Notice of Intent to List: Styrene

Feb 27, 2015

The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) intends to list styrene as known to the State to cause cancer under the Safe Drinking Water and Toxic Enforcement Act of 1986.¹ This action is being proposed under the authoritative bodies listing mechanism.²

Chemical (CAS No.)	Endpoint	Reference	Occurrence and Uses
Styrene (100-42-5)	Cancer	NTP (2011)	An aromatic hydrocarbon used in the synthesis of polymers and resins that are used to fabricate various industrial and household products including polystyrene packaging, synthetic rubber, fiberglass, automobile parts, and food containers. Also present in tobacco smoke and motor vehicle exhaust.

Background on listing via the authoritative bodies mechanism: A chemical must be listed under the Proposition 65 regulations when two conditions are met:

An authoritative body formally identifies the chemical as causing cancer (Section 25306(d)³).
The evidence considered by the authoritative body meets the scientific sufficiency criteria contained in the regulations (Section 25306(e)).

However, the chemical is not listed if scientifically valid data which were not considered by the authoritative body clearly establish that the sufficiency of evidence criteria were not met (Section 25306(f)).

The National Toxicology Program (NTP) is one of several institutions designated as authoritative by the States Qualified Experts for the identification of chemicals as causing cancer (Section 25306(m)).

OEHHA is the lead agency for Proposition 65 implementation. After an authoritative body has made a determination about a chemical, OEHHA evaluates whether listing under Proposition 65 is required using the criteria contained in the regulations.
OEHHA’s determination: Styrene meets the criteria for listing as known to the State to cause cancer under Proposition 65, based on findings of the NTP (2011).

Formal identification and sufficiency of evidence for styrene: In 2011, NTP published the Twelfth Edition of the Report on Carcinogens (NTP, 2011). This report satisfies the formal identification and sufficiency of evidence criteria in the Proposition 65 regulations for styrene. NTP concluded that styrene is “reasonably anticipated to be a human carcinogen based on limited evidence of carcinogenicity from studies in humans, sufficient evidence of carcinogenicity from studies in experimental animals, and supporting data on mechanisms of carcinogenesis” (emphasis in original). OEHHA is relying on NTP’s discussion of data and conclusions in the report that styrene causes cancer. Evidence described in the report includes studies showing that styrene increased the incidence of combined malignant and benign lung tumors in two strains of male mice (CD-1 and B6C3F1) and increased the incidences of malignant and combined malignant and benign lung tumors in female CD-1 mice:

“Styrene caused lung tumors in several strains of mice and by two different routes of exposure. The most robust studies are two-year-studies of inhalation exposure in CD-1 mice (Cruzan et al., 2001) and oral exposure (by stomach tube) in B6C3F1 mice (NCI, 1979). Inhalation exposure caused benign lung tumors (alveolar/bronchiolar adenoma) and increased the combined incidence of benign and malignant lung tumors (alveolar/bronchiolar adenoma and carcinoma) in CD-1 mice of both sexes; in females it also increased the separate incidence of malignant lung tumors. In male B6C3F1 mice, oral exposure to styrene increased the combined incidence of benign and malignant lung tumors (alveolar/bronchiolar adenoma and carcinoma), and a positive dose-response trend was observed (NCI 1979).”

Thus, NTP (2011) found that styrene causes increased incidences of combined malignant and benign lung tumors in two strains of male mice, exposed by different routes of administration (i.e., oral and inhalation), and increased incidences of malignant and combined malignant and benign lung tumors in female mice.

A prior Notice of Intent to List styrene as known to cause cancer was published on June 12, 2009 under the Labor Code listing mechanism (Health and Safety Code section 25249.8(a)), based on a monograph published by the International Agency for Research on Cancer that identified styrene as a Group 2B carcinogen with less than sufficient evidence in animals but supporting mechanistic data. The proposed listing was withdrawn based on the Court of Appeal decision published on October 31, 2012 (Styrene Information and Research Center v Office of Environmental Health Hazard Assessment (2013) 210 Cal.App. 4th. 1082). In January 2013, OEHHA proposed the listing of styrene under the Labor Code listing mechanism, based on the Report on Carcinogens (twelfth edition) published by the NTP. That notice was withdrawn in March 2013, pending the results of federal litigation and additional peer review of the NTP’s Report on Carcinogens by the National Academy of Sciences of the National Research Council. The litigation was resolved in favor of the NTP and the National Research Council review confirmed the NTP findings of the carcinogenicity of styrene⁴. In the interim, certain provisions of the federal Occupational Safety and Health Administration regulations were extensively amended. Those regulations no longer identify the NTP as a definitive source for identifying chemicals for listing via the Labor Code mechanism. Therefore, OEHHA is noticing its intent to list styrene via the authoritative bodies listing mechanism based on the NTP report.

Request for comments: OEHHA is requesting comments as to whether styrenemeets the criteria set forth in the Proposition 65 regulations for authoritative bodies listings. In order to be considered, OEHHA must receive comments by 5:00 p.m. on April 29th ~~March 30~~, 2015. We encourage you to submit comments in electronic form, rather than in paper form. Comments transmitted by e-mail should be addressed to P65Public.Comments@oehha.ca.gov with “NOIL - styrene” in the subject line. Comments submitted in paper form may be mailed, faxed, or delivered in person to the addresses below:

Mailing Address: Monet Vela
Office of Environmental Health Hazard Assessment
P.O. Box 4010, MS-19B
Sacramento, California 95812-4010
Fax: (916) 323-2265
Street Address: 1001 I Street
Sacramento, California 95814

Comments received during the public comment period will be posted on the OEHHA web site after the close of the comment period.

If you have any questions, please contact Sam Delson at sam.delson@oehha.ca.gov or at (916) 445-6900.