Fate of Natural Estrogens in Agro-Impacted Soils and Sediments.

The detection of natural, manure-borne estrogenic compounds in surface water near agricultural land has ignited concern in recent years because of their potential to disrupt endocrine function, activate hormone responses, and alter secondary sex characteristics in non-target organisms at low environmental concentrations.  Of particular concern are 17a-estradiol (aE2), 17b-estradiol (bE2), and estrone (E1).  Once in surface water, sediments can act as a sink for these estrogenic compounds. Little is known, however, about the biotransformation processes of aE2, bE2, and E1 in sediments under anaerobic conditions.  The purpose of this study was to characterize the relative biotransformation rates and compounds formed for these estrogens under aerobic conditions in agro-impacted soils and under the full range of redox conditions present in agro-impacted ditch/stream sediment.  Specifically, our goals were to (i) quantify the relative degradation rates under aerobic conditions; (ii) to ascertain if inter-conversion occurs between the parent compounds (aE2 and bE2) under anaerobic conditions; (iii) determine if the primary metabolite (E1) transforms back to its precursors (aE2 and bE2) and under what redox conditions; and (iv) determine if the E2 isomers degrade at the same rate under both aerobic and anaerobic conditions. Aerobic batch microcosms under 2 agriculture soils were amended with aE2 and bE2 to determine their respective aerobic degradation rates. For the anaerobic studies, anaerobic batch microcosms under controlled redox conditions were amended with aE2, bE2, or E1, and stored in the dark in an anaerobic chamber until time of sacrifice. Electron acceptor concentrations were analyzed on a Seal AQ-2 and microcosms re-amended as needed.  Sterile controls were used to discern between biotic and abiotic processes for all conditions. Microcosms were analyzed for the parent compounds and known metabolites on an LC/MS/MS.  Preliminary results from the nitrate-reducing and sulfate-reducing microcosms show inter-conversion between the aE2 and bE2, likely through E1 as the intermediate.  Reversible transformation from the primary metabolite E1 to both parent compounds was observed, with preferential transformation back to bE2.  The alpha isomer had longer half-lives than bE2 under both redox conditions, but no statistically significant difference was observed under aerobic conditions.  Iron-reducing and methanogenic experiments are forthcoming.  The results-to-date indicate that while soils and sediments may serve as a sink for estrogenic compounds, anaerobic conditions provide a unique environment where metabolites may transform back to their parent compounds, which are often the more potent contaminants of concern.