Washington: The movement of the herbicide dicamba off crops through the atmosphere, known as "dicamba drift," can cause unintentional damage to neighbouring plants.
Other chemicals, usual amines, are mixed with dicamba to "lock" it in place and prevent it from volatilizing, or turning into a vapour that moves more easily in the atmosphere.
New research from Kimberly Parker's lab at Washington University in St. Louis' McKelvey School of Engineering has shed new light on this story by demonstrating for the first time that these amines themselves volatilize, often more than dicamba itself.
Their findings were published in the journal Environmental Science and Technology.
The volatilization of amines in the presence of dicamba may aid in explaining the processes that cause dicamba drift. However, amines are also used in other herbicides, including glyphosate, the world's most widely used herbicide. Regardless of herbicide, the researchers discovered that amines volatilized.
If amines are released into the environment, they can have a negative impact on human health by forming cancer-promoting substances. They also have an effect on the climate and atmospheric chemistry. Because of their potential danger and prevalence, the scientific literature is replete with studies on how they are released into the atmosphere -- except when used in herbicide-amine formulations.
"Amines also undergo reactions to form particulate matter -- tiny particles that can make their way into the body when inhaled," Parker said. "Those particles are also toxic and carcinogenic," and they carry consequences for atmospheric chemistry by affecting 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 we have seen, despite the fact that large quantities of herbicide-amine mixtures are being sprayed onto crops across the country," Parker said.
"We were really surprised to see that this source had been overlooked."
Her lab has conducted research on the use of amines in conjunction with herbicides in agriculture. The amines were added in those scenarios to prevent the herbicide dicamba from volatilizing. However, the technique was frequently ineffective, and the dicamba ended up drifting to nearby crops.
First author Stephen Sharkey, a PhD student in Parker's lab, led that earlier research studying dicamba volatilization from dicamba-amine mixtures and wondered, "If the dicamba is volatilizing, what's happening to the amine that's supposed to be there stopping the volatilization process?"
Sharkey measured the number of amines present over time when mixed with different herbicides to find out. What were the outcomes? The amines from the herbicide-amine mixtures volatilized in all of the mixtures. Sharkey also collaborated with Brent Williams' lab, an associate professor of energy, environmental, and chemical engineering, to confirm that amines were entering the gas phase from herbicide-amine mixtures by capturing and measuring amines in the air.
Parker pointed out that amines are not only mixed with dicamba in agricultural settings, but also with other herbicides such as 2,4-D and the widely used glyphosate.
Sharkey, in addition to experimenting, quantified the number of amines that were actually entering the atmosphere, which required some detective work. He used two data sets: estimated rates of herbicide application and survey data from farmers in the United States that showed which specific amines were used with which herbicides.
Sharkey concluded that herbicide use causes the release of approximately 4 gigatonnes (4,000 metric tons) of amines in the United States each year.
Parker was taken aback by the findings, not only because the chemistry does not immediately suggest that amines volatilize in this manner, but also for a more practical reason.
"There has been extensive work looking at the different ways in which amines enter the atmosphere," she said. "There has been a lot of effort put into understanding where amines come from, but research into its use with herbicides just wasn't considered before." —ANI