California Adds Four Substances to Proposition 65 Carcinogen List

On July 17, 2026, the Office of Environmental Health Hazard Assessment (OEHHA) under the California Environmental Protection Agency issued a notice adding four substances—Hydrochlorothiazide, Voriconazole, Tacrolimus, and Welding Fumes—to the carcinogen list under the Safe Drinking Water and Toxic Enforcement Act (commonly known as Proposition 65).

Three Pharmaceuticals Added

The three pharmaceuticals newly listed as carcinogens are all clinically commonly used drugs:

Drug Name	Generic Name	Primary Use
Hydrochlorothiazide	Hydrochlorothiazide (HCTZ)	Diuretic, widely used to treat hypertension and edema
Voriconazole	Voriconazole (VRCZ)	Broad-spectrum antifungal agent, used for invasive fungal infections
Tacrolimus	Tacrolimus (TAC)	Immunosuppressant, used for post-transplant anti-rejection and autoimmune diseases

Welding Fumes Simultaneously Added

Alongside the three pharmaceuticals, welding fumes were also added to the list. Welding fumes are mixtures of metal oxide particles generated during welding operations. Long-term exposure to high concentrations of welding fumes has been confirmed by multiple epidemiological studies to increase the risk of lung cancer and other cancers among workers.

Impact on Businesses

Under California Proposition 65, any business operating in California must provide clear and reasonable warning labels if its products, premises, or emissions contain listed chemicals at exposure levels exceeding the safe harbor threshold, informing consumers or workers that the substance may cause cancer or reproductive toxicity.

Warnings may be issued through various means, such as: affixing labels to consumer products, posting notices in workplaces, distributing notifications in rental housing complexes, or publishing announcements in newspapers. The warning requirement takes effect one year after the chemical is listed.

Furthermore, the proposition explicitly prohibits businesses from knowingly and intentionally discharging listed chemicals into any waters that may become sources of drinking water during their operations within California. From the date the chemical is listed, businesses must complete emission control measures within twenty months to ensure full compliance with this prohibition.

All substances under Proposition 65 can be queried through ChemRadar GCIS:

https://www.chemradar.com/en/tools/cis/inv/64924a20e7fff39f787f1b0d?utm_medium=gcis&utm_campaign=cis

About CIRS

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If you need any assistance or have any questions, please get in touch with us via service@cirs-group.com.

Further information

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