STUDY OF SORPTION PROCESSES OF SELECTED PESTICIDES ON SOILS AND CERAMIC POROUS CUPS USED FOR SOIL SOLUTION SAMPLING

Soil sorption constants of four organochlorine (lindane, dicofol, chlorfenson and tetradifon) and three organophosphorus pesticides (dimethoate, fenitrothion and methidathion) were measured using two different soils at six concentrations. Soil samples were collected at depths of 0-20 cm and around 100 cm from an experimental citrus crop field. Effects of soil properties (organic matter, moisture content, pH and texture) on the sorption processes were also investigated. Partitioning of pesticides between soil and solution was investigated after batch equilibration, using pesticide concentrations ranging from 10 to 200 mu g l(-1). The equilibration time was estimated in 2 h for organochlorine, and 72 h for organophosphorus pesticides. Data fitted to Freundlich types adsorption isotherms. Analytical determinations were carried out by gas chromatography with ECD and NPD detectors, after liquid-liquid extraction with dichloromethane of the water supernatant. Moreover, a validation of the use of suction samplers used to collect soil solution samples from the vadose zone, based on a short term study in the laboratory was determined.