Use of a clay-based nanoformulation of R-imazaquin in an agricultural soil to reduce the pollution potential and improve the efficacy of this herbicide

Imazaquin is a chiral compound that can exist as two enantiomers: R-imazaquin and S-imazaquin. It is known that me herbicidal activity of imazaquin is due to the R-enantiomer mainly. This herbicide is characterized by a high mobility In alkaline soils, which may cause groundwater and surface water pollution. So, in order to avoid the addition of the less active S-enantiomer and reduce the great mobility of imazaquin, a clay-base-d nanoformulation of imazaquin containing exclusively the biologically active enantiomer was prepared. After evaluating several clay materials, cetyltrimethylammonium-saturated montmorillonite was selected as a carrier of the herbicide. due to its high loading capacity and great stability of the resulting nanoformulation. Next, the benefits of applying this nanoformulation compared to the use of the free (water dissolved) racemic herbicide or the free pure R-imazaquin enantiomer were assessed based on the leaching behavior and bioefficacy of the herbicide under a simulated intensive rain even to The results showed that the leaching of imazaquin was slower when the herbicide was added as nanoformulation in comparison with the free herbicide in the form of racemic mixture or pure R enantiomer. This was attributed to the sustained release of imazaquin from the nanoformulation, which reduced the amount of herbicide available for leaching. In a simulated scenario of a high water input shortly after herbicide application, the bioassay experiments showed that reduction of imazaquin losses as a consequence of the use of the nanoformulation led to a higher herbicidal efficacy than those for free racemic mixture and free R-imazaquinPeer Reviewe

A clay-based formulation of the herbicide imazaquin containing exclusively the biologically active enantiomer

8 páginas.-- 5 figuras.-- 2 tablas.-- 42 referencias.-- Supporting information may be found in the online version of this article in http://dx.doi.org/10.1002/ps.5296BACKGROUND: Imazaquin is a chiral herbicide which displays high mobility in soils. Like other imidazolinones, imazaquin is available for use only as racemic mixture of its enantiomers. In this work, several clay materials were assayed as adsorbents of imazaquin, and then the most suitable material was selected to prepare a clay-based slow release imazaquin nanoformulation containing exclusively the biologically active R-enantiomer. Next, laboratory experiments were conducted to illustrate the benefits of using the clay-based R-imazaquin formulation over the free (non-supported) racemic herbicide or the free pure R-imazaquin enantiomer regarding its leaching behavior and bioefficacy. RESULTS: The clay material selected as a carrier for R-imazaquin, hexadecyltrimethylammonium-saturated montmorillonite (SA-HDTMA), combined a high affinity for the herbicide and a high stability of the clay-herbicide adsorption complex. In a simulated scenario of high water input shortly after herbicide application, the clay-based R-imazaquin formulation displayed reduced leaching and increased bioefficacy compared to free racemic imazaquin and free R-imazaquin. CONCLUSION: The new clay-R-imazaquin formulation prepared, besides avoiding the environmental impact caused by the application of the less active S-enantiomer, reduced the herbicide leaching losses and prolonged the herbicidal activity, by increasing the residence time of the herbicide in the topsoil.This work was financed by the Spanish Ministry of Economy and Competitiveness (MINECO grants AGL2014-51897-R and AGL2017-82141-R), co-financed with FEDER-FSE funds. R.López-Cabeza also thanks MINECO for a pre-doctoral fellowship(grant BES-2012-059945) and B. Gámiz and I. Buerge for valuablesuggestions.Peer reviewe

Stereoselective Metabolism of the Sterol Biosynthesis Inhibitor Fungicides Fenpropidin, Fenpropimorph, and Spiroxamine in Grapes, Sugar Beets, and Wheat

9 páginas.-- 5 figuras.-- 3 tablas.-- 22 referencias.-- The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.jafc.6b00919.Metabolism of chiral pesticides in crops is typically studied using achiral analytical methods and, consequently, the stereoisomer composition of residues is unknown. In this study, we developed an enantioselective GC-MS/MS method to quantify residues of the fungicides fenpropidin, fenpropimorph, and spiroxamine in plant matrices. In field trials, the fungicides were applied to grapevines, sugar beets, or wheat. Fenpropidin was metabolized with no or only weak enantioselectivity. For fenpropimorph, slightly enantioselective metabolism was observed in wheat but more pronounced in sugar beets. This enantioselectivity was due to different rates of metabolism and not due to interconversion of enantiomers. The four stereoisomers of spiroxamine were also metabolized at different rates, but selectivity was only found between diastereomers and not between enantiomers. trans-Spiroxamine was preferentially degraded in grapes and cis-spiroxamine in wheat. These findings may affect the consumer dietary risk assessment because toxicological end points were determined using racemic test substances.We thank the field teams of Agroscope in Wadenswil (D. Malo, ̈ R. Schmon, C. Total, T. Wins) and Zürich (P. Walther, F. Kaser) ̈ for performing and supervising the trials, A. Schürmann (Official Food Control Authority of the Canton of Zurich), E. Arrigoni and D. Baumgartner (Agroscope) for helpful discussions concerning homogenization and extraction of plants, M. Keller (Agroscope) for agronomic issues, and S. Huntscha (Agroscope) for support in the laboratory.Peer reviewe

Behavior of the Chiral Herbicide Imazamox in Soils: PH-Dependent, Enantioselective Degradation, Formation and Degradation of Several Chiral Metabolites

8 páginas.- 5 figuras.- 1 tabla.- 20 referenicas.- The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.est.8b07209Many pesticides show a pronounced biphasic degradation in soil, typically with a faster initial phase, followed by a slower decline. For chiral compounds, a biphasic decline of the total concentration may result from enantioselective degradation. In this study with the chiral herbicide imazamox, biphasic degradation was observed in most of the 18 soils investigated. In neutral soils, degradation was, in fact, enantioselective with faster degradation of (+)-imazamox. In slightly acidic soils, differences between enantiomers were not pronounced, and in strongly acidic soils, degradation was again enantioselective, but with reversed preference. Additional experiments with pure enantiomers indicated no interconversion. Enantioselective degradation thus contributed to the biphasic decline of the total concentration in certain soils. However, this was not the only factor since degradation of the individual enantiomers was biphasic in itself. In addition to the observed correlation between enantioselectivity and pH, degradation was generally faster in neutral than in acidic soils with half-lives ranging from only 2 to >120 days. Half-lives were also determined for two known metabolites and a further chiral metabolite, the structure of which was characterized by high resolution tandem mass spectrometry. As for the parent compound, half-lives of the metabolites varied considerably in the different soils. © 2019 American Chemical Society.Peer reviewe