Cyclodextrins as complexation and extraction agents for pesticides from contaminated soil

Abstract

The binding constants of seven commonly used pesticides (2,4-D, acetochlor, alachlor, dicamba, dimethenamid, metolachlor, and propanil) with native and derivatized cyclodextrins (α-CD, β-CD, γ-CD, hydroxypropyl-β-CD, methyl-β-CD, sulfated-β-CD, and carboxymethyl-β-CD) were measured using affinity capillary electrophoresis. All cyclodextrins showed significant binding interactions with each of the seven pesticides investigated, with the exception of sulfated-β-CD which exhibited negligible binding to acetochlor, alachlor, and metolachlor. Propanil was found to bind most strongly to the cyclodextrins in this study. The ability of cyclodextrins to extract these pesticides from contaminated soil was also assessed. A general correlation between the pesticide-cyclodextrin binding constants and the percent extraction enhancements was found. In most cases, aqueous cyclodextrin extraction of pesticides from soil produced soluble pesticide-cyclodextrin complexes with a Type AL solubility diagram. Hydroxypropyl-β-CD and methyl-β-CD generally displayed the greatest levels of extraction enhancement. However, most pesticides with γ-CD (and a few cases with α-CD and β-CD) produced relatively insoluble pesticide-cyclodextrin complexes in these soil extraction studies, resulting in Type BS solubility diagrams. Therefore, the measured aqueous extraction level for these pesticide-cyclodextrin combinations was lower relative to the control (1.0mM phosphate at pH=7.0). The results of this study may be used for future novel methods of contaminated soil remediation, which overcome the disadvantages of organic solvent and surfactant use. In addition, such binding studies may be applicable toward the development of pesticide-cyclodextrin formulations.