Proposal for the Adoption of a Unit Risk Factor for Ethylbenzene

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The Office of Environmental Health Hazard Assessment (OEHHA) is required under the Air Toxics Hot Spots Act to prepare risk assessment guidelines for use in implementing the Air Toxics Hot Spots program (Health and Safety Code Section 44300 et seq.), and to conduct health assessments of Toxic Air Contaminants.  The risk assessment guidelines include cancer potency factors for carcinogenic compounds.  The statute requires both public comment and review by the Scientific Review Panel.

Ethylbenzene was identified as a Toxic Air Contaminant in 1993 pursuant to Health and Safety Code Section 39657(b), which requires the identification of all Federal Hazardous Air Pollutants as Toxic Air Contaminants.  OEHHA has already adopted, after review by the Panel, a Chronic Reference Exposure Level for ethylbenzene, which is designed to protect against non-cancer health effects.  However, recent new data from NTP and an evaluation by IARC have indicated a possible cancer risk from exposure to ethylbenzene.  OEHHA was therefore asked by the California Air Resources Board to review these new data and, if appropriate, develop a cancer risk assessment and unit risk factor for ethylbenzene.  A draft document describing this risk assessment was posted on this site for public review starting April 23, 2007.  Some public comments were received, and the document has been modified to reflect these.  The document will be reviewed by the Scientific Review Panel at their next meeting, scheduled for September 26, 2007.  This would, if approved, form an addendum to Part II of the Air Toxics Hot Spots Program’s Technical Support Document for Describing Available Cancer Potency Factors.