Persistence, mobility, and adsorption of the herbicide flufenacet in the soil of winter wheat crops

Synthesis, crystal structure and Hirshfeld surface analysis of N-(4-fluoro-phen-yl)-N-isopropyl-2-(methyl-sulfon-yl)acetamide

The synthesis and crystal structure of the title compound, C₁₂H₁₆FNO₃S, which is related to the herbicide flufenacet, are presented. The dihedral angle between the amide group and the fluorinated benzene ring is 87.30 (5)° and the N-C-C-S torsion angle defining the orientation of the methyl-sulfonyl substituent relative to the amide group is 106.91 (11)°. In the crystal, inversion-related mol-ecules form dimers as a result of pairwise C-H⋯O hydrogen bonds, which appear to be reinforced by short O⋯π contacts [O⋯Cg = 3.0643 (11) Å]. A Hirshfeld surface analysis was used to qu-antify the various types of inter-molecular contacts, which are dominated by H atoms.

Field insights into leaching and transformation of pesticides and fluorescent tracers in agricultural soil

The frequent detection of residues from pesticides in various natural water types has raised public awareness. This study investigated the pesticide transformation in soil and their loss to shallow groundwater in a small agricultural catchment in Northern Germany. The pesticide Flufenacet and its transformation product Flufenacet ESA were examined in Luvisol and Colluvic Gleyosol under field conditions during two consecutive years. In the second year, a fluorescent tracer experiment applying Uranine and Sulforhodamine - B was carried out to gain additional insights into leaching and formation of transformation products in soil during and after a drought. We found preferential flow in response to low precipitation as an important transport pathway for Flufenacet in dry soil, as a Flufenacet concentration (1.57 μg L^-1) was detected in shallow groundwater within 10 days after application. Leaching of Flufenacet to shallow groundwater by preferential flow posed greater risks during the dry than during the wet period. In contrast, Flufenacet ESA was detected in all groundwater samples. During the dry period, we detected no formation of TP510 (tracer transformation product) in the immediate topsoil. A fraction of both tracers remained there, suggesting also long-term residues of pesticides in the topsoil caused by limited living conditions for microorganisms under dry conditions. Newly formed transformation products of Uranine and Flufenacet were mainly trapped in upper soil if capillary flow was marginal. Formation of TP510 could be related to a soil water optimum and a soil temperature threshold. The occurrence of increased TP510 amounts in soil after drought was concurrent with the main peak of Flufenacet ESA in shallow groundwater. This suggested similar retention and transformation processes of fluorescent tracers and organic pesticides inside the soil. This study contributed to an extended understanding of the leaching and transformation of organic pollutants in agricultural soil under real field conditions.

Field measurement and modelling of chlorotoluron and flufenacet persistence in unamended and amended soils

The dissipation and persistence of two cereals herbicides, chlorotoluron and flufenacet, were studied in a field experiment including three replicated plots of unamended soil (S), soil amended with spent mushroom substrate (S + SMS), and soil amended with green compost (S + GC), during the winter wheat cultivation campaign. The SMS and GC organic residues were applied to the soil at rates of 140 or 85 t residue ha^-1, and herbicides were sprayed as Erturon® and Herold® formulations for chlorotoluron and flufenacet, respectively. Concentrations of both herbicides and of their metabolites were regularly measured in the three soil treatments (0-10 cm) from 0 to 339 days. The dissipation kinetics fitted well the single first order (SFO) model, except that of chlorotoluron that fitted the first order multi-compartment (FOMC) model better in the unamended soil. The dissipation rates of herbicides were lower in amended than in unamended soils. The results also showed that the DT₅₀ of chlorotoluron (66.2-88.0 days) and flufenacet (117-145 days) under field conditions were higher than those previously obtained at laboratory scale highlighting the importance of the changing environmental conditions on the dissipation process. Similarly, the formation of chlorotoluron and flufenacet metabolites under field conditions was different from that previously observed in the laboratory. The performance of the MACRO pesticide fate model, parameterized with laboratory data, was then tested against field data. There was a very good agreement between measured and simulated chlorotoluron residue levels in the three soil treatments, while the ability of the model to reproduce the dissipation of flufenacet was good in the unamended soil and very good in S + SMS and S + GC soils. MACRO might be used to estimate the remaining amounts of herbicides in amended soils from degradation data previously obtained at laboratory scale. This would help to manage herbicide doses in different environmental conditions to preserve the sustainability of agricultural systems.

Leaching of S-metolachlor, terbuthylazine, desethyl-terbuthylazine, mesotrione, flufenacet, isoxaflutole, and diketonitrile in field lysimeters as affected by the time elapsed between spraying and first leaching event

The effect of elapsed time between spraying and first leaching event on the leaching behavior of five herbicides (terbuthylazine, S-metolachlor, mesotrione, flufenacet, and isoxaflutole) and two metabolites (desethyl-terbuthylazine and diketonitrile) was evaluated in a 2011-2012 study in northwest Italy. A battery of 12 lysimeters (8.4 m(2) long with a depth of 1.8 m) were used in the study, each filled with silty-loam soil and treated during pre-emergence with the selected herbicides by applying a mixture of commercial products Lumax (4 L ha(-1)) and Merlin Gold (1 L ha(-1)). During treatment periods, no gravity water was present in lysimeters. Irrigation events capable of producing leaching (40 mm) were conducted on independent groups of three lysimeters on 1 day after treatment (1 DAT), 7 DAT, 14 DAT, and 28 DAT. The series was then repeated 14 days later. Leachate samples were collected a few days after irrigation; compounds were extracted by solid phase extraction and analyzed by high-performance liquid chromatography and gas chromatography-mass spectrometry. Under study conditions, terbuthylazine and S-metolachlor showed the highest leaching potentials. Specifically, S-metolachlor concentrations were always found above 0.25 µg L(-1). Desethyl-terbuthylazine was often detected in leached waters, in most cases at concentrations above 0.1 µg L(-1). Flufenacet leached only when irrigation occurred close to the time of herbicide spraying. Isoxaflutole and mesotrione were not measured (<0.1 µg L(-1)), while diketonitrile was detected in concentrations above 0.1 µg L(-1) on 1 DAT in 2011 only.

Effect of buffer strips and soil texture on runoff losses of flufenacet and isoxaflutole from maize fields

The influence of buffer strips and soil texture on runoff of flufenacet and isoxaflutole was studied for two years in Northern Italy. The efficacy of buffer strips was evaluated on six plots characterized by different soil textures; two plots had Riva soil (18.6% sand, 63.1% silt, 18.3% clay) while the remaining four plots had Tetto Frati (TF) soil (37.1% sand, 57% silt, 5.9% clay). Additionally, the width of the buffer strips, constituted of spontaneous vegetation grown after crop sowing, was also compared for their ability to abate runoff waters. Chemical residues in water following runoff events were investigated, as well as their dissipation in the soil. After the first runoff events, concentrations of herbicides in water samples collected from Riva plots were as much as four times lower in waters from TF plots. On average of two growing seasons, the field half-life of flufenacet in the upper soil layer (5 cm) ranged between 8.1 and 12.8 days in Riva soil, 8.5 and 9.3 days in TF soil. Isoxaflutole field half-life was less than 1 day. The buffer strip was very affective by the uniformity of the vegetative cover, particularly, at the beginning of the season. In TF plots, concentration differences were generally due to the presence or absence of the buffer strip, regardless of its width.