Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/28/2000
Publication Date: N/A
Citation: Interpretive Summary: Sorption (binding) of pesticides to soil particles controls the amount of pesticide that leach through soil or run off into surface water. Pesticide sorption has been most commonly characterized using a slurry, an unrealistic situation in the field. The objective of this study was to further investigate the applicability of a technique recently developed in my lab to determine sorption of the herbicide linuron in field- moist soils. Experiments were performed using low density supercritical carbon dioxide to remove linuron from the water phase only, thus allowing calculation of sorption coefficients at low water contents. Sorption of linuron was characterized for soils with different physical and chemical properties at different water contents that would be observed in the field and at different tempertures. Linuron sorption was affected by soil water content, soil organic matter content, and temperature. For instance, sorption increased by a factor of 2 to 3 when soil increased from very dry to very moist, an effect that would not have been observed using the traditional slurry method. Scientists now have a more accurate characterization of linuron 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: Pesticide sorption coefficients (Kd) have been most commonly determined using batch slurry, column, or centrifugation techniques. These techniques suffer from a number of drawbacks. For instance, they require soils with water contents above field capacity so that soil and soil solution can be separated before analysis. The experiments are usually carried out after drying the soils and water content is expected to have a great influence o pesticide sorption. Also, the extraction procedure usually alters the physical and chemical characteristics of the soil, resulting changes in properties of the binding sites during the experiment. Therefore, techniques are needed where Kd can be determined in field-moist soils. The selectivity of SFE has recently been used to extract atrazine and sulfonylurea herbicides from soil solution without also extracting residues bound to the soil particles. The objective of this study was to further investigate the SFE technique and determine linuron sorption in field-mois soils. Experiments were performed using low density (i.e. 0.25 g/mL) supercritical carbon dioxide to remove linuron from the water phase only, thus allowing calculation of sorption coefficients at low water contents. Kd values for soil at 12% moisture content was about 10 mL/g for a sandy soil and 20 for a clay soil. The higher Kd on the clay is presumably due its higher organic carbon content. Influence of SFE temperature and moisture content on sorption behavior will be studied further.