Submitted to: Water Resources Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/30/2008
Publication Date: 8/1/2008
Citation: Fan, Z., Casey, F.X., Hakk, H., Larsen, G.L. 2008. Modeling of Coupled Degradation, Sorption, and Transport of 17beta-Estradiol in Undisturbed Soil. Water Resources Research 173:456-467. Interpretive Summary: 17 beta-estradiol is a natural hormone that is excreted into the environment most extensively by female mammals in their urine and feces. As a hormone 17 beta-estradiol can interfere, even at part-per trillion concentrations, with another organism's endocrine system, particularly aquatic organisms, and as such it is important to determine its fate once it is excreted. Once 17 beta-estradiol is released into the environment from human and animal sources, its fate and transport is controlled by factors such as absorption and transformation, which need to be understood to fully assess potential exposures. The objective of this study was first to determine experimentally the amount of 17 beta-estradiol that is exchanged between the aqueous layer and soil (i.e., reversible and irreversible soil absorption sites; soil batch experiments) and secondly 17 beta-estradiol absorption to soil and chemical and biological changes that occur as 17 beta-estradiol in an aqueous solution moves through soil (undisturbed soil column experiments). To achieve this objective, several controlled experiments were used to discern individual processes, and a novel modeling approach was used to describe and quantify these processes. This study provided innovative procedures that linked data from batch soil and undisturbed soil column experiments. Strong agreement was demonstrated between the experimental data obtained from these soil experiments and model.
Technical Abstract: The presence of 17 beta-estradiol in the environment, even at part-per trillion concentrations, may raise significant concern regarding the health of aquatic organisms. Once 17 beta-estradiol is released into the environment from human and animal sources, its fate and transport is controlled by factors such as sorption and transformation, which need to be fully understood to fully assess potential exposures. The objective of this study was first to discern, through controlled batch experiments, the simultaneous transformation (i.e., chemical and biological) of natural estrogenic compounds and their mass exchange between the aqueous and solid phase (i.e., reversible and irreversible sorption sites). Secondly, a comprehensive model was developed that used a series of first-order expressions to describe the various fate and transport processes of parent and metabolite estrogens in the nonequilibrium batch experiments. A stochastic ranking evolutionary strategy, a global optimization method, was used to estimate the parameters of this nonequilibrium batch model. The model provided an excellent description of the data and the parameter estimates were unique. These independently estimated parameters from the batch studies were then incorporated into a convective-dispersive model to describe two undisturbed column experiments. The strong consistency of parameter estimates between the batch and column experiments indicated a high capability and reliability of this model and the parameter values.