Notice of Adoption of Air Toxics Hot Spots Program Technical Support Document for the Derivation of Noncancer Reference Exposure Levels and 6 RELs

Dec 19, 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 initially developed Technical Support Documents (TSDs) in 1999-2000 in response to this statutory requirement, including two which described acute and chronic Reference Exposure Levels (RELs). (A REL is an airborne level of a chemical that is not anticipated to present a significant risk of an adverse non-cancer health effect.) 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 two 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.

A draft of the TSD was released on November 2, 2007 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 February 28, 2008. Revised versions of the document reflecting new data and comments from the public and the SRP were discussed at meetings held on May 16, 2008 and June 18, 2008. At the latter meeting, the SRP approved the final versions of the methodology section and the associated methodological appendices.

Following this process, and by this memo, OEHHA is finalizing and adopting the TSD, along with acute, 8-hour and chronic Reference Exposure Levels (RELs) for six chemicals (acetaldehyde, acrolein, arsenic, formaldehyde, manganese [no acute REL was derived for this chemical], and mercury). The values of the RELs are listed in the table attached. OEHHA also hereby adds acetaldehyde, arsenic, formaldehyde, manganese, and mercury to the list of Toxic Air Contaminants that may cause infants and children to be especially susceptible to illness. Acrolein has already been listed in this way. This listing, specified by the Children’s Environmental Health Protection Act, requires that any Air Toxic Control Measures which CARB determines to be necessary for listed chemicals shall be adequate to protect the health of infants and children.

Adoption of the TSD does not automatically affect the other existing acute and chronic RELs (which are listed in the appendices to the TSD). However, the RELs for the six chemicals that OEHHA is adopting today illustrate the use of the new guidelines. These proposed RELs were initially presented for public comment and SRP review along with the Technical Support Document, and were discussed further at the meeting of the Scientific Review Panel on October 30, 2008. At the meeting of the Scientific Review Panel on December 5, 2008, the RELs and their supporting documentation were approved. The toxicological summaries describing their derivation, and the values for acute, 8-hour and chronic RELs, are presented in the appendices to the new TSD. Any further new or revised RELs approved by the SRP will be adopted and also included in these appendices.