Chlormequat chloride in oats: what it means for us

Shockingly little is known about chlormequat chloride. Soon, it may be used on crops all over the country.

It’s common to hear about the harms of pesticides—cancer risk, birth defects, lung damage. A major reality is that pesticides are often used long before their effects are understood, for better or for worse.

Chlormequat chloride, or chlormequat for short, is a pesticide that stunts plant growth. Chlormequat blocks growth and strengthens the stem, keeping plants upright to facilitate harvesting. It’s currently allowed in the U.S. for ornamental plants (house plants) and is used in other countries on crops like oats, which can be challenging to harvest if they bend over from growing too tall.

For example, chlormequat is common in the European Union, the United Kingdom, and Canada and has been used for many years. “It's not really on the radar of anybody in the U.S.,” notes Alexis Temkin, a senior toxicologist at the Environmental Working Group (EWG).

In 2018, the Environmental Protection Agency (EPA) first allowed the importation of chlormequat, though it was not allowed for domestic use on crops. Thus it was introduced into American diets. The EWG realized that while some research indicated potential impacts on mammalian fertility and development, the USDA and FDA were not testing for chlormequat in foods or conducting any research on it. Here, they saw an opportunity to study the chemical as it was being introduced into the country. The EWG took their first round of samples, hoping to measure the concentrations across time to see if the regulations would impact exposure. In 2020, the EPA raised the threshold for importation concentrations.

On Feb 15, 2024, the EWG published the results of this pilot study monitoring chlormequat levels in Americans. They not only found a higher detection frequency, but also higher concentrations from 2018 to the present. For some consumers, this may mean little in terms of changing eating habits: another pesticide in our food, so what? For others, avoiding certain oat products is the way to go. Which is it?

Knowledge of the effects of chlormequat chloride on humans is limited. Martin Sørensen, a researcher at the Danish Institute of Agricultural Sciences, was one of the few around the world who studied the effects of chlormequat on mammalian fertility. However, after finding “no effect of chlormequat in the experiments on male fertility,” he decided to stop pursuing the topic. “There is no support for a ban in our data,” he states. “The issue has previously been debated in Denmark, but seldom now.”

Temkin, however, is still wary. There are many variables, she explains, that can influence the reproducibility of a health effect or observed result. Research has studied boars and mice, typically focusing on the male reproductive system but not on females. Timing of the exposure, such as during pregnancy or early life, can also impact results. “I definitely think more research is needed to confirm those findings,” Temkin states. “An epidemiological study would be a really good next big study,” as there is shockingly no epidemiological data regarding human exposure to chlormequat. Noelle Eckley Selin, MIT professor in the Institute for Data, Systems and Society (IDSS) and director of MIT's Technology and Policy Program (TPP), adds that “the danger that different chemicals pose to human health very much depends on the concentrations, and that’s why it’s important to have thorough and effective assessment and testing processes.”

Even amidst this mystery, in 2023, the EPA began to review a proposal that would allow domestic use of chlormequat on crops. One of the major flaws in pesticide regulation, Temkin explains, is that companies that manufacture pesticides submit an application to the EPA and “then also provide the data for which safe levels are determined. That’s usually from animal studies,” which may be outdated, use very high doses, or completely skip factors such as developmental neurotoxicity, which is not required in a pesticide submission.

However, this push for domestic use does not come purely from manufacturers. With grain production, climate change-related high winds, high storms, and flooding that can cause crops to fall over, chlormequat can combat this. Given that Canada and the EU have allowed domestic use for many years, American farmers are at a disadvantage when it comes to crop yield.

Selin notes the “need for increased cooperation and information-sharing” as “chlormequat is just one of many pesticides present in our food supply.” With domestic use being the potential next development, worker exposure is another major concern.

Given the existing data gaps, the EWG feels it may be best to be precautionary and set a low safe dose to account for some uncertainty. Regulatory agencies don’t always see it this way, as they weigh the costs and benefits. Regardless, it is still too early to tell what the impacts of chlormequat chloride are on human health.

Rather than hoping to elucidate the effects of chlormequat, EWG hopes to fill some of the gaps in research and monitoring and bring attention to the issue. The study by EWG was small, only including 96 people. “We don’t necessarily want to be doing this,” Temkin states. “This is something that the USDA should be measuring for in their oat and grain samples. The FDA should be measuring for it when they collect processed foods. And the CDC National Biomonitoring program, which is regularly looking for a variety of different chemicals and different pesticides in people, hopefully, they will add it to their testing program. That's ultimately what we want to see.”