California to Try Again to Add Styrene To Proposition 65 List of Carcinogens

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By Carolyn Whetzel

Feb. 27 — The California Office of Environmental Health Hazard Assessment has launched a new attempt to add styrene to the list of carcinogens maintained under Proposition 65.

The Feb. 27 notice of intent follows two earlier efforts, one of which a state appeals court blocked after deciding the agency lacked sufficient evidence that styrene is “known” to cause cancer (Styrene Info. & Research Ctr. v. OEHHA, Cal. App. Ct., No. C064301, 10/31/12)).

This time around, the agency is relying on the 2011 report from the National Toxicology Program that concluded styrene is “reasonably anticipated to be a human carcinogen,” a classification that the National Academies supported in a 2014 report.

The Styrene Information & Research Center successfully challenged the OEHHA's initial effort to list the chemical under Proposition 65's “labor code” listing mechanism, based on evidence in a monograph the International Agency for Research on Cancer published in 2009.

Here, the OEHHA is using an alternative administrative authority to list styrene, one that allows chemicals to be listed once an authoritative body, such as the NTP, formally identifies the chemical as a carcinogen.

Under the Safe Drinking Water and Toxic Enforcement Act of 1986, better known as Proposition 65, California must maintain a list of chemicals known to cause cancer, birth defects or reproductive toxicity. Businesses must provide clear warnings whenever the public is exposed to an unsafe level of a listed substance.

Styrene is used in the manufacture of a wide variety products, including construction materials, fiberglass, automobile parts, synthetic rubbers, lighting fixtures, packaging materials and disposable food containers.

Reliance on NTP Findings 

The OEHHA said the NTP's findings on styrene are “based on limited evidence of carcinogenicity from studies in humans, sufficient evidence of carcinogenicity from studies in experimental animals and supporting data on mechanisms of carcinogenesis.”

Specifically, the OEHHA is relying on the NTP's finding that styrene, when administered to male and female mice through inhalation or stomach tubes, causes increased incidences of malignant lung tumors and combined malignant and benign lung tumors.

In a written statement, Styrene Information & Research Center Executive Director Jack Snyder said the announcement was expected and that the industry will develop a response to the proposed listing.

“Evaluation is needed to clarify whether or not the criteria used in NTP's Report on Carcinogens adequately aligns with and supports the Prop 65 listing criteria under the ‘authoritative body mechanism,' ” Snyder said.

The American Chemistry Council said the proposed listing should not alarm consumers.

“This action is based on a review of styrene by the National Toxicology Program, which itself agrees the safety of polystyrene in foodservice is not in question,” Mike Levy, senior director for the council's Plastics Foodservice Packaging Group, said in a written statement.

“Polystyrene is an FDA-approved and sanitary choice for foodservice packaging made by schools, hospitals, restaurants, food carts and stadiums,” Levy said. “Its ability to insulate and maintain food temperature make polystyrene a great choice for keeping food fresh, hot or cold and ready to eat. It is also used in a variety of other important consumer products, such as insulation and cushioning for shipping delicate electronics.”

To contact the reporter on this story: Carolyn Whetzel in Los Angeles at

To contact the editor responsible for this story: Larry Pearl at

A copy of the OEHHA notice of intent to list styrene is available at


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