ATRAZINE SORPTION-DESORPTION IN FIELD-MOIST SOILS

Methods commonly used to obtain sorption coefficients require that the soils be above field capacity moisture so that the aqueous phase cont aining the pesticide to be quantified can be separated from the soil. We have developed a system using supercritical CO, that can remove the pesticide from soil solution of unsaturated soil without first requir ing the separation of the solution from soil. Sorption coefficients in creased with soil organic carbon and clay contents for three field-moi st soils. Also, sorption significantly increased in a sand as moisture content increased from 4.0 to 16% and in a silt loam as moisture incr eased from 9.6 to 27%. Isosteric heats of sorption were easily determi ned with the supercritical fluid system and ranged from -10 to -12 kca l mol(-1) and were correlated to organic carbon and clay contents of t he soils. Sorption coefficients in field-moist soils were much greater than are typically obtained with the batch slurry system, while heats of sorption were much more negative, indicating greater sorption at l ow moisture contents.