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The present study investigates the transformation of the antidepressant fluoxetine (FLX) by photo- and biodegradation and shows similarities and differences in transformation products (TPs). TPs were identified using LC–high-resolution mass spectrometry with positive and negative electrospray ionization. In a sunlight simulator, photodegradation was carried out using ultrapure water (pH 6, 8, and 10) and surface water (pH 8) to study the effect of direct and indirect photolysis, respectively. The well-known metabolite norfluoxetine (NFLX) proved to be a minor TP in photolysis (≤2% of degraded FLX). In addition, 26 TPs were detected, which were formed by cleavage of the phenolether bond (O-dealkylation) which primarily formed 3-(methylamino)-1-phenyl-1-propanol (TP 166) and 4-(trifluoromethyl)­phenol, by hydroxylation of the benzyl moiety, by CF3 substitution to benzoic aldehyde/acid, and by adduct formation at the amine group (N-acylation with aldehydes and carboxylic acids). Higher pH favors the neutral species of FLX and the neutral/anionic species of primary TPs and, therefore, photodegradation. In zebrafish embryos, the bioconcentration factor of FLX was found to be 110, and about 1% of FLX taken up by the embryos was transformed to NFLX. Seven metabolites known from photodegradation and formed by hydrolysis, hydroxylation, and N-acylation as well as three new metabolites formed by N-hydroxylation, N-methylation, and attachment of an amine group were identified in zebrafish embryos. The study highlights the importance of considering a broad range of TPs of FLX in fresh water systems and in ecotoxicity tests and to include TP formation in both environmental processes and metabolism in organisms.

Fluoxetine has been recognized as one of the most toxic pharmaceuticals in the aquatic environment. Since there is growing evidence that the toxic potential of fluoxetine in surface waters is markedly influenced by its own metabolism in aquatic species, this study investigated the biotransformation of fluoxetine in the zebrafish embryo − an aquatic model organism of intermediate complexity. Zebrafish embryos were exposed to 0.1, 1.0, 10, 50, and 5000 μg/L of fluoxetine from 48 to 120 h postfertilization (hpf), and the accumulation of fluoxetine and its metabolites was analyzed over time. Additionally, depuration of fluoxetine and its metabolites from 96 to 120 hpf was investigated, and autoinhibitory effects of fluoxetine on phase I biotransformation were analyzed. Exposure to 5000 μg/L fluoxetine resulted in elevated 7-ethoxyresorufin-O-deethylase (EROD) activity of cytochrome P450 enzymes and continuous accumulation of fluoxetine and 11 fluoxetine metabolites. Embryos exposed to 10 and 50 μg/L fluoxetine were able to reduce fluoxetine accumulation from 94 to 120 hpf. During depuration, accumulation of fluoxetine and most metabolites was clearly reduced, and biotransformation shifted in favor of norfluoxetine, the primary fluoxetine metabolite in humans. Findings demonstrated that norfluoxetine is the only metabolite of fluoxetine that accumulates in zebrafish embryos at environmentally relevant exposure scenarios.

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The dispersion behavior of carbon nanotubes (CNTs) is influenced by both their physicochemical properties and by the aqueous media properties (e.g. ionic strength, presence of divalent cations and natural organic matter) in which they are dispersed. In the current study, the dispersibility and dispersion stability of four multi-walled CNTs (MWCNT) and a single walled CNT (SWCNT) with different physicochemical properties were investigated in three freshwater growth media (with and without natural organic matter; NOM) used in algae and daphnia ecotoxicity studies. CNT dispersion behavior was also investigated in a natural freshwater for comparison. SWCNTs and non-functionalized MWCNTs showed similar dispersibility irrespective of the media type (SWCNTs = 0.5-0.9 mg/L; MWCNTs = 1.5-2.8 mg/L). Functionalized MWCNTs exhibited higher dispersion concentrations, but were more dependent upon the ionic strength and divalent cation concentration of each media (MWCNT-COOH = 3.0-6.6 mg/L). In contrast, CNT surface oxygen content had no influence on CNT dispersibility in the natural water (all MWCNTs = 0.9-1.4 mg/L). Functionalized MWCNTs were affected more by the differences in media properties than non-functionalized MWCNTs. The dispersed CNT concentration decreased over time for all CNT types and in all media due to sedimentation, but was influenced by both CNT and media properties. The study shows how a complex interplay between CNT and media properties can influence the environmental fate of CNTs. Furthermore, the study demonstrates how different CNT types and/or ecotoxicological media in aquatic tests influences the dispersion behavior of the CNTs, and thus their exposure and toxicity to aquatic organisms.