A California appeals court has determined that the Office of Environmental Health Hazard Assessment (OEHHA) may not add styrene or vinyl acetate to the Proposition 65 (Prop. 65) list of chemicals known to the state to cause cancer because they have been identified as “possible” but not known carcinogens. Styrene Info. & Research Ctr. v. OEHHA, No. C064301 (Cal. Ct. App., 3d Dist., decided October 31, 2012). Styrene is used in food packaging.

The International Agency for Research on Cancer (IARC) had categorized the substances as Group 2b chemicals, which are “possibly” carcinogenic to humans, based on less than sufficient evidence of carcinogenicity in experimental animals. The court acknowledged that the California Health and Safety Code requires that the Prop. 65 list contain “at a minimum, the substances identified by reference in Labor Code section 6382, subdivision (d),” which addresses “hazardous substances” that extend “beyond those that cause cancer or reproductive toxicity.” And it was on this basis that OEHHA announced its intent to list the chemicals. Noting that this Labor Code reference “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,” the court ruled that chemicals included in a 2b IARC listing “may not qualify for Proposition 65 listing on that basis alone.”

The court expressly accorded OEHHA’s interpretation of Prop. 65 “little or no deference.” According to the court, OEHHA did not use the Labor Code method for listing chemicals in the first 15 years after Prop. 65’s enactment. “This has been OEHHA’s practice only during the last 10 years or so. ‘[A]n agency’s vacillating practice—i.e., adopting a new interpretation that contradicts a prior interpretation—is entitled to little or no weight.’ And OEHHA has not adopted any formal regulations to this effect.” The court also noted that administrative agencies may not “alter or amend” a statute or “enlarge or impair its scope.”

Thus the court concluded, “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.” Finding no other basis in the record for listing the chemicals, the court affirmed a trial court decision granting the trade group and chemical manufacturer’s motion for judgment on the pleadings.