Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/1997
Publication Date: N/A
Interpretive Summary: Sorption-desorption is one of the key processes 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 interaction between pesticides and the different soil components in the soil. We determined the sorption-desorption of the herbicides atrazine and simazine on binary and ternary mixtures of model soil components: clay (montmorillonite), iron compounds (ferrihydrite), and organic matter (humic acid). Iron chemical and organic matter coatings on clay particles increased the sorption of the herbicides on the clay. We have completed a key step in a systematic effort to finally determine the binding mechanisms of these types of herbicides to soil. These results will help to understand changes in sorption that may result upon associations between the individual soil components.
Technical Abstract: Association processes between the different soil constituents may greatly influence the sorptive behavior of soil aggregates. In this work we studied the sorption-desorption of the s-triazine herbicides atrazine and simazine on binary and ternary model associations of montmorillonite, ferrihydrite and humic acid using the batch equilibration procedure. Results were compared with sorption-desorption on the single model constituents. Iron species and humic substance coatings on montmorillonite increased the sorption of the herbicides on the clay. Protonation of atrazine and simazine catalyzed by hydroxy iron polymers and functional groups of humic acid on the surface of montmorillonite was proposed to be responsible of enhanced sorption on the clay. Sorption studies of atrazine and simazine on a clay-ferrihydrite-humic acid model soil aggregate indicated that humic substances can hinder the access of herbicide molecules to iron species coatings on montmorillonite, especially when there is a high interaction by organic matter-iron coated clay. Sorption- desorption of atrazine and simazine by the sorbents studied was found to be reversible.