Submitted to: Crop Protection Council British Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 1/24/2000
Publication Date: N/A
Citation: Interpretive Summary: The most widely used method to cleanup contaminated sites is the removal of the organic pollutants by binding them to charcoal. Because of the character of their surfaces, clays are very good at binding certain types of organic molecules, but poor for other types of compounds. The binding capacity of the clays however, can be significantly enhanced by replacement tof metals on the clay surface with certain types of organic molecules (organoclays). In present paper, we used the herbicide imazamox as a test compound to comparatively evaluate the ability of two clays and their organoderivatives (organoclays) as potential sorbents for cleanup of negatively charged organic molecules, which are a concern because they are weakly retained by most soil and sediment components. The results of this work showed that negatively-charged imazamox was moderately bound to clays within the organic chemicals on the surface whereas very little was bound to pure clays. It was shown that once the imazamox was bound, it did readily come off the organoclay. While the results appear promising, additional research is still needed to determine if these types os organoclays would be economically viable for cleanup of contaminated soil and water.
Technical Abstract: The sorption and desorption of the anionic herbicide imazamox (pKa1 nearly equal to 3.9, pKa2 nearly equal to 2.0) by organoclays (alkylammonium- exchanged montmorillonite) and organohydrotalcites (alkylsulfate-exchanged hydrotalcite) was compared with that of the neutral fungicide triadimefon, to test the potential use of these sorbents for decontamination purposes and slow release formulations as related to the charge characteristics of the pesticide. In general, interlayered organoclays and organohydrotalcites were much more sorptive for imazamox and triadimefon than the untreated minerals. Depending on the sorbent, triadimefon sorption on organoclays and organohydrotalcites was 5 to 200 times greater than that observed for imazamox anion. In contrast, whereas imazamox sorption on the organoclays was highly irreversible, triadirnefon sorption by the organoclays and organohydrotalcites was moderate to low. Imazamox sorption, as well as the reversibility of the sorption-desorption process, increased with decreasin pH, due to protonation and further sorption of molecular imazamox species. The results of this work indicate that the diverse sorbents assayed may find application as filters in water decontamination for imazamox anion and as filters and supports for slow release formulations in the case of molecular imazamox and triadimefon.