|Hermosin, M Carmen|
Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/10/2005
Publication Date: 9/21/2005
Citation: Cruz-Guzman, M., Celis, R., Hermosin, M., Koskinen, W.C., Cornejo, J. 2005. Adsorption of pesticides from water by functionalized organobentonites. Journal of Agricultural and Food Chemistry. 53(19):7502-7511. Interpretive Summary: Pesticides 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 widely-used pesticides 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. Previously, synthetic organic clays obtained by exchange of the original inorganic exchangeable cation on the natural clay by large quaternary ammonium ions, containing alkyl or aryl chains, without specific functional groups, showed an increased adsorption capacity for organic pollutants, such as polar pesticides in water. In this work, we evaluated the ability of montmorillonite clay exchanged with four naturally occuring organic cations containing diverse functional groups (carnitine, cysteine, and thiamine) as sorbents of pesticides varying in their chemical structures. The results demonstrated that selective modification of clay minerals with natural organic cations containing appropriate functional groups can be a useful strategy to improve the performance of organoclays for the removal of specific pesticides from the environment. These results will aid scientists in their development of inexpensive and efficient organoclays to be used to decontaminate spill sites.
Technical Abstract: Replacement of natural inorganic cations of clay minerals with organic cations through ion exchange reactions has been proposed as a strategy to improve the adsorptive capacity of clay minerals for organic compounds, including pesticides. The organic cations most commonly used for this purpose have been quaternary ammonium ions, containing alkyl or aryl chains, without specific functional groups. In this work, we evaluated the ability of montmorillonite exchanged with four natural organic cations containing diverse functional groups (L-carnitine, L-cysteine ethyl ester, L-cystine dimethyl ester, and thiamine) as sorbents of pesticides varying in their chemical structures (simazine, hexazinone, triadimephon, alachlor, imazethapyr, and carbaryl). The organic cations were selected on the basis of: i) their natural origin, which should reduce concern about the incorporation of these materials into soil and aquatic environments compared to the classical alkyl- and aryl-ammonium cations; and ii) the presence of diverse functional groups in their structures, with the aim to establish relationships between pesticide sorption and the structural characteristics of both the organic cation and the sorbing pesticide. Most organoclays displayed higher affinity for the pesticides than the untreated clay, but the improvement in sorption capacity varied with the characteristics of the pesticide and the interlayer organic cation. Thus, triadimefon, imazethapyr, and carbaryl displayed the highest affinity for carnitine, cystine, and thiamine, respectively, whereas alachlor was sorbed similarly by all organoclays. Relationships between sorption and the nature of the pesticides and the organoclays are discussed. The results demonstrated that selective modification of smectitic clay minerals with natural organic cations containing appropriate functional groups can be a useful strategy to improve the performance of organoclays for the removal of specific pesticides from the environment.