Adsorption reactions are one of many processes to consider when attempting to predict and understand the movement of contaminants through the subsurface. This dissertation presents the work of four individual but related studies that measured and quantified adsorption reactions of chemical contaminants onto a variety of particulate subsurface media with special consideration of the reactivity of the bacterial surface. Chapter 2 describes the adsorption of an ionic liquid onto mineral oxides, clay, and bacteria. The experimental results reveal that 1-Butyl, 3-methylimidazolium chloride (Bmim Cl) is unstable in water below pH 6 and above pH 10 and that it exhibits pH independent and ionic strength dependent adsorption onto Na-montmorillonite with 0.4, 0.8, 1.0, 1.2, and 2.0 g/L of clay. We observed no adsorption of the Bmim Cl onto Bacillus subtilis (3.95 or 7.91 g (dry weight) bacteria/L) at pH 5.5 to 8.5 or onto gibbsite (500 or 1285 g/L) or quartz (1000 and 2000 g/L) over the pH range 6-10. The measured adsorption was subsequently quantified using a distribution coefficient approach. Chapter 3 focuses specifically on the reactivity of the bacterial surface using the new technique of combining titration calorimetry with surface complexation modeling to produce site-specific enthalpies and entropies of proton and Cd adsorption. Our results provide mechanistic details of these adsorption reactions that are impossible to gain from previous techniques used to study the bacterial surface. Chapters 4 and 5 present work measuring and quantifying the adsorption of U and Np onto B. subtilis under a variety of conditions. Np adsorption exhibited a strong ionic strength dependence and unusual behavior under low pH high ionic strength conditions that was consistent with reduction of Np(V) to Np(IV). U adsorption, in constrast to Np adsorption, was extensive under all conditions studied. Thermodynamic modeling of the data suggests that uranyl-hydroxide, uranyl-carbonate and calcium-uranyl-carbonate species each can form stable surface complexes on the bacterial cell wall. These studies investigate a variety of adsorption reactions and provide parameters to quantify adsorption that may aid in integration of these reactions into geochemical models to predict contaminant transport in the subsurface.