Hexabromodiphenyl ether and heptabromodiphenyl ether (C-octaBDE)

Commercial octabromodiphenyl ether (c-octaBDE) is a mixture of several polybrominated diphenyl ethers and congeners. These synthetic brominated compounds have mainly been used as flame retardants. In addition to octaBDE isomers, c-octaBDE contains significant amounts of other component groups (such as pentabromodiphenyl (pentaBDE) and hexabromodiphenyl ethers) with persistent organic pollutant (POP) characteristics.

Adverse effects

The available ecotoxicity data for the c-octaBDE product show little or no effect on aquatic organisms (short-term fish study and a longer-term Daphnia magna study), sediment organisms (Lumbriculus variegatus) and soil organisms (three species of plant and earthworms Eisenia fetida) (European Commission 2003). However, the EU Risk Assessment Report identifies a risk of secondary poisoning in other species (via ingestion of earthworms) for the hexabromodiphenyl ether component in the c-octaBDE product (from use in polymer applications).

Within the EU, c-octaBDE has been classified as “Toxic”, due to its effects on human health, with the risk phrases "may cause harm to unborn child", and "possible risk of impaired fertility".

The presence of lower brominated diphenyl ethers in the c-octaBDE products is of concern also from the human health point of view as they are likely to have a higher potential to cause adverse effects.

Persistence

OctaBDE has been found to photodegrade rapidly in a mixture of organic solvents, with a half life of around 5 hours, but the environmental significance of such a finding is uncertain (European Commission, 2003). Besides, octaBDE is predicted to adsorb strongly onto sediment and soil, which means that only a fraction of this PBDE will be exposed to sunlight, thus having the potential to photodegrade. No information is available on the hydrolysis of octaBDE, but it is not expected to be an important process for octaBDE in the environment.

Regarding biotic degradation, octaBDE is not readily biodegradable in standard tests (no degradation seen over 28 days) and is not expected (by analogy with other brominated diphenyl ethers) to degrade rapidly under anaerobic conditions. Nevertheless, other more highly brominated congeners (deca and nonabromodiphenyl ether) have been found to degrade anaerobically in sewage sludge, although at a very slow rate (Gerecke et al. 2005). The evidence seems to indicate that there is little significant biotic or abiotic degradation of octaBDE.

It's worth noting that degradation of polybrominated diphenyl ethers (PBDEs) can yield byproducts that are lower brominated congeners. For instance, Ahn et al. (2006) showed that decaBDE immobilised on specific soil/sediment and mineral aerosols yielded a number of penta to triBDEs, via octaBDE as an intermediate step. This may pose an additional environmental concern, as these lower brominated diphenyl ethers are usually more toxic and much more bioaccumulative.

More information

 

References:

Adapted from EU proposal to include C-octaBDE in the Stockholm Convention (Word file)

Hatfield Consultants The World Bank funded by the Canadian POPs Trust Fund through the      
Canadian International Development Agency
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