GEOCHEMICAL FATE AND TRANSPORT OF SERTRALINE IN NATURAL SOILS

Pharmaceutical compounds enter waterways typically through wastewater, after being discarded or egested. These compounds often make their way downstream, interacting with soil as well as plant and animal life. Limited research has previously existed to determine the effects these compounds may have on ecosystems exposed to them. Due to steadily increasing rates of depression in the US and recent expiration of its patent, the drug sertaline, also known as Zoloft, is a worthy candidate for study as it pertains to water and soil systems. Sertraline is a primarily non-polar organic molecule with a solubility in water of 3 g/L in water and a pKa of 9.48 due to presence of an amine functional group in the molecule.

The main objective for this study was to examine sorption and transport behavior of sertraline in natural soils. Pristine A- and B-horizon soils collected from a natural forest near Charleston, SC, USA were utilized for laboratory experimentation. These soils were characterized by organic matter (OM) content between 0.6 and 7.6%, clay content between 6 and 20%, and a pH between 3.7 and 4.9. A-horizon soils had higher OM content while B-horizon soils had higher clay content. Soil samples were exposed to sertraline in different experimental settings to measure sorption and transport behavior while sertraline was analyzed using liquid chromatography (HPLC and LCMS) techniques.

Kinetic sorption experiments demonstrated that sertraline sorption in soils was a first-order reaction and that sorption reached equilibrium in approximately 48 h. Sorption isotherms measured using batch experiments were nonlinear and were fit using Freundlich and Langmuir models. Sorption data also showed that sertraline sorbs more strongly with clay-rich soil. This is likely because sertraline is a positively charged molecule at pHs below the pKa and this molecule sorbs with negatively charged clay minerals that are abundant in B-horizon soils. Transport behavior of sertraline in laboratory columns was predictable based on sorption experiments – sertraline was more strongly retarded in B-horizon soils than in A-horizon soils. These results have strong implications for management of pharmaceutical chemicals effluents and discharges to natural waters.