title: Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications.
abstract: Mechanisms governing the enantioselectivity of the processes that determine the behavior of chiral pollutants in the environment need to be better understood. Understanding these mechanisms should help improve predictions of the hazards and risks chiral compounds can pose to people and the environment. We report the results of batch sorption experiments indicating that the sorption of the chiral fungicide metalaxyl on soil from non-racemic initial solutions was enantioselective. While from a racemic initial solution the two enantiomers of metalaxyl were sorbed on the soil to the same extent, increasing the fraction of R-enantiomer in the initial solution led to enhanced sorption of this enantiomer and to reduced sorption of the S-enantiomer. Considering the shape of the sorption isotherms (S-type) and the sorption behavior of model sorbents, we attributed this effect to molecular interactions between metalaxyl enantiomer species at the sorbed state, where R-R metalaxyl interactions appeared to be more favorable than R-S metalaxyl interactions. We discuss important environmental implications of the proposed mechanism, such as those related to the fact that the biological degradation of metalaxyl is known to be an enantioselective process that can yield non-racemic residues in soils shortly after application of the fungicide as a racemic mixture.
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Sevilla, Spain. Electronic address: rcelis@irnase.csic.es.
authors.forename: Rafael
authors.initials: R
authors.lastname: Celis
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Sevilla, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Gámiz
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Sevilla, Spain.
authors.forename: Gracia
authors.initials: G
authors.lastname: Facenda
authors.affiliation: Instituto de Recursos Naturales y Agrobiología de Sevilla (IRNAS), CSIC, Avenida Reina Mercedes 10, P.O. Box 1052, 41080 Sevilla, Spain.
authors.forename: María C
authors.initials: MC
authors.lastname: Hermosín
mesh_terms: D000327:Adsorption; D000409:Alanine / Q000031:analogs & derivatives* / Q000737:chemistry / Q000302:isolation & purification; D000465:Algorithms; D001673:Biodegradation, Environmental; D004787:Environmental Pollution / Q000032:analysis*; D005659:Fungicides, Industrial / Q000737:chemistry* / Q000302:isolation & purification; D012989:Soil Pollutants / Q000737:chemistry* / Q000302:isolation & purification; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D013237:Stereoisomerism; D013816:Thermodynamics; D014961:X-Ray Diffraction
chemical_list: D005659:Fungicides, Industrial; D012989:Soil Pollutants; D012996:Solutions; C028175:metalaxyl; D000409:Alanine
keywords: Chiral pesticides; Enantiomers; Non-racemic mixtures; Soil; Sorption