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Air Toxicology and Epidemiology

Proposed Revisions to the Technical Support Document for Noncancer Risk Assessment
[4/24/08]

Responses to public comments and updated version of documents for presentation to the Scientific Review Panel

The Office of Environmental Health Hazard Assessment (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). OEHHA is now developing a revised draft TSD: Air Toxics Hot Spots Program Technical Support Document For the Derivation of Noncancer Reference Exposure Levels, which is designed to replace those original TSDs. This 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.

A draft of this document was released on November 2, 2007 to solicit public comment. Following this public comment period, the document is undergoing review by the State’s Scientific Review Panel on Toxic Air Contaminants (SRP). It was initially presented to the SRP on February 28, 2008. A version of the document is now presented here for consideration at the next SRP meeting on May 16, 2008 with changes which reflect new data and comments from the public and the SRP. OEHHA’s responses to the public comments are also included.

Information about the location and agenda for the May 16 meeting of the Scientific Review Panel can be obtained from the ARB web page at http://www.arb.ca.gov/srp/srp.htm. Follow the links below to download the document in sections:

• Technical Support Document For the Derivation of Noncancer Reference Exposure Levels
• 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
• APPENDIX H. Target Organs or Systems used in Acute, 8-Hour and chronic Hazard Index Calculations
• Responses to public comments received on the draft Technical Support Document and RELs

The proposed new Reference Exposure Levels for five of the six chemicals noted above appear in Appendix D. The summary and comments for manganese will be provided at a later date.