The California Court of Appeals of the Third Appellate District held on Wednesday chemicals that fall under Proposition 65’s coverage must be known to cause cancer or reproductive toxicity. Proposition 65 (“Prop 65”) prohibits businesses form discharging chemicals known to the state to cause cancer or reproductive toxicity into drinking water and requires businesses to warn the public if they knowingly and intentionally expose individuals to such chemicals.

After groups challenged the listing of two chemicals, California’s Office of Environmental Health Hazard Assessment (“OEHHA”) charged with implementing Prop 65 argued the list of Prop 65 chemicals should include a group of chemicals called “Group 2B,” identified by the International Agency for Research on Cancer (“IARC”) as chemicals that are “possibly” carcinogenic to humans.

The Court rejected OEHHA’s argument, recognizing chemicals may be in IARC Group2B with less than sufficient evidence of carcinogenicity in either humans or experimental animals. Looking closely at the legislative intent and statutory language of Prop 65, the Court held the language is clear that the Prop 65 list of chemicals is limited to chemicals determined by OEHHA or through a prescribed method in the Labor Code “known to cause cancer or reproductive toxicity.” Since inclusion in the IARC’s Group 2B chemicals does not meet that statutory standard, OEHHA cannot include chemicals on the Prop 65 list solely based on the IARC’s Group 2B classification.

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