Farm Progress

Science does not support declaring glyphosate a carcinogenRecent proposal goes against agency declaration in 2007 that herbicide does not cause cancerDeclaration could restrict glyphosate use

tfitchette, Associate Editor

October 29, 2015

4 Min Read
<p>California regulators want to declare glyphosate, a popular herbicide used in many agricultural applications, a carcinogen under Prop. 65.</p>

A California agency has reversed a previous declaration and is now pushing to declare the popular glyphosate herbicide as a carcinogen.

Early in September, the California Office of Environmental Health Hazard Assessment (OEHHA) filed a “notice of intent” to list the chemicals tetrachlorvinphos, parathion, malathion and glyphosate as cancer-causing agents and therefore necessary for listing under the state's Proposition 65.

At the heart of the issue is the decision to include glyphosate, an herbicide widely used by agriculture, homeowners and public agencies, on its list of known carcinogens. As one could expect, the proposal was met with immediate push back by an array of agricultural organizations.

Surprising in the move is the fact that no regulatory agency has ever considered glyphosate a carcinogen. Even the OEHHA in 2007 declared glyphosate safe when used as labeled after conducting a risk assessment of the herbicide.

Prop. 65 is California’s “safe drinking water and toxic enforcement act of 1986,” enacted as a ballot initiative. It is intended to “protect California citizens and the state’s drinking water sources from chemicals known to cause cancer, birth defects, or other reproductive harm, and to inform citizens about exposures to such chemicals.”

The public comment period for the action closed in late October.

If successful, the action would list glyphosate and the other chemicals as carcinogens, perhaps paving the way for further restrictions on the chemicals that have previously been vetted and approved for specific uses.

The action comes after the International Agency for Research on Cancer (IARC) declared without proof that glyphosate causes cancer, according to John Combest, media manager for Monsanto, a leading manufacturer of glyphosate.

Monsanto filed a lengthy response to the proposed action during the comment period, saying in short that the intent to list glyphosate as a carcinogen under Prop. 65 is unsupported by science.

In its response, Monsanto writes: “Indeed, OEHHA itself has closely reviewed the science and concluded: ‘based on the weight of evidence, glyphosate is judged unlikely to pose a cancer hazard to humans’.”

Opposition is widespread

Monsanto’s comments go on for several pages, outlining how glyphosate is widely used, has a long history of safe use and is environmentally beneficial to California.

Moreover, glyphosate has undergone extensive toxicological, ecotoxicology and environmental testing over the past 40 years to acquire global regulatory approval.

“Global regulatory authorities and independent experts all agree that glyphosate is not carcinogenic,” says Monsanto.

Glyphosate is approved for use in more than 250 agricultural crop applications in California, plus for weed control ons in non-cultivated settings, says Monsanto. No other active ingredient compares in terms of number of approved uses.

Monsanto is not the only organization calling on the OEHHA to reject the declaration.

Twenty-two Ag organizations signed on in opposition to the proposed listing, including: Western Growers Association, the California Association of Winegrape Growers, California Tomato Growers Association, Western Plant Health Association, California Fresh Fruit Association, California Citrus Mutual, Almond Hullers and Processors Association, California Association of Pest Control Advisors, the California Cotton Ginners and Growers Associations and the Western Agricultural Processors Association. 

In the joint comment in opposition to the proposal, the overall group points out that no herbicide can be used until it has been thoroughly reviewed and approved for its intended use. In addition, the chemical has a long history of safe use “supported by decades of data from more than 800 scientific studies.”

Monsanto and the coalition point out that the IARC classification of glyphosate overlooks decades of robust analysis by regulatory agencies.

Also troubling to the agricultural groups is the way the OEHHA is going about the declaration.

The OEHHA wants to declare glyphosate a carcinogen through a mechanism cited in the California Labor Code, which does not require scientific study or basis for the declaration. It only looks at the IARC declaration in making the recommendation.

“Under its interpretation of the law, OEHHA does not look at any scientific studies or data,” says Monsanto spokesman Samuel Murphey.

Murphey says internal procedures within OEHHA require the agency to reach its final listing decision within one year of its notice of intent. It was filed Sept. 4.

Murphey says it is unknown how such a declaration could impact the use of glyphosate.

University of California weed scientist Brad Hanson says the move “would be a pretty big barrier to some weed managers” as the state mandates that public agencies avoid the use of Prop. 65 products if possible.

“This would really tie the hands of some wildland weed managers, roadsides and right-of-way managers and those who manage ball fields and parks,” Hanson said.

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About the Author(s)


Associate Editor, Western Farm Press

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