A California appeals court has refused to allow the California Office of Environmental Health Hazard Assessment (OEHHA) to identify styrene and vinyl acetate as carcinogens under the Safe Drinking Water Toxic Enforcement Act of 1986 (Prop. 65), ruling that the agency failed to provide sufficient evidence that the chemicals are “known” to cause cancer. Styrene Info. & Research Ctr. v. OEHHA, No. C064301 (Cal. App. Ct. 10/31/12).

OEHHA had sought to identify the two chemicals as carcinogens under Prop. 65 by citing the California Labor Code, which references a group of chemicals that the International Agency for Research on Cancer (IARC) has found to possibly cause cancer. Prop. 65 requires the state to annually update a list of substances known to cause cancer, birth defects and reproductive harm. It bars the listed chemicals from being discharged into sources of drinking water and requires businesses in the state to provide warnings whenever anyone is exposed to a listed substance.

Several industry and other groups challenged listings via the Labor Code mechanism, which allows OEHHA to administratively list substances that state and federal labor codes have identified as causing cancer and reproductive toxicity. Although the court upheld the use of labor codes to list substances under Prop. 65, both the lower court and the appeals court held that the Prop. 65 list was limited to chemicals for which it has been determined that “the chemical is known to cause cancer or reproductive toxicity.” Since the IARC finding was that the chemicals “possibly cause cancer,” it did not meet the Prop. 65 standard.