US EPA

In August 2013, EPA submitted a revised draft IRIS assessment of trimethylbenzenes to the agency's Science Advisory Board (SAB) and posted this draft on the IRIS website. EPA had previously released a draft of the assessment for public comment, held a public meeting about the draft, and then revised it based on the comments received. The SAB CAAC-Trimethylbenzenes panel will review this draft assessment. Details about the meeting dates, times, and location are available via the Federal Register Notice posted on March 25, 2014. The SAB provided information on how the public can participate in the external peer review meetings, as well as instructions about how to provide comments to the SAB in the notice. Additional information on the "SAB review of trimethylbenzenes" is on the SAB website.

Report Information: The Toxicological Review of Trimethylbenzenes was originally released for a 60-day public comment period on June 29, 2012. [Federal Register Notice Jun 29, 2012] EPA revised the toxicological review in response to the public comments received. EPA has released the revised external review draft trimethylbenzenes assessment and the SAB CAAC is conducting a peer review of the scientific basis supporting the assessment that will appear in the Integrated Risk Information System (IRIS) database. Information regarding the peer review can be found at the "SAB review of trimethylbenzene" website.

Trimethylbenzenes (TMB) are a mixture of three isomers: 1,2,3-, 1,2,4- and 1,3,5-TMB. TMBs are produced during petroleum refining, and 1,2,4-TMB makes up approximately 40% of a certain petroleum product (the C9 fraction) which is used as a component of gasoline. Because of this, vehicle emissions are a major source of TMBs. Other uses of TMBs include solvents in research and industry, dyestuff intermediate, paint thinner, and as a UV oxidation stabilizer for plastics.

EPA is reassessing its IRIS toxicological review of Trimethylbenzenes (1,2,3-;1,2,4-;1,3,5-). This trimethylbenzene reassessment consists of an oral reference dose (RfD), an inhalation reference concentration (RfC), an inhalation unit risk (IUR) and a cancer weight of evidence descriptor. This is the first assessment developing an RfC or IUR for this compound. This assessment is intended to provide human health data to support agency regulatory decisions.

EPA’s SAB will hold two meetings in May and June 2014 for the external peer review of the trimethylbenzenes IRIS assessment. Information on the peer review can be found at the SAB Trimethylbenzenes website. Following external peer review, the assessment will be revised taking into consideration the comments received. It will then undergo a final internal review by EPA, and other federal agencies and the Executive Office of the President. After completing this review it will be posted to the IRIS database.

U.S. EPA. IRIS Toxicological Review of Trimethylbenzenes (Revised External Review Draft). U.S. Environmental Protection Agency, Washington, DC, EPA/635/R-13/171, 2013.