California Lists Styrene as a Carcinogen under Prop 65; Proposes NSRL

April 27, 2016

The California Office of Environmental Health Hazard Assessment (OEHHA) added styrene (CAS No. 100-42-5) to the Proposition 65 list, effective April 22, 2016.  The listing is under the authoritative bodies mechanism based on formal identification by the National Toxicology Program (NTP) that the chemical is “reasonably anticipated to be a human carcinogen.”  OEHHA has proposed a No Significant Risk Level (NSRL) for styrene of 27 µg per day.

Proposition 65 is a “right to know” California statute that requires companies to provide warning statements where their products cause an “exposure” to carcinogens and/or reproductive toxicants.  The warning requirements do not apply where a particular exposure falls within the “safe harbor,” which is defined by reference to:

  • The NSRL for listed carcinogens, which is the level of a chemical calculated to result in one excess case of cancer in an exposed population of 100,000, assuming lifetime (70-year) exposure to the chemical at the level in question; or
  • The maximum allowable dose level (MADL) for reproductive toxicants, which is the level at which a chemical would have no observable effect assuming exposure at 1,000 times that level.

Warning requirements for styrene for exposures in excess of a safe harbor will take effect twelve months after the formal listing date.  The listing of styrene on Proposition 65 has been anticipated for a while. For more background information, see the article, OEHHA to Identify Chemicals Being Considered for California’s Prop. 65 List under Authoritative Bodies Mechanism. Comments on the Proposed NSRL are due by June 6, 2016.