title: Molecular interactions of pesticides at the soil-water interface.
abstract: High-resolution magic angle spinning (HR-MAS) NMR spectroscopy combined with saturation-transfer double difference (STDD) NMR can be used to analyze the molecular-level interactions of pesticides and whole soils occurring at the soil-water interface. Here 1H HR-MAS STDD NMR has been applied to some common pesticides (trifluralin, acifluorfen, and (4-nitro-3-(trifluoromethyl) phenol) and a pesticide degradation product (1-naphthol). Results indicate that dipolar interactions, H-bonding, hydrophobic associations, and potentially pi-pi interactions are the predominant sorption mechanisms for these molecules at the soil-aqueous interface. It is evident that the physical and chemical characteristics of soil are highly influential in determining the mechanisms of pesticide sorption, as they significantly affect soil conformation. In particular, different binding mechanisms were observed for 1-naphthol in soil swollen using a buffer versus D2O, indicating that the K(oc) alone may not be enough to accurately predict the behavior of a molecule in a real soil environment. Preliminary kinetic-based studies suggest that both the swelling solvent and soil moisture content significantly influence the sequestration of trifluralin. These studies demonstrate that HR-MAS and STDD NMR are powerful and versatile tools which can be applied to expand our knowledge of the mechanistic interactions of agrochemicals at the molecular level.
authors.affiliation: Department of Chemistry, University of Toronto, Scarborough College, 1265 Military Trail, Toronto, Ontario M1C 1A4, Canada.
authors.forename: Azadeh
authors.initials: A
authors.lastname: Shirzadi
authors.forename: Myrna J
authors.initials: MJ
authors.lastname: Simpson
authors.forename: Rajeev
authors.initials: R
authors.lastname: Kumar
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Baer
authors.forename: Yunping
authors.initials: Y
authors.lastname: Xu
authors.forename: André J
authors.initials: AJ
authors.lastname: Simpson