FDA to test foods for controversial herbicide

Evidence mixed on glyphosate’s health effects


CROP COVER  The FDA will begin testing food for the herbicide glyphosate, which is in widespread use, thanks in part to the development of crops genetically engineered to tolerate it. 

Chafer Machinery/Flickr (CC BY 2.0

The U.S. government will test various foods for exposure to glyphosate, the active ingredient in several herbicides.

Tests on foods including soybeans, corn, milk and eggs are set to begin this year, says Food and Drug Administration spokesperson Lauren Sucher. In 2014, the Government Accountability Office called on the FDA and the U.S. Department of Agriculture to strengthen their monitoring of glyphosate, the most widely used herbicide in the world. Previously, methods for such testing would have been too costly and labor intensive, Sucher says, but new methods now make it more feasible.  

Evidence for glyphosate’s ill effects is mixed and often clouded by spin on both sides. But there is little doubt that human exposure has increased along with a sharp increase in the herbicide’s use (SN: 2/6/16, p. 22).

Introduced in the 1970s in Monsanto’s Roundup, glyphosate soon dominated the pesticide market; more than 250 million pounds are applied yearly to agricultural lands in the United States today. Initially, the herbicide, which interferes with an essential enzyme found in plants, was primarily used to clear weeds from fields before planting. In the 1990s, the development of crops genetically engineered to tolerate glyphosate, and the expiration of patents, led to a dramatic increase in its use, including applications to fields during growing season. Today, an estimated 90 producers in 20 countries make glyphosate, which is also used throughout the world for controlling house and garden weeds.

Despite its widespread use, regulatory agencies have concluded that the herbicide has low toxicity and there has been no routine testing for glyphosate in food or people. A onetime study by the USDA’s Agricultural Marketing Service in 2011 found glyphosate residues in 90 percent of tested soybeans and a glyphosate metabolite in more than 95 percent of the samples. All the levels were below the acceptable dietary level for soybeans established by the U.S. Environmental Protection Agency of 20 parts per million, although the highest concentration was a close 18.5 ppm.

Numerous toxicology studies, many conducted by industry as required by the EPA, have found that glyphosate is relatively harmless. Animals don’t have the enzyme that glyphosate acts on and therefore shouldn’t be directly affected by it. Other research suggests ill effects. Yet evidence of harm isn’t clear-cut and has been stained by a handful of much-publicized and widely discredited studies. Such a muddled research history is all the more reason for standardized studies by independent scientists and for general monitoring, says Ana Soto, an expert in endocrine disrupting chemicals at Tufts University School of Medicine in Boston.

“If there is evidence of problems that keep coming up, and the chemical is in such widespread use, we need to study it,” says Soto. “That’s not revolutionary, that’s common sense.”

The World Health Organization’s International Agency for Research on Cancer conducted its own review of more than 400 studies in 2015 and rated glyphosate as “probably carcinogenic to humans.” This designation of a 2A carcinogen is in part due to finding limited evidence from real-world exposures in humans. Studies in Canada, Sweden and the United States, for example, have shown that people who work with glyphosate-based herbicides have increased risks for non-Hodgkin’s lymphoma, although a separate large U.S. study found no such link.

Designating glyphosate as “probably carcinogenic” also rests on evidence from studies of cancer in animal experiments and mechanistic evidence of how damage from glyphosate might occur at the cellular level. Other agents classified by the IARC as having similar strength of evidence for cancer-causing capabilities include the insecticide malathion, indoor emissions from wood-burning stoves and red meat (SN: 11/28/15, p.9).

The IARC assessment of herbicides that include glyphosate includes only studies that are in the public domain and can be independently reviewed, says Kathryn Guyton, senior toxicologist at the IARC Monographs Program and lead author on a paper summarizing the findings in the May 2015 Lancet Oncology. Therefore, many unpublished industry studies, which are accepted by regulatory agencies in the United States, were excluded. Also excluded are studies that don’t provide enough data for independent analysis, such as a widely disputed study by French researchers linking Roundup to kidney problems and tumors in rats.

Following the IARC’s designation, the European Food Safety Authority reassessed glyphosate’s risks to health and the environment. The EFSA assessment, which was more narrowly focused on glyphosate alone and included some studies not reviewed by the IARC, was published in November 2015. It concluded that glyphosate “is unlikely to pose a carcinogenic hazard to humans,” and it raised the acceptable daily intake of glyphosate from 0.3 milligrams per kilogram of body weight per day to 0.5 mg/kg body weight per day.But it also pointed to gaps in both toxicological and environmental data and established for the first time an “acute reference dose” — the maximum amount that can be ingested in a short time period — based on new toxicity data from rabbit studies (also 0.5 mg/kg body weight per day).

The FDA’s decision to monitor food for glyphosate residue coincides with a statement of concern over glyphosate exposure published online February 17 in Environmental Health. The statement cites some dubious science (such as the retracted rat-tumor study). Nonetheless, given the conflicting evidence, its recommendations seem sound, says Soto. These include routine testing for glyphosate residues in human fluids by the U.S. Centers for Disease Control and Prevention.

Monsanto spokesperson Charla Lordsays that if the FDA decides to rigorously test for glyphosate residue, the company is confident that the monitoring will reaffirm the product’s safety. 

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