Notice of Public Comment for Proposed Revised Reference Exposure Levels for Toluene Diisocyanate and Methylene Diphenyl Diisocyanate

The Office of Environmental Health Hazard Assessment (OEHHA) is releasing draft documents describing proposed revised Reference Exposure Levels (RELs) for toluene diisocyanate and methylene diphenyl diisocyanate to solicit public comment.  OEHHA is required to develop guidelines for conducting health risk assessments under the Air Toxics Hot Spots Program (Health and Safety Code Section 44360 (b) (2)).  OEHHA has developed Technical Support Documents (TSDs) in response to this statutory requirement, including one which described acute and chronic RELs, which was adopted in December 2008.  This TSD (which replaces earlier guidance documents on this topic) presents methodology revised to reflect the latest scientific knowledge and techniques, and in particular to explicitly include consideration of possible differential effects on the health of infants, children and other sensitive subpopulations, in accordance with the mandate of the Children’s Environmental Health Protection Act (Senate Bill 25, Escutia, chapter 731, statutes of 1999, Health and Safety Code Sections 39669.5 et seq.).  In addition to acute and chronic RELs, the new method allows for the estimation of 8-hour RELs, which may be useful in dealing with some special circumstances in Hot Spots risk assessments.  These guidelines have already been used to develop updated RELs for several chemicals, and OEHHA is now presenting draft updates to the RELs for two further chemicals: toluene diisocyanate and methylene diphenyl diisocyanate.

We are seeking comments on these documents, in particular on the revised RELs and the application of the revised methodology to protect infants and children and other sensitive subpopulations.  Following this public comment period, the documents and any comments received, along with OEHHA’s response to these comments, will undergo review by the State’s Scientific Review Panel on Toxic Air Contaminants.

The draft documents become available on the OEHHA Home Page at on April 23, 2010.  The availability of the document on this site will commence a 60-day public review period that will end on June 22, 2010. 

Public workshops will be held during this period: time and location will be announced shortly.  Please direct your comments on the documents, in writing or by e-mail, and any inquiries concerning technical matters or availability of the documents to:

Dr. John Budroe
Chief, Air Toxicology and Risk Assessment Section
Air, Community, and Environmental Research Branch
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA, 94612


Telephone: (510) 622-3145

Information about dates and agenda for meetings of the Scientific Review Panel can be obtained from the ARB web page at