Fate and Transformation of an Estrogen Conjugate and Its Metabolites in Agricultural Soils Suman L. Shrestha, † Francis X. M. Casey,* ,† Heldur Hakk, ‡ David J. Smith, ‡ and G. Padmanabhan § † Department of Soil Science, School of Natural Resource Sciences, North Dakota State University, Fargo, North Dakota 58108-6050, United States ‡ Animal Metabolism-Agricultural Chemicals Research Unit, Biosciences Research Laboratory, USDA-ARS, Fargo, North Dakota 58102, United States § Department of Civil Engineering, North Dakota State University, Fargo, North Dakota 58108-6050, United States ABSTRACT: In the environment, conjugated estrogens are nontoxic but may hydrolyze to their potent unconjugated, ‘free’ forms. Compared to free estrogens, conjugated estrogens would be more mobile in the environment because of their higher water solubility. To identify the fate of a conjugated estrogen in natural agricultural soils, batch experiments were conducted with a 14 C labeled prototype conjugate, 17β- estradiol-3-glucuronide (E2-3G). Initially, aqueous dissipation was dominated by biological hydrolysis of E2-3G and its oxidized metabolite, estrone glucuronide (E1-3G), both of which were transformed into the free estrogens, 17β-estradiol (E2) and estrone (E1), respectively. Following hydrolysis, hydrophobic sorption interactions of E2 and E1 dominated. Depending on soil organic matter contents, dissolved E2-3G persisted from 1-14 d, which was much longer than what others reported for free estrogens (generally <24 h). Biodegradation rate constants of E2-3G were smaller in the subsoil (0.01-0.02 h -1 ) compared to topsoil (0.2-0.4 h -1 ). Field observations supported our laboratory findings where significant concentrations (425 ng L -1 ) of intact E2-3G were detected in groundwater (6.5-8.1 m deep) near a swine (Sus scrofa domesticus) farm. This study provides evidence that conjugate estrogens may be a significant source of free estrogens to surface water and groundwater. ■ INTRODUCTION For the purpose of this study, estrogens refer to steroidal, female, reproductive hormones and their metabolites, which are either natural (e.g., E2, E1, estriol (E3)) or synthetic (e.g., the oral contraceptive, 17α-ethinylestradiol (EE2)). Estrogens from anthropogenic and livestock sources have drawn considerable concern and debate regarding their potential impacts on the environment and human health. 1,2 Studies on the feminization of male fish near wastewater treatment plants 3 (WWTPs) or the collapse of a fish population in an experimental lake 4 have fueled this debate. Lowest observed adverse effect levels (LOAEL) for aquatic organisms from natural and synthetic estrogens are around 10 parts per trillion (ppt), 3 which is orders of magnitude lower than other anthropogenic endocrine disrupting compounds. 1,5 Furthermore, widespread detections of estrogens in surface water 6,7 and groundwater 8 have heightened the urgency to understand their fate and transport. For example, a national reconnaissance of 139 streams across 30 U.S. states detected reproductive hormones above the LOAEL in over 40% of their samples. 6 The global human population of about 7 billion 9 is estimated to release 30,000 kg yr -1 of natural estrogens (E1, E2, and E3) and an additional 700 kg yr -1 of synthetic estrogens from contraceptive usage. 10 However, the potential contribution of estrogens to the environment from farm animals is much greater, where it is estimated in U.S. and European Union alone that the annual estrogen excretion by farm animals is more than double that of the global human population or about 83,000 kg yr -1 . 11 Indeed, possible associations have been made between animal feeding operations (AFOs) and the detection of estrogens in surface and subsurface water. 12 Laboratory studies find estrogens to be short-lived 13,14 and immobile 15,16 in soil, which seemingly contradicts their relatively high detection frequencies at concentrations of concern in surface waters. 6 The divergent results between laboratory and field studies may be related to estrogen conjugates, the environmental fate of which is not understood clearly. To eliminate excess estrogens, mammals will enzymati- cally conjugate glucuronic acid or sulfate moieties to the estrogen molecule, increasing its water solubility and facilitating its urinary or biliary excretion. 12 Humans excrete around 90- 95% of estrogens as conjugates, 17,18 while swine, poultry (Gallus gallus), and cattle (Bos taurus) excrete approximately 96, 69, and 42% of their estrogens as conjugates, respectively. 19 Between the two major conjugated forms, i.e. the glucuronides Received: May 31, 2012 Revised: August 21, 2012 Accepted: September 10, 2012 Published: September 11, 2012 Article pubs.acs.org/est © 2012 American Chemical Society 11047 dx.doi.org/10.1021/es3021765 | Environ. Sci. Technol. 2012, 46, 11047-11053