On  March 5, 2025, as part of its ongoing commitment to transparent chemical safety practices, Health Canada has published a detailed fact sheet explaining the moiety approach - a scientific methodology used to assess groups of chemical substances—under the Canadian Environmental Protection Act, 1999 (CEPA). This approach plays a key role in how the Government of Canada evaluates potential risks to both the environment and human health from substances that share a common chemical component.

What Is the Moiety Approach in CEPA Risk Assessment?

In chemical risk assessments under CEPA, the moiety approach evaluates the risk of a shared chemical structure or element - called a moiety - in a group of substances. Instead of analyzing each substance individually, assessments focus on the common moiety and its potential to cause harm. This allows for more efficient and holistic evaluations, particularly when dealing with complex families of chemicals.

For example, assessments using the moiety approach have been conducted for the benzothiazole group and for zinc and its compounds. The zinc assessment, focused on all substances capable of releasing zinc ions, whether from elemental zinc, zinc salts, organometallic compounds, or unknown/variable composition materials (UVCBs). These substances were assessed based on their ability to contribute to total zinc exposure in the environment.

How Does Health Canada Assesses Chemical Effects Using the Moiety Approach?

Ecological risk assessment under the moiety approach focuses on the toxic effects of the moiety in aquatic, sediment, and soil organisms. Health Canada and Environment and Climate Change Canada conduct targeted reviews of scientific literature and databases to determine toxicity thresholds. When sufficient reliable data are available, a Predicted No-Effect Concentration (PNEC) is established using species sensitivity distributions or assessment factors.

Environmental toxicity can vary due to factors such as pH, water hardness, and dissolved organic matter, particularly for metals. Therefore, PNECs may be adjusted to account for these conditions.

For human health assessments, scientists examine the toxicity of the moiety itself and assess whether any specific substances in the group pose higher risks. If a particular substance is found to be more hazardous than the moiety as a whole, it may be evaluated separately.

Exposure Assessment

The exposure assessment under the moiety approach considers all sources of environmental release that could lead to the presence of the moiety in air, water, soil, biota, or consumer products. This includes both anthropogenic (man-made) and natural sources. Exposure estimates are derived using both measured and modelled data, helping to quantify potential risk across the full range of environmental and human receptors.

Human biomonitoring data, such as concentrations found in blood, urine, or breast milk, are also considered. This provides a more complete picture of total exposure through all routes, including inhalation, ingestion, and skin contact.

CEPA Conclusions Based on the Moiety Approach

In assessing whether a moiety poses a potential risk, Health Canada uses all available evidence on exposure and effects. The evaluation may also consider:

• Vulnerable environments (e.g. sensitive ecosystems)

• Sensitive human subpopulations (e.g. children or pregnant women)

• Environmental and human exposure from nanomaterials, if applicable

While engineered nanomaterials are typically evaluated under a separate CEPA framework, their presence in environmental media can still be indirectly captured in moiety-based assessments if they release a relevant moiety.

Why This Approach Matters

The moiety approach enhances Canada’s ability to efficiently manage chemical risks by:

• Streamlining assessments for groups of related substances.

• Identifying shared hazards and exposure risks.

• Ensuring that regulatory action can be taken based on the core toxic component.

By grouping substances based on a common chemical identity, the Government of Canada ensures that emerging risks are addressed early, even when individual substances have not been prioritized for separate evaluation.