Setting B2 values

The ACB List sets out over 4800 B2 values. Approaches used by the ministry to establish a B2 value are considered conservative - exceeding a B2 value does not necessarily mean an adverse effect is expected. If a person demonstrates that the concentration of a contaminant is at or below a B2 value, no adverse effect is anticipated. If a person demonstrates that the concentration of a contaminant is above a B2 value, further work must be done to determine whether an adverse effect is likely at the concentration. The B2 value for a contaminant may be exceeded if a toxicological assessment shows that no adverse effect is expected at the point of impingement concentration.

Generally, B2 values are set by the ministry using a process that includes an internal peer review and public notification. Most B2 values are set from values used by other jurisdictions. The ministry may also set B2 values based on previous toxicological assessments and resulting recommendations made under the approvals program. These approaches are further discussed below.

Jurisdictional screening level (JSL) (Source: SL-JSL)

The JSL list was first introduced by the ministry in 2008 in response to requests from stakeholders to further streamline and expedite the review of air contaminants without limits. The JSL screening levels are based on a review of air quality values available in other jurisdictions and established using the following steps:

  • Step 1: Chronic air quality values (intended to protect against adverse health effects from long-term exposure) and their associated averaging time periods are compiled from 11 agencies for which we are confident that their values are based on health considerations only. They include Health Canada, the United States Environmental Protection Agency (USEPA), the World Health Organization, the National Institute for Public Health and the Environment of the Netherlands (RIVM), and the Environmental Protection Agencies from California, Massachusetts, Michigan, Minnesota, New York, North Carolina, and Texas. For carcinogens where a risk level or averaging period is not specified, concentrations reflecting a one in one million (10-6) incremental cancer risk are included with an annual averaging period.
  • Step 2: All chronic air quality values are converted to an equivalent concentration representing a 24-hr averaging time period in order to select the median. The equivalent 24-hour concentration is calculated using the conversion-factor equation set out in subsection 17(3) of O. Reg. 419/05.
  • Step 3: For each contaminant, the JSL is set according to the following criteria:
    • for a contaminant with an odd number of limits, the limit representing the median is set as the JSL
    • for a contaminant with an even number of limits, the limit just below the median is set as the JSL
    • if only two limits are available, the lower of the two limits is selected as the JSL
    • if only one limit is available for a contaminant, the limit is divided by 10 to account for the uncertainty in using a single value as the JSL

Ministry-derived (MD) screening levels (Source: SL-MD)

In the context of an ECA application, the ministry performs in-house toxicological assessments on modelled concentrations of air contaminants without limits to attempt to ensure against adverse effects. Assessments entail a review of the physical/chemical characteristics, toxicity information, existing jurisdictional values available for a contaminant and existing ministry B1 benchmarks if appropriate (e.g. if present in particulate form, the suspended particulate matter standard may be an appropriate value to assess against). A ministry derived screening level is a value taken from an in-house toxicological assessment which recommends a concentration that is considered to be protective against adverse effects.

Previously accepted (PA) screening levels (Source: SL-PA)

In the context of an ECA application, the ministry performs in-house toxicological assessments on modelled concentrations of air contaminants without limits to determine the likelihood of adverse effect. Through this process, some modelled concentrations for a contaminant are deemed "acceptable" (i.e. below a concentration associated with a potential adverse effect level). These accepted concentrations are compared to B2 values set using the JSL approach described above. If an accepted concentration of the contaminant is higher than the JSL value, the accepted concentration was used as the B2 value.

In this way, ministry assessment which consider toxicological information specific to a contaminant replaces a lower JSL value which represents a median of air quality values. These screening values are a modelled concentration potentially emitted from a facility, and therefore do not necessarily represent the highest concentration which the ministry would consider acceptable.

Ministry expectations

Both an ESDM report under O. Reg. 419/05 and an EASR ESDM report under O. Reg. 1/17 must be prepared in accordance with section 26 of O. Reg 419/05. As set out in section 26 of O. Reg. 419/05, the report must list all contaminants discharged from the property. If the concentration of a contaminant at a point of impingement is below a B2 value set out in the ACB List, it is not likely that an adverse effect would occur. If the assessment indicates a concentration that is above a B2 value, a toxicological assessment would need to be performed to determine the potential for adverse effect at such a concentration.

If it is determined that an adverse effect may occur at the concentration set out in the ESDM report, it is expected that the toxicological assessment would indicate the concentration below which an adverse effect would not be likely in the particular circumstances being assessed.

Also note that if a contaminant is not listed in the ACB List, a person must assess the potential for the concentration of the contaminant to cause an adverse effect. Further information on how to consider contaminants with no values set out in the ACB List is provided in the Procedure for preparing an Emission Summary and Dispersion Modelling report.