The Report to the Minister from the Siloxane D5 Board of Review was released on October 20, 2011. The Report is significant because it flows from the first substantive hearing by a Board of Review established pursuant to the Canadian Environmental Protection Act to review the nature and extent of danger to the environment posed by a chemical.  Siloxane D5 had been proposed to be added to Schedule 1 of the Canadian Environmental Protection Act following the completion of a Screening Assessment conducted by Environment Canada and Health Canada as part of Canada’s Chemical Management Plan.  Gowling Lafleur Henderson LLP represented the Silicones Environmental, Health and Safety Council of North America before the Board of Review.


Siloxane D5 is a odourless, colourless liquid that has many consumer and industrial applications. It is used as an ingredient in a number of personal care products, including deodorants, antiperspirants, cosmetics, shampoos and body lotions. It is also used as a dry cleaning solvent and in industrial cleaning.

Pursuant to Section 74 of the Canadian Environmental Protection Act, 1999 (“CEPA 1999”), the Ministers of the Environment and of Health conducted a Screening Assessment of D5. During the categorization process, D5 had been identified as a high priority for a Screening Assessment on the basis that it met the ecological categorization criteria for persistence, bio-accumulation potential and inherent toxicity to non-human organisms, and that it was known to be in commerce in Canada. The Screening Assessment concluded that, based upon the available information on its potential to cause ecological harm, D5 was considered to be entering the environment in a quantity or concentration or under conditions that has or may have an immediate or long-term harmful effect on the environment or its biological diversity. On that basis it was concluded that D5 met one or more of the criteria of Section 64 of CEPA 1999.

A Notice of Objection was filed with supporting information objecting to the conclusion reached in the Screening Assessment and a request was made to establish a Board of Review pursuant to Section 77(8) of CEPA 1999. Based upon the new scientific data provided, the Minister of the Environment agreed that a further inquiry into the nature and extent of the danger posed by D5 was warranted and accordingly established the Board of Review.

Report of the Board of Review

The Board considered all available information about the intrinsic physical and chemical properties of D5, along with its toxicity, uses, exposures and effects.  Based upon the evidence, the Board  concluded that:

  • D5 does not pose a danger to the environment;
  • while D5 may exceed the regulatory threshold for persistence it does not exceed the thresholds established in the Persistence and Bioaccumulation Regulation;
  • D5 does not bio-magnify, although it may bio-accumulate, and
  • there is no evidence to identify that D5 is toxic to any organism tested up to the limit of solubility in any environmental matrix.

Procedural Matters

The Report of the Board of Review summarizes a number of relevant procedural matters to be considered in the event of the establishment of any future Board of Review. These are:

  • the mandate of the Board may be constrained to only consider the extent of danger to the environment, and not human health as a consequence of the decision of the Minister establishing such a Board of Review; the hearing before the Board is a de novo assessment of the available science;
  • the Board’s review is not an appeal per se of the Screening Assessment; and
  • there is to be a full exchange of available information prior to commencement of the hearing. In addition to filing of all pertinent scientific data and reports, there was an opportunity to submit interrogatories and file supplementary data and reports in response to interrogatories. In addition, witness statements providing a summary of the evidence to be given by the witness were required to be provided.  As stated in the Report, “as a result before the hearing began, parties and the Board had a comprehensive and extensive record relating to Siloxane D5”.

Legislation and Regulations

The mandate of the Board was to determine the scope and extent of the danger to the environment posed by D5. The Board concluded that its mandate was not to conduct an appeal of the Screening Assessment, recognizing that the Board should not ignore the analysis and conclusions expressed in the Screening Assessment. The Board concluded that its mandate did not include a determination on whether D5 was “CEPA-Toxic” according to Section 64 nor whether it should or should not be added to Schedule 1 to CEPA as a toxic substance.

In considering however the nature and extent of the danger posed by D5, the Board interpreted its mandate to mean that it was required to determine whether detrimental effects were caused or might be caused to the environment by D5 taking into account all of the available, relevant, scientific information about D5. Importantly the Board concluded that it was required to take into account “information about the “intrinsic” physical and chemical properties of the substance along with its uses, releases, dissipation, transformation, and degradation, pathways of exposures, toxicity and effects.”  Further, the Board concluded that its review should be rooted in real-world terms and should not be a hypothetical assessment based on worst-case scenarios, insofar as the available data did not warrant that manner of proceeding.

The Persistent and Bioaccumulation Regulations were considered by the Board. A critical question addressed by the Board was the extent to which the intrinsic properties of the substance should be considered in assessment of persistence and bioaccumulation. Should the Regulations be interpreted to mean that the intrinsic properties of a substance should only be taken into account in cases where it is not possible to rely on the generally recognized methods of the OECD or other similar organizations when assessing persistence and bioaccumulation? The Board determined that:

“when assessing persistence and bioaccumulations evaluators should take into account the other factors referred to in section 5: the intrinsic properties of a chemical, the ecosystem under consideration, and conditions in the environment. Furthermore, the Board interpreted the term “intrinsic properties” to mean intensive properties such as vapour pressures and solubility as well as extensive properties such as toxicity.”

On the issue of bioaccumulation the Board decided that the determination of whether a substance is bio-accumulative is not based solely on the bioaccumulation factor (“BAF”), the bio-concentration factor (“BCF”) or the logarithm of its octanol-water partition coefficient (“Kow”), but may take into account other measures of bioaccumulation such as the bio-magnification factor (“BMF”), tropic magnification factor (“TMF”) and fugacity. In other words, the values of BAF, BCF or Kow may be used to screen chemicals out from further consideration or to prioritize chemicals for further study but should not be used to determine whether the chemical itself will pose a danger. Rather the Regulations require consideration of the intrinsic properties of the substance as well as other aspects of bioaccumulation.

Last, with respect to the application of the “precautionary principle”, the Board determined that the degree to which this principle should be applied depends upon the credibility and trustworthiness of scientific information about the substance.  If there is sufficient credible and trustworthy scientific information to conduct a scientifically robust and meaningful risk assessment then the Board concluded that it did not need to rely solely on the precautionary approach.

Nature, Use, Distribution, Concentrations and Toxicity of D5

Some observations taken from the Report of the Board which may be relevant for the purpose of assessing other substances are set out below.

  • Environment Canada regularly uses models to estimate releases to the environment, as well as the fate and distribution of a substance after release. The Board concluded that these models and tools have limitations and inaccuracies and consequently the interpretations based on the models were of limited use. Where empirical monitoring data is available, greater weight was given to measured values and the estimates provided by the models.
  • Long range transport by itself is an insufficient basis upon which to conclude a substance may pose a danger to the environment. In the case of D5 notwithstanding that D5 can be transported relatively long distances, depositions to soil or water are limited.
  • It is inappropriate to determine that a substances poses danger to the environment based on data from an extreme worst-case scenario, not representative of the concentrations released into the environment in other locations in Canada.
  • Persistence is not necessarily an indicator of danger in and of itself.
  • The Board followed a heirarchical evaluation of bioaccumulation. The Board considered the evidence of BAF and concluded that the values for BAF were equivocal and did not support a conclusion that the regulatory threshold for BAF had been met. The Board considered alternative methods of expressing bio-accumulation including multi-media BAF (“mmBAF”) but concluded that it would not be appropriate to rely on either mmBAF or relative BAF. BCF is the second factor to be considered and the Board concluded that the values for BCF were equivocal . The Board went on to consider the biota-sediment accumulation factor (“BSAF”), the BMF and TMF and based upon a review of all of the data, including depuration rates concluded that D5 does not bio-magnify, notwithstanding that it can be accumulated from environmental matrices or food into organisms. Accordingly, the Board rejected the conclusion in the Screening Assessment that D5 should be classed a bio-accumulative simply by comparing the values of BAF and/or BCF to the threshold values in the Regulations.
  • The Board concluded that such an approach may be appropriate in a lower – tiered screening assessment and in the absence of additional information of that intrinsic properties of a substance, but that where there is robust information then a more refined assessment of the potential danger should be conducted. The Board concluded that adverse effects from D5 are only observed in very large concentrations, in excess of solubility limits for the various environmental matrices, which cannot be obtained in the environment as a result of normal release.
  • The Screening Assessment calculated Hazard Quotations for D5. In the Board’s opinion, the Hazard Quotations were based on incorrect assumptions and parameters used to predict concentrations in the event resulting in a overly conservative estimate of the risk of D5. The Board rejected that over estimate.
  • The Board prepared probability plots for the purpose of determining danger to plants or animals and concluded that the risks were minimal.

Observations and Recommendations

The Board also made a number of observations and recommendations. These include the following:

  • The Persistence and Bioaccumulation Regulations should be reviewed periodically to ensure that they reflect current scientific standards and risk assessment methodologies.
  • A guidance document should be issued to describe how parameters such as persistence, bioaccumulation and intrinsic properties are to be examined in the risk assessment.
  • The Board encouraged Environment Canada to update its models or tools regularly, to seek outside input to ensure the integrity of those models and to ensure that users are aware of the strengths and weaknesses of the models or tools. The Board recommended that the models become transparent.

Conclusion and Summary

The Board concluded that D5 did not present a risk to the environment. While the Report of the Board may be considered as being restricted to D5, it is useful for the purposes of determining how other substances should be evaluated, how the applicable Regulations should be interpreted, and the kind of information that will be required in the event that there is any dispute with the conclusions reached in a Screening Assessment.

In order to review the Report please see: