METABOLIC FATE OF CHEMICAL AND BIOLOGICAL CONTAMINANTS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Fate and transformation of an estrogen conjugate and its metabolites in agricultural soils
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: September 6, 2012
Publication Date: September 11, 2012
Citation: Shrestha, S.L., Casey, F.X.M., Hakk, H., Smith, D.J., Padmanabhan, G. 2012. Fate and transformation of an estrogen conjugate and its metabolites in agricultural soils. Environmental Science and Technology. 46:11047-11053.
Interpretive Summary: Estrogens are constantly being eliminated by production animals as non-toxic, water-soluble conjugates. However, biologically active unconjugated estrogens are commonly found in surface waters. We hypothesized that after application to agricultural soil, estrogen conjugates are water-transported through soil and eventually converted to parent estrogen. If true, this hypothesis would provide a mechanism for estrogen transport into surface and groundwater. In laboratory studies, we added conjugated estrogen to various agricultural soils saturated with water and studied the fate of the conjugate over time. Consistent with our hypothesis, degradation of the estrogen conjugates to free estrogens readily occurred. Depending on the type of soil, estrogen conjugates could persist in the water phase much longer than free estrogens persist (free estrogens are rapidly degraded). Our findings suggest that the common practice of manure injection into soil might aid the entry of estrogens into groundwater.
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.