Desorption of atrazine and cyanazine from soil

Removal of soluble soil organic carbon (SSOC) during herbicide desorption studies using the batch equilibrium method may affect the herbicide-soil-solution equilibrium particularly if herbicide-SSOC complexes can form. Desorption characteristics of atrazine (2-chloro-4-ethylamino-6-isopropylamino-s-triazine) and cyanazine (2-{[4-chloro-6-(ethylamino)-s-triazine-2-yl]amino}-2-methylpropion trile] were determined in a Ves clay loam (Aquic Hapludolls). For adsorption, the soil was equilibrated with 0.01 M CaCl₂ solutions containing atrazine or cyanazine. Desorption with 0.01 M CaCl₂ each day for 5 d resulted in hysteresis when compared to the adsorption isotherm. Replacement of the equilibration solution with soil extract for 5 d, while maintaining a higher SSOC content in the desorption equilibration solution than did the CaCl₂ solution, did not change desorption isotherm equations. The SSOC-herbicide complexes were not detected in any of the adsorption and desorption equilibration solutions by ultrafiltration (membranes with molecular mass cut offs of 10000 and 500 daltons), HPLC, or TLC techniques. Either s-triazine-SSOC complexes were not formed in sufficient quantities or they were not stable enough to affect desorption of the herbicide during batch equilibration.