On April 22, 2016, California’s Office of Environmental Health Hazard Assessment (OEHHA) added styrene to the Proposition 65 list of carcinogens. OEHHA maintains a list of chemicals required under Proposition 65 (formally, the California Safe Drinking Water and Toxic Enforcement Act) that are “known to the state” to be reproductive toxicants or carcinogens based on Proposition 65 criteria. OEHHA also proposed a No Significant Risk Level, or NSRL, for styrene of 27 µg per day. Under Proposition 65, companies that sell products in the state must inform consumers if their products or establishments will expose consumers to a listed chemical above the NSRL.

OEHHA’s listing follows a litigation settlement with the Sierra Club. The settlement agreement required OEHHA to decide whether to list a number of substances under Proposition 65’s “authoritative bodies” listing mechanism if there is sufficient evidence to conclude that the chemical is a carcinogen to humans. OEHHA’s listing is based on a 2011 action by the National Toxicology Program’s (NTP) Report on Carcinogens, which listed styrene as “reasonably anticipated to be a human carcinogen.”

Comments on the proposed NSRL are due by June 6, 2016.