Adsorption and desorption of atrazine, deethylatrazine, deisopropylatrazine, hydroxyatrazine, and metolachlor in two soils from Virginia

The objective of this study is to characterize the adsorption-desorption properties of atrazine, deethylatrazine (DEA), deisopropylatrazine (DIA), hydroxyatrazine (HA), and metolachlor in the Emporia (fine loamy, siliceous, thermic Typic Hapludult) and Cullen (clayey, mixed, thermic Typic Hapludult) soils. Adsorption and desorption isotherms were determined using the batch equilibrium procedure. Four solution concentrations (2.5, 7.5, 13.2, and 26.4 mu mol L(-1)) were prepared of each chemical and four 24-h desorption periods at each concentration followed immediately after the adsorption process. Organic carbon distribution coefficients (K-oc) ranged from 140 to 234 for atrazine, 80 to 110 for DEA, 128 to 130 for DIA, 493 to 609 for HA, and 162 to 190 for metolachlor. For desorption, all chemicals exhibited hysteresis. Hysteresis was quantified: omega = [1/n(ads) + 1/n(des) - 1] x 100. Soil type affected the degree of atrazine, DEA, and metolachlor hysteresis (omega), and initial concentration had a significant effect on omega only in the Cullen soil. The amount of chemical desorbed, expressed as the percentage of the amount adsorbed, was about 60% for DEA, 43% for atrazine, 40% for metolachlor, 37% for DIA, and 31 and 17% for HA on the Emporia and Cullen soils, respectively. Soil type and initial concentration had no significant effect on the percentage of chemical desorbed except for HA. The sorption properties for atrazine and metolachlor In these soils are similar. The tendency of HA to leach will be low in these soils compared with atrazine, while the tendency of DEA to leach will be high.