Sludge Watch ==> HBCD flame retardatant in sewage sludge - scary

[Maureen Reilly]

Scientists call for research on HBCD flame retardant
Scientists have highlighted the need for more data on the environmental fate 
and behaviour of HBCD, a brominated flame retardant used in polystyrene 
foam.1 The call comes even though the compound has been under an EU risk 
assessment for the past nine years.
The review, published in Environmental Science and Technology by a an 
international team of researchers, concludes that hexabromocyclododecane 
(HBCD) is an emerging pollutant of mainly European origin.
Global production of HBCD in 2001 was 16,700 tonnes, over half of which - 
9,500 tonnes - was used in the EU. This puts HBCD as the second-highest 
volume brominated flame retardant used in the EU, behind tetrabromobisphenol 
A used in circuit boards. There are currently no restrictions on the use of 
either product.
Human health and environmental risk assessments of HBCD under the EU 
existing substances regulations began in 1997 but neither has reached a 
final conclusion. The review reports that the compound does not appear to be 
acutely toxic but may interfere with thyroid hormone metabolism and induce 
developmental neurotoxic effects in animals.
The scientists report that one of the difficulties in assessing the 
environmental effects of HBCD is that it has 16 stereoisomers, of which only 
three, alpha-, beta- and gamma-HBCD, are commonly reported. The physical 
properties of these isomers - and their uptake and metabolism in wildlife - 
may vary greatly.
The review concludes that it is important for the different stereoisomers to 
be measured and reported if the environmental behaviour of the compound is 
to be understood in detail. Commercial HBCD formulations consist mainly of 
gamma-HBCD, although alpha- and beta- forms may each be present at around 
10%. The isomers can rearrange at over 160C, so the composition may change 
during processing.
HBCD is hydrophobic and binds strongly to soils and particles. It is 
widespread in dust, sewage sludge, soil and sediment. The compound 
accumulates in wildlife and biomagnifies along food chains, but the industry 
disputes whether it is persistent.
In a recent letter to Environmental Science and Technology, Dieter Drohman 
of the HBCD industry working group said that studies showed "rapid" 
degradation in soil. However, the authors maintain that the most reliable 
studies indicate that the half-life of the compound in soil is more than six 
months.
Another point of contention with industry is whether HBCD is subject to 
long-range transport in the atmosphere. The authors point to its detection 
in air samples in remote areas of northern Scandinavia, the contamination of 
Arctic wildlife and its presence in Swiss mountain lakes.
Environmental levels of HBCD are generally highest close to point sources, 
such as the former Great Lakes production site in County Durham (ENDS Report 
340, p 13 ). However, lower levels result from diffuse sources such as 
sewage works and waste sites.
One of the major puzzles is that gamma-HBCD is the major constituent of 
commercial formulations but wildlife samples show a preponderance of 
alpha-HBCD (see figure). The trend appears to become even more marked 
further up the food chain.

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   http://pubs.acs.org/subscribe/journals/esthag-w/2005/mar/science/kb_hbcd.html
Science News –
March 2, 2005
More clues to HBCD isomer mystery
European scientists have published the most compelling explanation to date 
for why a trace component of the very popular hexabromocyclododecane (HBCD) 
flame retardant is bioaccumulating in North American and European wildlife. 
The new research by Jan Boon of the Royal Netherlands Institute for Sea 
Research (NIOZ) and his colleagues, which was recently posted to ES&T’s 
Research ASAP website (es049209t ) is raising questions about whether HBCD 
is a suitable replacement for the “Penta” and “Octa” polybrominated diphenyl 
ether (PBDE) flame retardant formulations that have been banned in Europe 
and are being phased out in North America.

Photodisc
Tests of common dolphins from European waters have found that they are 
taking up only the α isomer of the widely used HBCD flame retardant. 
Scientists believe that this trace component of the HBCD product is 
bioaccumulating because the compound is not broken down by the cytochrome 
P450 enzymes that aid human and animal livers in attacking toxic substances, 
such as organohalogens like HBCD.
HBCD is the third most widely used brominated flame retardant in the world 
and is considered to be a high-production-volume (HPV) chemical in Europe. 
Toxicological studies suggest that this brominated flame retardant can 
disrupt thyroid function and may have developmental neurotoxicity effects. 
Both in vivo and in vitro toxicological studies on HBCD are under way as 
part of the EU’s FIRE project.
HBCD’s unexpected behavior first came to light when researchers looked for 
the compound’s individual chemical isomers in wildlife. They discovered that 
the relative abundance of the isomers in the environment is often very 
different than the composition of the commercial product, which is added to 
polystyrene foams in insulation and upholstered furniture.
The alpha (α) isomer that often predominates in wildlife samples represents 
only about 6% of the commercial HBCD product. Boon and his colleagues from 
the University of Amsterdam and the Vrije Universiteit (both in The 
Netherlands) and the University of Aberdeen (U.K.) report that the α isomer 
was the only form of HBCD found in blubber samples they tested from 10 
harbor porpoises and 9 common dolphins from European seas.
This new study represents the first instance in which only the α isomer has 
been found in more than just a few wildlife samples, says Boon. Other 
researchers agree that this finding is attributable to the high trophic 
level at which cetaceans such as porpoises and dolphins operate as top 
carnivores in the marine food chain. “The only animals higher on the food 
chain are orcas and polar bears,” Boon points out.
The complete predominance of the α isomer is surprising because it is 
different than what scientists have been seeing in the Arctic, says Gregg 
Tomy, a contaminant scientist at the Freshwater Institute in Winnipeg, which 
is run by Fisheries and Oceans Canada, a governmental organization. He 
explains that although his tests of Arctic animals occupying higher trophic 
levels show that they are mainly bioaccumulating the α isomer, these animals 
are also taking up the β and γ isomers, which are found in greater abundance 
in the commercial product. The γ isomer comprises 70–90% of the HBCD 
formulation, says Mehran Alaee, a research scientist with the Aquatic 
Ecosystem Protection Research Branch of the National Water Research 
Institute, which is part of Environment Canada.
Studies of the Lake Ontario food web show that HBCD, and particularly the α 
isomer, is more likely to bioaccumulate up the food chain than PCBs, 
dichlorodiphenyldichloroethylene (DDE), the degradation production of the 
pesticide DDT, or PBDEs, says Tomy.
Boon and his colleagues also found persuasive evidence for why the α isomer 
is so much more likely to bioaccumulate than the other two isomeric forms. 
They did this by testing to see how HBCD was processed by the cytochrome 
P450 system. Researchers had previously hypothesized that cytochrome P450 
enzymes, which aid human and animal livers in breaking down toxic 
substances, such as organohalogens like HBCD, might play a key role in 
biotransforming the isomers. Because they did not have cetacean liver 
samples prepared in the manner necessary for such tests—which requires that 
tissue be frozen in liquid nitrogen and subsequently stored at –80 °C, 
rather than the customary storage in a freezer at –20 °C—Boon’s group 
resorted to using liver tissue from laboratory rats and a freshly dead 
harbor seal for their experiments. In unpublished research, Boon and his 
group have found that harbor seals also bioaccumulate only the α isomer.
The tests showed that the cytochrome P450 system readily metabolized the β 
and γ isomers. In contrast, the α isomer did not appear to be metabolized; 
researchers familiar with the study agree that this finding provides strong 
evidence for why the α isomer is so much more likely to bioaccumulate.
Perhaps just as importantly, Boon’s group showed that the cytochrome P450 
system was producing hydroxylated metabolites from the β and γ HBCD isomers. 
“The biotransformation makes these compounds more polar and therefore 
potentially more easily excretable. But you also add a reactive group, and 
there are many examples where such a compound binds to physiologically 
active endogenous compounds and becomes more toxic than the parent compound. 
This is the case for many of the PCBs and PBDEs,” Boon explains. He says 
that he has found that fish also produce HBCD metabolites, in 
as-yet-unpublished research.
The hydroxylated metabolites are a potential concern, agrees Linda Birnbaum, 
director of the EPA’s experimental toxicology division. “We don’t know 
whether it’s the parent compound or the metabolites which have the potential 
for adverse effects. There may be multiple mechanisms involved here,” she 
adds.
“The results call for identification of metabolites being formed from HBCD, 
as well as new toxicological studies of the individual isomers,” adds Åke 
Bergman of Stockholm University.
For all the importance of the new discoveries, “there are a lot of holes in 
our knowledge still,” Boon stresses. One is whether the relative enrichment 
of the α isomer is the result of another biotransformation. After all, “when 
you look at the sediments, most still resemble the technical mixture,” Boon 
cautions. Indeed, Tomy says that he has found evidence that at least some 
fish species from the Great Lakes are biotransforming the γ and β isomers 
into the α isomer. Microbes in sediments could also be selectively taking up 
the α isomer or biotransforming the other isomers, Boon says. However, the 
P450 enzymes in single-cell and multicell animals differ, he adds.
Because the HBCD molecule is known to be isomerized by heating at 
temperatures above 160 °C, another potential explanation for the 
predominance of α isomer in the environment could be any heating involved 
when the flame retardant is added to the products that it is meant to 
protect. However, the fact that most of the sediments that have been tested 
still resemble the technical mixture implies that at least some of the 
transformation is taking place in the environment, Boon says.
In the meantime, research into the compound is revealing even more 
complexities. Scientists at the Norwegian Institute of Public Health report 
that the mirror-image enantiomers of the HBCD isomers may have different 
chemistries in the environment. In research recently posted to ES&T’s 
Research ASAP website (es0484909), the researchers show that whiting and bib 
fish are more likely to bioaccumulate the positive (+) α HBCD enantiomer. 
Other researchers have reported finding δ and ε isomers of the compound.
“This compound frankly scares the heck out of me in terms of the fact that 
it clearly is persistent and it is bioaccumulative,” Birnbaum says. “Alpha 
clearly is hard to get rid of. Why we would [consider HBCD as an 
environmentally acceptable alternative to PBDEs] is confusing,” she 
adds. —KELLYN BETTS