Ultimate fate of herbicide tembotrione and its metabolite TCMBA in soil

Persistence and degradation of tembotrione in loamy soil: Effect of various organic amendments, moisture regimes and temperatures

In the present study, persistence and degradation of tembotrione, a triketone herbicide, was studied in loamy soil collected from maize field. Effects of organic amendments, moistures and temperatures on tembotrione dissipation were evaluated. Soil samples were processed according to the modified QuEChERS involving dichloromethane solvent and MgSO4 without PSA. Analysis using LC-MS/MS showed >95% recoveries of tembotrione its two metabolites TCMBA and M5 from fortified soils. Tembotrione residues dissipated with time and 85.55 to 98.53% dissipation was found on 90th day under different treatments. Tembotrione dissipation increased with temperature and moisture content of the soil. Among organic amendments, highest dissipation was observed in vermicompost amended soil. Minimum and maximum half-lives of tembotrione were recorded under 35 °C (15.7 days) and air-dry (33 days) conditions, respectively. Residues of tembotrione declined with time while that of TCMBA increased steadily up to 10-45th day in different treatments and declined thereafter. Residues of M5 were not detected in our experiments. Tembotrione persistence was negatively correlated with the organic carbon (%), moisture regimes, and temperature. A good correlation between soil microbial biomass carbon and degradation was found. A two-way ANOVA indicated significant differences between the treatments at 95% confidence level (p < 0.05).

Sorption and mobility assessment of tembotrione in soils of upper, trans and middle Gangetic plain zones of India

The presence of undesired agrochemicals residues in soil and water poses risks to both human health and the environment. The behavior of pesticides in soil depends both on the physico-chemical properties of pesticides and soil type. This study examined the adsorption-desorption and leaching behavior of the maize herbicide tembotrione in soils of the upper (UGPZ), trans (TGPZ) and middle Gangetic plain zones of India. Soil samples were extracted using acetone followed by partitioning with dichloromethane, whereas liquid-liquid extraction using dichloromethane was used for aqueous samples. Residues of tembotrione and its metabolite TCMBA, {2-chloro-4-(methylsulfonyl)-3-[(2,2,2-trifluoroethoxy) methyl] benzoic acid}, were quantified using liquid chromatography-tandem mass spectrometry. The data revealed that tembotrione adsorption decreased with increasing pH and dissolved organic matter but increased with salinity. The maximum adsorption occurred at pH 4, 0.01 m sodium citrate and 4 g/L NaCl, with corresponding Freundlich constants of 1.83, 2.28 and 3.32, respectively. The hysteresis index <1 indicated faster adsorption than desorption. Leaching studies under different flow conditions revealed least mobility in UGPZ soil and high mobility in TGPZ soil, consistent with groundwater ubiquity scores of 4.27 and 4.81, respectively. Soil amendments decreased tembotrione mobility in the order: unamended > wheat straw ash > wheat straw > farm yard manure > compost. The transformation of tembotrione to TCMBA and its mobility in soil columns were also assessed.

A novel Zn2+-coordination fluorescence probe for sensing HPPD inhibitors and its application in environmental media and biological imaging

Mesotrione, topramezone, tembotrione, and sulcotrione are four types of 4-hydroxyphenylpyruvate dioxidase (HPPD) inhibitor herbicides that are extensively employed in agricultural practices, but their usage also leads to environmental pollution and poses risks to human health. A probe (E)-1-((2-(pyridin-2-yl) hydrazineylidene) methyl) naphthalen-2-ol (CHMN) based on chelation enhancement (CHEF) effect synthesized. CHMN was first chelated with Zn2+ to form a probe system with green, which can be further used to detect mesotrione, topramezone, tembotrione and sulcotrione in complicated environment. CHMN-Zn2+ detection of four pesticides was accurate, with an excellent linear relationship between 0 and 100 μM. The detection limits were LODmesotrione = 7.79 μM, LODtopramezone = 1.91 μM, LODtembotrione = 1.38 μM and LODsulcotrione = 2.43 μM. The detection time is 1 min, and it is successfully applied in real water sample and bioimaging. This work can provide a novel method for studying the migration and behavior of environmental pollutants.

Assessing the effect of organic amendments on the degradation of profoxydim in paddy soils: Kinetic modeling and identification of degradation products

The fate and behavior of herbicides can be altered in an unpredictable way when organic amendments are added to soil as a beneficial management tool. The objective of this work was to investigate the effect exerted by the addition of two different organic amendments (alperujo compost and biochar) to soil in the degradation of one of the most relevant new generation rice herbicides, profoxydim. In unamended soils, the degradation of profoxydim was quite fast and was governed by both chemical (DT50steril soil = from 1.52 to 9.21 days) and microbial (DT50nonsterile soil = from 0.47 to 0.53 days) processes. Alperujo- and biochar-amended soils significantly increased the persistence of the herbicide in both soils, especially in the presence of biochar, due to the high capacity absorption of this amendment, increasing DT90 from 1.92 to 3.54 days for DT90unamended to 41.02-48.41 days for DT90biochar amended. Different kinetics models applied to fit the observed dissipation datasets showed that a HS biphasic model fits well with the dissipation of profoxydim in amended and unamended soils. For the first time, five degradation products (DPs) were identified by HPLC-QTOF-MS/MS in soil and a degradation pathway was described. Main DP was generated via oxidation of the sulfur atom to give rise to the corresponding sulfoxide derivative, with this DP being more persistent than the active substance. These outcomes can be very useful for the assessment of the environmental risk associated with the use of profoxydim in rice crops and the application of organic amendments as potential measures for minimizing the risk of contamination of natural water resources.

Sustainable intensification of climate-resilient maize-chickpea system in semi-arid tropics through assessing factor productivity

Global trends show that the rapid increase in maize production is associated more with the expansion of maize growing areas than with rapid increases in yield. This is possible through achieving possible higher productivity through maize production practices intensification to meet the sustainable production. Therefore, a field experiment on "Ecological intensification of climate-resilient maize-chickpea cropping system" was conducted during consecutive three years from 2017-2018 to 2019-2020 at Main Agricultural Research Station, Dharwad, Karnataka, India. Results of three years pooled data revealed that ecological intensification (EI) treatment which comprises of all best management practices resulted in higher grain yield (7560 kg/ha) and stover yield compared to farmers' practice (FP) and all other treatments which were deficit in one or other crop management practices. Similarly, in the succeeding winter season, significantly higher chickpea yield (797 kg/ha) was recorded in EI. Further EI practice recorded significant amount of soil organic carbon, available nitrogen, phosphorus, potassium, zinc, and iron after completion of third cycle of experimentation (0.60%, 235.3 kg/ha,21.0 kg/ha,363.2 kg/ha,0.52 ppm and 5.2 ppm respectively). Soil enzymatic activity was also improved in EI practice over the years and improvement in each year was significant. Lower input energy use was in FP (17,855.2 MJ/ha). Whereas total output energy produced was the highest in EI practice (220,590 MJ ha-1) and lower output energy was recorded in EI-integrated nutrient management (INM) (149,255 MJ/ha). Lower energy productivity was noticed in EI-INM. Lower specific energy was recorded in FP and was followed by EI practice. Whereas higher specific energy was noticed is EI-INM. Each individual year and pooled data showed that EI practice recorded higher net return and benefit-cost ratio. The lower net returns were obtained in EI-integrated weed management (Rs. 51354.7/ha), EI-recommended irrigation management (Rs. 56,015.3/ha), integrated pest management (Rs. 59,569.7/ha) and farmers' practice (Rs. 67,357.7/ha) which were on par with others.

Regulating pathway for bacterial diversities toward improved ecological benefits of thiencarbazone-methyl·isoxaflutole application: A field experiment

Herbicide abuse has a significantly negative impact on soil microflora and further influences the ecological benefit. The regulating measures and corresponding mechanisms mitigating the decreased bacterial diversity due to herbicide use have rarely been studied. A field experiment containing the application gradient of an efficient maize herbicide thiencarbazone-methyl·isoxaflutole was performed. The relationship between soil bacterial community and thiencarbazone-methyl·isoxaflutole use was revealed. Modified attapulgite was added to explore its impacts on soil microflora under the thiencarbazone-methyl·isoxaflutole application. Based on the analytic network process-entropy weighting method-TOPSIS method model, the ecological benefit focusing on microbial responses was quantitatively estimated along with technical effectiveness and economic benefit. The results showed that the diversity indices of soil microflora, especially the Inv_Simpson index, were reduced at the recommended, 5 and 10 times the recommended dosages of thiencarbazone-methyl·isoxaflutole use. The Flavisolibacter bacteria was negatively correlated with the residues in soils based on the random forest model and correlation analysis, indicating a potential degrader of thiencarbazone-methyl·isoxaflutole residues. The structural equation model further confirmed that the high soil water content and soil pH promoted the function of Flavisolibacter bacteria, facilitated the dissipation of thiencarbazone-methyl·isoxaflutole residues and further improved the diversity of soil microflora. In addition, the presence of modified attapulgite was found to increase the soil pH, which may improve bacterial diversity through the regulating pathway. This explained the high ecological benefits of the treatment where the thiencarbazone-methyl·isoxaflutole was applied at the recommended dosage rates in conjunction with modified attapulgite addition. Therefore, the comprehensive benefits of thiencarbazone-methyl·isoxaflutole application with a focus on ecological benefits can be improved by regulating the soil pH with modified attapulgite.

Design, Synthesis, and Bioactivity of Novel Ester-Substituted Cyclohexenone Derivatives as Safeners

Tembotrione, a 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitor, has been widely used in many types of plants. Tembotrione has been reported for its likelihood of causing injury and plant death to certain corn hybrids. Safeners are co-applied with herbicides to protect certain crops without compromising weed control efficacy. Alternatively, herbicide safeners may effectively improve herbicide selectivity. To address tembotrione-induced Zea mays injury, a series of novel ester-substituted cyclohexenone derivatives were designed using the fragment splicing method. In total, 35 title compounds were synthesized via acylation reactions. All the compounds were characterized using infrared spectroscopy, ¹H and ¹³C nuclear magnetic resonance spectroscopy, and high-resolution mass spectrometry. The configuration of compound II-15 was confirmed using single-crystal X-ray diffraction. The bioactivity assay proved that tembotrione phytotoxicity to maize could be reduced by most title compounds. In particular, compound II-14 exhibited the highest activity against tembotrione. The molecular structure comparisons as well as absorption, distribution, metabolism, excretion, and toxicity predictions demonstrated that compound II-14 exhibited pharmacokinetic properties similar to those of the commercial safener isoxadifen-ethyl. The molecular docking model indicated that compound II-14 could prevent tembotrione from reaching or acting with Z. mays HPPD (PDB: 1SP8). Molecular dynamics simulations showed that compound II-14 maintained satisfactory stability with Z. mays HPPD. This research revealed that ester-substituted cyclohexenone derivatives can be developed as potential candidates for discovering novel herbicide safeners in the future.

Ultimate fate and possible ecological risks associated with atrazine and its principal metabolites (DIA and DEA) in soil and water environment

Atrazine (AT) is a triazine herbicide widely used to control weeds in several crops. De-isopropylatrazine (DIA) and de-ethylatrazine (DEA) are two of the eight primary metabolites produced by AT breakdown in soil and water. The physico-chemical properties of the soil determine their final fate. So, this study aimed to assess the function of clay loam and sandy loam soils in determining their ultimate fate and the potential ecological risks to non-target species during their persistence in soil and transportation to water bodies. The soil in pots was spiked with standard solutions of AT, DEA, and DIA at 0.3 and 0.6 mg/kg for the persistence study. The leaching potential was determined by placing soils in Plexi columns and spiking them with 50 and 100 µg standard solutions. Liquid-liquid extraction was used to prepare the samples, which were then analyzed using GC-MS/MS. The dynamics of dissipation were first-order. AT, DEA and DIA disappeared rapidly in sandy loam soil, with half-lives ranging from 6.2 to 8.4 days. AT and its metabolites had a significant amount of leaching potential. In sandy loam soil, leaching was more effective, resulting in maximal residue movement up to 30-40 cm soil depth. The presence of a notable collection of residues in leachate fractions suggests the potential for surface and groundwater contamination. In particular, DEA and DIA metabolites caused springtail Folsomia candida and earthworm Eisenia fetida to have longer and greater unacceptable risks. If the residues comparable to the amount acquired in leachate fractions reach water bodies, they could cause toxicity to a variety of freshwater fish, aquatic arthropods, amphibians, and aquatic invertebrates. Future studies should take a more comprehensive approach to evaluate ecological health and dangers to non-target species.

Persistence, leaching and associated toxicity risks of insecticide pyriproxyfen in soil ecosystem

Pyriproxyfen is a pyridine-based insecticide used for pest control in fruits and vegetables. It is a potent endocrine disruptor and hormone imitator. Considering its potential hazards to non-target organisms and the associated environment, a lab study was conducted for assessing persistence, mobility in sandy loam soil and associated risk to various non-target organisms and soil enzymes. Pyriproxyfen formulation was applied at 0.05 and 0.10 µg g^-1 soil which was equivalent to recommended and double dose of 100 and 200 g a.i. ha^-1, respectively. Three methods namely QuEChERS, liquid-solid extraction (LSE) and matrix solid phase dispersion (MSPD) were compared for achieving efficient sample preparation. MSPD was applied for final analysis as it gave better recoveries (94.2 to 104.3%) over other methods with limits of detection and quantification (LOD and LOQ) as 0.0001 and 0.0005 µg g^-1, respectively. Dissipation followed first order kinetics with half-lives of 7.6 and 8.2 days in both doses but residues retained over 45 days in soil. Leaching studies conducted at 50 and 100 µg of pyriproxyfen showed extremely poor leaching potential. Retention of over 90% residues in top 5 cm soil surface indicated minimal threat of ground and surface water contamination. Toxicological study demonstrated very different behaviour toward different enzymatic activities. Pyriproxyfen was relatively toxic for alkaline phosphatase and fluorescein diacetate hydrolase enzymes. β-glucosidase activity was triggered whereas arylsulfatase activity remained unaffected. Unacceptable risk to soil invertebrates at double dose application clearly indicated that its longer persistence in soil could be toxic to other non-target organisms and needs further investigations.

Dissipation, adsorption-desorption, and potential transformation products of pinoxaden in soil

This study established and validated a simple and sensitive analytical approach for determining pinoxaden residues in soil. The dissipation and adsorption-desorption of pinoxaden in four kinds of Chinese soil were comprehensively investigated for the first time, and the possible metabolic products and pathways were identified. The developed method was successfully applied in dissipation and adsorption-desorption trials. Several influential factors, including temperature, organic matter, and moisture content, affected the dissipation rate of pinoxaden in soil. During the dissipation process, 1 hydrolytic intermediate and 13 possible transformation products were identified, and predicted metabolic pathways were composed of electron rearrangement, oxidation, cyclization, carboxylation, and so on. Both the adsorption and desorption isotherms of pinoxaden in four kinds of Chinese soil followed the Freundlich equation, and the Freundlich K_f values were positively correlated with the soil cation exchange capacity. According to the calculated Gibbs free energies, the adsorption of pinoxaden was an endothermic reaction and mainly a physical process. These results could provide some useful data for the determination of pinoxaden in other matrices and the evaluation of the environmental fate of pinoxaden in soil and other ecosystems.