Notice of Public Comment Period/Workshops on Draft Air Toxics Hot Spots Program Technical Support Document for Noncancer Risk Assessment Nov 2007

The Office of Environmental Health Hazard Assessment (OEHHA) is releasing a draft document, Air Toxics Hot Spots Program Technical Support Document For the Derivation of Noncancer Reference Exposure Levels 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 previously developed Technical Support Documents (TSDs) in response to this statutory requirement, including two (in 1999-2000) which described acute and chronic Reference Exposure Levels (RELs).  This revised draft TSD is designed to replace those original TSDs, and presents methodology revised to reflect scientific knowledge and techniques developed since the previous guidelines were prepared, 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 the previously defined 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.  The revised draft also contains proposed Reference Exposure Levels for six chemicals (acetaldehyde, acrolein, arsenic, formaldehyde, manganese, and mercury), which illustrate the intended use of the new guidelines as well as updating the health protective levels for these compounds. 

We are seeking comments on this document (including the RELs), in particular on the revisions to the existing approved methodology, and the appropriateness of the revised methodology to protect infants and children and other sensitive subpopulations.  Following this public comment period, the document 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 document becomes available on the OEHHA web site on November 2, 2007.  The availability of the document on this site will commence a 60-day public review period that will end on January 2, 2008. 

Public workshops will be held at 10.00 am – 4.00 p.m. on November 30th in Diamond Bar and at 10.00 am – 4.00 p.m. on December 7th, 2007 in Oakland.  Location information is as follows:

Room CC2
South Coast Air Quality Management District 
21865 Copley Dr, 
Diamond Bar, CA 91765


Room 12,
Elihu Harris Building
1515 Clay St., 2nd Floor
Oakland, CA 94612

Please direct any inquiries concerning technical matters or availability of this document to Dr. Andrew G. Salmon at (510) 622-3191 or

Please direct your comments, in writing, regarding the document to:
Dr. Andrew G. Salmon
Chief, Air Toxicology and Risk Assessment Unit
Office of Environmental Health Hazard Assessment
1515 Clay St., 16th Floor
Oakland, CA  94612. 

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


List of Appendices:

APPENDIX A: List of Acronyms
APPENDIX B: Acute, 8-Hour, and Chronic Reference Exposure Levels (RELS) Summary Table
APPENDIX C: Substances for Which Emissions Must Be Quantified
APPENDIX D: Individual Acute, 8-Hour and Chronic Reference Exposure Level Summaries
APPENDIX E: Toxicokinetics
APPENDIX F: Estimating Human Equivalent Concentrations Using the U.S. EPA Default Approach
APPENDIX G: Value of the Haber's Law Exponent (N) for Various Gases and Vapors for Acute RELS Developed Using OEHHA (1999) Procedures