Binding of waterborne steroid estrogens to solid phases in river and estuarine systems

Abstract

Natural and synthetic steroid estrogens have been detected in sewage treatment work effluents discharged into rivers. An understanding of the partitioning of these estrogens between water and sediment is critical for the prediction of their fates in river systems. Hence, a series of experiments was conducted to ascertain the effects of differing environmental conditions on estrogen partitioning to sediment. Fugacity level 1 (sediment phase) output data demonstrated a good correlation with removal of estrogens from the water phase. Synthetic estrogens, with their higher Kow values, were removed more readily from the water phase than the natural estrogens. Maximum sorption to the sediment phase was attained after 1 h of shaking. At higher estrogen concentrations, there was a decrease in estrogen removal, while higher levels of sediment induced greater removal. The sorption of estrogen to sediments correlated with total organic carbon content. However, the presence of organic carbon was not a prerequisite for sorption. Iron oxide alone was demonstrated to have a sorption capacity of 40% of that of a sediment containing 1.1% total organic carbon. Laboratory saline water was found to increase estrogen removal from the water phase which was found to be consistent with partitioning experiments using actual field water samples. The addition of estradiol valerate, a synthetic estrogen with a particularly high Kow, suppressed sorption of other estrogens suggesting that it competed with the other compounds for binding sites.