Publication after screening assessment of substance - Polybrominated diphenyl ethers that have the molecular formula C12H(10-n)BrnO in which "n" is 4 to 6 and polybrominated diphenyl ethers that have the molecular formula C12H(10-n)BrnO in which "n" is 7 to 10 - (Subsection 77(1) of the Canadian Environmental Protection Act, 1999)

[ Notices | 2004 ]

2004-05-08 - Canada Gazette Part I, Vol. 138 No. 19

Whereas a summary of the assessment of polybrominated diphenyl ethers, identified under subsection 73(1), is annexed hereby,

Notice therefore is hereby given that the Ministers of the Environment and of Health propose to recommend to Her Excellency the Governor in Council that Polybrominated diphenyl ethers that have the molecular formula C12H(10-n)BrnO in which "n" is 4 to 6 and Polybrominated diphenyl ethers that have the molecular formula C12H(10-n)BrnO in which "n" is 7 to 10 be added to the List of Toxic Substances in Schedule 1 to the Canadian Environmental Protection Act, 1999.

Notice therefore is further given that the Ministers of the Environment and of Health propose the implementation of virtual elimination under subsection 65(3) of Polybrominated diphenyl ethers that have the molecular formula C12H(10-n)BrnO in which "n" is 4 to 6.

Public comment period

As specified under subsection 77(5) of the Canadian Environmental Protection Act, 1999, any person may, within 60 days after publication of this notice, file with the Minister of the Environment written comments on the measure the Ministers propose to take and the scientific considerations on the basis of which the measure is proposed. More information regarding the scientific considerations may be obtained from the CEPA Registry Web site (http://www.ec.gc.ca/CEPARegistry). All comments must cite the Canada Gazette, Part I, and the date of publication of this notice and be sent to the Director, Existing Substances Branch, Environment Canada, Gatineau, Quebec K1A 0H3, (819) 953-4936 (facsimile), or by electronic mail to ESB.DSE@ec.gc.ca.

In accordance with section 313 of the Canadian Environmental Protection Act, 1999, any person who provides information in response to this notice may submit with the information a request that it be treated as confidential.

JOHN ARSENEAU

Director General

Risk Assessment Directorate

On behalf of the Minister of the Environment

Director General

Safe Environments Programme

On behalf of the Minister of Health

ANNEX

Summary of the Screening Assessment of Polybrominated Diphenyl Ethers Identified under Subsection 73(1)

Pursuant to paragraph 74(a) of the Canadian Environmental Protection Act, 1999, the Ministers of the Environment and of Health have conducted a screening assessment on polybrominated diphenyl ethers, CAS No. 40088-47-9, 32534-81-9, 36483-60-0, 68928-80-3, 32536-52-0, 63936-56-1, 1163-19-5.

Polybrominated diphenyl ethers (PBDEs) are a class of substances which contain an identical base structure, but differ in the number of attached bromine atoms (n=1 to 10). Of the ten isomer groups, seven are on the Domestic Substances List and are considered in this assessment, including tetra- to decabromodiphenyl ethers (tetra- to decaBDEs). PBDEs are generally present in the form of mixtures, referred to as commercial pentabromodiphenyl ether (which is predominately a mixture of penta-, tetra-, and hexaBDE), commercial octabromodiphenyl ether (which contains mainly hepta-, octa-, and hexaBDE, but may also contain small amounts of nona- and decaBDE) and commercial decabromodiphenyl ether (of which current formulations are almost entirely decaBDE with a small amount of nonaBDE). PBDEs are used in Canada as additive flame retardants in a wide variety of consumer products, including internal electric/electronic components of and casings for household appliances/electronics (e.g. hair dryers, televisions, computers), furniture upholstery and cushioning, and wire and cable insulation.

The identical base structure and combinations of congeners within the different commercial mixtures support consideration of a category approach to assessment of these compounds. In addition, to the extent that the data permit comparison, consideration of these compounds as a group is supported by trends in physical/chemical properties with increasing degree of bromination.

Results from a section 71 Notice with Respect to Certain Substances on the Domestic Substances List (DSL) conducted for the year 2000 indicated that no PBDEs were manufactured in Canada, although approximately 1 300 tonnes of PBDE commercial products were imported or shipped into the country. Based on quantities reported, commercial pentabromodiphenyl ether was imported in the greatest volume, followed by commercial decabromodiphenyl ether and commercial octabromodiphenyl ether.

Environment

PBDEs may be released to the environment during manufacturing and polymer processing operations, throughout the service life of articles containing them, and at the end of article service life during disposal operations. With their low vapour pressures, low water solubility and high log Kow values, it is expected that PBDEs entering the environment will tend to bind to the organic fraction of particulate matter, notably in sediment and soils, with only small amounts partitioning into water and air.

Empirical and predicted data indicate that all PBDEs under consideration are highly persistent and are subject to long-range transport, and each satisfies the requirements for persistence as defined by the CEPA 1999 Persistence and Bioaccumulation Regulations. Although considered persistent, evidence suggests that PBDEs are susceptible to some degree of metabolic transformation and photodegradation and, under certain circumstances, may undergo some anaerobic biodegradation. Studies have shown the transformation of higher brominated PBDEs (e.g. hepta- to decaBDEs) to lower brominated congeners (e.g. congeners of tetraBDE, pentaBDE and hexaBDE) which are associated with high levels of bioaccumulation. The degree to which these processes affect the overall risk to the environment from tetra- to hexaBDEs is not clear.

PBDEs have been detected in a variety of species worldwide, and evidence from many studies indicates that their levels in biota in North America (including the Canadian Arctic) are increasing steadily and even substantially over time.

Measured data indicate that tetra-, penta- and hexaBDEs are highly bioaccumulative and satisfy the criteria for bioaccumulation as described in the CEPA 1999 Persistence and Bioaccumulation Regulations. Despite their large molecular size, a low level of uptake of heptaBDEs and decaBDE in biota is supported by the fact that concentrations have been measured in the tissues of wild fish, mammals and/or bird eggs. There is a weight of evidence suggesting that highly brominated PBDEs such as octa- and decaBDE are precursors of the more toxic, bioaccumulative and persistent lower brominated PBDEs.

Risk quotient analyses, integrating known or potential exposures with known or potential adverse environmental effects, were performed for each of the three commercial PBDE products subject to this assessment. The results indicate that the greatest potential for risk from PBDEs in the Canadian environment is due to the secondary poisoning of wildlife from the consumption of prey containing elevated concentrations of congeners from commercial penta- and octabromodiphenyl ethers. Elevated concentrations of components of commercial pentabromodiphenyl ether in sediments may present risk to benthic organisms. HexaBDE is a component of both commercial penta- and commercial octabromodiphenyl ethers and could be a product of hepta- to decaBDE transformation. Therefore, risks associated with congeners found in commercial pentabromodiphenyl ether may also be due to the release of commercial octabromodiphenyl ether, or debromination of highly brominated PBDEs found in commercial decabromodiphenyl ether. The risk analyses for soil organisms indicate that risk quotients were below 1 for commercial penta-, octa- and decabromodiphenyl ethers, although there is considerable uncertainty given the lack of data characterizing PBDE concentrations in soil and sewage sludge applied to soil. The PBDEs would present a low potential for risk due to direct toxicity to pelagic organisms. In the water column, risk associated with tetra-, penta- and hexaBDE congeners may be due to bioaccumulation and toxicity to secondary consumers.

There is a lack of data characterizing the toxicity of PBDEs to wildlife. Recent studies using rodents provide evidence that exposure to PBDEs may lead to behavioural disturbances, disruptions in normal thyroid hormone activity and liver effects.

The PBDEs subject to this assessment have low vapour pressures and Henry's Law constants and are not expected to partition significantly into the atmosphere. As such, they are considered to present a negligible risk with respect to atmospheric processes such as global warming, stratospheric ozone depletion and ground-level ozone formation.

Pyrolysis and extreme heating can cause all PBDEs to form brominated dibenzo-p-dioxins and dibenzofurans. These transformation products are considered to be brominated analogues of the Government of Canada Toxic Substances Management Policy (TSMP) Track 1 substances polychlorinated dibenzo-p-dioxins and dibenzofurans.

Available data indicate the potential for exposure of organisms to PBDEs at concentrations of concern. Although concentrations of homologues from commercial decabromodiphenyl ether may not currently exceed known effect thresholds, those homologues are persistent and may contribute to the overall loadings of lower brominated PBDEs over the long term. The long-range transport of PBDEs has resulted in their widespread occurrence, including in remote regions. The persistent and bioaccumulative character of these substances can lead to prolonged exposure and potential accumulation in organisms. Field evidence indicates increasing concentrations in organisms over time. All PBDEs also have the potential to transform to other compounds of concern. Based on this evidence, it is concluded that PBDEs, including tetraBDEs, pentaBDEs, hexaBDEs, heptaBDEs, octaBDEs, nonaBDEs and decaBDE, which are found in commercial penta-, octa-, and decabromodiphenyl ethers, 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 are considered to be "toxic," as defined under paragraph 64(a) of CEPA 1999.

Human health

Critical targets for PBDE-induced health effects reported for the various congeners and commercial mixtures are similar. As a result, the critical effect level considered most appropriate for assessment of risk to human health for this group of PBDEs in a screening context is the conservative value of 0.8 mg/kg-bw/day (for pentabromodiphenyl ether). This is based on neurobehavioural effects which were dose and time related observed in neonatal mice administered a single oral dose by gavage on post-natal day 10 and observed for a subsequent five-month period.

Comparison of the critical effect level (i.e. 0.8 mg/kg-bw) to the upper bounding estimate of exposure for the total intake of all PBDEs for the potentially most highly exposed age group (2.6 µg/kg-bw/day in breast-fed infants) results in a margin of exposure of approximately 300. The selected critical effect level and deterministic estimates of exposure are considered quite conservative, consistent with the objective of screening health assessments.

The conservative nature of the margin of exposure does not, however, take into account the potential continuing increase in body burden of PBDEs (based on data for breast milk), should similar use patterns continue. Prediction of trends in body burdens is precluded by the limited relevant information. This includes lack of information on the behaviour of PBDEs in human blood and tissue and transfer from human breast milk to infants as well as the uncertainty in timeframes for removal processes for PBDEs in environmental media. Determination of the adequacy of this margin to address elements of uncertainty associated with limitations of the database for health effects and population exposure (in which confidence overall is considered to be moderate), intraspecies and interspecies variations in sensitivity, as well as the biological adversity or severity of the effects deemed critical requires additional in-depth evaluation of the relevant data. It also requires development of additional, more meaningful information on population exposure to PBDEs.

However, in view of the proposed recommendation to add PBDEs to the List of Toxic Substances based on environmental considerations, more in-depth evaluation of PBDEs from a human health perspective is considered a low priority, unless information becomes available to indicate that measures recommended to control exposure of environmental organisms to PBDEs will not be protective for human health. This priority is based on the smaller margin between the most conservative estimated critical values for exposure and effects on the environment in comparison with that for human health (approximately 7 (see footnote 1) versus 300) and experience in other countries that risk management actions to protect the environment have resulted in a reduction of exposure of humans.

Conclusion

On the principal basis of environmental considerations, it is proposed that PBDEs are considered "toxic" as defined in section 64 of CEPA 1999. The tetraBDEs, pentaBDEs, and hexaBDEs are persistent and bioaccumulative in accordance with the Regulations, their presence in the environment results primarily from human activity, and they are not naturally occurring radionuclides or naturally occurring inorganic substances.

[19-1-o