The interaction of hydrophobic organic compounds with natural solids and dispersed organic polymers.

The accurate prediction and characterization of sorption is central to understanding and modeling the fate and transport of organic contaminants in natural aquatic environments. Attempts to estimate the sorption of organic micropollutants to date have been largely empirical and only moderately successful. Moreover, the role of widely distributed heterogeneous organic polymers in such sorption processes is not well understood. The research presented herein developed a series of semiempirical models, derived in large measure from thermodynamic principles, which can be used to predict and understand the sorption of hydrophobic organic contaminants by natural solids in complex aquatic systems. A method which applies state-of-the-art high performance reverse phase liquid chromatography (HPRPLC) solute retention data for prediction of sorption was also developed. In comparison with sorption models which utilize octanol/water partition coefficients and aqueous solubilities as surrogate predictors of sorption behavior, this technique yielded superior correlations in all cases tested. A modified Flory-Huggins equation was applied to estimate the association of organic contaminants to humic and other organic polymers dispersed in the aqueous phase. Model predictions as well as experimental evidence all seem to indicate that the presence of these heterogeneous macromolecules in the aqueous phase can bind or complex hydrophobic organic micropollutants, thus hindering the sorption of these contaminants onto solids. This semi-empirical approach was found to predict equilibrium binding constants to within a factor of 2.5 of experimentally measured values. A simple phase transfer model was developed to determine the effect of humic substances in the aqueous phase on sorption processes This model incorporated the modified Flory-Huggins equation for purposes of estimating equilibrium contaminant-polymer binding constants. Experimental results and model predictions both show that the sorption of moderately hydrophobic compounds by lacustrine sediments was relatively unaffected by the presence of dispersed organic polymers, while the partitioning of highly insoluble organic contaminants by the same sorbents was sensitive to even small amounts of background polymers. These observations may have serious implications with regard to understanding the fate and transport pathways of various classes of organic pollutants.PhDBiological SciencesEarth SciencesEnvironmental scienceGeochemistryHealth and Environmental SciencesLimnologyUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/128210/2/8821559.pd