Photolysis of the herbicide dicamba in aqueous solutions and on corn (Zea mays) epicuticular waxes

Tracing pesticide dynamics: High resolution offers new insights to karst groundwater quality

Generally, karst aquifers and springs are highly susceptible to contamination due to the high permeability and, therefore, groundwater flow velocities. The often thin soil cover, accompanied by dolines, can lead to fast infiltration of precipitation water loaded with mobilized contaminants such as pesticides and their transformation products. To date, continuous, temporally highly resolved in-situ monitoring to decipher concentration dynamics for a broad range of pesticides is missing. Therefore, a transportable HPLC-HRMS/MS system (MS2field) was positioned at two karst study sites in the Swiss Jura. Water samples were collected and analyzed for pesticides and their transformation products in-situ every 20 min for 6 weeks in 2021 and 8 weeks in 2022. During the spraying season in 2021, six rain events at site 1 and three at site 2 in 2022 were captured. Concurrently, the water quality parameters electrical conductivity, pH, nitrate, turbidity, and water level, were monitored continuously at high temporal resolution. Further, bacterial cell counts were monitored via online flow cytometry. In 2021, several pesticides and pesticide transformation products were detected in peak concentrations after rain events, of which metamitron showed the highest concentration of up to 1000 ng/L. In one rain event, the Swiss federal and EU drinking water limit of 100 ng/L was exceeded for up to 38 h. Compared with highly frequent MS2field samples collected every 20 min, 42-hours composite samples severely underestimated peak concentrations for all compounds, especially for labile ones. Therefore, it was demonstrated that exceedences of the regulatory limit would have been missed if just composite sampling would have been conducted. Peak concentrations of pesticides coincided with peaks in nitrate concentration and bacterial cell counts following rain events. The correlation analysis showed strong correlations between the three analyzed contaminants (pesticides, nitrate and bacteria), and the proxy parameters electrical conductivity, and pH. The investigation of a second spring revealed similar dynamics indicating that these can be expected in other karst aquifers as well.

A comparative study of programs to predict direct photolysis rates in wastewater systems

A wide range of contaminants of emerging concern (CECs) are known to photodegrade in the surface layers of natural waters and wastewater systems. Computer programs such as GCSolar, ABIWAS, APEX, EXAMS and WASP model the direct photolysis rates and half-lives of CECs, usually as a function of the solar irradiance, water molar light extinction, chemical molar light absorption and reaction quantum yield. These programs have been used extensively for studies in natural water systems in the northern hemisphere. However, their applicability to wastewater treatment systems such as waste stabilisation ponds and/or southern hemisphere conditions is not well studied. Here we present a comparative review of the major software used and their potential applicability to predicting direct photolysis rates and half-lives in wastewater. The newer equivalent monochromatic wavelength, approach, which enables the approximation of polychromatic photodegradation via a monochromatic wavelength is also discussed. Current software appears to be less suitable for modelling photodegradation in wastewater systems in the southern hemisphere than the northern hemisphere as their internal databases are based on data from natural waters in the northern hemisphere. This may be because there have been few attempts to model CEC photolysis in wastewater systems, particularly in the southern hemisphere. This indicates that either new software needs to be developed, or these programs need to be updated with data on wastewater matrices and/or the southern hemisphere. We anticipate this review will promote the adaptation of these programs as tools to further the understanding CEC photodegradation in wastewater treatment plants.

Synthesis and Surface Properties of Piperidinium-Based Herbicidal Ionic Liquids as a Potential Tool for Weed Control

A series of piperidinium-based herbicidal ionic liquids (HILs) were synthesized and investigated. The designed HILs, obtained with high yields, consisted of cation 1-alkyl-1-methylpiperidinium with surface activity and a commercially available herbicidal anion: (3,6-dichloro-2-methoxy)benzoates (dicamba). The above-mentioned compounds were characterized in terms of surface activity and phytotoxicity. Preliminary results were obtained at higher wettability for all HILs when compared to the wettability of commercial Dicash, with HIL having 18 atoms in the carbon chain being the best effectiveness in wetting surfaces (weeds and crop leaves), whereby a drop of HILs with short alkyl chains (C₈-C₁₀) could not slide down a leaf. Our findings present that wettability or mobility of HILs drops varied depending on the plant species. Moreover, in this study, by zeta potential and atomic force microscopy measurements, we provide conclusive evidence to demonstrate that alkyl chain elongation plays a significant role in the evolution of surface properties of HILs.

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.