Monsanto wants a California court to prohibit a state listing of glyphosate as a known carcinogen.

The petition, filed in Fresno County Superior Court, addresses action by the Office of Environmental Health Hazard Assessment (OEHHA) and Acting Director Lauren Zeise to add glyphosate to the state’s Proposition 65 list of chemicals that are “known to the state of California to cause cancer.”

Proposition 65 was enacted by California voters in 1986 to address public concerns about exposure to toxic chemicals. Known formally as the Safe Drinking Water and Toxic Enforcement Act of 1986, Proposition 65 requires California to publish a list of chemicals California says can cause cancer or reproductive toxicity.

A September notice of intent by OEHHA seeks to place the popular herbicide on the Prop. 65 list of carcinogens. That proposed listing included the chemicals Tetrachlorvinphos, Parathion, and Malathion. The agency seeks to use provisions of the California Labor Code to make this ruling, bypassing other more formal means of such a declaration.

In its petition to the court, Monsanto attorneys argue that the so-called “Labor Code listing mechanism” violates the company’s constitutional rights under the California and U.S. Constitution.

At the heart of Monsanto’s complaint is how OEHHA arrived at its determination and the apparent reversal of opinion within the agency over the toxicity of glyphosate.

In comments to the agency during the public comment period, and again in the complaint, Monsanto says the agency improperly relied on a declaration by the International Agency for Research on Cancer (IARC) that glyphosate causes cancer.

In response to the OEHHA proposal and as part of public comment, Monsanto presented 15 pages of annotated and footnoted comments to the agency late last year, saying effectively that peer-reviewed science does not support listing glyphosate as a carcinogen.

Even OEHHA said as much within the past 20 years. In 1997 and again in 2007, the state agency said that glyphosate is “unlikely to pose a cancer hazard to humans.” Four separate studies cited by the IARC and numerous entities agreed that glyphosate was not linked to tumors in laboratory tests.

A Prop. 65 declaration would limit the use of glyphosate by municipalities as some of them prohibit the use of chemicals listed under the law. That means public agencies would be forced to consider other less-efficacious or costly means of weed control, according to Monsanto.

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