Field degradation of aminopyralid and clopyralid and microbial community response to application in Alaskan soils

Biocompatible Nano-Cocrystal Engineering for Targeted Herbicide Delivery: Enhancing Efficacy through Stimuli-Responsive Release and Reduced Environmental Losses

In addressing the critical challenges posed by the misuse and inefficiency of traditional pesticides, we introduce a Nano-Cocrystal material composed of the herbicide clopyralid and coformer phenazine. Developed through synergistic supramolecular self-assembly and mechanochemical nanotechnology, this Nano-Cocrystal significantly enhances pesticide performance. It exhibits a marked improvement in stability, with reductions in hygroscopicity and volatility by approximately 38%. Moreover, it intelligently modulates release according to environmental factors, such as temperature, pH, and soil inorganic salts, demonstrating decreased solubility by up to four times and improved wettability and adhesion on leaf surfaces. Importantly, the herbicidal activity surpasses that of pure clopyralid, increasing suppression rates of Medicago sativa L. and Oxalis corniculata L. by up to 27% at the highest dosage. This Nano-Cocrystal also shows enhanced crop safety and reduced genotoxicity compared to conventional formulations. Offering a blend of simplicity, cost-effectiveness, and robust stability, our findings contribute a sustainable solution to agricultural practices, favoring the safety of nontarget organisms.

Ecotoxicological impact of butisanstar and clopyralid herbicides on soil microbial respiration and the enzymatic activities

The application of herbicides in soil has been noted for its detrimental effect on the soil microbial community, crucial for various biochemical processes. This study provides a comprehensive assessment of the impact of butisanstar and clopyralid herbicides, both individually and in combination at different dosage (recommended field dose (RFD), ½, 2 and 5-times RFD). The assessment focuses on soil basal respiration (SBR), cumulative microbial respiration (CMR), and the activities dehydrogenase (DH), catalase (CAT), urease, acid and alkaline phosphatases (Ac-P and Alk-P) enzymes, along with their variations on days 10, 30, 60, and 90 post-herbicide application. Results indicate that, although herbicides, even at lower doses of RFD, demonstrate inhibitory effects on DH, CAT, and microbial respiration, they paradoxically lead to a significant enhancement in urease and phosphatase activities, even at higher doses. The inhibitory/enhancing intensity varies based on herbicide type, incubation period, and dosage. Co-application of herbicides manifests synergistic effects compared to individual applications. The most notable inhibitory effects on DH, CAT, and SBR are observed on the 30th day, coinciding with the highest activities of urease and phosphatases on the same day. The persistent inability to restore respiration and enzyme activities to initial soil (control) levels emphasizes the lasting adverse and inhibitory effects of herbicides, especially clopyralid, over the long term. It becomes apparent that soil microorganisms require an extended duration to decompose and acclimate to the presence of herbicides. Consequently, these agrochemical compounds pose a potential risk to crucial biochemical processes, such as nutrient cycling, ultimately impacting crop production.

Reactive Oxygen Species and Chromophoric Dissolved Organic Matter Drive the Aquatic Photochemical Pathways and Photoproducts of 6PPD-quinone under Simulated High-Latitude Conditions

The photochemical degradation pathways of 6PPD-quinone (6PPDQ, 6PPD-Q), a toxic transformation product of the tire antiozonant 6PPD, were determined under simulated sunlight conditions typical of high-latitude surface waters. Direct photochemical degradation resulted in 6PPDQ half-lives ranging from 17.5 h at 20 °C to no observable degradation over 48 h at 4 °C. Sensitization of excited triplet-state pathways using Cs+ and Ar purging demonstrated that 6PPDQ does not decompose significantly from a triplet state relative to a singlet state. However, assessment of processes involving reactive oxygen species (ROS) quenchers and sensitizers indicated that singlet oxygen and hydroxyl radical do significantly contribute to the degradation of 6PPDQ. Investigation of these processes in natural lake waters indicated no difference in attenuation rates for direct photochemical processes at 20 °C. This suggests that direct photochemical degradation will dominate in warm waters, while indirect photochemical pathways will dominate in cold waters, involving ROS mediated by chromophoric dissolved organic matter (CDOM). Overall, the aquatic photodegradation rate of 6PPDQ will be strongly influenced by the compounding effects of environmental factors such as light screening and temperature on both direct and indirect photochemical processes. Transformation products were identified via UHPLC-Orbitrap mass spectrometry, revealing four major processes: (1) oxidation and cleavage of the quinone ring in the presence of ROS, (2) dealkylation, (3) rearrangement, and (4) deamination. These data indicate that 6PPDQ can photodegrade in cool, sunlit waters under the appropriate conditions: t1/2 = 17.4 h tono observable decrease (direct); t1/2 = 5.2-11.2 h (indirect, CDOM).

Photochemical Pathways of Rotenone and Deguelin Degradation: Implications for Rotenoid Attenuation and Persistence in High-Latitude Lakes

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.

Sulfate radical-based oxidation of the aminopyralid and picloram herbicides: The role of amino group on pyridine ring

The widespread utilization of pesticides has attracted increasing attention to their environmental impacts and effective removal strategies. In the present study, the degradation of herbicides picloram (PCLO) and aminopyralid (AMP) with similar structures were investigated systematically by thermo activated persulfate. Overweight SO₄^•- was determined to be the predominant oxidizing species by quenching experiment. Obtained by laser-flash photolysis (LFP), reaction rate constants of SO₄^•- towards AMP and PCLO were determined at 1.56 × 10⁹ M^-1s^-1 and 1.21 × 10⁹ M^-1s^-1, respectively. Product analysis revealed that both substances underwent similar oxidation paths, namely, successive oxidation on pyridine ring and formation of coupling-products as well as further hydroxylation and decarboxylation. Amino group on the pyridine ring was identified as the main reactive site, which was further confirmed by DFT calculation. It was susceptible attacked by SO₄^•- to form deamination, nitration, and self-coupling products. These couples could be further oxidatively dehydrated to form azo and a series of azo derivatives. EOCSAR program predicted significant hazards on aquatic species during the formation of these couplings and azo derivatives. Our work emphasized the potential ability and toxicity of contaminates to produce azo substances in the presence of amino groups on the pyridine ring.

Effects of sulfonylurea herbicides chlorsulfuron and sulfosulfuron on enzymatic activities and microbial communities in two agricultural soils

Sulfonylurea herbicides are widely used for weed control in agriculture, and they are suspected to alter microbial communities and activities in the soil. This study investigates the impact of two sulfonylurea herbicides chlorsulfuron and sulfosulfuron on microbial community and activity in two different soils taken from two sites in west part of the Slovak Republic. The soil from the Malanta site was silt-loam luvisol with pH_(H2O) 5.78 while the soil from the Stefanov site was sandy-loam regosol with pH_(H2O) 8.25. These soils were not treated by sulfonylurea herbicides at least for 2 years prior to the study. In laboratory assay, the herbicides were applied to soil in their maximal recommended doses 26 and 25 g per hectare of chlorsulfuron and sulfosulfuron, respectively. Their effect was evaluated on the 3rd, 7th, 14th, 28th, 56th, and 112th day after application to soil. Illumina high-throughput amplicon sequencing of the 16S rRNA gene and ITS region was used to monitor changes on prokaryotic and fungal community composition. Enzymatic activity was evaluated using 11 substrates. Physiological profile of microbial community was analyzed using Biolog© ecoplates. Significant changes in enzymatic activity caused by the application of herbicides were found during the first 28 days. The application of herbicides altered the activity of cellobiohydrolase, arylsulphatase, dehydrogenase, phosphatase, and FDA hydrolase. Chlorsulfuron caused a more varying response of enzymatic activity than sulfosulfuron, and observed changes were not the same for both soils. In Malanta soil, chlorsulfuron decreased dehydrogenase activity while it was increased in the Stefanov soil. Phosphatase activity was decreased in both soils on 7th and 14th day. There were only minor changes in prokaryotic or fungal community or physiological profiles regarding pesticide application. Differences between soils and incubation time explained most of the variability in these parameters. Diversity indices, physiological parameters, and enzymatic activity decreased over time. The results have shown that chlorsulfuron and sulfosulfuron can affect the function and activity of the soil microbial community without significant change in its composition.

Residue determination of triclopyr and aminopyralid in pastures and soil by gas chromatography-electron capture detector: Dissipation pattern under open field conditions

In this study, a new method for the simultaneous quantitative determination of triclopyr and aminopyralid in forage grass, hay, and soil was developed and validated using gas chromatography coupled with electron capture detector (GC-ECD). In this method, a simple and maneuverable esterification reaction was applied to convert the two acidic herbicides into their ester form with methanol. The target compounds were extracted with 1% hydrochloric acid-acetonitrile, esterified, purified by florisil solid-phase extraction cartridge, and detected in a single run by the GC-ECD. The average recoveries using this method, at different fortified levels, ranged from 80% to 104% with intra-day and inter-day RSDs in the range of 1.2-10.8% and 3.3-10.3% for both the herbicides, respectively. The LODs were below 0.02 mg/kg while the LOQs were below 0.05 mg/kg, both of which were much lower than the maximum residue limits (MRLs) of 25-700 mg/kg in pastures, as established by the USA (the code of federal regulations). The open field dissipation and residual analysis in pastures and soil were conducted with the commercial formulation at two locations. With time, both triclopyr and aminopyralid dissipated via first-order kinetics. In forage grass, both compounds degraded rapidly over the first 14- or 21-d period and at a slow rate over the remainder of experimental days. In soil, they degraded at a relatively slow rate, and dissipated steadily to below or close to the LOQ by 60-d post application. The half-lives of triclopyr were 1.4-1.8 d and 6.2-9.0 d and aminopyralid were 1.7-2.1 d and 8.2-10.6 d in terms of forage grass and soil, respectively. The terminal residue results indicated that on 7 d after the treatment, the residues of aminopyralid and triclopyr in forage grass and hay were lower than the MRLs set by the USA. This work can provide guidance on the reasonable use of these herbicides and also provide an analytical method for the determination of triclopyr and aminopyralid in pasture and soil.

Influence of oligomeric herbicidal ionic liquids with MCPA and Dicamba anions on the community structure of autochthonic bacteria present in agricultural soil

The aim of this study was to evaluate the impact of selected herbicidal ionic liquids (HILs), which exhibit high efficacy in terms of weed control and low toxicity, but may be persistent due to limited biodegradability, on the community structure of autochthonic bacteria present in agricultural soil. Four different oligomeric HILs (with two types of cations and different ratio of herbicidal anions) were synthesized and characterized by employing (1)H and (13)C NMR. The results of biodegradation assay indicated that none of the tested HILs could be classified as readily biodegradable (biodegradation rate ranged from 0 to 7%). The conducted field studies confirmed that the herbicidal efficacy of the HILs was higher compared to the reference herbicide mixture by 10 to 30%, depending on the dose and weed species. After termination of field studies, the soil treated with the tested HILs was subjected to next generation sequencing in order to investigate the potential changes in the bacterial community structure. Proteobacteria was the dominant phylum in all studied samples. Treatment with the studied HILs resulted in an increase of Actinobacteria compared to the reference herbicidal mixture. Differenced among the studied HILs were generally associated with a significantly higher abundance of Bacteroidetes in case of 1-HIL-Dicamba 1/3 and Firmicutes in case of 2-HIL-Dicamba 1/3.