Undergraduate students in an environmental chemistry laboratory course were taught QuEChERS (quick, easy, cheap, effective, rugged, and safe), a sample preparation procedure that is commonly used in pesticide laboratories involving an acetonitrile salt-out extraction of fresh produce samples followed by solid-phase dispersive cleanup using a combination of sorbents. The cleaned extract was solvent exchanged into toluene and analyzed for pesticides by capillary gas chromatography–mass spectrometry in selective ion monitoring mode (GC–MS/SIM). Students utilized QuEChERS to analyze spiked and incurred pesticide residues in several types of plant foods and applied GC–MS/SIM for the simultaneous quantitation and identification of pesticides. Several chemistry, laboratory, and instrumental concepts were demonstrated such as sample preparation, aspects of method validation, and interpretation of chromatographic and mass spectrometric results. This experiment received favorable responses from the students because of the “real-world” applicability of the QuEChERS procedure, the use of GC–MS analysis, and concepts transferred from lecture to the laboratory.

Chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide, CAP; water solubility 1.023 mg·L) was recently registered for application on California rice fields. Air- and soil-water partitioning of CAP were investigated under simulated California rice field conditions through calculation of K and ΔH and a batch equilibrium method following OECD 106 guidelines, respectively. K and ΔH were determined to be 1.69 × 10 - 2.81 × 10 atm·m·mol (15-35 °C) and 103.68 kJ·mol, respectively. Log(K) ranged from 2.59 to 2.96 across all soil and temperature treatments. Log(K) ranged from 0.61 to 1.14 across all soil, temperature, and salinity treatments. Temperature and salinity increased sorption significantly at 35 °C (P < 0.05) and 0.2 M (P < 0.0001), respectively, while soil properties impacted sorption across all treatments. Overall results, corroborated using the Pesticides in Flooded Applications Model, indicate that volatilization of CAP is not a major route of dissipation and sorption of CAP to California rice field soils is moderately weak and reversible.

The direct and indirect photochemical degradation of rotenone (ROT) and deguelin (DEG), the primary reduced nicotinamide adenine dinucleotide-inhibiting rotenoid components of the piscicide CFT Legumine, were investigated under simulated sunlight conditions relevant to their dissipation from high-latitude surface waters. Photochemical degradation dominated the elimination of ROT and DEG from surface waters with half-lives ranging from 1.17 to 2.32 and 4.18 to 20.12 h for DEG and ROT, respectively, when the rotenoids were applied in the formulation CFT Legumine. We assessed enhanced degradation processes using argon-purged and cesium chloride-amended water, which demonstrated the rotenoids to rapidly decompose from excited triplet states. We further assessed the influence of reactive oxygen species by hydroxyl radical quenching and thermal generation of singlet oxygen. The studied reactive oxygen species did not significantly contribute; however, alcohols such as isopropanol may inhibit degradation by quenching ROT excited states or preventing intersystem crossing. Finally, we compared photochemical degradation in water collected from Hope Lake, Alaska, to a solution of Suwanee River fulvic acids, which demonstrated that dissolved organic matter (DOM) quality is a major factor that modulates ROT attenuation through a combination of shielding (light attenuation) and excited-state quenching mechanisms and is temperature-dependent. Molecular-level characterizations of DOM may help account for the site-specific degradation of these rotenoids in the environment.

Chlorantraniliprole (3-bromo-N-[4-chloro-2-methyl-6-(methylcarbamoyl)­phenyl]-1-(3-chloro-2-pyridine-2-yl)-1H-pyrazole-5-carboxamide; CAP) was granted supplemental registration for use in rice cultivation in California through December, 2018. Previous work investigated the partitioning of CAP in California rice field soils; however, its degradation in soils under conditions relevant to California rice culture has not been investigated. The degradation of CAP in soils from two California rice fields was examined under aerobic and anaerobic conditions with varying salinity via microcosm experiments. Results indicate that soil properties governing bioavailability may have a greater influence on degradation than flooding practices or field salinization over a typical growing season. Differences between native and autoclaved soils (t 1/2 = 59.0–100.2 and 78.5–171.7 days) suggest that biological processes were primarily responsible for CAP degradation; however, future work should be done to confirm specific biotic processes as well as to elucidate abiotic processes, such as degradation via manganese oxides and formation of nonextractable residues, which may contribute to its dissipation.