Risk assessment of chemical substances

The information described on this page and each related fact sheet may change as our chemical substances risk assessment program, policies, and methods evolve over time.

Substances, such as individual chemicals and polymers, have many different properties and many different uses. Some are used to make plastics flexible while others help to put out fires. Some are formed through common chemical reactions that occur naturally in the environment. Still others are present in foods and in products we use as part of our day-to-day activities, such as shampoos, floor cleaners, clothing fabrics, and children's toys.

In the same way that substances have different uses, some can also be harmful in different ways. For instance, some may harm fish, while some are linked to life-threatening diseases, such as cancer. Others may be carried long distances through the air and affect people or the environment far away.

The risks posed by a substance are determined both by its hazardous properties and by the nature of the exposure that takes place. Scientific evaluations or risk assessments are conducted under the Canadian Environmental Protection Act, 1999 (CEPA 1999) to determine whether there are risks resulting from exposure of Canadians to a substance or from releases of a substance into the environment, and the specific ways Canadians or the environment can be affected.

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The CEPA 1999 risk assessment process

Under the purview of the Minister of Health and the Minister of the Environment, scientists assess existing substances that are in commerce in Canada [substances on the Domestic Substances List (DSL)] and new substances intended to be imported into or manufactured in Canada (not yet on the DSL), to determine whether these substances present or may present a risk to the environment or to human health. Decisions are based on a scientific evaluation of the risk posed by a substance, which considers both the hazardous properties of the substance (such as toxicity to aquatic organisms or cancer-causing properties) and the nature and extent of the exposure of Canadians or the environment to the substance. This allows the Government of Canada to determine whether a risk management measure is needed, and if so, what type of control is best suited for reducing or preventing the potential harm.

The unique characteristics of substances need to be considered when making decisions about the need for risk control measures. For example, it may be straightforward to assess a substance that has a single use. It gets more complicated, however, for substances that have many different uses, enter the environment in different ways, or could affect humans or other organisms differently depending on the nature of the exposure.

As a result, there are various types of risk assessments that may be undertaken. These are described within the Risk Assessment Toolbox. In addition, substances that may be of concern and warrant a risk assessment are identified through the ongoing consideration of new information. An approach outlining the process for identification of risk assessment priorities (IRAP) was published in 2014.

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Data on the amount and the rate at which a substance enters the environment, how it enters the environment, as well as its chemical properties, provide information about how the substance is or may become distributed in the environment. How long it will reside in the environment, and whether it is present at levels that may be harmful to Canadians or the environment are also considered. All the above information is combined to assess the fate of the substance in the environment and therefore understand how exposure occurs or may occur.

Different approaches for characterizing exposure may be used depending on the information available regarding sources, uses, handling, and disposal of the substance. For human health assessments, certain parameters used in estimating exposure are standardized to ensure consistency of approach (exposure factors). Among the various sources and uses of substances that may result in exposures, everyday products and food-related uses are often considered in risk assessments for human health and the environment.

The potential effects of the substance on humans and the environment are evaluated (hazard characterization). The most susceptible populations (such as children) or receptors (such as early life stages of fish) as well as critical effects (such as mortality, reproductive and developmental impairment, endocrine effects, and carcinogenicity) are identified.

A key component of an ecological risk assessment is determining the potential for a substance to cause adverse effects to organisms. The assessment of adverse effects may include the derivation of a predicted no-effect concentration (PNEC). PNECs, which may be based on published water quality guidelines, are used in ecological assessments with the aim of identifying the concentrations of a substance below which adverse effects are unlikely to occur. There are generally 2 approaches used to determine concentrations of substances that would be protective of all species. The first is the assessment factor approach, used in cases where a substance has been studied on only a few species. The second is the species sensitivity distribution (SSD) that is used when the toxicity of a substance has been studied on a broader range of species. Both are described further in 2 fact sheets.

In the assessment and management of substances, the Government takes into consideration subpopulations who, due to greater susceptibility or greater exposure, may be more vulnerable to experiencing adverse health effects from exposure to substances. The Government is exploring opportunities to strengthen its approach.

A combination of qualitative and quantitative approaches may be used to characterize the overall risk of a substance. This includes data generated through laboratory or field testing, and modelling approaches, as examples. The results inform both ecological and human health assessments.

New approach methods (NAMs) are used in chemical risk assessments and include any technology, methodology, approach or a combination of these that can be used to replace, reduce or refine animal testing and allow for more rapid or effective prioritization and/or assessment of chemicals. In Canada, the Government develops, validates and uses NAMs to support risk assessment, including for screening, prioritizing, grouping, and informing decisions in both the existing and new substances programs under CEPA 1999.

Examples of the use of NAMs in both human health and ecological assessment activities are provided and described in recent science approach documents (SciADs). For human health, the bioactivity exposure ratio SciAD describes a high-throughput computational approach for chemical prioritization and screening level assessment. On the environmental side, the Ecological Risk Classification of organic substances (ERC) Approach is an example of an innovative science approach for prioritizing substances and classifying risks.

A common issue in the risk assessment of substances is a lack of available experimental data. In the absence of experimental data on a substance, other approaches (that is, NAMs) may be used to address data needs, such as the use of computational modelling and "read-across". For read-across, data from substances that have a similar structure and physical-chemical properties to the substance being assessed are used to address gaps in toxicity data.

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The risk assessment process for existing substances

An essential first step in risk assessment is the collection of information on each substance or substance group. A range of information is considered in an assessment, including chemical properties, quantities manufactured in or imported into Canada, releases to and concentrations in the environment, environmental fate and behaviour, hazards, and nature of exposure. Information is gathered from a wide variety of published and unpublished sources. These include literature and database searches, information submitted by stakeholders through voluntary or mandatory surveys, and previous reviews or assessments of substances conducted by other national or international agencies. Information is also generated by government researchers or stakeholders carrying out studies, testing, or monitoring of substances. For example, biomonitoring surveys on humans provide data on the levels of a substance in a person's blood or urine that represent sources of exposure to a given substance.

Throughout the risk assessment process, expert and stakeholder engagement is an important component. The screening assessments undergo external peer review and/or consultation involving experts from government, academia, industry, and non-governmental organizations, to obtain expert input on critical technical issues. As well, draft screening assessments are subject to a 60-day public comment period. While all comments are taken into consideration, the final content and conclusion of screening assessments remain the responsibility of Health Canada and Environment and Climate Change Canada.

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The risk assessment process for new substances

Prior to a substance being imported or manufactured in Canada, the new substance must undergo an ecological and human health risk assessment. This process begins with a pre-import or pre-manufacture notification of the substance. This means that any company or individual intending to import or manufacture a new substance in Canada is required to submit a package containing all information prescribed in the New Substances Notification Regulations. This information will be used to conduct a risk assessment.

In general, the risk assessments of new substances are conducted similarly to those for existing substances. See the New Substances program for more information.

Risk conclusions under CEPA 1999

For the purposes of section 64 in Part 5 of CEPA 1999, a substance is toxic if it is entering or may enter the environment in a quantity or concentration or under conditions that:

  1. have or may have an immediate or long-term harmful effect on the environment or its biological diversity,
  2. constitute or may constitute a danger to the environment on which life depends or
  3. constitute or may constitute a danger in Canada to human life or health.

A determination of whether or not a substance or group of substances meet these criteria takes into consideration the relevant information available such as its hazard (effects) and its potential exposure to the Canadian environment and humans as well as any uncertainties. Maintaining transparency is key to a credible assessment process. Therefore, care is taken to ensure uncertainties are captured and communicated in the screening assessment.

If a substance is determined to be toxic or capable of becoming toxic as defined in section 64 of CEPA 1999, then risk management measures are considered to prevent or control risks identified. Follow-up activities may be undertaken for those substances recognized for their potential effects of concern.

In conducting a risk assessment, a weight of evidence approach and precaution are applied. Key information across multiple lines of evidence is taken into consideration, along with uncertainties when concluding the risk assessment. In order to estimate the likelihood of effects or potential for risk, a comparison of levels of exposure to humans or ecological organisms to levels that are known to cause adverse effects is conducted. These are referred to as margins of exposure (MOEs) or risk quotients (RQs) and are used in risk assessments of substances.

Approaches used to carry out risk assessments are similar to those used by other regulatory jurisdictions. The results of international assessments on substances are used to inform CEPA 1999 risk assessments.

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