Degradation and metabolite formation of estrogen conjugates in an agricultural soil
Estrogen conjugates are precursors of free estrogens such as 17ß-estradiol (E2) and estrone (E1), which cause potent endocrine disrupting effects on aquatic organisms. In this study, microcosm laboratory experiments were conducted at 25 °C in an agricultural soil to investigate the aerobic degradation and metabolite formation kinetics of 17ß-estradiol-3-glucuronide (E2-3G) and 17ß-estradiol-3-sulfate (E2-3S). The aerobic degradation of E2-3G and E2-3S followed first-order kinetics and the degradation rates were inversely related to their initial concentrations. The degradation of E2-3G and E2-3S was extraordinarily rapid with half of mass lost within hours. Considerable quantities of E2-3G (7.68 ng/g) and E2-3S (4.84 ng/g) were detected at the end of the 20-d experiment, particularly for high initial concentrations. The major degradation pathway of E2-3G and E2-3S was oxidation, yielding the primary metabolites 17ß-estrone-3-glucuronide and 17ß-estrone-3-sulfate, respectively. Common metabolites were E2, the second primary metabolite, and E1, the secondary metabolite. Additionally, ring B unsaturated estrogens and their sulfate conjugates were tentatively proposed as minor metabolites. The persistence of E2-3G and E2-3S (up to 20 d) suggests that the high rate of application of conjugated estrogen-containing substances could be responsible for the frequent detection of free estrogens in surface and subsurface water.