No abstract

Pesticide sorption coefficients (K(d)) are generally obtained using batch slurry methods. As a consequence, the results may not adequately reflect sorption processes in field-moist or unsaturated soil. The objective of this study was to determine sorption of metsulfuron methyl, a weak acid, in field-moist soils. Experiments were performed using low density (i.e., 0.3 g mL(-)(1)) supercritical fluid carbon dioxide (SF-CO(2)) to convert anionic metsulfuron methyl to the molecular species and remove it from the soil water phase only, thus allowing calculation of sorption coefficients (K(d)) at low water contents. K(d) values for sorption of the metsulfuron methyl molecular species on sandy loam, silt loam, and clay loam soil at 11% water content were 120, 180, and 320 mL g(-)(1), respectively. Using neutral species K(d) values, the pK(a) of metsulfuron methyl, and the pH of the soil, we could successfully predict the K(d) values obtained using the batch slurry technique, which typically has a predominance of anionic species in solution during the sorption characterization. This application of supercritical fluid extraction to determine sorption coefficients, combined with sulfonylureas' pK(a) values and the soil pH, will provide an easy method to predict sorption in soil at different pH levels.

We used near infrared reflectance spectroscopy (NIR) combined with chemometric methods to predict the sorption of lindane and linuron to 27 agricultural soils from Sweden. The NIR predictions were calibrated by principal component analysis (PCA) of the NIR spectra and sorption data obtained using the batch equilibrium technique. Partial least square regression PLSR of the NIR data could predict 85% of the soil sorption (K (d)) for lindane and 84% for linuron, respectively. The results indicate that NIR can be used as a rapid and simple method to predict pesticide sorption to and leaching from soils.

A method for the supercritical fluid extraction of ionic alkyllead species from solid samples has been developed. Preliminary experiments indicated that methanol was a superior modifier in comparison to water and acetone in supercritical carbon dioxide (added as solutions corresponding to 10% of the extraction cell volume), and it was used in all subsequent work. Following collection in methanol, the ionic alkylleads were extracted as diethyldithiocarbamate complexes into hexane, propylated using a Grignard reagent, and quantified using gas chromatography-mass spectrometry. Optimization of the extraction temperature and pressure was performed using response surface methodology, yielding recoveries of 96, 106 and 80% for trimethyllead, triethyllead and diethyllead, respectively, from spiked sediment samples under optimal conditions (temperature, 80 "C, pressure, 45 MPa). To demonstrate the validity of the method, an urban dust sample distributed by the European Communities Measurements and Testing Programme as part of an intercalibration exercise was analysed using the developed procedure. The concentration of trimethyllead obtained, 6.6 k 0.5 ng g-1 (expressed as trimethyllead) was in agreement with the mean value from the intercalibration study (6.6 k 1.3 ng g-9.

Pesticide sorption or binding to soil is traditionally characterized using batch slurry techniques. The objective of this study was to determine linuron sorption in field-moist or unsaturated soils. Experiments were performed using low-density (i.e., 0.25 g mL(-)(1)) supercritical carbon dioxide to remove linuron from the soil water phase, thus allowing calculation of sorption coefficients (K(d)) at low water contents. Both soil water content and temperature influenced sorption. K(d) values increased with increased water content, if less than saturated. K(d) values decreased with increased temperature. 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 (DeltaH(i)) were -41 and -35 kJ mol(-)(1) for the silty clay and sandy loam soils, respectively. The sorption coefficient obtained using the batch method was comparable (K(f) for sandy loam soil = 7. 9 microg(1)(-)(1/)(n)() mL(1/)(n)() g(-)(1)) to that obtained using the SFE technique. On the basis of these results, pesticide sorption as a function of water content must be known to more accurately predict pesticide transport through soils.