SORPTION BEHAVIOR OF METOLACHLOR, ISOPROTURON, AND TERBUTHYLAZINE IN SOILS

Abstract

The sorption-desorption of metolachlor [2-chloro-N-(ethyl-6-methyl phenyl)-N-(2-methoxy-1-methyl ethyl) acetamide], isoproturon [3-(4-isopropyl phenyl)-1,1-dimethyl urea] and terbuthylazine [N⁶-tert butyl-6-chloro-N⁴-ethyl- 1,3,5-triazine-2,4-diamine] herbicides was studied in two German soils at 1:10 soil to water ratio by batch method. Equilibrium of herbicides between soil and water (0.01 M CaCl₂) was attained in 2 h. Sorption data fitted very well to Freundlich equation, represented by very high correlation coefficient (r² > 0.934). Comparison of Freundlich K values indicated that sorption of all the three herbicides was most pronounced in soil having higher organic carbon content. K_oc values were as expected nearly identical for each herbicide in the two soils. The Freundlich constant (1/n) was about 1 for metolachlor and less than 1 for terbuthylazine and isoproturon indicating a L-type of sorption isotherms.

Desorption of all the three herbicides showed hysteresis. Nearly equal amounts of metolachlor, isoproturon and terbuthylazine were desorbed from both soils. There was a good correlation between K_oc and solubility.

Keywords:

• Metolachlor
• Isoproturon
• Terbuthylazine
• Adsorption
• Desorption
• Organic carbon

ACKNOWLEDGMENTS

Neera Singh thanks the Indian National Science Academy, New Delhi, India and DFG, Bonn, Germany for providing financial support to conduct this study at the Fraunhofer-Institute for Environmental Chemistry and Ecotoxicology, Schmallenberg, Germany.