California | Notice of Intent to List Chemicals by the Labor Code Mechanism: Molybdenum Trioxide and Indium Tin Oxide

The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) intends to list the following chemicals as known to the state to cause cancer under the Safe Drinking Water and Toxic Enforcement Act of 1986 (Proposition 65): molybdenum trioxide (CAS No. 1313-27-5) and indium tin oxide (CAS No. 50926-11-9).  This action is being proposed pursuant to the “Labor Code” listing mechanism. zOEHHA has determined that each of these substances meets the criteria for listing by this mechanism.

Background on listing by the Labor Code mechanism:  Health and Safety Code section 25249.8(a) incorporates California Labor Code section 6382(b)(1) into Proposition 65.  The law requires that certain substances identified by the International Agency for Research on Cancer (IARC) be listed as known to cause cancer under Proposition 65.  Labor Code section 6382(b)(1) refers to substances identified as human or animal carcinogens by IARC.  OEHHA has adopted regulations concerning these listings in Title 27, Cal.Code of Regs., section 25904.  As the lead agency for the implementation of Proposition 65, OEHHA evaluates whether a chemical’s listing is required.

OEHHA’s determination:  Molybdenum trioxide and indium tin oxide meet the requirements for listing as known to the state to cause cancer for purposes of Proposition 65.

IARC has published on its website “IARC Monographs on the Evaluation of Carcinogenic Risks to Humans, Volume 118. Welding, Molybdenum Trioxide, and Indium Tin Oxide.” (IARC 2018).  IARC concludes that molybdenum trioxide and indium tin oxide are classified in Group 2B (“possibly carcinogenic to humans”) based on sufficient evidence of carcinogenicity in animals (IARC 2018).

Opportunity for comment:  OEHHA is providing this opportunity to comment as to whether the chemicals identified above meet the requirements for listing as causing cancer specified in Health and Safety Code section 25249.8(a), Labor Code section 6382(b)(1), and Title 27, Cal. Code of Regs., section 25904(b).  Because these are ministerial listings, comments should be limited to whether IARC has identified the specific chemical or substance as a human or animal carcinogen.  Under this listing mechanism, OEHHA cannot consider scientific arguments concerning the weight or quality of the evidence considered by IARC when it identified these chemicals and will not respond to such comments if they are submitted (Title 27, Cal. Code of Regs., section 25904(c)).

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