Hydrogen Bonding Site Number Predicts Dicamba Volatilization from Amine Salts

Making Waves: Formulation components used in agriculture may serve as important precursors for nitrogenous disinfection byproducts

N-Nitrosamines, many of which are carcinogenic, mutagenic, and teratogenic, are disinfection byproducts (DBPs) formed from the reaction of chloramine with nitrogenous organic compounds during water disinfection. The identification of major nitrosamine precursors is important to understand and prevent nitrosamine formation. In this analysis, we propose that efforts to identify nitrosamine precursors must look beyond conventionally evaluated active agent chemicals to consider inert or inactive chemicals as potentially relevant precursors. Using agricultural chemicals applied in the US as an example, we demonstrate that amines widely used as inactive agents in herbicide formulations (i.e., dimethylamine [DMA], a known N-nitrosamine precursor) are potentially much more important than active agent herbicides previously evaluated as potential nitrosamine precursors (i.e., the herbicides diuron or trifluralin). Accounting for use rates and nitrosamine yields, amines used in herbicide formulations represent potential nitrosamine precursor inputs to the environment that are similar in magnitude to recognized precursors like the pharmaceuticals ranitidine and metformin. Because the amounts of amines used as inert agents in herbicide formulations have increased dramatically over recent decades, particularly in certain US regions, we suggest that identification of potential nitrosamine precursors should consider variation in the inputs of both active and inactive agents over time, as well as geographical variation in use that may alter the relative importance of specific precursors in certain locations.

Cocrystal engineering for sustained release of dicamba: Mitigating secondary drift and reducing leaching

The off-target effects of herbicides present significant challenges in agricultural practices, posing serious threats to both ecological systems and human health. Dicamba, one of the most widely used herbicides, is particularly problematic due to its high volatility and water solubility, which can lead to rapid environmental dispersal, non-target toxicity, and groundwater contamination. To mitigate these issues, we synthesized a novel cocrystal of dicamba and phenazine (DCB-PHE cocrystal) through a combination of theoretical prediction and mechanochemical screening. The DCB-PHE cocrystal was characterized using single-crystal and powder X-ray diffraction, Fourier-transform infrared spectroscopy (FT-IR), and thermal analysis. Compared to pure dicamba, the DCB-PHE cocrystal exhibited a substantial reduction in volatility by 59 % and a decrease in equilibrium solubility by up to 5.4 times across various temperatures (15 °C, 25 °C, 35 °C). Additionally, the dissolution rates were significantly lowered by over 94 %. Leaching experiments demonstrated that the DCB-PHE cocrystal reduced total leachate by 4.9 % and delayed percolation. In greenhouse trials, the DCB-PHE cocrystal caused less damage to exposed soy plants and enhanced herbicidal activity against target weeds, with fresh weight reduction of chicory and ryegrass by 32 % and 28 %, respectively, at the highest dosage. Furthermore, safety assays confirmed that the DCB-PHE cocrystal's safety profile was comparable to that of dicamba in terms of its impact on wheat, and it did not exhibit increased genotoxicity to broad beans. These findings suggest that the DCB-PHE cocrystal is a promising candidate for reducing the environmental impacts of dicamba while maintaining its herbicidal efficacy.

Elucidating Factors Contributing to Dicamba Volatilization by Characterizing Chemical Speciation in Dried Dicamba-Amine Residues

Dicamba is a semivolatile herbicide that has caused widespread unintentional damage to vegetation due to its volatilization from genetically engineered dicamba-tolerant crops. Strategies to reduce dicamba volatilization rely on the use of formulations containing amines, which deprotonate dicamba to generate a nonvolatile anion in aqueous solution. Dicamba volatilization in the field is also expected to occur after aqueous spray droplets dry to produce a residue; however, dicamba speciation in this phase is poorly understood. We applied Fourier transform infrared (FTIR) spectroscopy to evaluate dicamba protonation state in dried dicamba-amine residues. We first demonstrated that commercially relevant amines such as diglycolamine (DGA) and n,n-bis(3-aminopropyl)methylamine (BAPMA) fully deprotonated dicamba when applied at an equimolar molar ratio, while dimethylamine (DMA) allowed neutral dicamba to remain detectable, which corresponded to greater dicamba volatilization. Expanding the amines tested, we determined that dicamba speciation in the residues was unrelated to solution-phase amine pKa, but instead was affected by other amine characteristics (i.e., number of hydrogen bonding sites) that also correlated with greater dicamba volatilization. Finally, we characterized dicamba-amine residues containing an additional component (i.e., the herbicide S-metolachlor registered for use alongside dicamba) to investigate dicamba speciation in a more complex chemical environment encountered in field applications.

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.

Driving a sustainable application of s-triazine ametryn and atrazine herbicides through multicomponent crystals with improved solubility

Engineered multicomponent crystals of Atrazine and ametryn herbicides have shown enhanced solubility and can be an alternative for the production of safe and eco-friendly agrochemical products.