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Fate and transformation of an estrogen conjugate and its metabolites in agricultural soils

Shrestha, Suman L., Casey, Francis X. M., Hakk, Heldur, Smith, David J., Padmanabhan, G.
Environmental science & technology 2012 v.46 no.20 pp. 11047-11053
agricultural soils, animal production, biodegradation, chemical residues, conjugated estrogens, endocrine-disrupting chemicals, environmental fate, estrone, farms, groundwater, hydrophobicity, oxidation, secondary metabolites, soil organic matter, sorption, steroid hormones, swine, topsoil, toxicity
Estrogens are naturally produced steroid hormones that are constantly being eliminated by many life forms, including production animals. An important form of release of estrogens is as water-soluble conjugates, which are not toxic, but may readily be hydrolyzed back to parent estrogens, which are known endocrine disruptors. To identify the fate of a conjugated estrogen in an agricultural soil, batch experiments were conducted with a prototypic estrogen conjugate, i.e. 17B-estradiol-3-glucuronide (E2-3G). While some conjugate oxidation of E2-3G to estrone-3-glucuronide (E1-3G) was observed (7-8%), the primary dissipation pathway of the conjugate was the biological hydrolysis of E2-3G and E1-3G to the estrogens 17B-estradiol (E2) and estrone (E1). Hydrophobic sorption of E2 and E1 to soil was then the dominant feature for the fate of E2-3G. Depending on soil organic matter content, E2-3G persisted for 1–14 d in the aqueous layer, which was much longer than previous studies on E2 or E1 (generally <24 h). Biodegradation rate constants of E2-3G were smaller in the low organic content subsoil (0.01–0.02 h-1) compared to high organic content topsoil (0.2–0.4 h-1). Separate field observations confirmed laboratory results in that relatively high concentrations of the conjugated E2-3G were detected in groundwater (425 ng L-1) near a swine farm that fertilizes with manure. This study provided evidence that conjugated estrogens may be a significant source of endocrine disrupting estrogens in surface and groundwater.