SORPTION, DEGRADATION, AND TRANSPORT OF NAPROXEN AND IBUPROFEN IN SOILS AND WATER

Discharge of common pharmaceutical chemicals into the environment through excretion and various disposal methods can lead to contamination of natural soil and water. Because of the complex chemical structure of these organic compounds, sorption is expected to be very strong in organic matter (OM)-rich soils. The objective of this study is to characterize and determine the transport and degradation behavior of naproxen and ibuprofen in OM-rich natural soils. Ibuprofen and naproxen are both amphiphilic, carboxylic acids with a low solubility in water. The log K_OW for ibuprofen (3.6) and naproxen (3.2) indicate both are hydrophobic compounds. The acid dissociation constant (pKa) of naproxen (4.2) and ibuprofen (4.6) indicates their ability to react as ions in soils. The log D_OW values for naproxen (1.7) and ibuprofen (2.2) suggest that while the deprotonated forms of naproxen and ibuprofen are less hydrophobic than their neutral forms, they still contain nonpolar characteristics.

Our previous studies have shown that OM in soils can degrade both naproxen and ibuprofen into their respective ketone analogs. These degradants were absent in soils that had low OM content. In this study, an A-horizon soil with 9.5% organic matter content was used to analyze sorption and degradation behavior of ibuprofen and naproxen during one-dimensional transport experiments. Soil was uniformly packed into glass chromatography columns, saturated with dilute CaCl₂ solution, and injected with tracer solutions containing naproxen or ibuprofen. Effluent solutions were analyzed using high performance liquid chromatography (HPLC) and liquid chromatography mass spectrometer (LCMS). Our preliminary experiments indicated that sorption to the soil was stronger for ibuprofen than naproxen. Degradation products formed during the sorption front of the transport experiment and these compounds were similar to the ones observed during our previous studies. The formation of these compounds closely tracked the sorption and desorption fronts during our experiments. This assessment of potential transformation of these pharmaceuticals, as well as their mobility through soils, was performed in order to understand their behavior and fate in the environment.