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ARS Home » Research » Publications at this Location » Publication #156532
Title: INTERACTIONS OF CHLORPYRIFOS WITH COLLOIDAL MATERIALS IN AQUEOUS SYSTEMS

Author
item WU, JIGANG - VIRGINIA STATE UNIVERSITY
item Laird, David

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2004
Publication Date: 9/29/2004
Citation: Wu, J., Laird, D.A. 2004. Interactions of Chlorpyrifos With Colloidal Materials in Aqueous Systems. Journal of Environmental Quality. 33(5):1765-1770.

Interpretive Summary: More than 3 million kg of chlorpyrifos are applied to agricultural fields in the US annually for control of insect pests. Chlorpyrifos is known to be highly toxic to fish and other aquatic organisms. The most likely way for chlorpyrifos to get into lakes and rivers is when soil on which chlorpyrifos has been applied is eroded and transported to lakes or rivers as suspended sediment. We found quite a bit of variability in the extent to which chlorpyrifos is adsorbed on and desorbed from various types of clays, organic matter and suspended sediment collected from a river in Iowa. The organic matter held the chlorpyrifos very tightly and so did some of the clays. But other clays held the chlorpyrifos only weakly and released it back to the water. The suspended sediment behaved more like one of the clays than the organic matter even though the suspended sediment contained a large amount of organic matter. This research will help scientists to better predict the fate of chlorpyrifos that is transported with eroded soil into lakes and rivers. The research may also help policymakers and regulatory agencies to better assess the risk to aquatic environments associated with the widespread use of chlorpyrifos in production agriculture.

Technical Abstract: An understanding of sorptive processes is key to describing the fate of chlorpyrifos in aquatic environments. The objectives of this study were to evaluate isotherms for sorption and desorption of chlorpyrifos on colloidal materials and to elucidate the mechanism of their interactions. Six Ca-saturated reference smectites, one Ca-saturated humic acid (Ca-humate), and one suspended sediment sample, collected from the Upper Cedar River, Iowa, were studied. A batch equilibration technique was employed to quantify sorption and desorption isotherms for chlorpyrifos over the 0 to 100 mg L-1 concentration range in a 0.01 M CaCl2 background. Large differences in sorption affinity and variation in desorption hysteresis were found among the smectites. Neither chlorpyrifos sorption nor its desorption were correlated with cation-exchange capacity, surface area, or surface charge density of the smectites. The evidence suggests that physical interaction between chlorpyrifos and smectites is the dominant mechanism for sorption of chlorpyrifos in aqueous systems. Chlorpyrifos was very strongly sorbed on Ca-humate and was not desorbed from the Ca-humate back into the aqueous solution. Chlorpyrifos was moderately sorbed on river sediment, and a large sorption-desorption hysteresis was also found. The study implies that both organic and inorganic materials in suspended sediment can influence the fate of chlorpyrifos in aquatic environments.