Halogenated 17β-Estradiol Surrogates: Synthesis, Estrogenic Activity, and Initial Investigations of Fate in Soil/Water Systems

17 beta-Estradiol (E2), a natural, endocrine-disrupting, steroid hormone, is excreted by all vertebrates and can enter the environment from domestic animal and wildlife wastes. Multiple field studies using livestock manures as E2 sources suggest significant background concentrations of E2 (e.g., wildlife sources, hydrolysis of E2 conjugates, previous inputs). To accurately understand field fate and transport processes of E2, it is necessary to address the issue of background detections. In this study, two fluorinated and three brominated surrogate compounds of E2 were synthesized and compared to native E2 using soil/water batch experiments and for estrogenic activity. Analytical difficulties presented by the two fluorinated congeners deemed these compounds to be unsuitable surrogates of E2, and further assessment was abandoned. However, the brominated congeners proved promising, with log(K-oc) values that fell within the range previously reported for E2. Batch studies yielded similar relative aqueous concentrations and linear sorption isotherms across time for E2 and 2-bromo-17 beta-estradiol; however, the relative aqueous concentrations and linear sorption isotherms of 4-bromo-17 beta-estradiol and 2,4-dibromo-17 beta-estradiol were different from E2 but similar to one another. All three brominated congeners possessed estrogenic activity by E-Screen assay, albeit three orders of magnitude less than native E2, putatively due to steric interference introduced by the large bromine atom on the phenolic ring, the group that mediates interaction with the estrogen receptor. The data suggest that 2-bromo-17 beta-estradiol may serve as a suitable surrogate for E2 in planned field scale tracer studies designed to distinguish between antecedent and de novo inputs.