Categorizing substances on the domestic substances list

Toxic substances can have different effects on human health and the environment. A substance that might be dangerous to wildlife in low levels might have no effect on people even at much higher levels. The opposite is also true: some substances can do more harm to humans than to the environment.

For this reason, Health Canada and Environment and Climate Change Canada used different but complementary criteria when sorting through the approximately 23 000 substances on the domestic substances list (DSL). This was to make sure that every substance that could potentially affect human health or our environment was evaluated to determine the need for further attention.

Environment

Persistence, bioaccumulation and inherent toxicity to the environment

Under the Canadian Environmental Protection Act 1999 (CEPA), the Existing Substances Evaluation Program is responsible for categorizing DSL substances to identify those that are suspected to be either:

1. persistent (P): chemical substances that take a very long time to break down in the environment - sometimes many years. These substances can affect the environment for a long period of time. Because they last for so long, they can travel long distances and pollute a much wider area than those that break down quickly.
   
2. bioaccumulative (B): chemical substances that can be stored in the organs, fat cells or blood of living organisms and remain for a long time. Over time, concentrations can build up and reach very high levels, and can also be transferred up the food chain.
   
   or
   
3. inherently toxic to the environment (iT_E): chemical substances that are known or suspected, through laboratory and other studies, to have a harmful effect on wildlife and the natural environment on which it depends.

Human health

Greatest potential for human exposure and inherent toxicity to humans

Under CEPA, the Existing Substances Program at Health Canada is responsible for identifying substances that have the greatest potential for exposure and are inherently toxic to humans.

1. greatest potential for exposure (GPE): when assessing human exposure to chemical substances, scientists look at more than persistence and bioaccumulation. Some shorter-lived substances might affect humans just as much as persistent ones. To get the complete picture, scientists look at how a substance is used. Health Canada identified those chemical substances on the DSL to which people are expected most likely to be exposed.
   
2. inherently toxic to humans (iT_H): these are chemical substances that are known or suspected of having harmful effects on humans. Substances were examined for a number of human health effects, including cancer, birth defects and damage to genetic material.

Chemical substances that can potentially affect human health were also placed in a priority sequence so the Government of Canada can first deal with those suspected of presenting the highest hazard and greatest potential for exposure.

The categorization process that was followed by Health Canada and Environment and Climate Change Canada is illustrated in the figure below.

Related links

• Categorization of existing substances
• Domestic substances list: overall categorization results
• Search engine for substances