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Draft Technical Support Document for Noncancer Risk Assessment Jul 2008

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 has developed 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. OEHHA has also developed revised 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. Approval of these RELs is pending the next meeting of the Scientific Review Panel.

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 reflecting new data and comments from the public and the SRP was presented on May 16, 2008. OEHHA’s initial responses to the public comments were also included. A further revision of the document, appendices and responses to public comments were discussed at the SRP meeting which was held on June 18, 2008. At that meeting, the Panel approved the methodology sections and associated Appendices which are provided below. The next SRP meeting is scheduled for September 9, 2008, and the Panel will likely conclude its review of the proposed RELs. The revised RELs will be posted upon approval by the SRP.

Information about the location and agenda for the September 9th meeting of the Scientific Review Panel can be obtained from the ARB web page at http://www.arb.ca.gov/srp/srpmeetings.htm.

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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
Appendix H: Target Organ Systems