California’s Office of Environmental Health Hazard Assessment (OEHHA) recently added styrene, CAS No. 100-42-5, as a carcinogen on the Prop 65 List of Chemicals. The updated Prop 65 list can be found here. OEHHA also proposed a safe harbor level.

The listing comes despite heavy industry criticism and push-back. OEHHA initially proposed to list styrene in 2009 based on the International Agency for Research on Cancer’s identification of styrene as a Group 2B carcinogen. However, it withdrew the proposed listing as the result of a lawsuit brought by the Styrene Information and Research Center. OEHHA later proposed to list styrene in January 2013 based on the National Toxicology Program’s (NTP) 12th Report on Carcinogens; however, the listing proposal was withdrawn shortly thereafter due to pending federal litigation and pending peer review results regarding NTP’s Report.

OEHHA most recently proposed to list styrene in February 2015, again based on NTP’s Report on Carcinogens. Thirteen comments were submitted raising various objections to the conclusions in the NTP Report and OEHHA’s interpretation of those conclusions. All of the comments were rejected via detailed responses when OEHHA proceeded with the listing.

Prop 65 warnings will be required for styrene starting on April 22, 2017.

Proposed Safe Harbor Level for Styrene

In addition to listing styrene, OEHHA also proposed a safe harbor level of 27 micrograms per day for styrene. If the proposal is enacted, Prop 65 warnings would only be required for styrene exposure above 27 micrograms per day. Comments for this proposal are due by June 6, 2016.