title: Modelling the biphasic sorption of simazine, imidacloprid, and boscalid in water/soil systems.
abstract: The sorption kinetics of simazine (6-chloro-N,N'-diethyl-1,3,5-triazine-2,4-diamine), imidacloprid (1-(6-chloro-3-pyridylmethyl)-N-nitroimidazolidin-2-ylideneamine), and boscalid (2-chloro-N-(4'-chlorobiphenyl-2-yl)nicotinamide), three pesticides of wide use in agriculture, was determined in five different water/soil systems over a time interval from the initial few seconds to about 1 month. In all the experiments, sorption kinetics showed a biphasic pattern characterized by an initial, relatively short phase with a high sorption rate and a later phase with much a lower sorption rate. Initial sorption capacity increased with soil organic carbon content and with sorbate hydrophobicity. We postulate that the first phase of the process involves a fast second-order sorption reaction on superficial sites of soil particles, whereas the second phase depends on diffusion-controlled migration to internal binding sites. A kinetic equation based on this hybrid model accurately fitted all data sets. Less satisfactory results were obtained employing the pseudo-first order, pseudo-second order, Elovich, two site non-equilibrium, or Weber-Morris equation. The superior performance of the hybrid model for describing boscalid sorption probably reflects the high hydrophobic character and consequent low diffusion rates of this compound. The accuracy of modelling was in any case strongly dependent on the time interval considered.
authors.affiliation: a Department of Environmental, Biological and Pharmaceutical Sciences and Technologies , Second University of Naples , Caserta , Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Salvestrini
authors.forename: Silvana
authors.initials: S
authors.lastname: Canzano
authors.forename: Pasquale
authors.initials: P
authors.lastname: Iovino
authors.forename: Vincenzo
authors.initials: V
authors.lastname: Leone
authors.forename: Sante
authors.initials: S
authors.lastname: Capasso
mesh_terms: D000327:Adsorption; D000383:Agriculture; D001713:Biphenyl Compounds / Q000737:chemistry*; D002851:Chromatography, High Pressure Liquid; D005659:Fungicides, Industrial / Q000737:chemistry; D006540:Herbicides / Q000737:chemistry; D007093:Imidazoles / Q000737:chemistry*; D007306:Insecticides / Q000737:chemistry; D008962:Models, Theoretical; D000073943:Neonicotinoids; D009536:Niacinamide / Q000031:analogs & derivatives* / Q000737:chemistry; D009574:Nitro Compounds / Q000737:chemistry*; D010575:Pesticides / Q000737:chemistry*; D012839:Simazine / Q000737:chemistry*; D013997:Time Factors
chemical_list: D001713:Biphenyl Compounds; D005659:Fungicides, Industrial; D006540:Herbicides; D007093:Imidazoles; D007306:Insecticides; D000073943:Neonicotinoids; D009574:Nitro Compounds; D010575:Pesticides; D009536:Niacinamide; C550088:2-chloro-N-(4-chlorobiphenyl-2-yl)nicotinamide; C082359:imidacloprid; D012839:Simazine
keywords: Simazine; biphasic sorption; boscalid; diffusion-controlled kinetics; imidacloprid; kinetic hybrid model; pseudo-second order reaction; soil sorption