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DEPARTMENT OF THE ENVIRONMENTDEPARTMENT OF HEALTH CANADIAN ENVIRONMENTAL PROTECTION ACT, 1999 Publication after Assessment of a Substance -- Hexachlorobutadiene -- Specified on the Priority Substances List (Subsection 77(1) of the Canadian Environmental Protection Act, 1999) Whereas a summary of a draft report of the assessment of the substance hexachlorobutadiene specified on the Priority Substances List 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 hexachlorobutadiene be added to the List of Toxic Substances in Schedule 1 to the Canadian Environmental Protection Act, 1999. 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. All comments must cite the Canada Gazette, Part I, and the date of publication of this notice and be sent to the Director, Commercial Chemicals Evaluation Branch, Department of the Environment, Hull, Quebec K1A 0H3, (819) 953-4936 (Facsimile), or by electronic mail to the PSL Webmaster, PSL.LSIP@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. Annex Summary of the Draft Report of the Assessment of the Substance Hexachlorobutadiene Specified on the Priority Substances List Hexachlorobutadiene, or HCBD, has never been commercially produced in Canada. Formerly, the substance was imported into Canada for use as a solvent, but it is no longer imported. There are no natural sources of HCBD in the environment. Current Canadian sources are minor but potentially numerous and include possible releases in landfill leachates, releases during refuse combustion and releases as a by-product in the production of some chlorinated chemicals. At present, the most significant point source of HCBD in Canada appears to be the Cole Drain, which discharges into the St. Clair River, at Sarnia, Ontario, and includes outfalls from several industrial companies. The inadvertent production and use of HCBD in the United States are other potential sources of HCBD releases to the Canadian environment via long-range transport through the atmosphere or transboundary movement in shared water systems. When released into the environment, HCBD partitions to air, soil, water and sediments but tends to remain mostly in the compartment to which it was released. HCBD is slowly removed from the atmosphere by photooxidation, with an estimated half-life of up to three years. Evidence for long-range transport of HCBD exists, as the substance has been detected in samples taken from various sediment depths in Great Slave Lake. HCBD biodegrades slowly in aerobic water, with an estimated half-life of up to a year, but it would persist considerably longer under anaerobic conditions. HCBD accumulates in the tissues of freshwater organisms, with a maximum reported bioconcentration factor of 19 000, but it is quite easily metabolized and therefore does not biomagnify through food chains. Available data indicate that HCBD meets the criteria for persistence and bioaccumulation according to the Persistence and Bioaccumulation Regulations of the Canadian Environmental Protection Act, 1999 (CEPA 1999). HCBD has been detected in Canadian surface waters, sediments, aquatic organisms and, occasionally, air. Acute and chronic toxicity data are available for pelagic aquatic organisms, but no information is available on the toxicity of HCBD to benthic organisms. Concentrations of HCBD in Canadian surface water are lower than the adverse effects thresholds predicted for sensitive pelagic aquatic organisms. Concentrations of HCBD in the sediment of highly contaminated sections of the St. Clair River are high enough that sensitive benthic organisms could experience adverse effects because of their inability to move to less contaminated areas. HCBD is not likely to contribute significantly to ground-level ozone formation, but it does have the potential to contribute somewhat to depletion of stratospheric ozone and to climate change. The magnitude of these effects would depend upon the concentration of HCBD in the atmosphere; in recent years, the concentration of HCBD in Canadian air has been very low. Available data upon which to base estimates of population exposure to HCBD in Canada are extremely limited; however, food and, possibly, air appear to be the major routes of exposure. Based on results of studies conducted in experimental animals, the kidney appears to be the target organ of HCBD-induced toxicity. Kidney tumours have also been observed in rats following long-term exposure to HCBD, but only at doses associated with non-neoplastic renal effects. The estimated average daily intake by the general population in Canada from environmental sources is less than a Tolerable Intake derived on the basis of a benchmark dose or effect levels for non-neoplastic renal effects. A Tolerable Intake is the level of intake to which it is believed a person may be exposed daily over a lifetime without deleterious effect. Based on available data, it is concluded that hexachlorobutadiene is 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. It is concluded that hexachlorobutadiene is not entering the environment, in Canada, in a quantity or concentration or under conditions that constitute or may constitute a danger to the environment on which life depends; or that constitute or that may constitute a danger in Canada to human life or health. Thus, it is proposed that hexachlorobutadiene be considered "toxic" as defined in section 64 of the Canadian Environmental Protection Act, 1999 (CEPA 1999). Because HCBD meets the criteria for persistence and bioaccumulation according to the Persistence and Bioaccumulation Regulations of the Canadian Environmental Protection Act, 1999 and is present in the environment as a result of human activity, the substance will be proposed, under subsection 77(4) as a candidate for virtual elimination under subsection 65(3). Pursuant to subsection 77(4), because HCBD is proposed to be toxic under the Act and meets the criteria for persistence and bioaccumulation in accordance with the Persistence and Bioaccumulation Regulations, is present in the environment primarily as a result of human activity, and is not a naturally-occurring radionuclide or a naturally-occurring inorganic substance, implementation of virtual elimination under subsection 65(3) of HCBD is being proposed. It is recommended that sources of HCBD as a by-product in the production of other chlorinated chemicals, such as vinyl chloride, allyl chloride and epichlorohydrin be identified and measures to reduce these releases be investigated. HCBD releases during refuse combustion were identified. Preliminary information indicates that sources of HCBD from combustion are similar to those of dioxins, furans and hexachlorobenzene. It is recommended that measures to reduce emission of HCBD from combustion sources complement initiatives currently underway to address dioxins, furans and hexachlorobenzene. Since HCBD is persistent, bioaccumulative, likely to cause effects to aquatic species at low levels of exposure and is not currently used in commerce in Canada, options to prevent its reintroduction into the Canadian market should be explored. J. A. BUCCINI Director Commercial Chemicals Evaluation Branch On behalf of the Minister of the Environment
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