Submitted to: International Association of Environmental and Analytical Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 1/31/2002
Publication Date: N/A
Citation: 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, have these characteristics. If these chemicals 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 cation 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 a new class of herbicides and their breakdown products 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 an contaminated soil with highly adsorptive OCls appears to have potential to immobilize these chemicals. These are promising initial results. However, before these OCls can be used for remediation of contaminated sites, more research is necessary.
Technical Abstract: The sorption capacity and possible mechanisms of sorption of two new sulfonylaminocarbonyltriazolinone herbicides, methyl 2-[[[(4,5-dihydro-4- methyl-5-oxo-3-propoxy-1H-1,2,4-triazol-1-yl) carbonyl] amino] sulfonyl] benzoate (MKH 6561) and (4, 5 dihydro - 3 methoxy - 4 methyl - 5 - oxo- N- [ [2-(trifluoromethyoxy) phenyl] sulfonyl]- 1 H- 1, 2, 4- triazole-1-c) (MKH 6562), and their respective metabolites, 2,4-dihydro-4-methyl-5- propoxy-3H-1,2,4-triazol-3-one (6561M) and (2- trifluoromethoxybenzenesulfonamide (6562M) on octadecyl (C18) and dioctadecyldimethylammonium (DOD) saturated and Fe and Na saturated smectites has been investigated. Sorption of MKH 6561 on inorganic clays and C18 organoclays was much higher than for MKH 6562, but was similar on DOD saturated clays. For C18 saturated clays, sorption of both parent compounds increased with decreasing layer charge of the smectite. Sorption of 6561M, which was much lower than for its parent compound MKH 6561, was higher on inorganic and C18 saturated clays than on DOD saturated clays or inorganic clays. 6562M metabolite sorption, which was also lower than the corresponding parent compound MKH 6562, was higher on DOD saturated clays than on C18 or inorganic saturated clays. Results indicate that the sorption space between the exchangeable organocation (greater in low charge smectite and primary alkylcation saturation) is as relevant as hydrophobicity and basal spacing of the organoclay (greater in high layer charge smectite and quaternary alkylcation saturation), and confirm that partition mechanism is not the only mechanism of sorption of sulfonylurea- like or other polar organic compounds on organoclays.