Sorption of 17 β-estradiol onto selected soil minerals

Abstract

Sorption of the endocrine-disrupting chemical 17 β-estradiol (E 2) from aqueous solutions to goethite, an iron oxide, and the clay minerals kaolinite, illite, and montmorillonite (K and Ca forms) was measured at 25 °C. The clay minerals sorbed more E 2 than the oxide, with sorption capacity increasing in the order goethite ⩽ illite < kaolinite ⪡ montmorillonite. Uptake by goethite was rapid, with the maximum sorption (ca. 10% E 2 sorbed from a 1 ppm solution) reached within seconds. Initial sorption to the clay minerals was similar, but then it continued more slowly until about 10–15% of the total estradiol had been taken up after a period of 3 days by kaolinite and illite, and about 65% by montmorillonite. There was little pH dependence on the sorption, except for the goethite case where a sorption maximum occurred at pH 7–7.5. Most of the sorbed E 2 was desorbed from goethite, kaolinite, and illite into water or methanol easily and quickly (within seconds), but none was desorbed into either solvent from montmorillonite. These results suggest that E 2 is adsorbed at the surfaces of goethite, kaolinite and illite, but taken up into the interlayer spaces of montmorillonite. The c-axis spacing of montmorillonite decreased after sorbing E 2, indicating expulsion of water upon uptake of E 2 into the interlayer regions.