By Mary Ann Rose

Glyphosate is the most widely used herbicide in the world and is applied to most of the U.S. corn and soybean crops. For decades, it’s been considered one of the least harmful of pesticides, with very low mammalian toxicity. Given its widespread use, it may be troubling to hear reports of glyphosate residues found in breakfast cereals, dog food or other consumer products. On top of that, a jury recently awarded $289 million in damages to a California pesticide applicator who claimed that glyphosate use was responsible for terminal non-Hodgkin lymphoma, a form of cancer.

It is not surprising that consumers would react with alarm. Most people do not understand that some level of contamination in our environment is unavoidable, especially given the fact that modern analytical equipment can detect substances in minute quantities. The public especially fears unfamiliar chemicals such as pesticides, but discounts the environmental impact from more familiar products and necessities such as pharmaceuticals and personal care products — yes, these have significant environmental impact!

At what level do these contaminants affect our health? The U.S. EPA must evaluate health effects before it registers any pesticide. Prior to registration, pesticides are subject to rigorous, scientific laboratory testing to uncover potential harmful effects; and to determine tolerances, the amounts of pesticides considered harmless to consumers. To set the tolerance, the EPA estimates total dietary plus environmental exposure to the pesticide over a human lifetime. Once registered, pesticides are reviewed every 15 years to determine if new data alter the EPA’s risk assessment.

A recent stir was caused by a report that glyphosate was detected in breakfast cereals. The Environmental Working Group (EWG), a nonprofit organization concerned with health and the environment, found glyphosate in 43 out of 45 conventional cereals, and five out of 16 organic cereals. The highest level they detected was 1.3 ppm, and most were under 0.5 ppm. All levels that EWG reported were well below the EPA’s regulatory limits (30 ppm). In essence, EWG created its own benchmark and set off alarms when it found levels that exceeded that benchmark.

Does glyphosate cause cancer? The trial against Monsanto resulted in a $289 million award to a former school groundskeeper in August. The groundskeeper, who is dying of cancer, sued Monsanto over the claim that Roundup weed killer gave him the disease. The plaintiff had used products containing glyphosate 20 to 30 times per year since 2012, and he described several events in which his clothes were drenched with glyphosate tankmix. The plaintiff convinced a jury that his cancer would not have occurred without his exposure to the herbicide, and they awarded $289 million in punitive and compensatory damages. However, in October, a superior court judge made a tentative ruling that could take away the compensatory damages and prompt a new trial.

A decision by a European agency in 2015 likely influenced the jury’s decision in the Monsanto trial. The European organization IARC (International Agency for Research on Cancer) declared that glyphosate was a probable human carcinogen. After IARC’s announcement, there have been contradictory decisions from the U.S. EPA, European Chemicals Agency and similar regulatory agencies in Canada and Australia. The reason for the apparent contradiction was different objectives. IARC’s task was to determine “whether glyphosate could cause cancer under some circumstances,” which may include laboratory studies at very high concentrations. The IARC answer was yes. The other agencies conducted risk assessments, which determine the likelihood of cancer under real-world conditions. The EPA and the other agencies concluded that glyphosate is unlikely to be carcinogenic to humans through dietary or other types of exposure.

How much good science backs the EPA’s position? The U.S. Agricultural Health Study has examined how agricultural practices affect cancer and health outcomes among licensed pesticide applicators in Iowa and North Carolina since 1993. An analysis in 2001 showed no significant associations between glyphosate and cancer. In 2018, an updated analysis of the Agricultural Health Study data was published that included 54,252 pesticide applicators and 5,779 cancer cases. Glyphosate was not associated with any solid tumors or lymphoid malignancies, including non-Hodgkin lymphoma. While there was some indication of increased risk of acute myeloid leukemia in the highest-exposure quartile, this association was not statistically significant.

Current science suggests that using glyphosate does not pose an unacceptable risk. That is why the EPA allows its use in the United States. This is not the same as saying glyphosate is risk-free, however.

If you use glyphosate, what should you do? Read and follow the pesticide label. To keep pesticide residues in crops within legal tolerances, strictly adhere to limits on application frequency, preharvest intervals, and maximum-use rates per treatment or crop cycle. To protect yourself, always wear your personal protective equipment (PPE). Pesticide applicators understand that “the dose makes the poison.” Another way of saying this is that limiting the amount of exposure limits the potential harmful effects. Wearing the label-required PPE is one sure way to limit your exposure to glyphosate or any other pesticide.

For more information, email Mary Ann Rose at [email protected], or write to:

Mary Ann Rose, Ph.D.
Director, Pesticide Safety Education Program
College of Food, Agricultural, and Environmental Sciences
Ohio State University Extension
256 Howlett Hall
2001 Fyffe Court
Columbus, OH 43210

Rose is director of the Ohio State University Extension Pesticide Safety Education Program.