Author
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WU, JIGANG - IOWA STATE UNIVERSITY |
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Laird, David |
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Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only Publication Acceptance Date: 6/29/2000 Publication Date: N/A Citation: N/A Interpretive Summary: Technical Abstract: The objective of this study was to evaluate sorption and desorption of chlorpyrifos on a variety of smectites, and to investigate the effect of smectites on chlorpyrifos degradation and transformation in clay-water systems. Six reference smectites were evaluated in this study. The Ca-saturated smectites were analyzed using x-ray diffraction, total elemental analysis, and scanning electron microscopy (SEM) to characterize their structural and surface charge properties. Chlorpyrifos sorption and desorption isotherms were obtained using the batch equilibration procedure. The results show that all six smectites exhibited C-type sorption isotherms. A large difference in sorption affinity and variation in desorption was found among smectites. However, neither chlorpyrifos sorption affinity nor desorption hysteresis was correlated to surface charge density, cation exchange capacity, or surface area of the studied smectites. Based on these results and the non-polar nature of chlorpyrifos, we believe that sorption is driven primarily by entropy and that condensation in nanometer to micrometer scale capillaries is the dominant sorption mechanism for chlorpyrifos on smectites. The degradation study indicated that chlorpyrifos undergoes rapid hydrolysis to less toxic 3,5,6-trichloro-2-pyridinol in water. Sorption of chlorpyrifos on smectites inhibited chlorpyrifos hydrolysis in aqueous systems, suggesting that clay-bound chlorpyrifos introduced into rivers by surface runoff may increase the risk of exposure for aquatic organisms to chlorpyrifos. |
