Behavior of the enantiomers of the herbicide imazaquin in agricultural soils under different application regimes

Abstract

Sorption, persistence, and leaching of the enantiomers of the herbicide imazaquin, S-imazaquin and R-imazaquin, in two soils under different application regimes were studied. Imazaquin dissipation was evaluated after a single application of the racemic herbicide and the pure enantiomers, and after a repeated application of the racemic herbicide. The effects of adding two olive-mill wastes (ALP and ALPc), biochar (BC), and organoclay (SA-HDTMA) on sorption, dissipation, and leaching of imazaquin enantiomers applied as racemic herbicide to the soils was also evaluated. For all treatments, sorption, dissipation, and leaching of imazaquin in the soils were either non-enantioselective or scarcely enantioselective. No interconversion of Rimazaquin to S-imazaquin or vice-versa was observed in the experiments with the pure isomers. Addition of ALP, ALPc, or BC did not enhance the negligible sorption of imazaquin enantiomers by the soils, but accelerated their dissipation. Addition of SA-HDTMA increased sorption of both enantiomers and delayed their dissipation and leaching. The results illustrate how agricultural practices can impact the behavior of imazaquin enantiomers in soils and support the suitability of replacing currently used racemic formulations of imazaquin with formulations based on the single biologically-active (R) enantiomer to reduce the environmental impact of this chiral pesticide.

Appraising factors governing sorption and dissipation of the monoterpene carvone in agricultural soils

“…Consequently, the Kd coefficients calculated for the total (R+S) carvone concentrations coincided with those calculated for the individual enantiomers. Non-enantioselective sorption is a common observation when soil sorption studies are performed using racemic initial solutions of chiral compounds (Gámiz et al, 2017;Liang et al, 2016;López-Cabeza et al, 2017).…”

Chiral Analysis of Pesticides and Drugs of Environmental Concern: Biodegradation and Enantiomeric Fraction

“…In the original papers [21, 41 different compounds from 14 different pesticide classes are mentioned, with triazole fungicides and phenoxy herbicides being the two most represented classes (Figure 4). Dissipation studies and field-only experiments with no incubation experiments considered were left out [72,149,[156][157][158][159][160][161][162][163][164][165][166][167]. beta-cypermethrin soil laboratory incubation experiments under sterile and non-sterile conditions HPLC-VWD enantioselective degradation of beta-cypermethrin observed; different degradation rates observed for the four beta-cypermethrin isomers; EF variation noticed during the degradation process [143] beta-cypermethrinsoil laboratory incubation experiments under sterile and non-sterile conditions with acidic and alkaline matrices, and with racemic mixture and individual enantiomers HPLC-UV enantioselective degradation of racemic-beta-cypermethrin observed only in non-sterile soils; different degradation rates and half-lives observed for the four beta-cypermethrin isomers; no enantiomeric enrichment observed during degradation of individual enantiomers [144] Regarding the analytical methods used to quantify pesticides' enantiomers during biodegradation, the trend is clear and high-performance liquid chromatography with a diode array detector (HPLC-DAD) [117,122,123,126,128,134,135,140,152] and an ultraviolet detector (UV) [120,129,132,136,138,141,144,146,…”

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

“…For the chiral analysis, the column was a Chiralcel OD‐3R analytical column of 150 mm length × 4.6 mm internal diameter and 3 μm particle size (Chiral Technologies Europe, France). Under these conditions, S ‐imazaquin eluted at 6.4 min and R‐ imazaquin eluted at 7.3 min . Both for achiral and chiral analysis, five external standard solutions of analytical standard‐grade rac‐ imazaquin with concentrations in the range 0.1–6 mg L −1 were also injected.…”

“…Analytical standard‐grade racemic imazaquin (purity >99.9%) was supplied by Sigma‐Aldrich (Spain). The pure R ‐enantiomer of imazaquin was isolated by semipreparative high performance liquid chromatography (HPLC) from a 500 mg L −1 rac ‐imazaquin solution prepared in 0.001 mol L −1 HCl + acetonitrile (6 + 4 by volume), following the procedure described in López‐Cabeza et al Briefly, following injection of 50 μL of the rac ‐imazaquin solution into the HPLC system, the peak eluting at a retention time of 7.3 min was collected, and then neutralized with 0.1 mol L −1 NaOH to a pH value close to 6. Afterwards, the acetonitrile was evaporated from the neutralized collected fraction by means of a soft stream of nitrogen.…”

“…Nonetheless, formulations of imazaquin enriched with the active enantiomer are not currently commercialized; imazaquin is marketed exclusively as racemic mixture. Several factors support the use of pure R ‐imazaquin formulations: (i) the herbicidal activity of the R ‐enantiomer has been reported to be nearly eight‐fold greater than that of the S ‐enantiomer, (ii) both enantiomers of imazaquin are quite persistent in soil, and (iii) interconversion between the enantiomers does not appear to occur in soil …”