Linuron sorption-desorption in field-moist soils

Pesticide sorption or binding to soil is traditionally characterized using batch slurry techniques. The objective of this study was to determine Linur on sorption in field-moist or unsaturated soils. Experiments were performed using low-density (i.e., 0.25 g mL(-1)) supercritical carbon dioxide to re move linuron from the soil water phase, thus allowing calculation of sorpti on coefficients (K-d) at low water contents. Both soil water content and te mperature influenced sorption. K-d values increased with increased water co ntent, if less than saturated. K-d values decreased with increased temperat ure. K-d values for linuron sorption on silty clay and sandy loam soils at 12% water content and 40 degrees C were 3.9 and 7.0 mL g(-1), respectively. Isosteric heats of sorption (Delta H-i) were -41 and -35 kJ mol(-1) for th e silty clay and sandy loam soils, respectively. The sorption coefficient o btained using the batch method was comparable (K-f for sandy loam soil = 7. 9 mu g(1-1/n) mL(1/n) g(-1)) to that obtained using the SFE technique. On t he basis of these results, pesticide sorption as a function of water conten t must be known to more accurately predict pesticide transport through soil s.