The study shows that amines can become airborne

Dicamba drift, the movement of herbicide off crops and through the atmosphere, can lead to damage to neighboring plants. To prevent dicamba drift, other chemicals, usually amines, are mixed with dicamba to “lock” it in place and prevent it from turning into a vapor that moves more easily in the atmosphere.

New research from the lab of Kimberly Parker, assistant professor of energy, environmental and chemical engineering at Washington University’s McKelvey School of Engineering in St. Louis, shed new light on this, demonstrating for the first time that these amines volatilize themselves, often more than dicamba itself.

Their findings were published on September 23 in the journal Environmental Science and Technology.

Volatilization of amines when applied with dicamba may help explain the processes that cause dicamba drift. However, amines are also used in other herbicides, including ca glyphosate, the most used herbicide in the world. Regardless of the herbicide, the researchers found that the amines volatilized.

If the amines themselves are released into the atmosphere, they can have a negative impact on human health, as they can form cancer-promoting substances. They also affect climate and atmospheric chemistry.

Because of their potential prevalence, the scientific literature is full of research looking at how they are released into the atmosphere—except when it comes to their use in amine herbicide formulations.

“Amines also undergo reactions to form particles — tiny particles that can make their way into the body when inhaled,” Parker said. “Those particles are also toxic and carcinogenic” and have consequences for atmospheric chemistry by affecting the climate.

“Researchers have looked at industrial applications, animal operations and environmental sources of amines, but no one has looked at herbicides at all, as far as I’ve seen, despite the fact that large amounts of herbicide-amine mixtures are sprayed on crops across the country,” Parker said.

“We were really surprised to see that this source was overlooked.”

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Her lab has done research on the use of amines with herbicides in agriculture. In those scenarios, amines were added to stop dicamba volatilization. However, the technique was often ineffective and dicamba ended up in nearby crops.

First author Stephen Sharkey, a PhD student in Parker’s lab, led previous research studying dicamba volatilization from dicamba-amine mixtures and wondered, “if dicamba volatilizes, what happens to the amine that’s supposed to be there, stop the process of volatilization?”

To find out, Sharkey measured the change in the amount of amine present over time when it was mixed with different herbicides.

In all mixtures, the amines volatilized from the herbicide-amine mixtures. Sharkey also worked with the lab of Brent Williams, associate professor of energy, environmental and chemical engineering, to confirm that amines enter the gas phase from herbicide-amine mixtures by capturing the amines from the air for measurement.

In agricultural environments, Parker said, amines are mixed not only with dicamba but with other herbicides, including 2,4-D and glyphosate.

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In addition to the experiments, Sharkey quantified the amines entering the atmosphere, which required a little detective work. He used two separate data sets—estimated herbicide application rates and survey data from U.S. farmers—that showed which amines were used with different herbicides.

Sharkey concluded that herbicide use is responsible for the release of about four gigagrams (4,000 tons) of amines annually in the US.

The findings came as a surprise to Parker, not only because the chemistry doesn’t immediately suggest that amines volatilize in this way, but also for a more practical reason.

“There’s been extensive work looking at the different ways amines get into the atmosphere,” she said. “A lot of effort has gone into understanding where amines come from, but research into their use with herbicides has simply not been considered before.”