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United States Department of Agriculture

Agricultural Research Service

Title: Mechanisms for Retention of Chlorpyrifos on Smectites

item Laird, David
item Fleming, Pierce

Submitted to: Agronomy Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: November 4, 1999
Publication Date: N/A

Technical Abstract: Chlorpyrifos is a widely used, broad-spectrum organophosphorothioate insecticide. Understanding the mechanism for retention of chlorpyrifos on smectites and humic acid is fundamental for assessing fate and potential toxicity of chlorpyrifos bound to suspended colloids in aquatic environments. Six Ca-saturated reference smectites and one humic acid (Ca-humate) were analyzed to quantify sorption and desorption isotherms for chlorpyrifos over the 0 to 100 ng/mL range. The apparent Kd values ranged from 42 for Otay montmorillonite (dioctahedral) to 1272 for a saponite (trioctahedral). Substantial hysteresis was observed for desorption of chlorpyrifos from the smectites. Chlorpyrifos was 100% adsorbed on the Ca-humate and no detectable chlorpyrifos (<0.1 ng/mL) was desorbed from the Ca-humate. The results suggest that the nature and surface properties of suspended colloids significantly affect both the binding energy and sorption mechanisms for chlorpyrifos in aqueous systems.

Last Modified: 4/21/2015
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