Fate and Transport of EDCs in Soils: Estrone and Its Sulfate Conjugate's Adsorption from Mediator Solutions

The fate and transport of emerging contaminants have been major concerns for ecoenvironment and human health. This study presents the adsorption behavior of an endocrine disrupting chemical estrone (E1) and its sulfate conjugate estrone-3-sulfate (E1-3S) that are released to the environment via animal waste in significant amounts and direct exposures in grazed pasture systems. Both compounds have been shown to potentially contribute to endocrine disruption in wildlife, and knowledge about the adsorption behavior of these compounds is necessary for a sound environmental risk assessment. For labile compounds such as E1 and E1-3S, however, the standard protocols might overestimate adsorption by not considering metabolite formation or allowing for equilibration that exceeds the commonly reported half-lives of these compounds. Modified batch adsorption experiments with mediator solution of 0.005 M calcium chloride (Ca[Cl.sub.2]) and artificial urine (AU) solution were, therefore, conducted to determine the influence of these mediator solutions on the adsorption of E1 and E13S in three agricultural soils from Nasarawa State of Nigeria. Adsorption isotherms of both compounds were nonlinear, and the Freundlich equation was found adequate to describe the isotherms. The calculation of concentration-dependent effective distribution coefficients ([K.sub.d.sup.eff]) revealed that for a range of realistic exposure concentrations in a grazed farming system, the common approach of using Ca[Cl.sub.2] would deliver incorrect information for a sound risk assessment. Keywords Estrone (E1) * Estrone-3-sulfate (E1-3S) * Adsorption * Artificial urine (AU) * Soil