Modeling Sorption and Degradation of 17β-Estradiol-17-Sulfate In Agricultural Soils.

The natural steroid hormone, 17β-estradiol (E2), can be an endocrine disruptor at part-per trillion levels.  Laboratory studies indicate a low potential for E2 persistence and mobility in the environment; however, field studies consistently indicate the presence of E2 and its primary metabolite, estrone, at levels sufficiently high to impact water quality.  To facilitate urine excretion, animals may release E2 as a sulfated conjugate, which would have a higher aqueous solubility than the parent compound.  We hypothesize that E2 conjugates contribute to the detection of free estrogens in the environment.  The objective of this study was to determine the sorption, degradation, and mobility of a model conjugate, 17β-estradiol-17-sulfate (E2-17S), in agricultural soils.  Radiolabeled E2-17S ([¹⁴C]E2-17S) was chemically synthesized in a three-step process, and then batch experiments were conducted in natural and sterile soils. Additionally, soil organic carbon (OC) was varied (1.29 and 0.26%) to investigate its effect on the fate of [¹⁴C]E2-17S.  Liquid scintillation counting (LSC) was used in concert with high performance liquid chromatography (HPLC) to detect and quantitate parent compound and metabolites of E2-17S in the aqueous and bound phases.  Residual soil was combusted to determine non-extractable levels of ¹⁴C.  The E2-17S was relatively stable in the aqueous phase for natural and sterile soils.  Mono- and di- hydroxyl E2-17S were detected as metabolites of E2-17S in the aqueous phase above both sterile and natural soil.  Deconjugation to form E2 was not observed in aqueous phase; however, E2 and estrone were extracted from both natural and sterile soils.  A conceptual model was developed to simulate and identify the fate and transport processes of E2-17S.  Organic carbon was found to be an important factor affecting the sorption and degradation of E2-17S in soils.