Chemical Substances
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Chemicals Management Plan - Challenge Advisory Panel
Summary Report
From the meetings held April 11, 2008 and May 9, 2008
Panel members present April 11, 2008: Dr. T. Boadway (Chair), Dr. J. Bend, Dr. C. Brunk, Dr. S. Findlay, Mr. G. Granville, Ms. L. Lusby, Dr. S. Maguire, Dr. G. Muckle, Dr. P. Orris, Dr. D. Scott
Regrets: Dr. N. Cherry, Dr. J. Eyles
Panel members present May 9, 2008: Dr. T. Boadway (Chair), Dr. J. Bend, Dr. N. Cherry, Mr. G. Granville, Dr. S. Maguire, Dr. G. Muckle
Regrets: Dr. C. Brunk, Dr. J. Eyles, Dr. S. Findlay, Ms. L. Lusby, Dr. D. Scott
Outline:
The Challenge Advisory Panel meeting agendas for April 11 and May 9, 2008 were structured around two key questions (see below) provided to the Panel for deliberation, open discussion and debate. Government staff members were present to make brief presentations, answer questions and clarify information. The questions presented concerned procedures and policies applied in the screening assessment determinations. At the end of the discussions, Panel members were asked to craft a response to each of the questions.
In the text below, the Government question is quoted in its entirety from the documents provided to the Panel.
Meeting Summary:
Welcome and Introductory Comments
The Chair welcomed all members and government staff. The meeting began with introductory remarks from the Chair. A brief feedback session to evaluate the proceedings of meetings to date was opened to allow Panel members time to provide input to the Chair and Secretariat staff.
Panel Discussion
Question 1 – Health Priorities
For threshold effects, decision-making related to human health under the Challenge is based on margins of exposure between conservative estimates of effect levels and upper-bounding estimates of exposure to the general population, and applying a precautionary approach, taking into consideration confidence in the effects and exposure databases.
The screening assessment report for D4 is illustrative of Health Canada's approach for characterizing risk for threshold substances. Does the panel agree that the weight of evidence and application of precaution support the proposed conclusion that the substance is ‘not toxic’ to human health?
Consideration:
Although octamethylcyclotetrasiloxane was considered a high priority for action under the Challenge because of its reproductive toxicity, the critical effect level is based on effects in the liver. This effect level, however, is protective of reproductive effects as reproductive effects occurred at much higher doses.
Attachment:
Draft screening assessment report for octamethylcyclotetrasiloxane (D4) CAS 556-67-2
Panel Response to Question 1:
“The Panel agrees that the weight of evidence and application of precaution support the proposed conclusion that the substance is ‘not toxic’ to human health.”
Question 2 - Ecological Priorities
Draft screening assessments of the ten ecological-stream substances in Batch 2 have identified 1) six substances which are still considered as persistent, bioaccumulative, and inherently toxic to aquatic organisms, and 2) four which are now considered not to meet those three criteria. The general approaches taken for assessing and concluding on these two broad types of assessments have been considered and supported by the Advisory Panel during Batch 1.
The siloxane substance D4 in Batch 2 was identified as a high priority for both ecological and human health streams. The ecological component of this draft screening assessment is presented here as a further illustration of the application of the first approach for PBiT substances.
In the context of the Challenge, a predisposition exists in relation to whether a substance meets the definition of toxic under section 64(a) and/or (b) of CEPA. The predisposition is conditioned on current evidence that the substance is persistent, bioaccumulative, inherent toxicity as demonstrated by acute aquatic toxicity, and that the substance remains in commerce in Canada.
While there may be some conflicting evidence and significant uncertainties regarding the results, we are exercising a precautionary approach to propose that the substances meet the definition of toxic under s.64(a) and/or (b) of CEPA given the potential hazardous properties and potential risks posed by these high concern substances.
A specific example in Batch 2 is the case of D4. This substance was considered PBiT through categorization and, based on current information, large quantities still remain in commerce in Canada. The data considered in the screening assessment (physical and chemical properties, environmental fate, bioaccumulation, persistence and ecotoxicity data) included both experimental data and data estimated through the use of models (e.g., using quantitative structure-activity relationships, or QSAR).
The weight of evidence indicates that this substance meets the P & B criteria and could harm aquatic organisms (iT). In addition, since accumulations of P and B substances may be widespread and are difficult to reverse, a conservative response to uncertainty was believed justified and, based on the above, the substance is being proposed to meet the definition of toxic under section 64(a).
Does the Advisory Panel agree that the weight of evidence and application of precaution support the proposed conclusion that the substance is "toxic" to the environment?
Considerations:
Industry and others have further opportunity to provide information during the up-coming public comment period.
For P & B & iT substances that are concluded to be toxic under section 64, the risk management objective is virtual elimination of releases.
Attachment:
Draft Screening Assessment Report for D4 (CAS RN 556-67-2)
Panel Response to Question 2:
“The Panel agrees that the weight of evidence and application of precaution support the proposed conclusion that the substance is ‘toxic’ to the environment.”
