Application of cyclodextrins for remediation of organic compounds and heavy metals in soils.

Abstract

Cyclodextrins, being microbially produced compounds, were investigated for their potential to increase the removal of low-polarity organic compounds in subsurface remediation. It is found that the apparent solubilities of many hydrophobic organic compounds are significantly increased in hydroxypropyl-β-cyclodextrin (HPCD) solutions. The relative solubilities (S(t)/S ₒ) of compounds increase linearly with increasing HPCD concentrations. The solubilization power of HPCD is found to be much greater than that of miscible cosolvents and to be less than that of synthetic surfactants. The lower solubilization power of cyclodextrin can be increased by the addition of a third component such as cyclopentanol. The addition of 0.1% cyclopentanol significantly enhances the solubilization power of β -cyclodextrin (β -CD) for pyrene, acenaphthene, phenanthrene, and fluoranthene which are able to form 1:2 complexes with β-CD in the presence of cyclopentanol. In contrast, cyclopentanol produces no pronounced effect and a marked decrease in the solubilization power of β -CD for naphthalene and anthracene, respectively. These two compounds form 1:1 complexes with β -CD both in the absence and presence of cyclopentanol. The solubilization of all PAHs by γ-cyclodextrin (γ -CD) is significantly enhanced by 1% cyclopentanol. This result indicates that cyclopentanol can increase the hydrophobicity of β -CD cavity without inducing structure-dependent selectivity. We investigated the ability of a modified cyclodextrin, carboxymethyl- β-cyclodextrin (CMCD), to simultaneously complex with low-polarity organic compounds and heavy metals. The results of this experiment show that CMCD could simultaneously enhance the solubilities of the selected organic compounds and complex with Cd²⁺. The complexation of Cd²⁺ by CMCD is not significantly affected by changes in pH or by the presence of relatively high concentration of Ca²⁺.