How were substances categorized?
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 Canada used different but complementary criteria when sorting through the 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 identified for further attention.
Persistence, Bioaccumulation and Inherently Toxic to the Environment
Under the Canadian Environmental Protection Act, 1999 (CEPA 1999), Environment Canada was responsible for identifying and assessing the environmental risks of chemical substances that were suspected to be:
Either one of:
| a) |
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 substances that break down quickly. |
b) |
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. |
| AND |
| c) |
Inherently Toxic to the Environment (iTE): chemical substances that are known or suspected, to have a harmful effect on wildlife. |
| Combining the "P" from Persistent, the "B" from Bioaccumulative and the "iT" from Inherently Toxic, P/BiT (often called pee-bit) is an acronym commonly used by many international programs. |
Greatest Potential for Human Exposure and Inherently Toxic to Humans
Health Canada was responsible for identifying substances that have the Greatest Potential for Exposure or are Inherently Toxic to Humans.
- 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 often as persistent ones. To get the complete picture, scientists look at how a substance is used. On the DSL, Health Canada identified those chemical substances suspected to be the ones that people are most likely exposed to.
- Inherently Toxic to Humans (iTH): 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.
Benefits of Categorization
Categorization has given us more information than ever before on the chemical substances on the DSL. We now know many (roughly 19,000) do not need further action at this time. At the same time, the Government of Canada will look very closely at a number of others and, depending on the results, move quickly to protect the environment or human health.
Through categorization, the Government of Canada has identified approximately 4,000 of the 23,000 chemical substances on the DSL as meeting the criteria for further attention. But it is important to remember that in many cases more information is required to determine if these substances pose a risk to human health and/or the environment. More detailed information is available on how the government determines risk in the Assessing Chemical Substances section.
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