METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: Sorption and Degradation of 17ß-Estradiol-17Sulfate in Agricultural Soils
| Bai, Xuelian - |
| Casey, Francis - |
| Desutter, Thomas - |
| Oduor, Peter - |
| Khan, Eakalak - |
Submitted to: ASA-CSSA-SSSA Annual Meeting Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: June 28, 2010
Publication Date: October 31, 2010
Citation: Bai, X., Casey, F.X., Desutter, T., Hakk, H., Oduor, P., Khan, E. 2010. Sorption and degradation of 17ß-estradiol-17sulfate in agricultural soils. ASA-CSSA-SSSA International Annual Meeting Abstracts, October 31-November 4, 2010, Long Beach, CA. Presentation 251-4. Paper 59213. Available: http://a-c-s.confex.com/crops/2010am/webprogram/Paper59213.html
Interpretive Summary: 17ß-Estradiol (E2) is a natural steroid hormone found in all vertebrates, and is a potent endocrine disrupting compound, particularly to aquatic life, operating through the estrogen receptor. Production animals excrete relatively large amounts of this hormone, and its transport into the environment is the subject of intense scientific inquiry. Laboratory studies suggest no E2 should reach surface or groundwater, but detections in these systems are frequent, and of a concentration to suggest that some endocrine disruption may occur to exposed wildlife populations. A possible means of environmental introduction may be as hormone conjugates, i.e. polar metabolites which can break down to the parent compound. We synthesized a radioactive version of a common E2 conjugate in swine, i.e. E2-17-sulfate (E2-17S), and measured its behavior in soil/water systems. About 3/4ths of the E2-17S sorbed to soil in 14 d, with nearly twice as much remained in aqueous solution when the soil organic content was low. Under sterile conditions, nearly twice as much E2-17S remained in aqueous solution when compared to the comparable high and low organic content natural soils. Already at 4 h the E2-17S remained began to degrade and form two polar metabolites. The aqueous composition of these polar metabolites increased in for the next 14 d, but no parent E2 was detected. This data indicated that E2-17S did not readily degrade to E2 in the experimental time frame selected, and at this time does not explain how E2 is transported to surface and groundwater. Qualitatively the same results were obtained for sterile soil, suggesting E2-17S is not a preferred substrate for microorganisms involved in environmental decomposition.
In the environment, the natural estrogenic hormone, 17ß-estradiol (E2) can potentially induce endocrine disruptions at low concentrations, i.e. 1-10 ng/L. Laboratory based studies have found low potentials for the persistence and mobility of E2 in the environment due to its high degradation and/or soil retention. However, field studies have frequently measured estrogens that indicate they are sufficiently persistent and mobile to impact water quality. To facilitate urine excretion, mammals excrete E2 as sulfate or glucuronide conjugates, which have higher water solubilities than the parent compound. It is hypothesized that the discrepancy in detection between laboratory and field studies is caused by the greater mobility of E2 conjugated and their subsequent deconjugation back to parent. The conjugate, E2-17-sulfate (E2-17S) has been detected at a relatively high concentration in swine manure slurry; however, little is understood about its fate and transport in the environment. The objective of this study was to determine the persistence, sorption, and degradation of E2-17S in agricultural soils. In order to achieve this objective, radiolabel E2-17S ([14C]E2-17S) was chemically synthesized in our laboratory. Batch studies were conducted to identify the processes controlling aqueous dissipation of [14C]E2-17S in natural and sterile soils. Four concentrations of [14C]E2-17S in 0.01 M CaCl2 solutions were added to two soils that had similar mineral composition, but different organic carbon content (1.5 vs. 0.5%). Aqueous phase radioactivity was measured at seven time points using liquid scintillation counting. High performance liquid chromatography was used to determine speciation of the [14C]E2-17S. For the high and low organic natural soils, 12% and 30% of total radioactivity, respectively, remaining in the aqueous phase after 14 days. Aqueous phase radioactivity for two sterile soils was 23% and 46%, respectively. Aqueous phase radioactivity for two sterile soils was 23% and 46%, respectively. The [14C]E2-17S already began to degrade at the earliest time point (4 h) in both natural and sterile soils, to yield two polar metabolites, which increased in composition with time. Despite the elongated persistence of E2-17S aqueous solution, it did not degrade to parent E2 over the experimental time frame selected.