Sediment-water interactions of natural oestrogens under estuarine conditions

The natural human female hormones oestrone and 17beta-oestradiol have been implicated in the disruption of endocrine systems in some wildlife adjacent to sewage effluents. The sorption behaviour of these two compounds under estuarine conditions was studied by spiking either 2.55 mug of oestrone or 2.65 mug of 17beta-oestradiol in kinetic experiments. In equilibrium experiments, 3 ng of oestrone or 3.2 ng of 17beta-oestradiol was added in each of the centrifuge tubes. Sorption onto sediment particles was relatively slow, with sorption equilibrium being reached in about 70 and 170 h for oestrone and 17beta-oestradiol, respectively. The effects of a variety of environmental parameters on sorption were studied including salinity, sediment concentration (SC), the presence of a third phase, particle size and, also, surfactant concentrations. Results show that although salinity did not induce any statistically significant effect on the sorption of 17beta-oestradiol, it did statistically enhance the sorption of oestrone, and a salting constant of 0.3 1 mol(-1) was derived. The partition coefficient for both compounds decreased with increasing sediment concentration, a phenomenon that has been widely reported and attributed to the presence of colloids (which could enhance dissolved concentrations). In this paper, the true partition coefficients for sediment particles (K-p(true)) and colloidal particles (K-e(true)) have been calculated, and a K-p(true) value of 141 and 102 ml g(-1) was obtained for oestrone and 17beta-oestradiol, respectively. In addition, K-e(true) values for oestrone (222 x 10(2) ml g(-1)) and 17beta-oestradiol (135 x 10(2) ml g(-1)) were two orders of magnitude higher than their respective K-p(true) values, suggesting that the colloidal particles are significantly stronger sorbents for natural oestrogens than sediment particles, Particles of different sizes were found to have different partition coefficients due to the strong relationships between partition coefficients for the two compounds and particulate organic carbon (POC) contents and specific surface areas (SSAs). The presence of a surfactant was shown to reduce the partition coefficients for the two compounds, although its concentrations being used were higher than those normally found in the natural environment. (C) 2002 Elsevier Science B.V All rights reserved.