Pesticide kinetics and sorption allow to predict the equilibrium time of the reaction and to speculate over the reaction mechanisms involved.Therefore, their study is fundamental to understand the environmental fate of pesticides.The aim of this research was to evaluate the sorption and kinetics of the fungicide chlorothalonil in five distinct soils with different organic matter contents of the state of São Paulo (Brazil): Neossolo Quartzarênico órtico (RQo), Latossolo Vermelho distroférrico (LVdf-1 e LVdf-2), Latossolo Vermelho perférrico (LVj), and Gleissolo (G).The experiments were performed with a radiolabeled tracer, i.e., 14C-chlorothalonil, with radioactivity being measured by liquid scintillation spectrometry.The experiments were carried out under controlled laboratory conditions (25±2ºC), in a dark room. Kinetics was evaluated for 8 equilibrium periods: 0; 0.5; 1.0; 2.0; 4.0; 8.0; 12.0 and 24.0h. Desorption was performed in the samples equilibrated for 24hours, in 4steps. For sorption isotherm studies, the concentrations of chlorothalonil ranged from 0.05 to 0.76µgmL-1.The Elovich equation was fitted to the kinetics data whereas the Freundlich equation was fitted to the sorption isotherm studies.Chlorothalonil was highly sorbed to soils, except for the sandy soil with low organic matter content (RQo).Sorption was positively related to soil organic matter content.Moreover, sorption reaction occurred in two phases: a very fast phase occurring in the first few minutes responsible for most of the sorption, followed by a slow phase.The results show that a small fraction of the applied chlorothalonil would be available for groundwater leaching, but special attention is needed when it is applied to sandy soils with low organic matter content.Furthermore, chlorothalonil sorbed during the slow phase may be easily desorbed to the soil solution.
kinetics; pesticide; bound residues; organochlorines; retention