Technical Support Document for Cancer Potency Factors 2009

Jun 1, 2009

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 initially developed Technical Support Documents (TSDs) in 1999-2000 in response to this statutory requirement, including one which listed and described the derivation of cancer potencies for individual air contaminants. OEHHA has developed a revised draft TSD, “Air Toxics Hot Spots Program Technical Support Document for Cancer Potencies,” which is designed to replace the original TSDs. The revised TSD presents updated methodology that reflects 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.).

A draft of the TSD was released on June 20, 2008 to solicit public comment. The document was then reviewed by the State’s Scientific Review Panel on Toxic Air Contaminants (SRP). It was initially presented to the SRP on October 10, 2008. Revised versions of the document reflecting new data and comments from the public and the SRP were discussed at meetings held on December 5, 2008 and May 12, 2009. At the latter meeting, the SRP approved the final versions of the methodology section and the associated appendices.

Following this process, and by this memo, OEHHA is finalizing and adopting the TSD for Cancer Potency Factors. Adoption of the TSD does not automatically affect the existing cancer potency factors for individual air contaminants (which are listed in the appendices to the TSD). These existing cancer potency values are listed in Appendix A to the new TSD, and the toxicological summaries describing their derivation are presented in Appendix B. Any further new or revised cancer potencies approved by the SRP will be adopted and also included in these appendices.

Appendices

Appendix A. A lookup table containing unit risk and cancer potency values. updated 2011

Appendix B. Chemical-specific summaries of the information used to derive unit risk and cancer potency values. updated 2011

Appendix C. A description of the use of toxicity equivalency factors for determining unit risk and cancer potency factors for polychlorinated dibenzo-p-dioxins, dibenzofurans and dioxin-like polychlorinated biphenyls. Revised 01/20/11

Appendix D. A listing of Toxic Air Contaminants identified by the California Air Resources Board.

Appendix E. Descriptions of the International Agency for Research on Cancer (IARC) and U.S. Environmental Protection Agency (U.S. EPA) carcinogen classifications.

Appendix F. An asbestos quantity conversion factor for calculating asbestos concentrations expressed as 100 fibers/m3 from asbestos concentrations expressed as µg/m3.

Appendix G. Procedures for revisiting or delisting cancer potency factors by the program of origin.

Appendix H. Exposure routes and studies used to derive cancer unit risks and slope factors.

Appendix I. “Assessing susceptibility from early-life exposure to carcinogens”: Barton et al., 2005 (from Environmental Health Perspectives).

Appendix J. “In Utero and Early Life Susceptibility to Carcinogens: The Derivation of Age-at-Exposure Sensitivity Measures” – conducted by OEHHA’s Reproductive and Cancer Hazard Assessment Branch.