title: Influence of methanol on the dynamics of the retention and release of cyprodinil by an agricultural soil.
abstract: The influence of methanol on the adsorption of the fungicide cyprodinil by a crop soil was studied by equilibrium measurements and by determining the retention-release dynamics in a continuous stirred flow tank reactor (CSTR). Equilibrium measurements showed the effective coefficient of partition of cyprodinil between soil and solution, K(dc), decreases linearly as the concentration of methanol in the solution increases until a percentage of 20% is reached. In CSTR experiments, the retention of cyprodinil was found to be almost reversible; up to a 95% of the fungicide was desorbed. The retention-release dynamics showed biphasic behavior and was partially controlled by diffusion. This behavior was reproduced by a model of diffusion into micropores identifying the soil particles as spheres and taking into account both intraparticle nonlinear adsorption and nonlinear adsorption at external surfaces. In all cases, the sorption kinetics was not the limiting step. The main effect of methanol in the retention-release dynamics ended up being based on the changes produced in the adsorption equilibrium. Methanol also increased the effective diffusion coefficient and decreased the mass transfer coefficient. The optimized Freundlich's isotherm coefficients for <5% methanol were lower than those obtained from the batch experiments.
authors.affiliation: Soil and Agricultural Science Group, Plant Biology and Soil Science Department, and Nutrition and Bromatology Group, Analytical and Food Chemistry Department, Faculty of Food Science and Technology, University of Vigo, Ourense Campus, 32004 Ourense, Spain.
authors.forename: José Eugenio
authors.initials: JE
authors.lastname: López-Periago
authors.forename: Manuel
authors.initials: M
authors.lastname: Arias-Estévez
authors.forename: Benedicto
authors.initials: B
authors.lastname: Soto-González
authors.forename: Sara
authors.initials: S
authors.lastname: Trelles-Reinoso
authors.forename: Jesús
authors.initials: J
authors.lastname: Simal-Gándara
mesh_terms: D000327:Adsorption; D000383:Agriculture; D004058:Diffusion; D005659:Fungicides, Industrial / Q000737:chemistry*; D000432:Methanol / Q000494:pharmacology*; D011743:Pyrimidines / Q000737:chemistry*; D012987:Soil / Q000032:analysis*; D012996:Solutions
chemical_list: D005659:Fungicides, Industrial; D011743:Pyrimidines; D012987:Soil; D012996:Solutions; C108338:cyprodinil; D000432:Methanol