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

Abstract

17β-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( ) 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-17β-estradiol; however, the relative aqueous concentrations and linear sorption isotherms of 4-bromo-17β-estradiol and 2,4-dibromo-17β-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-17β-estradiol may serve as a suitable surrogate for E2 in planned field scale tracer studies designed to distinguish between antecedent and de novo inputs.

Microbial Degradation of Free and Halogenated Estrogens in River Water-Sediment Microcosms

“…Under these conditions, monoBrE2, diBrE2, and diClE2 exhibited average biodegradation half-lives that were 1.5, 2.3, and 2.6-fold longer than E2, respectively (Table ). This trend could reflect the fact that halogen substituents interfere with one or more estrogen biodegradation pathways involving the aromatic ring. , Alternatively, greater sorption of halogenated estrogens onto river colloids ,,− may provide a protective effect that slows biodegradation. Based on calculated half-lives and associated uncertainties, the trend was less clear at 1250 ng L –1 (Table ), which may reflect a change in the availability of sorption sites on colloids or the relative balance of degradation pathways at different initial estrogen concentrations.…”

“…These data (Table ) provide additional support for the idea that E1 forms degrade more slowly than E2 forms and that halogenated estrogens degrade more slowly than the corresponding free estrogens. Others have taken a similar approach to modeling E1 dynamics as a combination of formation from E2 degradation and removal by E1 degradation. ,,, While many studies have also investigated the interactions between estrogens and sediments, ,,− the mechanisms by which aqueous phase E1 behavior is influenced by sorption/desorption dynamics remain largely uncharacterized.…”

“…Others have taken a similar approach to modeling E1 dynamics as a combination of formation from E2 degradation and removal by E1 degradation. 49 , 52 , 69 , 77 While many studies have also investigated the interactions between estrogens and sediments, 12 , 15 , 78 − 82 the mechanisms by which aqueous phase E1 behavior is influenced by sorption/desorption dynamics remain largely uncharacterized.…”

“…These estrogens are formed during chlorine-based disinfection and may represent a large fraction of the total estrogen load in treated municipal wastewater effluent, , yet we know very little about the processes controlling their environmental fate. Based on equilibrium partition coefficients (Table S1), halogenated estrogens are expected to sorb more strongly than free estrogens to sediments and soils . Recent work has also shown that halogenated estrogen photolysis occurs on sub-hour timescales at circumneutral pH, significantly faster than the day–week timescales of free estrogen photolysis under similar conditions .…”

“…Based on equilibrium partition coefficients ( Table S1 ), halogenated estrogens are expected to sorb more strongly than free estrogens to sediments and soils. 15 Recent work has also shown that halogenated estrogen photolysis occurs on sub-hour timescales at circumneutral pH, significantly faster than the day–week timescales of free estrogen photolysis under similar conditions. 16 In the current study, we characterize halogenated estrogen biodegradation, a previously unstudied but potentially important removal pathway.…”