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November 7, 2012

Court Affirms Decision Preventing Proposition 65 Listing of Styrene and Vinyl Acetate As Carcinogens

The ACTA Group

On October 31, 2012, the Court of Appeals of the State of California, Third Appellate District, issued a decision affirming the decision of the trial court, which found that the California Office of Environmental Health Hazard Assessment (OEHHA) had failed to provide sufficient evidence that styrene and vinyl acetate are “known” to cause cancer and thus these substances could not be listed as carcinogens under Proposition 65. The decision, which is available online, has important implications for other chemicals under Proposition 65.


The case originated on June 12, 2009, when OEHHA proposed to add styrene, vinyl acetate, and several other chemicals to Proposition 65 based on the so-called Labor Code listing mechanism. For styrene and vinyl acetate, OEHHA based its decision on a 2002 Monograph by the International Agency for Research on Cancer (IARC), which classified styrene and vinyl acetate as Group 2B, “possibly carcinogenic to humans.” The Group 2B category is described as follows: “This category is used for agents for which there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals.”

On August 12, 2009, the Superior Court of the State of California granted a temporary restraining order sought by the Styrene Information and Research Center (SIRC) to prohibit OEHHA from following through with its intent to include styrene on the Proposition 65 list. In its ruling, the court concluded that OEHHA “presumed,” rather than “demonstrated,” that IARC found that styrene is a human carcinogen. According to the court, “as plaintiff points out, there is no finding of sufficient evidence that styrene is a carcinogen for either animals or human[s] in IARC’s 2002 monograph.” On December 17, 2009, the trial court entered orders granting in part and denying in part the motions for judgment on the pleadings submitted by SIRC, OEHHA, and Celanese, a producer of vinyl acetate, which intervened in the case. The court concluded OEHHA did not violate the Administrative Procedure Act (APA) with its methodology for selecting chemicals to be listed in Proposition 65 with the Labor Code mechanism. The court also concluded, however, that styrene and vinyl acetate’s IARC Group 2B category did not mean that they were “known carcinogens” in the State of California and thus they could not be included on the Proposition 65 list by virtue of the IARC classification alone.

Appellate Court Opinion

The only issue on appeal was whether chemicals categorized in Group 2B by an IARC monograph must be listed under Proposition 65. The court found that a “literal interpretation” of the Labor Code listing mechanism that could require any substance to be listed if it was a potential carcinogen “would be inconsistent with the voters’ intent underlying Proposition 65.” The court took the issue presented in the appeal as one of statutory construction, which it considered de novo. Specifically, in reconciling the provision in the Labor Code mechanism that could potentially require listing of substances based on an IARC Group 2B classification with the general Proposition 65 requirement that the list include “those chemicals known to the state to cause cancer or reproductive toxicity,” the court held the following:

Notwithstanding the requirement in Health and Safety Code section 25249.8, subdivision (a), that the list contain, at a minimum, the substances identified by reference in Labor Code section 6382, subdivision (d), that Labor Code provision addresses “hazardous substances,” which extends beyond those that cause cancer or reproductive toxicity. Thus, the reference to Labor Code section 6382 in Health and Safety Code section 25249.8, subdivision (a), must be read in conjunction with the prior language requiring the Governor to publish a list of chemicals “known to the state to cause cancer or reproductive toxicity.” Because chemicals may be included in IARC Group 2B based on less than sufficient evidence of carcinogenicity in either humans or experimental animals, they may not qualify for Proposition 65 listing on that basis alone.

The court concluded as follows:

We conclude the Proposition 65 list is limited to chemicals for which it has been determined, either by OEHHA through one of the methods described in section 25249.8, subdivision (b), or through the Labor Code method of adopting findings from authoritative sources, that the chemical is known to cause cancer or reproductive toxicity. Because the findings in the IARC monograph on which OEHHA relies to list styrene and vinyl acetate do not satisfy that standard, they cannot properly be included on the list on that basis alone. And because OEHHA does not propose any other basis for including those substances on the list, they must be excluded. Thus, the trial court properly granted judgment on the pleadings for plaintiffs on that issue.


This case is significant as the decision prohibits listing styrene and vinyl acetate as carcinogens based solely on their classification by IARC. More broadly, the decision is significant for its implications for other substances classified by IARC as Group 2B carcinogens and for which there is not sufficient evidence that exposure causes cancer in animals (i.e., Group 2B substances for which “there is limited evidence of carcinogenicity in humans and less than sufficient evidence of carcinogenicity in experimental animals”).

The case also is noteworthy because, despite OEHHA’s argument that its interpretations, guidance, and enforcement decisions were entitled to consideration and deference by the court, the court determined that OEHHA’s interpretation of Proposition 65 was “entitled to little or no deference.” The court made this determination based on the facts that OEHHA has not adopted any formal regulations on this issue, OEHHA had not utilized the Labor Code mechanism for listing chemicals solely based on their inclusion in an IARC monograph for the past 15 years, and OEHHA lacked the authority to “‘alter or amend’ a statute, or ‘enlarge or impair its scope.'” The court found this question presented to be one of statutory interpretation, which is an exercise of judicial power for the courts. As the court noted, “[w]hile OEHHA may have an interpretive advantage over the courts in determining whether a particular chemical causes cancer, it does not have such advantage in determining whether the appropriate standard under the statute is one of known cause or possible cause.”