Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/17/1996
Publication Date: N/A
Interpretive Summary: Sorption-desorption is one of the key precesses controlling the fate of pesticides in the soil-water environment. In order to understand the mechanisms involved in pesticide sorption-desorption in whole soil, knowledge is needed of the interactions between pesticides and the single soil components in the soil. We determined the differences in sorption- desorption behavior of the herbicides atrazine and simazine by single model soil components: clay (montmorillonite), iron compounds (ferrihydrite), and organic matter (humic acid). Sorption of the herbicides was greatest on the humic acid and least on the ferrihydrite. Sorption on the clay could be increased by increasing the acidity of the system. Changing the acidity of the sorbents changes the mechanism by which the herbicides are sorbed on the solid surface. We have completed the first step in a systematic effort to finally determine the binding mechanisms of these herbicides in soil. These results will help to understand changes in sorption that may result upon associations between the individual soil components. Research is now being conducted on sorption of these two herbicides on binary and ternary mixtures of the components.
Technical Abstract: Sorption-desorption of atrazine and simazine on montmorillonite, ferrihydrite and humic acid was determined using the batch equilibration procedure. Sorption of atrazine and simazine on humic acid was higher than that on the mineral sorbents; however, enhanced sorption on montmorillionite was measured after increasing the surface acidity of the clay. Results indicate sorption of s-triazine herbicides on montmorillonite as protonated species must be preceded by sorption as molecular species unless the pH of the bulk solution is very close to the pKa of the herbicide. In this latter case, cation exchange would be also operative. Sorption-desorption of atrazine and simazine by humic acid was more hysteretic than in the case of montmorillionite indicating that stronger forces are involved in the interaction of these herbicides with organic matter.