A release from the OEHHA:

The Air Toxics Hot Spots Information and Assessment Act of 1987 (Health and Safety Code Section 44300 et seq.), requires the California Air Resources Board and the Office of Environmental Health Hazard Assessment (OEHHA) to provide assistance and technical support to Air Pollution Control Districts in regulation of local emissions of air pollutants. In particular, OEHHA is required to develop guidelines for conducting health risk assessments under the program (Health and Safety Code Section 44360 (b)(2)). These guidelines include recommended methodology for conducting chemical- and site-specific risk assessments, and health protective values (Reference Exposure Levels for non-cancer health effects and Unit Risk values for carcinogenic effects)…

Ethylbenzene (CAS Registry Number: 100-41-4) enters the atmosphere both from emissions from industrial facilities and other localized sources, and from mobile sources. It is a natural constituent of crude petroleum and is found in gasoline and diesel fuels. It is also used as a chemical intermediate, primarily in the production of styrene. Ethylbenzene is already identified as a TAC as a result of its listing as a U.S. Hazardous Air Pollutant. For assessment of non-cancer effects, a Chronic Reference Exposure Level was adopted in 2000. Ethylbenzene was listed under Proposition 65 as a chemical known to the State of California to cause cancer on June 11, 2004, and was classified as Group 2B (possibly carcinogenic to humans) by the International Agency for Research on Cancer in 2000.

The full release is available here.