SORPTION OF CHLORPYRIFOS AND FONOFOS ON 4 SOILS AND TURFGRASS THATCH USING MEMBRANE FILTERS

Chemical transport in soil is a major factor influencing soil and wate r contamination. Four soils and turfgrass thatch, representing a wide range of organic carbon OC content were studied to determine sorption K-d and K-f parameters for the insecticides chlorpyrifos and fonofos. The batch equilibrium method was used. The concentration of insecticid e was measured in the solution as well as in the solid phase to determ ine the most accurate sorption data. Four soils and thatch were equili brated for 24 h at 22 +/- 1 degrees C with aqueous insecticide solutio ns. Four concentrations of the insecticides, each < 50% of their respe ctive water solubilities, were selected for the experiments. After ext raction with an organic solvent, the concentration of insecticides in the aqueous solution was determined by gas liquid chromatography using electron capture detection for chlorpyrifos, and nitrogen/phosphorus detection for fonofos. Data obtained were fitted to the log and simple linear form of the Freundlich equation. Mass balance Freundlich isoth erm exponents n ranged between 0.82 and 0.93 for chlorpyrifos. 0.82 an d 1.21 for fonofos, with r(2) greater than or equal to 0.97. K-oc (per cent of organic carbon %OC normalized sorption coefficient) values wer e calculated by using experimentally developed K-d and K-f coefficient s in relation to OC levels from 0.29 to 34.85%. K-d and K-f coefficien ts of both insecticides were positively correlated with OC (r(2) great er than or equal to 0.96), organic matter OC (r(2) greater than or equ al to 0.96), and cation exchange capacity CEC (r(2) greater than or eq ual to 0.90).