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April 28, 2016

Proposition 65: OEHHA Lists Styrene under Prop 65 and Proposes NSRL

Bergeson & Campbell, P.C.

On April 22, 2016, California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) issued a final notice listing styrene as known to the state to cause cancer under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Prop 65). OEHHA also issued a proposal to adopt a Prop 65 No Significant Risk Level (NSRL) of 27 micrograms per day for styrene.

The listing of styrene has been contentious. OEHHA previously attempted to propose styrene for listing via the Labor Code listing mechanism, but those proposals were withdrawn following successful legal challenges by the Styrene Information & Research Center (SIRC). OEHHA then re-proposed listing styrene on February 27, 2015, under the authoritative bodies listing mechanism. Effective April 22, 2016, OEHHA added styrene to the list of chemicals known to the state to cause cancer. Warning requirements will be triggered one year from the date of OEHHA’s listing, or by April 22, 2017.

Information regarding styrene’s Prop 65 listing is available in our memorandum Court Affirms Decision Preventing Proposition 65 Listing of Styrene and Vinyl Acetate As Carcinogens. Comments on the proposed NSRL are due on or before June 6, 2016.

Authoritative Body Listing

To be listed under Prop 65, an authoritative body must formally identify the chemical as causing cancer, and the evidence considered by the authoritative body must meet the scientific sufficiency criteria contained in the regulations. Styrene meets the criteria, according to OEHHA, for listing as known to the state to cause cancer under Prop 65, based on findings of the National Toxicology Program (NTP). 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 Prop 65 regulations for styrene. In its report, 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.

OEHHA received 13 comments on the proposed listing of styrene. In its Response to Comments, OEHHA provides its response to comments that the formal identification criteria are not met:

The 2011 NTP Report on Carcinogens, Twelfth Edition meets all three of the bases for establishing formal identification. More specifically, the report meets the criteria in Section 25306(d)(1) since styrene is included on a list of chemicals causing cancer issued by NTP, is the subject of a report that was published by NTP which concludes that styrene is reasonably anticipated to be a human carcinogen, and the NTP Report on Carcinogens indicates this identification is a final action. The report meets the criteria in Section 25306(d)(2) since styrene is specifically and accurately identified, and the report was reviewed by an advisory committee in a public meeting, was subject to public review and comment, and was formally published by the NTP.

OEHHA also responds to several comments arguing that the sufficiency of evidence criteria are not met. OEHHA does clarify and agree with comments submitted that styrene is not the same as polystyrene, that polystyrene is not the subject of the proposed listing, and that while free or unreacted styrene may be present in polystyrene products (e.g., food containers and food packaging materials), only styrene exposures that pose a significant cancer risk would require a warning.

Proposed NSRL

One exemption from the warning requirement applies to exposures for which the “person responsible” can show that the exposure presents “no significant risk” assuming lifetime exposure at the “level in question” for substances known to cause cancer.

For carcinogens, the “level in question” refers to “the chemical concentration of a listed chemical for the exposure in question,” which “includes the exposure for which the person in the course of doing business is responsible and does not include exposure to a listed chemical from any other source or product.” Title 27, California Code of Regulations § 25721(a). The regulations specify how lifetime exposure should be calculated. A level of exposure poses “no significant risk” where the level is determined by means of a “quantitative risk assessment” meeting outlined standards; by application of criteria regarding routes of exposure; or by application of the specified regulatory level or, if no level is established, by application of provisions regarding exposure to trace elements and levels based on state or federal standards.

To develop the proposed NSRL for styrene, OEHHA states in its Initial Statement of Reasons that it relied on the data analysis and cancer potency estimate presented in the December 2010 OEHHA Public Health Goal (PHG) for Styrene in Drinking Water document (2010 OEHHA PHG). OEHHA states that the cancer dose response assessment presented in the 2010 OEHHA PHG for styrene is a reliable scientific basis for the NSRL, and is consistent with OEHHA’s Section 25703 guidance. In the Initial Statement of Reasons, OEHHA describes how it selected the 2010 OEHHA PHG document to determine cancer potency, how it estimated cancer potency at 0.026 per mg/kg-day from the OEHHA PGH, and how it calculated the NSRL of 27 micrograms per day for styrene.


OEHHA has attempted for several years to list styrene under Prop 65, so it should come as no surprise that it has determined that the criteria are satisfied for listing under the authoritative body listing mechanism. SIRC has successfully challenged the proposed Prop 65 listing of styrene before, although under a different listing mechanism. If SIRC proceeds with another legal challenge, it may seek injunctive relief to preempt implementation of the listing. If SIRC does not challenge this listing, or if its challenge is unsuccessful (injunctive relief or otherwise), the warning requirements for styrene will be required commencing one year from the date of OEHHA’s listing, or by April 22, 2017.

OEHHA’s proposed NSRL of 27 micrograms per day for styrene is potentially helpful to the extent that an OEHHA-established NSRL eliminates the need for industry to develop its own NSRLs, provides consistency in establishing one NSRL instead of potentially different NSRLs developed by different companies, and potentially reduces or eliminates litigation costs by discouraging Prop 65 bounty hunters from bringing actions when they identify the presence of styrene in a product below the OEHHA-established NSRL. All of these advantages only apply, however, if OEHHA establishes a scientifically defensible and appropriate NSRL. There may be issues with OEHHA’s proposal, particularly since the 2010 OEHHA PHG is a five-year old document that does not include more recent information. Comments on the proposed NSRL are due on or before June 6, 2016.

Despite any potential legal challenge to the listing or comments that may modify the NSRL, companies should commence, to the extent they have not done so already, to review their products containing styrene and evaluate potential warning requirements.