DSL Categorization under CEPA 1999 Section 73: Ecological Categorization Criteria and Process

The Existing Substances Program identifies, prioritizes, and assesses the risks resulting from exposure to substances existing in Canada. These activities are conducted jointly by Environment Canada and Health Canada.

Environment Canada is responsible for identifying and categorizing the substances that are persistent (P) or bioaccumulative (B) and inherently toxic (iT) to non-human organisms. The P and B criteria are in accordance with the Persistence and Bioaccumulation Regulations (CEPA1999). The criteria for iT to non-human organisms for Environment Canada are outlined in the Guidance Manual for the Categorization of Organic and Inorganic Substances on Canada’s Domestic Substances List.

Persistence (P)

Persistence refers to the length of time a substance resides in the environment. A substance’s persistence is commonly measured by its half-life, i.e., the time required for the quantity of a substance to diminish or degrade to half of its original amount in a particular environmental medium. The persistence of a substance in each of the relevant media (i.e., soil, water, or air) must be evaluated and compared against the categorization half-life criteria, as described in Table 1.

Table 1. Criteria for persistence

Substances that have the potential to be transported to remote areas of the globe are considered persistent, and the relevant evidence for long-range transport (LRT) will be taken into consideration in determining the persistence of substances.

Bioaccumulation (B)

Bioaccumulation is a general term describing a process by which substances are accumulated in organisms directly from exposure to water and through consumption of food containing the substances. The regulations express preference for bioaccumulation factors (BAFs) over bioconcentration factors (BCFs) or log octanol-water partition co-efficient (log Kow). The bioaccumulation potential of a substance must be evaluated and compared against the categorization criteria described in Table 2.

Table 2. Criteria for bioaccumulation

Bioaccumulation factor (BAF) refers to the ratio of the concentration of a substance in an organism to the concentration in water, based on uptake directly from the surrounding medium and food.

Bioconcentration factor (BCF) refers to the ratio of the concentration of a substance in an organism to the concentration in water, based only on uptake directly from the surrounding medium.

The octanol-water partition co-efficient refers to the ratio of distribution of a substance in octanol compared to that in water.

Inherent Toxicity (iT) to non-human organisms

The term inherent toxicity has been introduced and used under CEPA 1999 to distinguish this criterion from the term CEPA “toxic,” which is defined under section 64. Inherent toxicity refers to the hazard a substance presents to an organism. It is demonstrated by the concentration of a substance that produces a toxic effect in an organism, tested under laboratory conditions or in other studies.

Environment Canada prefers to use acute toxicity studies over chronic toxicity studies because more studies and QSAR models are available for acute endpoints. This makes it easier to directly compare the properties of a large number of substances.

The categorization for inherent toxicity to non-human organisms is based on numerical criteria, as described in Table 3.

Table 3. Criteria for acute and chronic toxicity to aquatic species (algae, invertebrates, fish)

LC₅₀ represents the concentration of a substance in water causing death on 50% of the experimental organisms in the water.

EC₅₀ represents the concentration of a substance in water inducing toxic effects on 50% of the experimental organisms.

NOEC, the non-observed-effect concentration, refers to the highest concentration of a substance at which there is no adverse effect observed in a toxicological study.

Health Canada is also responsible for identifying those substances on the DSL that present the greatest potential for exposure (GPE) to Canadians and those substances that are P or B and iT to humans. For more information, please refer to the following website of Health Canada at http://www.hc-sc.gc.ca/ewh-semt/contaminants/existsub/index_e.html.

Figure 1 describes the operational framework under CEPA 1999 for categorizing substances on the DSL.

Figure 1. Categorization and Screening on the DSL: Operational Approach

For more background on the categorization and screening of the DSL, please see our fact sheet on that subject.

To facilitate the identification of substances that are P or B, and iT to non-human organisms, Environment Canada has grouped substances on the DSL into organics, inorganics, polymers, and unknown or variable composition complex reaction products and biological materials (UVCBs). By grouping substances with similar technical properties, Environment Canada was able to efficiently apply varying technical approaches for each group through the categorization process.

The technical approaches, the types of scientific data considered and the data preference strategies used to arrive at a categorization decision for the organic and the inorganic substances are outlined in Environment Canada’s Guidance Manual for the Categorization of Organic and Inorganic Substances on Canada’s Domestic Substances List.

Based on the available data, Environment Canada has applied the approaches described in the Guidance Manual for data preference, weight of evidence, and the selection of pivotal values for non-human organisms. A pivotal value is a representative value, selected from among all the data assembled for a given endpoint, and compared against the categorization criteria. This is done for each criterion: persistence, bioaccumulation, and inherent toxicity to non-human organisms. This comparison forms the basis of the categorization decisions.

Technical guidance on the categorization approaches that were taken for polymers, UVCBs and organometallics was released in April, 2005 and can be found in the guidance documents Approach for the Ecological Categorization of Polymers, Approach for the Ecological Categorization of UVCBs and Approach for the Ecological Categorization of Organometallics.

Figure 2 illustrates the categorization process that was applied to all substances on the DSL.

Figure 2. Categorization process for substances on the DSL

 

For more information on the results that Environment Canada has obtained for categorizing substances in different groups, please see our Categorization Results.

Disclaimer: Although care has been taken to ensure that the information found on this website accurately reflects the requirements prescribed in the Canadian Environmental Protection Act (1999), you are advised that, should any inconsistencies be found, the legal documents, printed in the Canada Gazette, will prevail.