Sorption and desorption of atrazine, deethylatrazine, and hydroxyatrazine by soil and aquifer solids

Adsorption kinetics and adsorption/desorption isotherms of atrazine (AT), and its degradation products, deethylatrazine (DEA) and hydroxyatrazine (HYA) on solids from two depths of a gleyic planosol and the underlying sandy aquifer were studied using laboratory batch systems. Adsorption of the three molecules decreased with the sampling depth of the solid. Atrazine and DEA were not adsorbed on the aquifer solids, whereas HBA was. For all three solids, the adsorption increased in the order DEA < AT << HyA. Adsorption equilibrium was reached after 72 h for the upper soil sample (0-0.33 m) and after 24 h for the deeper soil sample (0.9-1.05 m) for all three molecules. For HyA, equilibrium was reached after 24 h for the aquifer solid (6-7 m). High pressure liquid chromatography (HPLC) analyses showed no significant degradation of the three molecules after 72 h. The adsorption isotherms of the three molecules were described by Freundlich equations. The Kf(ads) values ranged from 3.1 to 0.4 L kg(-1) for AT, 1.5 to 0.3 L kg(-1) for DEA and 7.9 to 0.9 L kg(-1) for HyA. The K-oc values suggested that the affinity for the organic matter bound to the solid increased in the order DEA < AT << HyA. The desorption isotherms were also described by Freundlich equations. The Kf(des) value was 7.5 L kg(-1) for AT in the upper soil sample and ranged from 0.1 to 31.1 L kg(-1) for DEA and from 0.7 to 96.8 L kg(-1) for HyA, depending on the sample. In the upper soil sample, desorption was hysteretic and DEA and HyA formed nonextractable residues, HyA more so than DEA. For the deeper soil sample for all three compounds and the aquifer solids for HyA, adsorption was completely reversible and did not lead to the formation of nonextractable residues.