Fate and Transformation of an Estrogen Conjugate and Its Metabolites in Agricultural Soils

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 C-14 labeled prototype conjugate, 17 beta-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, 17 beta-estradiol (E2) and estrone (El), respectively. Following hydrolysis, hydrophobic sorption interactions of E2 and El 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.