Microbial degradation of clothianidin was characterized under aerobic and anaerobic California rice field conditions. Rate constants (k) and half-lives (DT50) were determined for aerobic and anaerobic microcosms, and an enrichment experiment was performed at various nutrient conditions and pesticide concentrations. Temperature effects on anaerobic degradation rates were determined at 22 ± 2 and 35 ± 2 °C. Microbial growth was assessed in the presence of various pesticide concentrations, and distinct colonies were isolated and identified. Slow aerobic degradation was observed, but anaerobic degradation occurred rapidly at both 25 and 35 °C. Transformation rates and DT50 values in flooded soil at 35 ± 2 °C (k = -7.16 × 10(-2) ± 3.08 × 10(-3) day(-1), DT50 = 9.7 days) were significantly faster than in 25 ± 2 °C microcosms (k= -2.45 × 10(-2) ± 1.59 × 10(-3) day(-1), DT50 = 28.3 days). At the field scale, biodegradation of clothianidin will vary with extent of oxygenation.

Clomazone (trade names Cerano and Command) is a popular herbicide used on California rice fields to control aquatic weeds. Its physicochemical characteristics indicate that it will persist primarily in the water column, where microbial degradation may drive its environmental fate. The objectives were to determine microbial degradation rates and compare the metabolic products under aerobic and anaerobic conditions similar to those in California rice fields during the summer. Time-series samples were extracted and analyzed by LC/MS/MS. Metabolic profiling revealed the following clomazone-derived transitions: m/z 240 --> 125 (clomazone), m/z 242 --> 125 (ring-open clomazone), m/z 256 --> 125 (5-hydroxyclomazone), m/z 256 --> 141 (aromatic hydroxyclomazone), m/z 268 --> 125 (unknown metabolite), and m/z 272 --> 141 (4'5-dihydroxyclomazone). Results indicate an anaerobic half-life of 7.9 days, with ring-open clomazone reaching 67.4% of application at 38 days. Aerobically, clomazone degraded more slowly (t(1/2) = 47.3 days), forming mostly soil-bound residues. Thus, under summer conditions, clomazone is likely to dissipate rapidly from fields via anaerobic degradation.

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.

High-latitude regions experience unique conditions that affect the degradation rate of agrochemicals in the environment. In the present study, data collected from 2 field sites in Alaska, USA (Palmer and Delta) were used to generate a kinetic model for aminopyralid and clopyralid degradation and to describe the microbial community response to herbicide exposure. Field plots were sprayed with herbicides and sampled over the summer of 2013. Quantification was performed via liquid chromatrography/tandem mass spectrometry, and microbial diversity was assessed via next-generation sequencing of bacterial 16S ribosomal ribonucleic acid (rRNA) genes. Both compounds degraded rapidly via pseudo-first-order degradation kinetics between 0 d and 28 d (t1/2  = 9.1-23.0 d), and then degradation slowed thereafter through 90 d. Aminopyralid concentration was 0.048 μg/g to 0.120 μg/g at 90 d post application, whereas clopyralid degraded rapidly at the Palmer site but was recovered in Delta soil at a concentraction of 0.046 μg/g. Microbial community diversity was moderately impacted by herbicide treatment, with the effect more pronounced at Delta. These data predict reductions in crop yield when sensitive plants (potatoes, tomatoes, marigolds, etc.) are rotated onto treated fields. Agricultural operations in high-latitude regions, both commercial and residential, rely heavily on cultivation of such crops and care must be taken when rotating.