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Characterization of Hysteresis in the Desorption of 2,4,5-T from Soils¹

ABSTRACT

Methods for characterizing adsorption-desorption of 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) in the soil were investigated. Using the conventional method, the adsorption isotherms conformed to the linearized Freundlich equation for initial 2,4,5-T concentrations of 2 to 176 µmol/liter. Desorption of 2,4,5-T from soils exhibited significant hysteresis at all concentrations, with lower concentrations showing greater hysteresis. The longer the equilibration time for desorption, the greater was the observed hysteresis. Therefore, nonattainment of equilibrium was not evident as a major cause of the hysteresis effect. Using a modified method, biochemical degradation of 2,4,5-T during the desorption process accounted for a significant amount of the hysteresis observed. In the Palouse soil, approximately 63% of the observed hysteresis was eliminated by taking into account the biochemical degradation. In the Glendale soil, approximately 35% of the hysteresis was attributed to biochemical degradation.

¹ Contribution from the Department of Agronomy and Soils, Washington State University, Pullman, 99164. Scientific Paper no. 5252. College of Agriculture Research Center, Project no. 1811. Research conducted under the Western Regional Research Project W-82.

² Graduate Research Assistant, Visiting Associate Professor (on leave from New Mexico State University), and Professor of Soils respectively.

Received for publication December 26, 1978. Accepted for publication May 22, 1979.

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