Screening Health Assessment of Existing Substances Under the Canadian Environmental Protection Act, 1999
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Background and Mandate
The Canadian Environmental Protection Act, 1999 (CEPA 1999) requires the federal
Ministers of the Environment and of Health to identify and determine which existing substances
already in the environment pose a risk to human health or to the environment. Existing
substances are those included in an inventory known as the Domestic Substances List (DSL),
published in 1994. The DSL is a compilation of about 23 000 substances used in, manufactured
in or imported into Canada for commercial purposes between January 1, 1984, and December 31,
1986, at a quantity of greater than 100 kg per year; substances that are not listed on the DSL are
considered as being new to Canada.1 The DSL is periodically amended to add substances that
have met the listing requirements under the New Substances Notification Regulations of CEPA
1999.
The identification of existing substances that may pose a risk to human health and
subsequent assessment of those risks are undertaken within the Existing Substances Division
(ExSD) of the Healthy Environments and Consumer Safety Branch of Health Canada. One of the
ways in which health risks are evaluated is through a screening health assessment.
Objective of a Screening Health Assessment
The objective of a screening health assessment2 is to consider in a preliminary fashion
whether or not a substance is likely to pose a risk to human health. It is part of an overall strategy
designed to focus action on those compounds that pose the greatest risks to the health of
Canadians. The focus of the screening health assessment is limited principally to the information
that is considered most critical in assessment of human exposure to a substance and its health-related
effects. It entails an initial look at this information only, thereby enabling a large number
of existing substances to be evaluated more quickly and efficiently. If needed, some substances
will undergo a more in-depth assessment of the risks to human health, but only after a screening
assessment has been conducted.
Substance Identification for Screening Assessment
There are three principal ways in which substances may be identified for a screening
assessment:
![Organization of Screening Assessment](/web/20071116022415im_/http://hc-sc.gc.ca/ewh-semt/images/hecs-sesc/contaminants/existsub/orgpage_chart3_e.jpg)
- Categorization of the DSL under Section 73 of CEPA 1999: This involves the
identification of:
- Substances on the DSL considered to pose to individuals in Canada the greatest
potential for exposure; or
- Substances on the DSL that are persistent and/or bioaccumulative that are also
deemed to be inherently toxic to humans or non-human organisms.
- Reviews of Decisions of Other Jurisdictions under Section 75 of CEPA 1999: Decisions
taken in other jurisdictions to prohibit or restrict substances for environmental or health
reasons are reviewed by the Ministers to determine whether the substance in question could
potentially represent a danger to human health or the environment in Canada. Depending
upon that review, a screening assessment of the substance may be conducted.
- Public Requests under Section 76(3) of CEPA 1999: The Act enables any person to write
to the Minister of the Environment and request that a substance be added to the Priority
Substances List (PSL). Substances so nominated for addition to the PSL would first typically
undergo a screening assessment.
Outcome of a Screening Health Assessment
On the basis of a screening assessment, the Ministers of the Environment and of Health
may recommend to take no further action in respect of the substance, to add the substance to the
PSL for a more in-depth assessment of risks to human health or the environment or to
recommend that the substance be added to the List of Toxic Substances in Schedule 1 of the Act,
which may set the stage for taking actions to manage the risk.
These outcomes are dependent, in part, on determining in a screening assessment whether
a substance is toxic or capable of becoming toxic as defined in Section 64 of CEPA 1999, which
states:
...a substance is toxic if it is entering or may enter 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;
- constitute or may constitute a danger to the environment on which life depends; or
- constitute or may constitute a danger in Canada to human life or health
This definition of “toxic” under CEPA 1999 is a legal one that may be considered in the
context of risk, since it embodies the concept that harm is a function of both the intrinsic toxicity
(i.e., toxicity in the traditional sense) and the extent of exposure. However, substances with high
intrinsic toxicity to human health (e.g., those that cause cancer through direct interaction with
genetic material) are also considered “toxic” under CEPA 1999.
Process for Screening Health Assessments
In broad terms, the process for conducting screening health assessments is as follows:
- Substance Identification: As noted above, there are three principal ways in which a
substance may be identified for a screening health assessment. Screening assessments would
also be conducted on any other substances for which preliminary assessment is desirable.
- Data/Information: Information on effects and exposure is obtained from a wide variety of
sources, such as web-based databases, surveys and previous reviews or assessments of
substances conducted by national or international agencies. Information is identified from
published and unpublished studies. Data gathering is robust, employing comprehensive
search strategies, like those used for the assessment of Priority Substances (see
http://www.hc-sc.gc.ca/hecs-sesc/exsd/psap.htm). Screening assessments take into account
existing, up-to-date, peer-reviewed national and international risk assessment evaluations to
the maximum extent possible.
- Preparation of the Draft Screening Health Assessment and Supporting Working
Documentation: Screening assessments of risks to human health focus directly on the most
critical effects and conservative effect levels and upper-bounding estimates of exposure, after
consideration of all relevant identified information. Documentation prepared as part of this
process includes:
- A Screening Health Assessment Report. This is a brief (e.g., typically 4–8 pages)
summary of the information on identity, production and uses, sources and levels of
human exposure and health effects. The report also outlines the objective of the
screening assessment, the approach to decision-making and conclusions and
transparently delineates the databases that serve as the basis for determination of the critical effect levels and upper-bounding exposure estimates. An explicit summary is
included in the text, and more detailed information that constitutes the basis for
estimations of exposure and assessment of effects is presented in accompanying
tables. A full reference list is included to ensure transparency of the identified
database. The screening health assessment report is posted on the ExSD website.
- A Supporting Working Document. This unpublished document provides greater
detail on the information used in the screening health assessment and decision-making
process. It is available upon request from ExSD.
- A joint amalgamated brief (3–6 paragraphs) scientific summary of the Health
Canada and Environment Canada screening assessments and the Ministers’ proposed
measure are published in the Canada Gazette.
- Internal Peer Review: The draft screening health assessment report and supporting working
documentation are reviewed at meetings involving senior ExSD technical staff to consider
the critical issues and conclusion.
- External Peer Review: The draft screening health assessment report and supporting working
documentation are then reviewed externally, primarily to address adequacy of data coverage
and defensibility of the conclusion.
- Public Comment: The draft screening health assessment report (and proposed conclusion
and Ministerial recommendation) are posted for public comment for a period of 60 days, as
mandated under CEPA 1999. Feedback received from the public comment period is then
taken into consideration in finalization of the conclusions and Ministerial recommendations.
Summaries of the comments and responses thereto are also posted, upon revision of the draft
screening health assessment.
Basis for Decision-Making in Screening Health Assessments
Decision-making for screening health assessments under CEPA 1999 is based on a “margin of exposure” approach. The “margin of exposure” is the magnitude of the ratio between
the level (dose) at which the critical effect is observed in studies conducted in animals or, in
some cases, humans and the upper-bound estimated (or measured) level of human exposure to a
substance. Recommendations are based on the adequacy of this margin of exposure, taking into
account confidence in the completeness of the identified databases on effects and exposure,
within a screening context:
- Generally, margins greater than 1000 are adequate as a basis for recommending no further
action for substances where the databases on exposure and effects are relatively complete.
- For margins less than 1000, limitations of and confidence in the exposure and effects
databases are carefully considered and documented.
- In some cases, consideration of some more complex information, such as that on mode of
action (i.e., the manner in which a substance induces toxic effects), and/or more refined
estimates of exposure and/or assessment of critical effect levels may be required.
However, in cases where an original comprehensive analysis of available data on mode of
action and/or the generation of such data are warranted to more fully inform decision-making,
the substance would be recommended for addition to the PSL for further in-depth
assessment.
- In some cases, where the margins of exposure are less than 1000, but the uncertainty in
the available databases on exposure and/or effects is significant, a conclusion of “suspected to be toxic” is proposed as a basis to solicit additional information to permit a
more definitive conclusion to be reached.
- For substances with high intrinsic toxicity to human health (e.g., those that cause cancer
through direct interaction with genetic material), with effects where there is some
probability of harm at any level of exposure, the substance would be proposed “toxic”
under Paragraph 64(c) of CEPA 1999 and recommended for addition to the List of Toxic
Substances under the Act, and guidance would be provided concerning priority of
analysis of options to reduce exposure. For substances with potentially high intrinsic
toxicity to human health, but with significant uncertainty in the available database on
effects, a conclusion of “suspected to be toxic” is proposed as a basis to solicit additional
information to permit a more definitive conclusion to be reached.
The relative uncertainty of and degree of confidence in exposure and effects databases
that serve as the basis for decision-making in the assessment of high intrinsic toxicity or the
adequacy of margins of exposure are explicitly delineated and consistent across screening
assessments. They are consistent with similar considerations made for the health risk assessment
of Priority Substances under CEPA 1999 and include, for example, consideration of aspects such
as:
- interspecies and intraspecies variation,
- nature of the critical effect,
- dose spacing in the critical study,
- steepness of the dose–response curve,
- extent of the database as the basis for characterization of hazard for all effects including
that considered critical,
- degree of protection provided by the critical effect level, and
- whether or not estimates of exposure are based on, for example, environmental monitoring or modelled data or higher-confidence internal doses (e.g., levels in blood).
Cut-Off Date for the Review of Data
A cut-off date for consideration of relevant data is specified in all screening health
assessment reports to ensure the full evaluation of identified information through several stages
of internal and external review. This approach is consistent with international practice and is designed to achieve transparency and defensibility of the process, while respecting the mandate
under CEPA 1999 to complete assessments on large numbers of existing substances
expeditiously. Information submitted after the cut-off date is considered primarily in the context
of its implications for risk management (if appropriate) or in setting priorities for reassessment at
a later date.
Comparison of Screening and Priority Substances List Health Assessments
The following table presents a comparison of some of the key differences and similarities
between a screening health assessment and the assessment of health risks conducted for Priority
Substances under CEPA 1999.
Issue |
Screening Assessment |
Priority Substances List Assessment |
Concept |
Initial assessment of whether a
substance poses a risk to human
health. |
A critical and comprehensive
analysis of the risks to human
health. |
Possible
Outcomes |
There could be no further action
on the substance, it could be
considered for risk management it could be considered for more in-depth
PSL risk ssessment. |
There could be no further action on
the substance or it could be
considered for risk management. |
Information
Gathering |
Comprehensive information
search strategies employed.
Similar to that for PSL
assessments. Greater reliance on
other peer-reviewed assessments
for identification and assessment
of previously reviewed data. |
Comprehensive information search
strategies employed. The search
strategies are noted in the PSL
assessment reports. |
Evaluation of
Exposure |
Focus on upper-bounding
estimates of exposure, after
consideration of all relevant
identified information. |
Detailed analysis (e.g., probabilistic)
of exposure, after consideration of
all relevant identified information. |
Evaluation of
Effects |
Focus directly on health-related
effects, which occur at lowest
concentration or dose. |
Detailed review of all relevant
health-related data and full weight
of evidence analysis for hazard
characterization. This includes
weighting of all relevant data, taking
into account factors such as
consistency, plausibility of observed
effects, etc. |
Hazard
Characterization |
Focus directly on the most
conservative effect level
associated with the critical health-related
effect and/or identification of substances with high intrinsic
toxicity to human health. |
Weight of evidence approach with
in-depth evaluation of mode of
action (i.e., how a substance induces
its toxic effects), toxicokinetics (how the substance is absorbed and
distributed within the body),
metabolism and exposure–response
(e.g., benchmark dose) relationships,
where data permit. |
Approach to
Dose–Response
Assessment |
Margin of exposure approach —
i.e., magnitude of the ratio
between conservative effect level
for effect considered critical and
upper-bound estimated (or
measured) level of human
exposure. |
Development of tolerable daily
intakes / concentrations, employing
default or compound-specific
adjustment factors where data
permit. Consideration/incorporation
of physiologically based
pharmacokinetic models or
biologically motivated case-specific
models, where data permit. |
Confidence /
Uncertainties in
the Assessment |
- Deals principally with
characterization of the extent of
the available database that serves
as basis for the delineation of the
critical data on exposure and
effects.
- Specified in the screening
assessment report and supporting
working documentation. |
- Deals with characterization of the
extent of the available database that
serves as basis for the delineation of
the critical data on exposure and
effects, but primarily with the
characterization of specific aspects
of dose–response.
- Specified in the PSL assessment
report. |
Documentation
Prepared |
- Screening health assessment
report (published).3
- Supporting working
documentation (unpublished).
- Short amalgamated summary of
health and environmental
screening assessments published
in the Canada Gazette. |
- Amalgamated health and
environmental risk evaluations
published in a PSL assessment
report.
- Supporting documentation
(unpublished) for the health
components (exposure and effects)
assessment.
- Synopsis of amalgamated health
and environmental assessments
published in the Canada Gazette. |
Delineation of
Follow-up
Actions |
- When the recommendation is to
add the substance to the PSL for
more in-depth assessment, the
additional work required is clearly
delineated in the screening
assessment report.
- When the recommendation is to
consider the substance “toxic”
under Paragraph 64(c) of CEPA
1999, the appropriate
considerations for follow-up and
guidance on the priority for the
development of options to reduce
exposure are clearly delineated in
the screening health assessment
report. |
- When the recommendation is to
consider the substance “toxic” under
Paragraph 64(c) of CEPA 1999, the
appropriate considerations for
follow-up and guidance on the
priority for the development of options to reduce exposure are
clearly delineated in the PSL
assessment report. |
Scientific Review
— Internal |
Internal review meetings by senior
ExSD technical staff to consider
critical issues and the conclusion
of the assessment. |
Review by senior ExSD technical
staff. |
Scientific Review
— External |
External review by small number
of experts primarily to address
adequacy of data coverage and
defensibility of the conclusion or
to address specific questions on
identified critical issues. All
reviewers must have declared
non–conflict of interest. |
External review often by convened
panels of experts for adequacy of
data coverage, defensibility of
selection of the critical data, dose–
response analysis and exposure
assessment. All reviewers must have
declared non–conflict of interest. |
Public Comment |
Sixty-day public comment period
mandated under CEPA 1999. |
Sixty-day public comment period
mandated under CEPA 1999. |
DSL Pilot Phase
Health Canada and Environment Canada selected 123 substances from the DSL to be part
of a pilot phase to assist in development of the process, procedure and criteria for decision-making
for the screening assessment program under CEPA 1999. Health Canada selected 30
substances on the basis that they likely present to individuals in Canada the greatest potential for
exposure. Environment Canada selected 93 substances considered to be persistent and/or
bioaccumulative and inherently toxic to non-human organisms. Over the next few years, the
screening assessments conducted will focus primarily on substances in the pilot phase.
Update
This document will be revised and updated as the approach to screening health
assessment becomes more refined, based upon the additional operational experience gained in
conducting such assessments on larger numbers of existing substances.
1 Substances new to Canada after December 31, 1986, are assessed under the new substances provisions of CEPA
1999.
2 Screening environmental assessments under CEPA 1999 are conducted by Environment Canada.
3 Screening environmental assessment report published separately.
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