The Ontario Ministry of the Environment (MOE) has identified the need to develop and/or update air quality standards for priority contaminants. The Ministry's Standards Plan (PA9E0004, released in October, 1996 and revised in November, 1999) identified candidate substances for the development of air standards. Priorities were identified based on a number of considerations including toxicity, the potential for exposure, and the quantity of air emissions in Ontario. The MOE is proposing to amend O.Reg. 419/05, made under the Environmental Protection Act, to introduce a new standard for twenty-nine (29) Dioxins, Furans and Dioxin-like PCBs.
In developing air quality standards for Ontario, the MOE reviews and considers air quality guidelines and standards used by leading agencies world-wide, key toxicological and risk assessment information, and comments received from stakeholders throughout the two-step consultation process.
The polychlorinated dibenzo-para-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) are two series of aromatic compounds with similar physical and chemical properties. They are formed as by-products of combustion (e.g. incineration of waste products, fuel and wood burning) and industrial processes (e.g. metals smelting and refining, etc). Dioxins and furans are very persistent in the environment and tend to accumulate in biological systems. This proposed standard will also apply to 12 polychlorinated biphenyls (PCBs) which exhibit biological activity similar to that of 2,3,7,8-tetrachlorodibenzo-para-dioxin (TCDD or “dioxin”, Chemical Abstract Services number: 1746-01-6) and, therefore, are referred to as ‘dioxin-like PCBs’.
TCDD is the most extensively studied and potent compound within this group of chemicals. The toxic potency of these dioxins, furans and dioxin-like PCBs is expressed relative to that of TCDD in units of TCDD equivalents (TEQs). Several agencies considered carcinogenicity as the critical effect of dioxin exposure, while others identified developmental/reproductive effects as the most sensitive. Based on the evaluation of the available scientific information, it is considered that developmental effects are the critical effects on which the development of an air standard for Dioxins, Furans and Dioxin-like PCBs should be based.
In developing an air standard for a particular contaminant, the MOE first develops an Ambient Air Quality Criterion (AAQC) for that contaminant. AAQCs are most commonly used in environmental assessments, special studies using ambient air monitoring data, and the assessments of general air quality in a community.
The current 24-hour average AAQC in Ontario for dioxins is 0.000005 TEQ μg/m3 (micrograms per cubic metre of air). The TEQ was based on a previously established set of International Toxicity Equivalency factors (TEFs). Based on the evaluation of the scientific rationale of air guidelines from leading agencies, an examination of current toxicological research information and on the comments from stakeholders, the MOE is proposing the following AAQC for Dioxins, Furans and Dioxin-like PCBs:
• 24-hour average AAQC of 0.0000001 WHO2005-TEQ μg/m3, based on the developmental effects associated with exposure to dioxins, furans and dioxin-like PCBs.
Proposed Standard for Dioxins, Furans and Dioxin-like PCBs in O. Reg. 419/05
The current half-hour and 24-hour guidelines for dioxins are 0.000015 TEQ μg/m3 and 0.000005 TEQ μg/m3, respectively. Based on the proposed AAQC above, the MOE is proposing the following air standards for Dioxins, Furans and Dioxin-like PCBs:
• 24-hour average standard of 0.0000001 WHO2005-TEQ μg/m3, based on the developmental effects associated with exposure to dioxins, furans and dioxin-like PCBs.
• Half-hour average standard of 0.0000003 WHO2005-TEQ μg/m3, based on the developmental effects associated with exposure to dioxins, furans and dioxin-like PCBs.
The 24-hour standard is proposed to be incorporated into Schedule 3 of O. Reg. 419/05 and the corresponding half-hour standard incorporated into Schedule 2. Since the proposed health-based standard is more stringent than the current guideline for Dioxins in Ontario, it is proposed that the health-based standards for Dioxins, Furans and Dioxin-like PCBs in Schedules 2 and 3 take effect five years from being incorporated into O. Reg. 419/05.
For a list of the 29 dioxins, furans and dioxin-like PCBs, and an illustration of how to apply this proposed air standard, please see the document titled "Rationale Document for Dioxins, Furans and Dioxin-like PCBs", for which a link has been provided.