Glyphosate, a popular herbicide used in commercial weed killers, has raised significant attention after being added to California's Proposition 65 list. Its listing primarily resulted from the World Health Organization International Agency for Research on Cancer's (IARC's) finding that glyphosate is "probably carcinogenic to humans."

In Monsanto Co. v. Office of Environmental Health Hazard Assessment, Super. Ct. No. 16CECG0018, a glyphosate manufacturer, along with intervening agricultural associations and business groups (collectively the petitioners), petitioned for a writ of mandate challenging glyphosate's Proposition 65 listing and the state's reliance on the World Health Organization's conclusion. The petitioners argued it is improper for California's legislature and executive to abdicate the power of determining which chemicals are known to cause cancer to a foreign entity that is unaccountable to the citizens of California.

Glyphosate's Prop 65 listing, and the World Health Organization's research, have become increasingly controversial since the US Environmental Protection Agency's December 18, 2017 opinion that glyphosate is "not likely to cause cancer in humans." Seventeen other groups have reached similar conclusions as EPA, "namely, that the small number of tumors observed in rodents subject to treatment with glyphosate in these studies were not related to glyphosate."

On April 19, 2018, the California Court of Appeal rejected this challenge to glyphosate's Proposition 65 listing and dismissed the writ of mandate and complaint. The court found that there has not been any delegation of authority "recognizable as potentially problematic under the law."

Proposition 65 lays out a broad scheme for determining which chemicals to list, and the court noted that the scheme allows for potential conflicts given the multiple sources for determining known carcinogens. The court observed that the statutory scheme is "inclusive," regardless of whether identified listing agencies or processes agree. The court found that the statutory scheme provides a framework to identify known carcinogens by relying on third-party determinations, and this determination can be made if the chemical is known to cause cancer "if a body considered to be authoritative by such experts has formally identified it as" such. The court concluded that the factual allegations concerning glyphosate's listing are insufficient to support a claim that the standards or safeguards are insufficient.See the full decision.

Given the numerous studies finding no evidence that glyphosate is carcinogenic, facial challenges to the World Health Organization's 2015 report and a recent injunction issued in federal court in California blocking warning labels on glyphosate products (see our recent alert), we have not likely seen the end of efforts to remove glyphosate from Proposition 65 listing.