Environmental Persistence of the Antidepressant Fluoxetine and Its Pharmaceutical Alternative: Kinetics of Oxidation and Mathematical Simulations

Abstract

To investigate the impact of antidepressants (ANT) in water, estimates of the direct and indirect photolysis of standard fluoxetine hydrochloride (FLX) and a pharmaceutical alternative, fluoxetine sulfate (FLXSO4), were evaluated. The second-order kinetic constants of the ANT and reactive photoinduced species (RPS) (singlet oxygen, 1O2; hydroxyl radicals, HO•; and triplet excited states of chromophoric dissolved organic matter, 3CDOM*) were obtained by competition kinetics under simulated solar radiation. These parameters were used in combination with water characteristics to assess the environmental persistence of the ANT based on mathematical kinetic simulations. The results indicated that the reactions with HO• (kFLX,HO• = (2.54 ± 0.06) × 109 L mol−1 s−1; kFLXSO4,HO• = (3.07 ± 0.03) × 109 L mol−1 s−1) and 3CDOM* (kFLX,3CDOM* = (2.67 ± 0.05) × 109 L mol−1 s−1; kFLXSO4,3CDOM* = (1.48 ± 0.03) × 109 L mol−1 s−1) play a more important role in the degradation of ANT compared to the reactions with 1O2 (kFLX,1O2 = (1.37 ± 0.07) × 107 L mol−1 s−1; kFLXSO4,1O2 = (1.63 ± 0.33) × 107 L mol−1 s−1). The main removal pathways were biodegradation and direct photolysis with persistence in the following order FLX > FLXSO4. Therefore, the presence of sulfate anions can contribute to the degradation of fluoxetine in sunlit environmental waters.