Submitted to: Clays and Clay Minerals
Publication Type: Peer reviewed journal
Publication Acceptance Date: 6/16/2004
Publication Date: 10/1/2004
Citation: Carrizosa, M.J., Hermosin, M.C., Koskinen, W.C., Cornejo, J. 2004. Interactions of two sulfonylurea herbicides with organoclays. Clays and Clay Minerals. 52:643-649. Interpretive Summary: Herbicides that are highly soluble in water, minimally sorbed by soil particles, and not readily degradable can move rapidly with water and hence, have a high potential to be found in surface and ground waters. Many acidic herbicides, including some of the newer classes of herbicides such as sulfonylureas, have these characteristics, and thus if accidentally reach high concentrations in soil as in an accidental spill, they have to be immobilized as soon as possible to avoid further potential water contamination. The potential off-site movement of these agrochemicals can be decreased by creation of sorptive or immobilizing zones in the soils by incorporating an appropriate adsorbent in the affected area. Synthetic organic clays (OCls), obtained by exchange of the original inorganic exchangeable cations on the natural clay by large alkylammonium ones, showed an increased adsorption capacity for organic pollutants, such as polar pesticides in water. The objectives of this work were to assess the adsorption-desorption capacity of different OCls for acidic herbicides to test their ability to immobilize them in soil. We found that by increasing the size of the organic group on the clay, the amount of the herbicides and breakdown products sorbed on the clay increased. The treatment of a contaminated soil with highly adsorptive OCls appears to have potential to immobilize these chemicals. These promising initial results, will aid scientists in designing field tests, which are necessary before these OCls can be used for remediation of contaminated sites.
Technical Abstract: Sorption of two sulfonylurea herbicides (SUs), metsulfuron and nicosulfuron, on pure clays and organoclays has been investigated. Three clays (hectorite, Arizona-smectite and Wyoming-smectite), which vary in surface properties, were saturated with amounts of two different alkylammonium cations (octadecyl-, and dioctadecyldimethylammonium) equal to 50 and 100 % of the clays' CEC. Sorption isotherms were fitted to the Freundlich equation. While no measurable sorption was found for the pure clays, metsulfuron sorption on organoclays ranged between 13 and 75 % of applied chemical, and nicosulfuron sorption ranged from 6 to 36 %. Contrary to other weak acid herbicides, such as phenoxy and picolinic acids, no clear relationships were found between sorption and layer charge, organic carbon content, and basal spacing of the organoclays for both SUs. Sorption on organoclays in both cases seems to involve hydrophobic and polar interactions for which the availability of the interlayer room between organocations is a very important factor. Variation on the type and amount of organic cation could be used to increase sorption and hence organoclays may find an environmental application as sorbents in soil containments barriers, or as carriers in slow release formulations.