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823756 
Technical Report 
AEGL 
Ontario air standards for trimethylbenzenes: 1,2,3-trimethylbenzene 1,2,4-trimethylbenzene 1,3,5-trimethylbenzene 
Ontario Ministry of the Environment :: MOE 
2007 
Standards Development Branch, Ontario Ministry of the Environment 
Ontario, Canada 
62 
English 
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, which was released in October, 1996 and revised in November, 1999, identified candidate substances for which current air quality standards will be reviewed or new standards developed. 1,2,4-Trimethylbenzene was identified as a priority for review based on both its pattern of use in Ontario and toxicological information that has been published subsequent to the development of the existing standard in 1988. Exposures to individual TMB isomers would be expected to occur rarely, and would likely be restricted to unique occupational or experimental situations. Therefore, the Ministry is expanding the current AAQC and POI value to apply to all isomers of trimethylbenzene and to any mixtures of these isomers. Once a decision is made on the air standards, they will be incorporated into Ontario Regulation 419: Air Pollution – Local Air Quality (O. Reg. 419/05). The Ambient Air Quality Criterion (AAQC) will be incorporated into Schedule 3 of the regulation and the half hour standards will be incorporated into Schedule 2. An ‘Information Document’ containing a review of scientific and technical information relevant to setting an air quality standard for 1,2,4-trimethylbenzenes was previously posted on the Environmental Bill of Rights Registry for public comments. This was followed more recently by the posting of a document providing the rationale (‘Rationale Document’) for recommending an Ambient Air Quality Criterion (AAQC) and a half hour standard for trimethylbenzenes. This document, referred to as the ‘Decision Document’, summarizes the comments received from stakeholders on the proposed standards and the Ministry responses to these comments. This document also provides the rationale for the decision on the air quality standards for trimethylbenzenes.