Tertiary-Butyl Acetate (TBAc) Inhalation Cancer Unit Risk Factor (IUR) Document - Scientific Review Panel on Toxic Air Contaminants (SRP) Review Draft

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The Office of Environmental Health Hazard Assessment (OEHHA) is releasing a revised draft document summarizing the carcinogenicity and derivation of an inhalation cancer unit risk factor (IUR) for tertiary-Butyl Acetate (TBAc).  Inhalation cancer unit risk factors are used to estimate lifetime cancer risks associated with inhalation exposure to a carcinogen. This document will be reviewed and discussed by the Scientific Review Panel on Toxic Air Contaminants (SRP) at its meeting on December 13, 2017 in Sacramento, CA. 

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)). In response to this statutory requirement, OEHHA develops IURs for many air pollutants. The TBAc IUR was developed using the most recent “Air Toxics Hot Spots Program Technical Support Document for Cancer Potency Factors,” finalized by OEHHA in 2009.

A draft of the TBAc IUR document was reviewed by the SRP at its meeting on December 14, 2016.  The TBAc IUR document was revised in response to comments made by the SRP at that meeting. The values proposed in the current document version are as follows:

  • Unit Risk Factor                    1.3 x 10-6 (µg/m3)-1
  • Inhalation Slope Factor          4.7 x 10-3 (mg/kg-day)-1
  • Oral Slope Factor                  5.0 x 10-3 (mg/kg-day)-1

We are not seeking further comments from the public on the draft document.  The SRP received a comment letter from LyondellBasell in March 2017. At the request of the Chair, OEHHA will address this comment at the meeting.

Please direct any inquiries concerning technical matters or availability of the documents to:

Dr. John Budroe
Chief, Air Toxicology and Risk Assessment Section
Air, Community, and Environmental Research Branch
Office of Environmental Health Hazard Assessment
1515 Clay Street, 16th Floor
Oakland, CA, 94612

E–mail: John.Budroe@oehha.ca.gov (link sends e-mail)
Telephone: (510) 622-3145

Information about dates and agenda for meetings of the Scientific Review Panel can be obtained from the California Air Resources Board web page at: http://www.arb.ca.gov/srp/srp.htm (link is external).