Concentration Dependent Sorption of Estrone to Soil.

Wastewater is a source of estrogenic compounds.  Use on agricultural landscapes may reduce their appearance in surface or groundwaters. Estrogen sorption studies have generally addressed the range of relatively high hormone concentrations reported for animal manures, and sorptive behavior of hormones at low (ng L^-1) concentrations, typical for soil and water environments, is a much less explored area. Therefore, our sorption experiments address a broader span of observable hormone concentrations, ranging from 1 to 160,000 ng L^-1 (or 0.001 to 160 ng mL^-1).

 

Experiments were carried out in triplicate using 0.2-g samples of Hagerstown soil. The samples were shaken at 25ºC with aqueous solutions (10 mL) of ³H-labeled estrone (at concentrations ranging from 0.001 to 160 ng mL^-1) amended with 0.005 M CaCl₂ to mimic soil solution ionic strength, and 0.001 M HgCl₂ to eliminate biodegradation (Xing and Pignatello, 1997). ³H-labeled estrone was utilized as it provided enhanced sensitivity over ¹⁴C-labeled estrone. Colluci and Topp (2001) earlier demonstrated the ability to achieve a 1000-fold reduction in analytical detection limits for 17 β-estradiol and 17a-ethynylestradiol through the use of commercially available ³H-labeled materials, and that there was no significant tritium exchange with bulk water.  After specific times, the aqueous phase was separated by centrifugation and analyzed by liquid scintillation counting for the remaining (not adsorbed) hormones.

 

Following a 24-h contact time, the adsorption isotherm was well-described by a linear sorption model (R²= 0.9935). With the organic carbon (1.1%) content of the Hagerstown soil used, this approximates to a log K_oc of 3.6, similar to but slightly larger than other reported literature values of estrogen hormones between 3.0 and 3.4.  It is hypothesized that our value may be slightly larger due to the lower hormone solution concentrations compared to other studies.