Chemicals Listed Effective April 21, 2023 as Known to the State of California to Cause Cancer: 1,1,1-Trichloroethane and Leucomalachite Green

Effective April 21, 2023, the Office of Environmental Health Hazard Assessment (OEHHA) is adding 1,1,1-trichloroethane (CAS Registry Number 71-55-6) and leucomalachite green (CAS Registry Number 129-73-7) to the list of chemicals known to the State of California to cause cancer for purposes of Proposition 65¹. The listing of these chemicals is pursuant to the “Labor Code” listing mechanism². The warning requirement for significant exposures to these chemicals will take effect on April 21, 2024.

The basis for the listings was described in a public notice published in the March 3, 2023, issue of the California Regulatory Notice Register (Register 2023, No. 9-Z). The title of the notice was “Notice of Intent to List Chemicals by the Labor Code Mechanism: 1,1,1-Trichloroethane and Leucomalachite Green.” The publication of the notice initiated a public comment period (March 3, 2023 – April 3, 2023).  No comments were received during the comment period.

A complete, updated Proposition 65 chemical list is available on the OEHHA website.

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 

1,1,1-Trichloroethane and leucomalachite green 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 Identification of Carcinogenic Hazards to Humans” Volume 130 “1,1,1-Trichloroethane and Four Other Industrial Chemicals” (IARC, 2022a) and Volume 129 “Gentian Violet, Leucogentian Violet, Malachite Green, Leucomalachite Green, and CI Direct Blue 218” (IARC, 2022b). IARC concluded that 1,1,1-trichloroethane is “probably carcinogenic to humans” (Group 2A) based on sufficient evidence of carcinogenicity in animals (IARC, 2022a).  IARC concluded that leucomalachite green is “possibly carcinogenic to humans” (Group 2B) based on sufficient evidence of carcinogenicity in animals (IARC, 2022b).