California: Scientific consensus not required to justify Prop 65 warning

California’s Office of Environmental Health Hazard Assessment does not need scientific "certainty" to require that companies provide Proposition 65 warnings on products, the state has argued to a federal court, as it seeks to lift a nearly two-year prohibition on cancer warning labels for products that cause exposure to the herbicide glyphosate.

If it cannot convince the court, California could have to show a broader scientific consensus to justify the need for a Prop 65 warning label for glyphosate and other chemicals, rather than simply accepting findings from one of the "authoritative bodies" referenced in the 35-year-old law.

And with more than 300 substances listed on California’s controversial right-to-know law through this mechanism, a court ruling against the state in the case could mean future legal challenges ahead for other chemicals with disputed science.

The state made its argument in a brief to the US District Court for the Eastern District of California, saying it should be able to use a modified warning label that makes clear there is disagreement among governmental bodies as to glyphosate’s carcinogenicity.

A lack of consensus over glyphosate’s human health effects was at the heart of the court’s February 2018 decision to issue a preliminary injunction blocking California from mandating cancer warning labels for products containing glyphosate.

The court said at the time that "the heavy weight of evidence", including findings from the US EPA, showed glyphosate is not "known" to cause cancer in humans. It would violate companies’ free speech rights under the First Amendment of the US Constitution to require a label indicating a product is a carcinogen if the statement is not clearly true, the court said.

The injunction has remained in place as the litigation continues.

Disagreement about the science underlying a warning isn’t enough to create a First Amendment controversy, California said in its brief, and debate in science is not unusual. Scientific agencies rely on different data, exposures, and protocols to reach their conclusions.

The level of certainty requested by the plaintiffs "would prevent consumers subject to significant exposures from receiving health and safety information about a chemical unless human studies have definitively proven that it causes cancer in humans," California said.

The plaintiffs in the case – including the National Association of Wheat Growers and Monsanto, which makes the glyphosate-containing herbicide RoundUp – have asked the court to uphold the warning label ban. Two years after the preliminary injunction was issued, the "overwhelming" weight of authority is still that glyphosate does not cause cancer, the groups said in their own brief, filed in February.

California, however, has told the court that a modified warning can both "convey that glyphosate is a known carcinogen under California law, and also comply with the First Amendment standard applicable to government-compelled speech about health and safety risks."

Conflicting science

Proposition 65 requires that employees and consumers be warned when they are exposed to a chemical listed by the state’s Office of Environmental Health Hazard Assessment (Oehha) as "known" to cause cancer or reproductive harm.

One route to listing under Prop 65 is a finding by an "authoritative body", including the US EPA, the US Food and Drug Administration, the National Toxicology Program of the US Department of Health and Human Services and the World Health Organization’s International Agency for Research on Cancer (Iarc).

Oehha added the herbicide to the Prop 65 list in 2017, after Iarc concluded glyphosate is "probably" carcinogenic. The warning label requirement was set to take effect in July 2018.

The National Association of Wheat Growers and other industry groups challenged Oehha’s decision to list glyphosate. The court upheld the state’s Prop 65 listing, but still blocked the state from mandating warning labels for products that contained glyphosate above certain levels.

In issuing the preliminary injunction, the court noted that the US EPA had concluded that glyphosate is not a human carcinogen. That means that a warning label saying glyphosate is "known" to California to cause cancer is not "uncontroversially" true, the court said.

The EPA waded into the debate in August 2019, issuing guidance saying it disagrees with Iarc’s assessment and that it considers California’s Prop 65 warning language for glyphosate to be "false and misleading".

That prompted Oehha to issue its own statement, calling the agency’s dismissal of the Iarc findings "disrespectful of the scientific process". Prop 65 warning labels, along with information available on the Oehha website, have contributed "to lower risks of chemical exposures and greater public health protections for Californians", the agency said.

Modified label

California hopes it can convince the court to restore the cancer warning for glyphosate by modifying the warning language to note that "the EPA has concluded that glyphosate is not likely to be carcinogenic to humans".

The court rejected a pair of modified warnings suggested by the state in 2018, when California asked for a rehearing on the preliminary injunction.

But a 2019 ruling from the US Court of Appeals for the Ninth Circuit shows that a clarified state-law warning can avoid conflict with the First Amendment, even if there is scientific debate, California told the court.

Existing case law shows "the First Amendment can accommodate a tailored warning that provides a full picture of these unusual circumstances by acknowledging EPA’s disagreement with Iarc’s conclusion", the state said in its brief asking the court to grant summary judgment in its favor.

The coalition challenging the Prop 65 listing, however, maintains that Iarc’s conclusions on glyphosate "remain an outlier". And it said the latest warning language from California still violates the First Amendment and the "clear and reasonable" requirements of Prop 65. The "problem cannot be fixed by tinkering further with the warning language", said the groups.

A hearing on the parties’ motions for summary judgment is scheduled for 15 June.

By Terry Hyland