Antimony (trivalent compounds) had been identified as a potential candidate for listing under Proposition 65, which aims to protect Californians from exposure to chemicals known to cause cancer, reproductive harm, or other adverse health effects. This potential listing was based on the conclusion of the International Agency for Research on Cancer (IARC), indicating its carcinogenicity to humans.

Evaluation Process:

The OEHHA (Office of Environmental Health Hazard Assessment) initiated a thorough evaluation process, seeking public input, and conducting a comprehensive review of scientific evidence. A public comment period was held from September 30, 2022, to October 31, 2022, during which the OEHHA received six sets of comments from concerned individuals and organizations.

Important Findings:

On May 5, 2023, the IARC published volume 131 of the IARC Monographs, titled "Cobalt, Antimony Compounds, and Weapons-Grade Tungsten Alloy." Following a careful review of this publication and considering the comments received during the public comment period, the OEHHA has determined that antimony (trivalent compounds) does not meet the criteria for listing as causing cancer via the Labor Code mechanism.

Scientific Rationale:

While the IARC's previous classification of "antimony (trivalent compounds)" placed it in Group 2B (carcinogenic to humans), the IARC (2023) clarified that this broader listing was primarily supported by mechanistic evidence in human primary cells and experimental systems specific to trivalent antimony. Additionally, there was sufficient evidence of the carcinogenicity of antimony trioxide, a specific compound, but not for antimony (trivalent compounds) as a whole.


As a result of this evaluation, the OEHHA will not proceed with the listing of antimony (trivalent compounds) under Proposition 65 at this time. It is significant to consider that this decision has no bearing on the antimony oxide (antimony trioxide) listing that has been enacted under Proposition 65 since 1990.

Reference: Antimony (Trivalent Compounds) Found Not to Meet Labor Code Listing Criteria - OEHHA (

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