Polybrominated diphenyl ethers

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Polybrominated diphenyl ethers or PBDE, are a flame retardant sub-family of the brominated flame retardant group. They have been used in a wide array of household products, including fabrics, furniture, and electronics. Polybrominated diphenylethers represent a class of flame retardant chemicals akin to that of PCB’s in their functionality, however there much debate about the potential health affects surrounding this recently synthesized chemical. Polybrominated diphenylethers, abbreviated as PBDEs, operate as a specific group of flame retardant chemicals commonly utilized as constituents in building materials, electronics, furnishings, motor vehicles, plastics, polyurethane foams, and textiles. There are three main types, referred to as penta, octa and deca for the number of bromine atoms in the molecule. After studies in Sweden found substances related to PentaBDE accumulating in breast milk and other tissues, Sweden reduced the use of this substance. A follow-up study has in the meantime indicated declining levels.[1]

The European Union has carried out a comprehensive risk assessment under the Existing Substances Regulation 793/93/EEC of Penta-, Octa- and DecaBDE. As a consequence the EU banned the use of penta-and octaBDE in 2004 and deca-BDE in 2008.[2]

An experiment done the at Woods Hole Oceanographic Institution in Massachusetts in 2005 showed that the isotopic signature of methoxy-PBDEs found in whale blubber contained carbon-14, the naturally occurring radioactive isotope of carbon. Methoxy-PBDEs are produced by some marine species. If the methoxy-PBDEs in the whale had come from artificial (human-made) sources, they would have only contained carbon-12 and no carbon-14 due to the fact that virtually all PBDEs which are produced artificially use petroleum as the source of carbon; all carbon-14 would have long since completely decayed from that source.[3] The isotopic signatures of the PBDEs themselves were not evaluated. PBDEs have also been found at high levels in indoor dust, sewage sludge and wastewater treatment plant effluents. In these circumstances natural sources can be ruled out.

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[edit] Sub-groups

Chemical structure of PBDEs
Chemical structure of PBDEs

The family of PBDEs consists of 209 different substances, which are called congeners (PBDE = C12H10−xBrxO (x = 1, 2, ..., 10 = m + n)). The 209 possible PBDE congeners are brominated with 2-10 bromine atoms, which attach to the two benzene rings of a diphenyl molecule. PBDEs are akin to PCBs in that both molecules contain 209 congeners, however the number of PBDE congeners utilized in commercial industry is a significantly smaller subset compared to the number of PCB congeners utilized in commercial industry. The 209 PBDE congeners are listed in ascending order, adhering to the IUPAC protocols concerning characterization of biphenyl's. The chemical reaction known as bromination depicts specific types of halogenations, which incorporates one or more bromine atoms into a diphenyl molecule thereby resulting in 1 of 209 combinations of congeners. PBDE congeners containing the same number of bromines atoms are referred to as a homolog. A PBDE homolog ranges from 2-10 bromines and classifies as follows: dibromodiphenyl ether, tribromodiphenyl ether, tetrabromodiphenyl ether, pentabromodiphenyl ether, hexabromodiphenyl ether, heptabromodiphenyl ether, octabromodiphenyl ether, nonabromodiphenyl ether, and decabromodiphenyl ether. In the United States, corporations offer marketable PBDEs with trade names: DE-60F, DE-61, DE-62, and DE-71 applied to pentaBDE mixtures; DE-79 applied to octaBDE mixtures; DE 83R and Saytex 102E applied to decaBDE mixtures.

There are two sub-groups:

Lower brominated PBDEs have 1-5 bromine atoms and are regarded as the most dangerous ones, because they are smaller molecules which can be absorbed by living organisms. Lower brominated PBDEs have been known to affect hormone levels in the thyroid gland. Studies have linked them to reproductive and neurological risks at certain concentrations or higher.[4]

Higher brominated PBDEs have more than 5 bromine atoms and were formerly regarded as environmentally harmless chemical compounds, but studies by the Swedish Environmental Board have linked them to thin egg shells for Peregrine falcons.[5]

The available commercial PBDE products are not purely uniform substances composed of one single congener homolog but rather are composed of an array or mixture of PBDE congener homologs. The commercial mixture, named pentabromodiphenyl ether, contains predomintaley pentabromodiphenyl ether homolog (50-62%), however the substance also contains tetrabromodiphenyl ether homolog (24-38%) and hexabromodiphenyl ether homolog (4-8%), and trace amounts of tribromodiphenyl ether homolog (0-1%). Similarly, commercial octabromodiphenyl ether is a mixture of homologs: hexa-, hepta-, octa-, nona-, and decabromodiphenyl ether.

[edit] Health concerns

Since 1998, there have been concerns raised about the safety of PBDEs after Swedish scientists noticed substances related to PentaBDE were accumulating in human breast milk.[6] Based on a comprehensive risk assessment under the Existing Substances Regulation 793/93/EEC, the EU has banned the use of Penta- and OctaBDE since 2004.[7]

Some studies in Canada have found notable concentrations of PBDEs in common food products such as salmon, ground beef, butter, and cheese.[8] In Canada there is no set limit for what upper amount of PBDEs in the human body is still considered to be safe, but there remains concern in the general public that the PBDEs are having harmful effects on human health and the environment.

Most people are exposed to low-level concentrations of PBDEs through ingestion of food and/or breathing and inhaling air, which contains PBDEs. PBDEs persistence prevails in the human body, as concentrations are present in the blood, breast milk, and fat tissues, a process referred to as bioaccumulation, indicating that most people are exposed to low levels of PBDEs. Occupational personnel in the business of manufacturing PBDE products experience a greater chance of exposure to higher levels of PBDEs than the average individual. The same can be said of occupational personnel involved with the recycling and repairs of products containing PBDEs, especially when working in confining spaces. Signs and symptoms: OctaBDE and pentaBDE exposure effects developmental and nervous system toxicity, disruption of estrogen and thyroid function.

Environmental organizations argue that all PBDEs should be banned as they aren’t needed and replacements are available.[citation needed] But, the electronics industry claims that PBDEs are applied to most newly manufactured electronic assemblies such as printed circuit boards and capacitors and thus are vital to their business.[citation needed]

There is some evidence that indicates these chemicals may possess liver toxicity, thyroid toxicity, and neurodevelopmental toxicity.[4][neutrality disputed]

In August, 2003, the State of California outlawed the sale of penta- and octa- PBDE and products containing them, effective January 1, 2008.[9] In April 2007, the legislature of the state of Washington passed a bill banning the use of PBDEs.[10] In May 2007, the legislature of the state of Maine passed a bill phasing out the use of DecaBDE.[11]

It has been postulated that increasing levels of PBDEs in the environment could be correlated with the increasing incidence of feline hyperthyroidism. However, a study in 2007 found that no association could be detected between hyperthyroid cats and serum PBDE levels.[12]

[edit] Testing for PBDE in plastics

Until recently, testing for PBDE has been cumbersome. Cycle time, inaccuracy, cost and level of expertise required for the test engineer has precluded the implementation of any screening of plastic component in a manufacturing or in a product qualification/validation environment.

Recently, with the introdction of a new analytical instrument IA-Mass, screening of plastic material alongside manufacturing line is possible. A 5 min. detection cycle and a 20 min. quantification cycle is available to test and to qualify plastic parts as they reach the assembly line.

As of June 1, 2006 the State of California began prohibiting the manufacture, distribution, and processing of flame retardant products containing pentabrominated diphenyl ether (pentaBDE) and octabrominated diphenyl (octaBDE). PBDEs are ubiquitous in the environment and according to the EPA exposure may pose health risks.

[edit] References

  1. ^ Y. Lind, P. O. Darnerud, S. Atuma, M. Aune, W. Becker, R. Bjerselius, S. Cnattingius and A. Glynn (2003). "Polybrominated diphenyl ethers in breast milk from Uppsala County, Sweden." Environmental Research 93(2): 186–194. PMID 12963403
  2. ^ New Thinking on Flame Retardants, Environmental Health Perspectives, 116(5), May 2008
  3. ^ Emma L. Teuten, Li Xu, Christopher M. Reddy (2005): "Two Abundant Bioaccumulated Halogenated Compounds Are Natural Products". Science, 307, 5711: 917–920
  4. ^ a b Environment and Science Technology article "Rapidly rising PBDE levels in North America"
  5. ^ Lindberg, P., U. Sellström, L. Haggberg and C. A. de Wit (2004): "Higher brominated diphenyl ethers and hexabromocyclododecane found in eggs of peregrine falcons (Falco peregrinus) breeding in Sweden." Environmental Science & Technology 38(1): 93–96. PMID 14740722
  6. ^ Science News Online article "New PCBs?"
  7. ^ DIRECTIVE 2003/11/EC OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL
  8. ^ Globe and Mail article "Common foods laced with chemical"
  9. ^ "BILL NUMBER: AB 302, An act to add Chapter 10 (commencing with Section 108920) to Part 3 of Division 104 of the Health and Safety Code, relating to toxic substances."
  10. ^ "Chemical ban puts industry on the defensive." State of Washington bans use of PBDEs.
  11. ^ "Maine Legislature votes to ban toxic Deca flame retardant." State of Maine bans use of DecaBDE.
  12. ^ Dye et al (2007) Elevated PBDE levels in pet cats: sentinels for humans? Environ Sci Technol. 41(18):6350-6

[edit] External links

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