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Prop 65 Fact Sheet for Styrene Includes Perplexing Recommendation

California State House

The California Office of Environmental Health Hazard Assessment (OEHHA) recently posted a fact sheet on styrene on its Proposition 65 warning website. That fact sheet includes a confusing recommendation concerning polystyrene. The Proposition 65 warnings website was a rulemaking initiative undertaken by OEHHA to increase the level of detail provided about chemicals on the Proposition 65 lists. (See the article, California’s Prop 65 Lead Agency Website has Launched, for more background information on the site.)  

OEHHA listed styrene as a carcinogen under the state’s Safe Drinking Water and Toxic Enforcement Act of 1986, also known as Proposition 65, on April 22, 2016, and on May 4, 2017, the California Office of Administrative Law approved a No Significant Risk Level (NSRL) for styrene of 27 µg per day.

Proposition 65 requires companies to provide a warning if exposure from the use of a product to a listed carcinogen will exceed a No Significant Risk Level derived using regulatory criteria. For some substances, like styrene, OEHHA has published NSRLs, which are deemed “safe harbors,” meaning that products associated with exposures below the NSRL need not carry a warning statement.

The styrene fact sheet suggests that “Small amounts of styrene can be transferred to some food from polystyrene-based food-contact items such as drinking cups, plates, and other containers.” One way to reduce potential exposure to styrene, suggested by OEHHA on the fact sheet is: “If possible, do not store or microwave food in polystyrene-based containers.” Including this recommendation is perplexing since, in a final statement of reasons supporting the NSRL for styrene of 27 µg per day, OEHHA stated:

“It should be emphasized that the chemical that is listed under Proposition 65 is styrene, not polystyrene. As noted by [the American Chemical Council], styrene is the monomer used for production of polystyrene. A warning for styrene would only be required in cases where residual levels of styrene in polystyrene food packaging materials result in exposures that pose a significant cancer risk, i.e., styrene exposures greater than 27 µg/day. The levels of such residual styrene in polystyrene food packaging materials are generally thought to be fairly low in most cases.” (See