|Rochette, Elizabeth - 3640-20-00 (FORMER ARS)|
Submitted to: International Association of Environmental and Analytical Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 7, 1996
Publication Date: N/A
Interpretive Summary: Sorption is one of the key processes controlling the fate of pesticides in the soil water environment. Methods commonly used to obtain sorption coefficients require that the soils be above field capacity moisture, conditions that may not adequately reflect conditions in the field, so that the aqueous phase containing the pesticide to be quantified can be separated from the soil. We have developed a system using supercritical carbon dioxide that can remove the pesticide from soil solution of unsaturated soil without first requiring the separation of the solution from soil. The objective of this study was to determine the effect of low water contents on atrazine sorption-desorption in soils with different physical and chemical properties. We have shown that we have developed a technique to determine sorption-desorption in field-moist soils. Atrazine sorption values obtained with this technique increased as the content of soil clay and organic carbon increased, which was an expected relationship between sorption and soil properties. Measured strength of sorption decreased as amount of atrazine increased, which suggests that soil-atrazine interactions were strongest for the soil with the largest atrazine sorption capacity as would be expected. However, it appears that differences in water content may have a greater effect on strength of sorption than differences in soils. Additional research in this area is needed
Technical Abstract: Methods commonly used to obtain sorption coefficients require that the soils be above field capacity moisture so that the aqueous phase containing the pesticide to be quantified can be separated from the soil. We have developed a system using supercritical CO2 that can remove the pesticide from soil solution of unsaturated soil without first requiring the separation of the solution from soil. Sorption coefficients increased with soil organic carbon and clay contents for three field-moist soils. Also, sorption significantly increased in a sand as moisture content increased from 4.0 to 16 percent and in a silt loam as moisture increased from 9.6 to 27 percent. Isosteric heats of sorption were easily determined with the supercritical fluid system and ranged from -10 to -12 kcal mol**-1 and were correlated to organic carbon and clay contents with the batch slurry system, while heats of sorption were much more negative, indicating greater sorption at low moisture contents.