|Moorman, Thomas - Tom|
Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/26/2000
Publication Date: N/A
Interpretive Summary: Sorption (binding) is one of the main processes determining the fate of organic pollutants, such as pesticides, in the soil. Thus, correctly characterized sorption is of great importance for an understanding and prediction of pollutant behavior in the environment. Traditionally, techniques for characterization of sorption is performed at unrealistic ratios between soil and water not found in the field, i.e. a small amount of soil is equilibrated with a large amount of water. Using a technique developed in our lab, we determined the sorption of triadimefon, a widely used fungicide, in soil at water contents that would be observed in the field. We found that sorption of triadimefon was affected by soil water content and temperature. For instance, sorption increased by a factor of 2 to 3 when soil moisture changed from very dry to very moist, an effect that would not have been observed using the traditional slurry method to characterize sorption. Scientists now have a more accurate characterizatio of triadimefon binding to soil, which will enable better prediction of its potential movement to ground and surface waters. These data can then be used to reduce potential exposure to nontarget organisms.
Technical Abstract: 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 (Kd) at field moist or unsaturated conditions. Triadimefon sorption was influenced by factors such as soil moisture content and temperature, with sorption increasing with moisture content, but less than saturated, and decreasing with temperature. For instance, Kd values for triadimefon on the silt loam and the sandy loam soils at 40 degrees C and 10 percent water content were 1.9 and 2.5 ml g-1, respectively, and at 18 percent water content, 3.3 and 6.4 ml g-1, respectively. Isosteric heat of sorption (DHi) 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 triadimefo was extracted from silt loam soil by 0.01 M CaCl2. Using the ASE system, which is basically a fast alternative to the batch equilibration system, gave a Kf sorption value of 27 ug1-1/n mL1/n g-1 and a DHi value of -29 kJ mol-1 for the silt loam soil.