwe; Birnbaum (2011). "Differences in tissue distribution of HBCD alpha and gamma between adult and developing mice". Toxicological Sciences 123 (1): 256–63. doi:10.1093/toxsci/kfr161. PMID 21705717. 
  14. ^ Dynamic Substance Flow Analysis Model for Selected Brominated Flame Retardants as a Base for Decision Making on Risk Reduction Measures, study for the Swiss National Science Foundation, 2007

External links[edit]