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Adsorption-Desorption Kinetics of Atrazine and Linuron in Freshwater-Sediment Aqueous Slurries¹

ABSTRACT

A fast sampling and filtration technique was used to determine the rapidity with which the herbicides atrazine (2-chloro-4-[ethylamino]-6-[isopropylamino]-s-triazine) and linuron (3-[3,4-dichlorophenyl]-1-methoxy-1-methylurea) are adsorbed or desorbed in sediment-water mixtures. When aqueous solutions of the herbicides were exposed to wet sediment, or when wet sediments containing the adsorbed herbicides were exposed to water, the resulting adsorption or desorption, respectively, was initially very fast, approaching 75% of equilibrium values within 3 to 6 min. Herbicide adsorption on the sediments was completely reversible after 2 h of adsorption time: kinetic parameters obtained from a statistical fit of a sequential-equilibria model to the adsorption data also fit desorption data. These results indicate that for these herbicides and similar nonionic solutes that have been in contact with sediment surfaces for 2 h, nonpoint pollution models for mixing streams may, to a first approximation, assume that adsorption-desorption reequilibration is reversible and established rapidly relative to stream movement and sedimentation times.

Key Words: hysteresis • herbicide • runoff • nonpoint pollution • pesticide

¹ Cooperative investigations of USDA-ARS, Stoneville, MS 38776 and The Center for Alluvial Plains Studies, Delta State Univ., Celveland, MS 38733.

² Research chemist, Southern Weed Sci. Lab., Stoneville, MS 38776 (currently at Southeast Watershed Res. Lab., USDA-ARS, Tifton, GA 31793); and professor, Physical Sci. Dep., Delta State Univ., Cleveland, MS 38733.

Received for publication November 24, 1983.

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