Updates to the Air Contaminants Benchmarks List

We are committed to protecting Ontario’s air, ensuring we have strong environmental standards that are protective of human health and the environment, and taking action to enforce local air quality standards.

As part of this work, Ontario publishes the Air Contaminants Benchmarks (ACB) List as a reference tool for the government and the regulated community to use when assessing contaminants released to air.

The ACB List compiles air standards, guidelines and screening levels for approximately 5,200 contaminants. It is primarily used by emitters to complete an Emission Summary and Dispersion Modelling (ESDM) report under Ontario Regulation 419/05 or Ontario Regulation 1/17.

The list is updated as needed to ensure it continues to serve as a single reference source for the regulated community with correct information about Ontario’s air standards and guidelines, and defensible up-to-date screening levels.

The 2023 updates to the ACB List include:

1. Updates to reflect regulatory phase-out of certain air standards:
   • removal of half-hour (Schedule 2) air standards. As of February 1, 2020, all facilities in Ontario are required to comply with Schedule 3 air standards and use the newer air dispersion models set out in section 6 of the regulation
2. Updates to non-regulatory screening levels:
   • providing new/updated screening levels based on recent assessments by the ministry
   • updating screening levels for certain compounds with updated jurisdictional benchmarks
   • notes providing guidance on the assessment of metal compounds

Purpose of policy

All contaminants released to air above negligible amounts must be assessed for their potential to cause adverse effects, under:

• Ontario Regulation 419/05 (Air Pollution - Local Air Quality)
• Ontario Regulation 1/17 (Registrations Under Part II.2 of the Act - Activities Requiring Assessment of Air Emissions)

The Air Contaminants Benchmarks (ACB) List itemizes approximately 5,200 contaminants with corresponding benchmarks (standards, guidelines, or screening levels), to be used by facilities when assessing their contributions of a contaminant to air. This information is primarily used to complete an Emission Summary and Dispersion Modelling (ESDM) report under Ontario Regulation 419/05 or Ontario Regulation 1/17.

Contaminants are assessed using standards, guidelines, and screening levels on the ACB List, if available, or by a toxicological assessment, if no ACB List value is available.

Standards and guidelines are not-to-exceed values. If they are exceeded, facilities need to take actions as outlined in regulation.

Screening levels are conservative benchmarks below which adverse health effects from air emissions are not expected. They were first introduced by the ministry in 2008 to respond to stakeholder requests to streamline and expedite the process of assessing contaminants without ministry standards or guidelines.

Screening levels serve as a tool to quickly screen out a contaminant as a concern for potential adverse effects. If a screening level is exceeded, or no screening level is available for the contaminant, further assessment is needed, which may include a toxicological assessment.

By expanding the number of screening levels, the ACB List helps to reduce the number of toxicological assessments required by regulated facilities without negatively impacting the environment or human health.

Other information

In addition to the Registry posting, the ministry engaged in additional consultation on the approaches to generating/updating screening levels. All commenters indicated support for:

• the provision of the additional screening levels
• ongoing updates to the ACB List
• a regular and predictable schedule for these updates.

By keeping the currency of the ACB List and expanding it slightly to ~5,200 contaminants, the ministry fulfills its commitment to maintaining the list via regular updates.

Using the contact information provided below, individuals who would like to add a specific screening level value for a specific contaminant to the ACB List are able, at any time, to provide their recommended screening level value along with the supporting toxicological assessment for ministry review. If deemed appropriate, the proposed screening levels will be considered for inclusion in the next ACB List update.