METABOLIC VARIABLES AFFECTING THE EFFICACY, SAFETY, AND FATE OF AGRICULTURAL CHEMICALS
Location: Animal Metabolism-Agricultural Chemicals Research
Title: The Fate and Transport of Reproductive Hormones and Their Conjugates in the Environment
Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: October 20, 2009
Publication Date: December 14, 2009
Citation: Casey, F., Shrestha, S., Hakk, H., Smith, D.J., Larsen, G.L., Padmanabhan, G. 2009. The Fate and Transport of Reproductive Hormones and Their Conjugates in the Environment. Eos Trans. AGU 90(52), Fall Meet. Suppl, Abstract H53A-0910.
Reproductive steroid hormones can disrupt the endocrine system of some species at ng/L concentrations. Sources of steroid hormones to the environment include human waste water effluents or manure produced at animal feeding operations (AFOs). Steroid hormones, such as 17ß-estradiol (E2) and estrone (E1), undergo various fate and transport processes, and laboratory studies have shown that they do not persist long (hours to few days), and have very little if any mobility in soil. Nonetheless, steroid hormones are detected at frequencies and concentrations of concern in the natural environment that would suggest their moderate persistence and mobility. One theory that may partially explain the disparity between field and laboratory studies is that conjugated forms of hormones are more mobile than their deconjugated counterparts. Glucuronide and sulfate conjugates are found in abundance in animal waste and are more soluble than their deconjugated forms. Laboratory studies were conducted to study the fate of a major urinary E2 conjugate, 17ß-estradiol glucuronide (E2G), in a Hamar soil (Sandy, mixed, frigid typic Endoaquolls) from the surface and subsurface horizons. Speciation studies using batch sorption indicated that E2G degraded to E2 and E1 within 24 hours in the upper horizon soil with organic carbon content (OC) of 1.35%; whereas it persisted more in the lower horizon soil containing 0.32% OC. For initial concentrations of 2.8–28 mg/L, more than 15% of the applied dose concentration was still intact in the conjugate form in the aqueous phase for 3 – 14 days, in the lower horizon soil. The decline of E2G in the aqueous phase in the upper horizon soil was approximated with a first–order rate constant (k), which ranged from -0.208 to 0.279/h. The k values ranged from -0.006 to -0.016/h for the lower soil horizon. The differences in k values between the two horizons could be attributed to differences in bacterial activity and/or differences in sorption capacities. The upper horizon would generally have more biological activity and perhaps more E2G bio-degradation. Also, the higher OC of the upper horizon would result in greater sorption of the hydrophobic hormones. Our results may have important implications for on-farm manure management. A prevailing practice is to inject manure slurry below the soil surface to reduce ammonia volatilization and odor. If slurries are injected too deep, then conjugated hormones in the manure could potentially be placed at soil depths that have less capacity to degrade and a greater potential to be transported. Time windows of 24 hours for surface manure application and 3 – 14 days for subsurface manure application may be decisive in determining whether E2G will be transported during runoff and leaching events.