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Adsorption-Desorption of Diuron by Freshwater Sediments¹

ABSTRACT

Freshwater sediments were collected from eight different locations in California to study the influence of sediment properties on the adsorption and desorption of the model herbicide, diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea). The sediments were characterized as to physical and chemical properties using the same methods used for soils. The sediments had a range of organic carbon of 0.91 to 19% and were high in silt and clay. The adsorption of diuron was described by the Freundlich equation. Adsorption at 25°C expressed as the Freundlich coefficient, k, was positively correlated to the amount of organic carbon present. There was no correlation with total CEC. The desorption of diuron was evaluated by taking the difference between the slopes of the adsorption and desorption isotherms. As the difference between these slopes increased, less diuron was desorbed. These differences were positively correlated to k and organic carbon. Adsorption at temperatures of 5, 25, and 40°C on three sediments indicated that the adsorption of diuron decreased as the temperature increased.

Key Words: herbicides • pesticides • water quality • sediment characteristics • organic matter content • apparent heats of adsorption

¹ Contribution of the Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA 92521. The research leading to this report was supported by the Univ. of California, Water Resour. Center, as part of Water Resour. Center Project UCAL-WRC-W-485.

² Graduate Research Assistant, Graduate Research Assistant, and Associate Professor of Soil Science, Univ. of California, Riverside, respectively. Current address of senior author: Cooperative Extension Service, Univ. of Nevada, P.O. Box 651, Overton, NV 89040. Senior author is presently Soil and Water Scientist, Univ. of Nevada Agricultural Experiment Station, Logandale, NV 89021.

Received for publication September 23, 1978.