Assessment of the movement of triazole fungicides by soil thin-layer chromatography

Soil TLC was used to assess and compare the mobility of 17 triazole fungicides in soil. A sample of Versailles soil (a silt loam with 2% organic matter) was passed through a 100-microns-meshed screen, and glass plates were coated with this fine fraction at a thickness of 250 microns or 500 microns. The non-labelled compounds were bioassayed to visualize their movement. Penicillium expansum was used as visualizing agent by spraying plates with an agar suspension of the fungus. Plates were then incubated at 28 degrees C, 100% RH. Inhibition areas usually appeared within 36 h. When [14C]triazoles were available, a linear detector and autoradiography were used to visualize the movement and measure the Rf. The Rf values obtained indicate that most of the fungicides were slightly mobile in the Versailles soil. Mobility of these fungicides was inversely related to their octanol/water partition coefficient. Successive leaching were also carried out with radiolabelled compounds, and movement was measured with the linear detector and compared with the position predicted from the initial value of Rf. The advantages and drawbacks of this technique are discussed.