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Herbicides are the agents of choice for use in weed control; however, they can enter the aquatic environment, with potentially serious consequences for non-target organisms. Despite the possible deleterious effects, little information is available regarding the ecotoxicity of the herbicide florasulam toward aquatic organisms. Accordingly, in this study, we investigated the toxic effect of florasulam on the freshwater microalga Chlorella vulgaris and sought to identify the underlying mechanisms. For this, we employed a growth inhibition toxicity test, and then assessed the changes in physiological and metabolomic parameters, including photosynthetic pigment content, antioxidant system, intracellular structure and complexity, and metabolite levels. The results showed that treatment with florasulam for 96 h at the concentration of 2 mg/L, 2.84 mg/L, and 6 mg/L in medium significantly inhibited algal growth and photosynthetic pigment content. Moreover, the levels of reactive oxygen species were also increased, resulting in oxidative damage and the upregulation of the activities of several antioxidant enzymes. Transmission electron microscopic and flow cytometric analysis further demonstrated that exposure to florasulam (6 mg/L) for 96 h disrupted the cell structure of C. vulgaris, characterized by the loss of cell membrane integrity and alterations in cell morphology. Changes in amino acid metabolism, carbohydrate metabolism, and the antioxidant system were also observed and contributed to the suppressive effect of florasulam on the growth of this microalga. Our findings regarding the potential risks of florasulam in aquatic ecosystems provide a reference for the safe application of this herbicide in the environment.

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Resistance to acetolactate synthase (ALS) inhibiting herbicides has recently been reported in Glebionis coronaria from wheat fields in northern Tunisia, where the weed is widespread. However, potential resistance mechanisms conferring resistance in these populations are unknown. The aim of this research was to study target-site resistance (TSR) and non-target-site resistance (NTSR) mechanisms present in two putative resistant (R) populations. Dose-response experiments, ALS enzyme activity assays, ALS gene sequencing, absorption and translocation experiments with radiolabeled herbicides, and metabolism experiments were carried out for this purpose. Whole plant trials confirmed high resistance levels to tribenuron and cross-resistance to florasulam and imazamox. ALS enzyme activity further confirmed cross-resistance to these three herbicides and also to bispyribac, but not to flucarbazone. Sequence analysis revealed the presence of amino acid substitutions in positions 197, 376, and 574 of the target enzyme. Among the NTSR mechanisms investigated, absorption or translocation did not contribute to resistance, while evidences of the presence of enhanced metabolism were provided. A pretreatment with the cytochrome P450 monooxygenase (P450) inhibitor malathion partially synergized with imazamox in post-emergence but not with tribenuron in dose-response experiments. Additionally, an imazamox hydroxyl metabolite was detected in both R populations in metabolism experiments, which disappeared with the pretreatment with malathion. This study confirms the evolution of cross-resistance to ALS inhibiting herbicides in G. coronaria from Tunisia through TSR and NTSR mechanisms. The presence of enhanced metabolism involving P450 is threatening the chemical management of this weed in Tunisian wheat fields, since it might confer cross-resistance to other sites of action.

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Flixweed (Descurainia sophia L.) is widely distributed in winter wheat (Triticum aestivum L.) fields in the North China Plain and has evolved resistance to herbicides, including the acetolactate synthase (ALS) inhibitor florasulam. However, the florasulam resistance status of flixweed in the North China Plain is poorly understood, which hinders the integrated management of this weed in winter wheat production systems. Thus, 45 flixweed populations were collected in wheat fields in these areas, and their sensitivity to florasulam and ALS-inhibitor-resistant mutation diversity were assessed. Meanwhile, alternative herbicides/herbicide mixtures for the control of florasulam-resistant flixweed were screened and evaluated under greenhouse and field conditions. Of the populations, 30 showed florasulam resistance (RRR and RR), 9 had a high risk of evolving florasulam resistance (R?) and 6 were susceptible. These populations had 5.3 to 345.1-fold resistance to florasulam, and 4 ALS resistance mutations (P197H, P197S, P197T and W574L) were observed. The subsequent herbicide sensitivity assay showed that the SD-06 population (with ALS1 P197T and ALS2 W574L mutations) exhibited cross-resistance to all ALS inhibitors tested, but was sensitive to MCPA-Na, fluroxypyr, carfentrazone-ethyl and bipyrazone. Meanwhile, the other HN-07 population with non-target-site resistance (NTSR) also showed resistance to all tested ALS inhibitors, and it was "R?" to MCPA-Na while sensitive to fluroxypyr, carfentrazone-ethyl and bipyrazone. The field experiments were conducted at the research farm where the SD-06 population was collected, and the results suggested that florasulam at 3.75-4.5 g ai ha-1 had little efficacy (0.6-12.1%), whereas MCPA-Na + carfentrazone-ethyl (87.1-91.2%) and bipyrazone+fluroxypyr (90.1-97.8%) controlled the resistant flixweed.

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A QuEChERS method with liquid chromatography-tandem mass spectrometry (LC-MS/MS) was modified and validated for the determination of florasulam and pyroxsulam residues in wheat grain and straw. The validated method was applied to cereals including oat, millet, corn and rice. Average recoveries were 76-113% with RSDs 2-15%. The limits of quantitation (LOQ) were 0.005 mg/kg for wheat grain and 0.01 mg/kg for wheat straw and four cereals. Ion suppression for florasulam (-28% to -76%) was observed in all the matrices except corn, whereas ion enhancement were shown for pyroxsulam (44% to 83%). Degradation rates of florasulam and pyroxsulam were 6% and 23%, respectively, in wheat grain and straw after eight-week storage at -20°C. The ultimate residues in field trials in ten regions were all ≤0.05 mg/kg, and long term dietary risk assessment indicated that hazard quotients were 0.02% and 0.001% for florasulam and pyroxsulam, respectively, which shows that it is safe to spray the two herbicides on wheat.

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Here, we aimed to investigate florasulam photodegradation in aquatic environments under UV-visible irradiation. LC-MS/MS was used to explore the photolysis kinetics of florasulam degradation with respect to different light source types, florasulam concentrations, water sources, and pH. We also tested whether the addition of the nitrate ions, Fe3+, or I- to the reaction solution influences florasulam photolysis kinetics. NO3- accelerates florasulam degradation at low concentrations (0.01-1 mg L-1), but decreases the process at higher concentrations. At low concentrations (≤ 0.1 mg L-1), Fe3+ enhanced florasulam photodegradation obviously. However, the addition of 0.01-10 mg L-1 I- decreased the degradation rate linearly. The florasulam photolysis rates in alkaline and neutral solutions were higher than that in acidic solutions. The florasulam degradation rate under mercury light irradiation was greater than that under xenon light. The rate of florasulam degradation in distilled water was greater than in tap water, lake water, and rice paddy water. As the concentration of florasulam increased, the photodegradation rate decreased. Six kinds of transformation products (TPs) were isolated and identified using UPLC/Q-TOF-MS. Based on these TPs and their evolutionary processes, we inferred the florasulam degradation mechanisms, identifying four possible florasulam degradation pathways. Cleavage of the florasulam sulfonamide bond yielded TPs2. TPs2 was intermolecularly rearranged to form a SO2 extrusion compound, TPs3. Cleavage of the [C-F] bonds led to the formation of TPsl, TPs4, and TPs5, while hydroxylation led to the formation of TPs6. We then predicted the stability of each of the florasulam TPs in water. TPs2 and TPs3 rapidly degraded after reaching maximum concentration due to poor light stability. TPs4 and TPs6 were more photostable than florasulam (the parent compound) and may be important contributors to water pollution.

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The dissipation kinetics and residual levels of florasulam and tribenuron-methyl in wheat field ecosystem were determined using a quick, easy, cheap, efficient, rugged and safe method (QuEChERS) with rapid resolution liquid chromatography tandem mass spectrometry (RRLC-MS/MS). The average recoveries of florasulam and tribenuron-methyl at three spiking levels in wheat plant, soil, wheat straw and wheat grain ranged from 72.8% to 99.2% with relative standard deviations (RSDs) were less than 10.1% and 82.5% to 103.8% with RSDs were less than 9.4%, respectively. The limits of quantification (LOQs) of florasulam and tribenuron-methyl for wheat plant, wheat straw, wheat grain and soil were 0.01, 0.01, 0.005, 0.005 mg kg(-1), respectively. The field trials results showed that the half-lives of florasulam were 2.76-10.83 d. Half-lives for tribenuron-methyl were found to be 1.27-5.37 d. The terminal residues in wheat grain were much lower than maximum residue limits (MRLs) set by China (0.01 mg kg(-1) for florasulam and 0.05 mg kg(-1) for tribenuron-methyl), which considered to be safe for human beings. These results will contribute to establishing the scientific basis of the dosage of florasulam and tribenuron-methyl for use in wheat field ecosystems.

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