The present study aimed to evaluate the effect of the most common antidepressants on aquatic protozoa. Spirostomum ambiguum was used as the model protozoan. The biological activity of four antidepressants, namely fluoxetine, sertraline, paroxetine, and mianserin, toward S. ambiguum was evaluated. Sertraline was found to be the most toxic drug with EC₅₀ values of 0.2 to 0.7 mg/L. The toxicity of the antidepressants depended on the pH of the medium and was the highest in alkaline conditions. Sertraline was also the most bioaccumulating compound tested, followed by mianserin. Slow depuration was observed after transferring the protozoa from the drug solutions to a fresh medium, which indicated possible lysosomotropism of the tested antidepressants in the protozoa. The biotransformation products were identified using a high-resolution mass spectrometer after two days of incubation of the protozoa with the tested antidepressants. Four to six potential biotransformation products were observed in the aqueous phase, while no metabolites were detected in the protozoan cells. Because of the low abundance of metabolites in the medium, their structure was not determined.

A large amount of pharmaceuticals are flushed to environment via sewage system. The compounds are persistent in environment and are very difficult to remove in drinking water treatment processes. Degradation of fluoxetine (FLU) and fluvoxamine (FLX) by ferrate(VI) were investigated. For the 10 mg/L of FLU and FLX, 35% and 50% of the compounds were degraded in the presence of 50 mg/L FeO₄²⁻ within 10 minutes, respectively. After 10 minutes of the reaction, degradation of FLU and FLX is affected by formation of by-products which were likely more reactive with ferrate and competed in the reaction with FeO₄²⁻. In the case of FLU, the identified degradation by-products were hydrofluoxetine, N-methyl-3-phenyl-2-propen-1-amine, 4-(trifluoromethyl)phenol and 1-{[(1R,S)-1-Phenyl-2-propen-1-yl]oxy}-4-(trifluoromethyl)benzene. In the case of FLX, the degradation by-products were fluvoxamine acid and 5-methoxy-1-[4-(trifluoromethyl)phenyl]pent-2-en-1-imine. The results of the ecotoxicological study based on protozoa Spirostomum ambiguum have shown that 50 mg/L FeO₄²⁻ reduced toxicity of 10 mg/L of FLU and FLX by around 50%. However, in the case of FLX, the results of the ecotoxicological study suggested formation of slightly more toxic compound(s) than FLX during reaction with FeO₄²⁻. Application of ferrate(VI) is a viable option for drinking water treatment process; however, caution is needed due to formation of by-products with unknown human health risk. GRAPHICAL ABSTRACT

Silicated hydroxyapatite powders enriched with small amounts of manganese (Mn²⁺) cations were synthesized via two different methods: precipitation in aqueous solution and the solid-state method. The source of Mn²⁺ ions was manganese acetate, while silicon was incorporated using two different reagents: silicon acetate and sodium metasilicate. Powder X-ray diffraction (PXRD) analysis showed that the powders obtained via the precipitation method consisted of single-phase nanocrystalline hydroxyapatite. In contrast, samples obtained via the solid-state method were heterogenous and contaminated with other phases, (i.e., calcium oxide, calcium hydroxide, and silicocarnotite) arising during thermal treatment. The transmission electron microscope (TEM) images showed powders obtained via the precipitation method were nanosized and elongated, while solid-state synthesis produced spherical microcrystals. The phase identification was complemented by Fourier transform infrared spectroscopy (FTIR). An in-depth analysis via solid-state nuclear magnetic resonance (ssNMR) was carried out, using phosphorus ³¹P single-pulse Bloch decay (BD) (³¹P BD) and cross-polarization (CP) experiments from protons to silicon-29 nuclei (¹H → ²⁹Si CP). The elemental measurements carried out using wavelength-dispersive X-ray fluorescence (WD-XRF) showed that the efficiency of introducing manganese and silicon ions was between 45% and 95%, depending on the synthesis method and the reagents. Preliminary biological tests on the bacteria Allivibrio fisheri (Microtox®) and the protozoan Spirostomum ambiguum (Spirotox) showed no toxic effect in any of the samples. The obtained materials may find potential application in regenerative medicine, bone implantology, and orthopedics as bone substitutes or implant coatings.