METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Sorption and degradation of estrogen conjugates in agricultural soils
| Casey, Francis - |
| Bai, Xuelian - |
| Shreshtha, Suman - |
| Desutter, Thomas - |
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 29, 2010
Publication Date: January 31, 2011
Citation: Casey, F.X., Bai, X., Shreshtha, S., Hakk, H., Desutter, T. 2011. Sorption and degradation of estrogen conjugates in agricultural soils. [Abstract] In: Proceedings of the USDA-NIFA Land Grant and Sea Grant National Water Quality Conference, January 31-February 1, 2011, Washington, DC. Available: http://www.usawaterquality.org/conferences/ 2011/abstracts_posters/Casey.pdf.
The natural estrogenic hormone, 17'-estradiol (E2), can disrupt the endocrine system of some aquatic species at ng/L concentrations. Laboratory studies have shown low potentials for E2 persistence and mobility in the environment due to high degradation and soil retention. However, field studies have measured estrogens at concentrations and frequency that indicate they are sufficiently persistent and mobile to impact water quality. To facilitate urine excretion, animals excrete E2 as sulfate or glucuronide conjugates, which have increased aqueous solubilities compared to their non-conjugated forms. It is hypothesized that the discrepancy between laboratory and field studies is partially caused by the deconjugation of estrogen conjugates to form free estrogens. The objective of this study was to determine in soils the sorption and persistence of the E2 conjugates, E2-3-glucuronide (E2-3G) and E2-17-sulfate (E2-17S), which have been found at relatively high concentrations in animal manures. Radiolabeled E2-3G and E2-17S were enzymatically and chemically synthesized, respectively. Batch experiments were used to identify fate and transport processes of these conjugates in surface (organic carbon, OC=1.5%) and subsurface (OC=0.5%) soils that were natural and sterile. Aqueous phase radioactivity was measured through time using liquid scintillation counting, and high performance liquid chromatography was used to identify E2 conjugated metabolites. The experimental factor with the greatest contribution to conjugate persistence in the aqueous phase was OC. In natural soil, the half-life (t1/2) of E2-3G was 4 h and 100 h for surface and subsurface soils, respectively. In the natural soil, the E2-17S was more recalcitrant compared to E2-3G, where the surface and subsurface t1/2 were 30 h and 170 h, respectively. Also, the E2-17S persisted in the aqueous layer throughout the duration of the 14 d experiment, in that 40% of its original concentration was measured at 14 d. Under the context of manure management these results are significant, because E2 conjugates may serve as an important mechanism of environmental transport of E2, since they can be potentially de-conjugated to yield free E2.