PBDEs

Polybrominated diphenyl ethers, PBDEs, have been used as flame retardants in many common household products such as blankets, couches, food wrappers, as well as in motor vehicles and airplanes.
A diphenyl ether molecule has the following structure:

One of the polybrominated diphenyl ether compounds is 2,2',4,4',5-pentabromodiphenyl ether and it has following structure
There are 209 possible substances which are included in the family of polybrominated diphenyl ethers (PBDEs) and these are called congeners. Congeners include dibromodiphenyl ethers, tribromodiphenyl ethers, tetrabromodiphenyl ethers, pentabromodiphenyl ethers, hexabromodiphenyl ethers, heptabromodiphenyl ethers, octabromodiphenyl ethers, nonabromodiphenyl ethers and decabromodiphenyl ethers.

PBDEs with 1-5 bromine atoms per molecule are considered to be more dangerous than PBDEs with more bromine atoms per molecules because they are more efficient at accumulating in living things. In humans they effect hormone levels in the thyroid which can lead to alterations in behaviour. Studies have shown that children in developed countries have higher levels of blood PBDEs than adults, ranging from 24 to 114 parts per billion.

Most PBDEs have either been banned or are in the process of being phased out, eg,:

• Penta and octa PBDEs are no longer manufactured in the USA because of the health risks while the European Union banned their use in 2004.
• Deca PBDE has commonly been used in the electronics industry but has now been banned in Europe.

There is, however, growing concern that PBDEs may have a long environmental life.

Reference
Crystal Y. Usenko, Eleanor M. Robinson, Sascha Usenko, Bryan W. Brooks, Erica D. Bruce. PBDE developmental effects on embryonic zebrafish. Environmental Toxicology and Chemistry, 2011; DOI: 10.1002/etc.570

Further Reading
Nomenclature
Haloalkanes
Structural Isomers
Functional Groups
Percentage Composition
Parts per Million Concentration

Study Questions

1. For the diphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
2. For the 2,2',4,4',5-pentabromodiphenyl ether molecule:
   • identify the ether functional group
   • give the molecular formula
   • calculate the molecular mass (formula weight)
   • calculate the percentage composition
3. How many bromine atoms would be found in a molecule of each of the following:
   
   • dibromodiphenyl ether
   • tribromodiphenyl ether
   • tetrabromodiphenyl ether
   • pentabromodiphenyl ether
   • hexabromodiphenyl ether
   • heptabromodiphenyl ether
   • octabromodiphenyl ether
   • nonabromodiphenyl ether
   • decabromodiphenyl ether
4. Draw one structural isomer of each of the molecules above.
5. Name each of the molecules you have drawn in question 4 above.
6. Give the molecular formula for the molecules you have drawn that have been considered to be the least dangerous.
7. The blood of a child is found to have 70ppb PBDE. Convert this to:
   • ppm
   • mg/g
   • g/L
8. Assuming the child above has 4.7L of blood in his/her body, calculate the mass of PBDE present.
9. In the USA, the EPA set a "safe" limit of 7 micrograms per kilogram of body weight for PBDE. If the child above has a mass of 18kg, is the amount of PBDE in his/her blood considered safe? Explain your answer.