Sorption of steroidal hormones by two iowa soil materials: Detection and modeling

The estrogenic hormones, for example, 17β-estradiol (E2) and estrone (E1), are regarded as some of the most potent of natural endocrine-disrupting compounds. At levels of a few nanograms per liter, E2 and E1 can interfere with normal sexual development in some aquatic species and could impose as yet unknown hazards to ecosystems. Both E2 and E1 have been added to soil through livestock waste from concentrated animal feeding operations. However, the fate and transport of these compounds in soils are not easily predicted, partly as a result of analytical challenges at low environmental concentrations and because of a weak understanding of adsorption mechanisms at the water-soil interface. Estradiol and E1 adsorption experiments were carried out by batch tests with two Iowa soil materials, Hanlon sand and Zook silty clay. Residual estrogen concentrations in the aqueous phase were determined by solid-phase extraction and derivatization, followed by quantification using gas chromatography-negative chemical ionization-mass spectrometry. Aqueous estrogenic concentrations were measured, and uptake by the soil materials was calculated assuming mass balance. The adsorption data were fit by both the Freundlich and linear models, and partition coefficients, Kd and Koc, were determined for each case. Over the entire range of concentrations studied, the linear model fit the sorption data well. Yet, at low equilibrium concentrations that could be determined by gas chromatography-negative chemical ionization-mass spectrometry, the nonlinear Freundlich model provided a better fit.