Summary of comments and responses: addition of precursors to particulate matter, chapter 1

1. Process

Comment received

The declaration of toxicity for the precursors is not based on a credible scientific process. Neither the PM Priority Substances List (PSL) report nor the Ozone Science Assessment Document (SAD) conclude that the precursors are toxic. A PSL assessment for each of the substances should be completed before any declarations of toxicity are made.


The Ministers' recommendation is based on sound science conducted over the past decade. The PSL Assessment for PM10, the PM SAD and the Ozone SAD were developed through a multi-stakeholder, peer-reviewed process, and these documents clearly identify the principal precursors to PM10 and ozone. This provides the Ministers with the appropriate scientific basis for proceeding with a recommendation under section 90(1).

In the case of the precursors, the ministers are confident that a formal PSL assessment is not required because the existing science supports the conclusion that the precursors participate in chemical reactions in the environment that result in the formation of PM10 and ozone, which are toxic.

It should also be noted that a precedent exists for adding precursors to a toxic substance to Schedule 1 (precursors to dioxins and furans).

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