Characterization of triadimefon sorption in soils using supercritical fluid (SFE) and accelerated solvent (ASE) extraction techniques

Sorption–desorption of the fungicide triadimefon in field‐moist silt loam and sandy loam soils were determined using low‐density supercritical fluid extraction (SFE). The selectivity of SFE enables extraction of triadimefon from the soil water phase only, thus allowing calculation of sorption coefficients ( K d ) at field‐moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature; sorption increased with increased moisture content up to saturation, and decreased with increased temperature. For instance, K d values for triadimefon on the silt loam and the sandy loam soils at 40 °C and 10% water content were 1.9 and 2.5 ml g −1 , respectively, and at 18% water content, 3.3 and 6.4 ml g −1 , respectively. Isosteric heats of sorption (Δ H i ) were −42 and −7 kJ mol −1 for the silt loam and sandy loam soils, respectively. Sorption–desorption was also determined using an automated accelerated solvent extraction system (ASE), in which triadimefon was extracted from silt loam soil by 0.01  M CaCl 2 . Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a similar Δ H i value (−29 kJ mol −1 ) for the silt loam soil ( K f  = 27 µg 1 − 1/n  ml 1/n  g −1 ). In order to predict transport of pesticides through the soil profile more accurately on the basis of these data, information is needed on sorption as a function of soil water content. © 2000 Society of Chemical Industry