California's Office of Environmental Health Hazard Assessment (OEHHA) has finalized a Proposition 65 No Significant Risk Level (NSRL) for styrene of 27micrograms per day (µg/day).
NSRLs represent the state’s safe harbor level below which “clear and reasonable warnings are not required under Proposition 65. The agency's action affirms the proposed level it developed when it added styrene to the Proposition 65 list of carcinogens in April 2016.
Comments submitted by the industry group Styrene Information and Research Center (SIRC) advocated a much higher safe harbor levels –2,100µg/day for exposure by inhalation, and 5,600µg/day for oral exposure by ingestion – based on an internal dose for the target sub-tissue, rather than using whole tissue or an administered dose.
In OEHHA’s final statement of reasons (FSOR), the agency characterized SIRC's proposed NSRL as "not well supported by the underlying data."
The agency contends that the physiologically based pharmacokinetic (PBPK) model used by SIRC to derive these levels was speculative and failed to "accurately model substantial elements of the available dataset.” SIRC’s method raised additional issues with the assumptions and models used in the analysis, according to OEHHA.
Consequently, the agency rejected SIRCs proposed NSRLs as “not likely to be sufficiently protective of human health," and established its’ 27µg/day limit as the appropriate value.
The FSOR also addressed comments submitted by the American Chemistry Council’s Plastics Foodservice Packaging Group (PFPG) on polystyrene food packaging.
OEHHA said in the document that a warning for styrene would only be required when exposures exceed the NSRL and that the levels of residual styrene in polystyrene food packaging materials "are generally thought to be fairly low in most cases."
The agency notes that it can provide compliance assistance for styrene exposure from specific products through development of safe use determinations (SUDs), upon request.