Laboratory persistence and fate of fluoxetine in aquatic environments

The persistence and fate of fluoxetine, a selective serotonin reuptake inhibitor, has been investigated in laboratory-scale experiments, including studies with various aqueous solutions, water/sediment systems, and activated sludge-amended medium. The samples were placed in the dark and/or in a growth chamber fitted with fluorescent lamps simulating the ultraviolet output of sunlight. Over a period of 30 d, fluoxetine was hydrolytically and photolytically stable in all aqueous solutions except synthetic humic water (pH 7), in which the degradation rate was increased by approximately 13-fold in comparison with buffered solutions at the same pH. Fluoxetine rapidly dissipated from the aqueous phase in water/sediment systems, primarily because of distribution to sediments. The dissipation rate from the aqueous phase was similar between light and dark systems, indicating a low contribution of photodegradation to the dissipation of fluoxetine in this system. The potential impact of fluoxetine in aquatic environments would be decreased because of adsorption to sediments. Based on results of ready-biodegradability investigations, fluoxetine would not be expected to rapidly biodegrade in wastewater treatment plants. A photoproduct was detected only in a sample of synthetic humic water and was identified as norfluoxetine formed by demethylation. Results indicate that fluoxetine is relatively recalcitrant to hydrolysis, photolysis, and microbial degradation and that it is rapidly removed from surface waters by adsorption to sediment, where it appears to be persistent.