Abstract

Common household chemicals, such as caffeine, enter groundwater systems via wastewater. The contaminants may experience sorption and/or degradation in groundwater. These compounds are commonly used as tracers for anthropogenic contamination, making it important to understand their chemical mobility in groundwater. The role of montmorillonite on groundwater contaminant adsorption was investigated using batch experiments and saturated soil columns. Results from this study indicated adsorption of the contaminants, sulfamethoxazole, carbamazepine, and bisphenol-A, is negligible, while adsorption of caffeine can be significant depending on soil composition. For example, the retardation factor for caffeine was 190 times higher in soils containing 0.2% montmorillonite clay compared to quartz play sand without the clay. However, caffeine adsorption decreased when other three compounds were in solution, indicating the possibility of competitive adsorption influencing montmorillonite. The study also investigated whether organic chemicals adsorb to suspended nanoparticles of clay and experience facilitated adsorption or transport. Results indicate caffeine may be an unreliable tracer in the presence of clay minerals or other contaminants and that some experimental methods for determining adsorption may not be representative of real-world conditions.

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