Many common herbicides are applied as amine salts to improve chemical properties such as increasing the solubilities of glyphosate and 2,4-D and reducing the volatilities of 2,4-D and dicamba. Current environmental research on these herbicides and their amine salts has focused on the fate of the herbicide molecule itself. Recent attention has been focused on the amine salts of 2,4-D and dicamba due to concerns of volatilization and drift leading to off-target damage. However, prior research has not investigated the fate of the amine counterion (i.e., dimethylamine, DMA; isopropylamine, IPA; diglycolamine, DGA; n,n-bis-(3-aminopropyl)methylamine, BAPMA), even though the amine is applied at an equimolar concentration to the herbicide. Since these amines have a higher vapor pressure than the herbicides they are applied with, we hypothesized that these amines are volatilizing from herbicide-amine formulations. Because amines are added to reduce dicamba and 2,4-D’s vapor pressures, the loss of the amine could contribute to increased herbicide volatilization. Additionally, if the amines volatilize from herbicide-amine salts, their application alongside herbicides may be an important but overlooked source of amines to the atmosphere, where they may impact human health and atmospheric chemistry. Upon measuring the losses of DMA and IPA from glyphosate, dicamba, and 2,4-D salts, we found that amine losses consistently exceeded that of the herbicides. Gas phase measurements of volatilized IPA in the headspace above glyphosate-IPA salts confirm that volatilization contributes to the measured loss. We then tested the impacts of higher temperatures, longer times, and reduced initial amine concentrations on the volatilization of dicamba and amine from salts containing DMA, IPA, DGA, and BAPMA and used these results alongside literature to propose processes that contribute to amine and dicamba losses. Finally, we utilized U.S. herbicide use rates to estimate the potential for herbicide-amine salts to contribute to atmospheric amine pollution.

Amine volatilization from herbicide salts: Implications for herbicide formulations and atmospheric chemistry

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