Fate of 17α-estradiol, 17β-estradiol, and estrone in agricultural soils and sediments

Michael L. Mashtare, Purdue University

Abstract

The shift to concentrated animal production facilities and increasing rural-urban migration has increased the localized land application of nearly 1 billion tons of manure and biosolids annually. Although these applications provide nutrients and contribute to soil tilth, they also serve as a source for an estimated 49 tons of the natural manure-borne estrogens, 17α-estradiol (17α-E2), 17β-estradiol (17β-E2), and estrone (E1). While these estrogens are critical to endocrine systems, the low concentrations observed in the environment can disrupt endocrine function in non-target organisms, e.g., altering secondary sex characteristics which can lead to changes in wildlife communities. Research presented here focuses on understanding natural endocrine fate, specifically: (1) the sorptive behavior of 17α-E2 and 17β-E2 on agricultural soils using batch sorption experiments on seven autoclave-sterilized soils, with a range of properties, where both solution and soil phase concentrations were measured; (2) the aerobic biodegradation of 17α-E2 and 17β-E2 in soils using aerobic soil microcosms on two soils with different taxonomic properties, sacrificed over a 3-week period; and (3) the biotransformation of 17α-E2, 17β-E2, and E1 in sediments using anaerobic microcosms under nitrate-reducing, iron-reducing, sulfate-reducing, and methanogenic conditions. For all degradation studies, sterile controls were used to discern between biotic and abiotic transformations. Water, soil, and sediment extracts were analyzed for hormones using negative electrospray ionization tandem mass spectrometry. Electron acceptor concentrations and gas production were also quantified. 17α-E2 and 17β-E2 exhibited stereospecific sorption with the highest β/α sorption ratio being 1.9. Sorption was best correlated to soil organic carbon (OC) with average log OC-normalized distribution coefficients (L kgoc-1) of 2.97 ± 0.13 for 17α-E2 and 3.14 ± 0.16 for 17β-E2. No statistical difference, however, was observed between the aerobic degradation rates of the isomers, which were relatively fast (t½ < 0.5 d), with residuals persisting with time. Under all anaerobic conditions, stereospecific degradation was observed with the magnitude of t½ following 17β-E2 < 17α-E2 < E1. The observed t½ of 17β-E2 was rapid under all conditions (< 1.5 d), while 17α-E2 exhibited higher persistence with an observed t½ of 4.3 d to 69.3 d depending on the redox condition. Interconversion between 17α-E2 and 17β-E2 was observed, as was the reversible transformation from E1 back to its E2 precursors with a preferential formation of the more potent 17β-E2 (e.g., up to 33 mol % in iron-reducing conditions within 1 d). Under both aerobic and anaerobic conditions, E1 was the primary metabolite of both isomers and sterile controls support that the observed transformations were primarily biotically mediated. The anaerobic studies mirror the trends observed in a reconnaissance field study that monitored hormone concentrations in sediments taken quarterly over a 2-year period in an agro-impacted ditch and stream network using quarterly grab samples. These findings are significant and suggest that careful attention is needed when evaluating resource and risk management strategies for these compounds. For example, given that 17α-E2 is more likely to be leached from agricultural soils than 17β-E2, assuming the isomers exhibit the same sorption behavior, as has been previously assumed, would underestimate the transport behavior for the α-isomer. Likewise, although the bulk of E2 appears to degrade within a day under aerobic conditions, using a first-order degradation model for E2 would fail to predict the residual concentrations remaining in the soil profile. In stream networks receiving hormone-containing discharge, hormones are likely to persist in anaerobic sediments. Given evidence of interconversion between 17α-E2 and 17β-E2 and the reversible transformation to E2 from E1 under reducing conditions, sediments may serve as both a source and a sink of hormones to the water column. Therefore, quantifying just the inputs into the water column from discharge and run off may not be sufficient for understanding the persistence of these compounds. This suggests that further research is needed in water and nutrient management strategies, including controlled tile drains and bioreactors, where an anaerobic environment conducive to these transformations may be an unintended consequence.

Degree

Ph.D.

Advisors

Lee, Purdue University.

Subject Area

Agronomy|Soil sciences|Organic chemistry|Environmental science

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