Amine Volatilization from Herbicide Salts: Implications for Herbicide Formulations and Atmospheric Chemistry.

Amines are frequently included in formulations of the herbicides glyphosate, 2,4-D, and dicamba to increase herbicide solubility and reduce herbicide volatilization by producing herbicide-amine salts. Amines, which typically have higher vapor pressures than the corresponding herbicides, could potentially volatilize from these salts and enter the atmosphere, where they may impact atmospheric chemistry, human health, and climate. Amine volatilization from herbicide-amine salts may additionally contribute to volatilization of dicamba and 2,4-D. In this study, we established that amines applied in herbicide-amine salt formulations undergo extensive volatilization. Both dimethylamine and isopropylamine volatilized when aqueous salt solutions were dried to a residue at ∼20 °C, while lower-vapor pressure amines like diglycolamine and n,n-bis-(3-aminopropyl)methylamine did not. However, all four amines volatilized from salt residues at 40-80 °C. Because amine loss typically exceeded herbicide loss, we proposed that neutral amines dominated volatilization and that higher temperatures altered their protonation state and vapor pressure. Due to an estimated 4.0 Gg N/yr applied as amines to major U.S. crops, amine emissions from herbicide-amine salts may be important on regional scales. Further characterization of worldwide herbicide-amine use would enable this contribution to be compared to the 285 Gg N/yr of methylamines emitted globally.

Herbicide Drift from Genetically Engineered Herbicide-Tolerant Crops.

In recent years, off-target herbicide drift has been increasingly reported to lead to damage to nontarget vegetation in the U.S. These reports have coincided with the widespread adoption of genetically modified crops with new herbicide-tolerance traits. Planting crops with these traits may indirectly lead to increased drift both by increasing the use of the corresponding herbicides and by facilitating their use as postemergence herbicides later in the season. While extensive efforts have aimed to reduce herbicide drift, critical uncertainties remain regarding the physiochemical phenomena that drive the entry of herbicides into the atmosphere as well as the atmospheric processes that may influence short- and long-range transport. Resolving these uncertainties will support the development of effective approaches to reduce herbicide drift.

Hydrogen Bonding Site Number Predicts Dicamba Volatilization from Amine Salts.

Amine-based formulations are widely used to decrease volatilization of carboxylic acid-containing herbicides including dicamba. Despite our reliance on these formulations, the underlying amine properties that determine their ability to control herbicide volatilization are poorly understood. In this study, we measured dicamba volatilization from solid (BAMPA) on glass as with dimethylamine (DMA), diglycolamine (DGA), and N,N-bis(3-aminopropyl)methylamine (BAPMA) as a function of temperature and amine-to-dicamba ratio, as well as in the presence of glyphosate. In all cases, we found that BAPMA had a greater ability to lessen dicamba volatilization than DMA or DGA. Even when only 1 BAPMA molecule was present for every 10 dicamba molecules, dicamba volatilization was still decreased by 70% relative to the free acid case. The particular ability for BAPMA to control dicamba volatilization could be attributed to several molecular features (i.e., molecular weight, type and number of amine functional groups). Using a set including 5 additional amines, we determined that dicamba volatilization is primarily influenced by the number of functional groups in the amine that can participate in hydrogen bonding. From these results, we propose that ability of an amine to form multiple intermolecular interactions (i.e., hydrogen bonds) in the residue may best predict their potential to prevent herbicide volatilization.

Deconvolution of octahedral Pt3Ni nanoparticle growth pathway from in situ characterizations.

Understanding the growth pathway of faceted alloy nanoparticles at the atomic level is crucial to morphology control and property tuning. Yet, it remains a challenge due to complexity of the growth process and technical limits of modern characterization tools. We report a combinational use of multiple cutting-edge in situ techniques to study the growth process of octahedral Pt3Ni nanoparticles, which reveal the particle growth and facet formation mechanisms. Our studies confirm the formation of octahedral Pt3Ni initiates from Pt nuclei generation, which is followed by continuous Pt reduction that simultaneously catalyzes Ni reduction, resulting in mixed alloy formation with moderate elemental segregation. Carbon monoxide molecules serve as a facet formation modulator and induce Ni segregation to the surface, which inhibits the (111) facet growth and causes the particle shape to evolve from a spherical cluster to an octahedron as the (001) facet continues to grow.