GEOCHEMICAL FATE AND TRANSPORT OF ANTIDEPRESSANTS IN NATURAL SOILS

Unintended exposure to antidepressant medications have become a worldwide concern due to increasing presence in water resources. They are commonly discharged from wastewater treatment plants in trace levels resulting in soil, sediment, and groundwater contamination. Trace levels of three antidepressants: fluoxetine (Prozac), sertraline (Zoloft), and bupropion (Wellbrutin and Zyban) have been reported in natural streams. All three molecules are amphiphilic organic molecules with one or more reactive amine functional groups resulting in a positively charged molecule in pHs<8.0.

The main objective of this study was to determine sorption and transport behavior of these antidepressants in natural soils. Laboratory studies were conducted using two types of uncontaminated, natural soils – organic rich A-horizon soils (3-5% organic matter) and clay-rich B-Horizon soils containing iron-oxides (clay mineral content~20%). These soils were used to conduct batch sorption isotherm and column transport experiments. The antidepressants were measured using UV-Vis, HPLC, and LC-MS techniques.

Batch kinetic experiments results were used to determine the equilibrium times of aqueous phase and soil for each antidepressant which ranged from 2 to 14 days. Sorption isotherms for all three compounds were nonlinear and were fit using Freundlich model. The data showed fluoxetine and sertraline sorbed more strongly to the clay-rich B-horizon soil while bupropion sorbed more strongly to organic-rich A-horizon soil. This means the positively-charged fluoxetine and sertraline preferentially sorbed with negatively-charged clay minerals in B-horizon soils. Bupropion sorption behavior suggests partitioning into organic-rich A-horizon soils. Transport behavior was measured by injecting tracer solutions into glass chromatography columns packed homogenously with soil. Data from breakthrough curves generated during transport experiments confirm sorption behavior observed in batch isotherm experiments. Overall, the experiments gave insight to the fate and transport of these antidepressants. The results show strong implications for environmental management of effluents and discharges that contain pharmaceutical chemicals.