Determination of distribution coefficients for polar herbicides

Distribution coefficients (K_d) are among the most important factors in determining the fate and transport of organic chemicals in the environment. These parameters are widely used in traditional contaminant modeling programs; therefore, it is essential that we develop rapid and accurate means of determining K_ds for whole soils and soil constituents. Aqueous distribution coefficients for nonpolar compounds on soil organic carbon (K_oc) are usually estimated from correlations with octanol-water partition coefficients (K_ow) and organic carbon-water partition coefficients. The K_d for a given soil is then based on its organic carbon content. These parameters fail to take into account interaction with inorganic soil constituents, which become important for more polar compounds and when soil organic carbon is low.; In this dissertation, several studies were undertaken to understand the role of minerals in polar organic chemical sorption. This work has demonstrated that for some chemicals, organic matter is not the predominant sorbent for polar chemicals. For example, glyphosate sorption can be estimated in a whole soil using surrogate clay minerals, which are representative of the soil. Additionally, inorganic additions of phosphate inhibit glyphosate sorption leading to greater mobilization of the chemical in soil systems. Additionally, this study has shown that in systems where organic matter is depleted K _ow and K_oc parameters fail to accurately predict the amount of sorption. This failure leads to the hypothesis that minerals must also play a role in low organic matter systems.; In order to examine low organic matter systems, a new method was developed. In this method, mineral phases were packed into small-volume columns and pressurized heated water (subcritical) was used as the mobile phase. By utilizing subcritical water chromatography, we were able to determine distribution coefficients for several striazines in systems with varying clay content. Clay, due to its low permeability, often interferes with determination by gravity flow columns. Comparison with K_ds determined in batch studies indicates that the column method is capable of obtaining similar values and shows promise for development as a routine method.