Competitive sorption between 17alpha-ethinyl estradiol and naphthalene/phenanthrene by sediments.

Steroid hormones such as 17alpha-ethinyl estradiol (EE2) have been frequently detected at various levels in surface waters downstream of many municipal wastewater treatment facilities. Their fate, transport, and environmental risk are currently not well characterized. This study examined the competitive sorption between EE2 and two aromatic hydrocarbon compounds, phenanthrene and naphthalene, by three sediments. The sorption isotherms of phenanthrene and naphthalene were measured at 22 +/- 0.5 degrees C using a batch technique with initial aqueous concentrations (Co) of EE2 at 0, 100, 500, and 2000 microg/L. Competitive sorption varied between EE2 and phenanthrene or naphthalene on the sediments. The linearity of the naphthalene sorption isotherm was found to increase as a function of the cosorbate EE2 concentration from 0 to 2000 microg/L. The single-point naphthalene KD value at equilibrium aqueous-phase naphthalene concentration (Ce) of 25 microg/L was reduced by 19-26% and 27-48% at Co (EE2) = 100 and 500 microg/L, respectively. The sorption of phenanthrene at its low Ce range was similarly affected by EE2, but to a much less extent, possibly because phenanthrene is more hydrophobic than EE2. At high phenanthrene Ce, no measurable change was observed even at CO (EE2) = 2000 microg/L. While the effect of naphthalene on EE2 sorption was insignificant, the competitive effect on the sorption of EE2 by phenanthrene was very significant at low EE2 concentrations. The measured single-point EE2 KD values decreased as much as 35% as the phenanthrene Ce increases from below 10 microg/L to slightly above 100 microg/L. This study suggests that the fate and transport of emerging pollutants such as EE2 could be affected in the presence of more hydrophobic pollutants in aquatic systems.