Summary

In July 2006, Environment Canada and Health Canada released the final Screening Assessment Reports for polybrominated diphenyl ethers (PBDEs). It was concluded that PBDEs [i.e., tetrabromodiphenyl ether (tetraBDE), pentabromodiphenyl ether (pentaBDE), hexabromodiphenyl ether (hexaBDE), heptabromodiphenyl ether (heptaBDE), octabromodiphenyl ether (octaBDE), nonabromodiphenyl ether (nonaBDE) and decabromodiphenyl ether (decaBDE)] -- which are found in commercial pentaBDE, octaBDE and decaBDE technical formulations, are entering the environment in a quantity or concentration or under conditions that have or may have an immediate or long-term harmful effect on the environment or its biological diversity, and thus meet the criteria under paragraph 64(a) of the Canadian Environmental Protection Act, 1999 (CEPA 1999). In addition, it was concluded that all seven PBDEs homologues met criteria for persistence, but only tetraBDE, pentaBDE and hexaBDE met the criteria for bioaccumulation as defined in the Persistence and Bioaccumulation Regulations under CEPA 1999. The analysis also noted that the higher brominated diphenyl ethers, and decaBDE in particular, could accumulate to some degree in biota and debrominate to bioaccumulative and persistent transformation products.

Since the completion of the Ecological Screening Assessment, a large amount of new information has been published regarding the accumulation of decaBDE in biota and the potential transformation of decaBDE to persistent and bioaccumulative products. The purpose of the present report is to provide an updated analysis of bioaccumulation and transformation of decaBDE, by summarizing evidence considered in the original Screening Assessment, and then examining the related new science published up to the end of March 2008.

With regards to bioaccumulation, factors such as low assimilation efficiency and metabolic transformation appear to be important determinants of accumulation in organisms. However, several studies indicate that decaBDE is clearly available for uptake and has potential to accumulate in biota to high levels. For instance, numerous recent studies have measured significant accumulation of BDE209 (another name for decaBDE) in several wildlife species such as kestrel, sparrowhawk, peregrine falcon, glaucous gull, red fox, shark, harbour porpoise and whitebeaked dolphin. These studies indicate that decaBDE can contribute, in some cases, to a significant proportion of the PBDE burden in biological tissues. It is also reasonable to conclude that decaBDE likely contributes to the formation of bioaccumulative and/or potentially bioaccumulative transformation products such as lower brominated BDEs in organisms and in the environment. Overall, the studies identified to 31 March 2008 indicate that decaBDE is bioavailable and may accumulate rapidly to potentially high and problematic levels in certain species. Nonetheless, available data do not show that the decaBDE itself meets the numeric thresholds for bioaccumulation as defined in the Persistence and Bioaccumulation Regulations under CEPA 1999.

The evaluation of decaBDE transformation in organisms found considerable evidence that fish and mammals are able to metabolically break down decaBDE. In fish, decaBDE may form heptaBDE, octaBDE and nonaBDE, and potentially pentaBDE and hexaBDE. In mammals, debromination of decaBDE to heptaBDE, octaBDE and nonaBDE has been observed. Debrominated products also appear to undergo hydroxylation to form phenols or catechols. Hydroxymethoxylated BDEs may also be formed.

The evaluation of transformation in the environment identified numerous laboratory studies that provide evidence that that decaBDE may break down in the environment, particularly as a result of photodegradation and biodegradation. Studies of photodegradation of decaBDE sorbed to solids in aqueous and dry systems have demonstrated transformation of decaBDE to triBDE, tetraBDE, pentaBDE, hexaBDE, heptaBDE, octaBDE and nonaBDE, tetraBDE and pentabrominated dibenzofurans (pentaBDFs) and unidentified products. Biodegradation studies have also shown potential break down of decaBDE mainly to nonaBDE, octaBDE and heptaBDE, while transformation to triBDEs has also been shown under enhanced laboratory conditions. Overall, biodegradation appears to occur at a much slower rate than that of phototransformation.

Modeling of bioaccumulation factors (BAFs) and biomagnification factors (BMFs) was conducted to estimate whether transformation products of decaBDE resulting from processes in organisms and in the general environment could be bioaccumulative. The evaluation found that many of the identified transformation products could be bioaccumulative (i.e., have BAFs in excess of 5000) and some could biomagnify in foodchains. The analysis also indicated that some potential transformation products (i.e., tetra- to hexaBDEs) are clearly bioaccumulative based on empirical evidence.

While laboratory studies on the transformation of decaBDE support a conclusion that transformation to lower BDEs and BDFs should be occurring in the environment, the phenomenon has not been conclusively shown through monitoring studies to occur in the environment. This suggests that the process of environmental transformation may be very slow and evidence of transformation may be shielded by existing patterns of PBDEs in the environment which are dominated by congeners found in the commercial products. The fact that relatively few studies specifically measure octaBDE and nonaBDE congeners in environmental samples makes it difficult to elucidate the debromination patterns of decaBDE in the environment.

While this report has focused on decaBDE, its analyses and conclusions provide useful inferences on alternative flame retardants with similar chemical structures and use patterns, such as decabromodiphenyl ethane (decaBD ethane). DecaBDE and decaBD ethane have only minor structural differences relating to the bond between their aromatic rings and, thus, these substances may have similarities in physical-chemical properties, persistence, transformation patterns, and accumulation in organisms. Based on the similarity in properties between decaBDE and decaBD ethane, the presence of decaBD ethane in Canadian wildlife, and the potential for decaBD ethane to be used as a large-scale replacement for decaBDE, there is also a need to further understand the potential risks from decaBD ethane in the environment and its capacity to accumulate in wildlife and transform to potentially bioaccumulative products.