In this study, the purpose was to investigate the histopathological, genotoxic effect, oxidative stress and cell death due to Metronidazole (MTZ), which is a 5-nitroimidazole compound used widely for the treatment of anaerobic organism infections in fish and humans on gill and liver tissues of Oncorhynchus mykiss.Trout fishes were exposed to 5, 10, and 20 mg/L of MTZ in the aquariums for 2, 4 and 8 days. Staining technics namely H&E, NOS immunohistochemistry, and TUNEL were performed to determine histopathological changes, oxidative damage and apoptosis. Additionally, smear preparations were also prepared from gill blood for genotoxic evaluations. The organ damage started in the 2nd day with 5 mg/L MTZ application and effects increased per duration and dose-dependent manner. It was observed that the gills had the primary and secondary lamellae lengths, with formation of clavate lamellae, fusion in secondary lamellae, separation of epithelium and aneurysm. Regional necrosis, vacuolization of hepatocytes, pycnotic nucleus, enlarged sinusoids were also determined in the liver. NOS immunoreactivity increased with the inducible immunoreactivity (iNOS) that was more prominent when compared to the endothelial immunoreactivity (eNOS). Apoptotic immunoreactivity was higher in the 10 mg 8th day experimental group at liver and gills, and was lower 20 mg 8th day experimental group. When the gills and liver compared with each other, in all doses, immunoreactivity was lower in gills, compared with liver. Genotoxic examinations showed that both number of micronucleated erythrocytes and nuclei abnormalities were higher in MTZ-treated groups.

In this work the risk posed to seawater organisms, predators and humans is assessed, as a consequence of exposure to 12 organic micro-pollutants, namely metronidazole, trimethoprim, erythromycin, simazine, flumequine, carbaryl, atrazine, diuron, terbutryn, irgarol, diphenyl sulphone (DPS) and 2-thiocyanomethylthiobenzothiazole (TCMTB). The risk assessment study is based on a 1-year monitoring study at a Spanish marine fish farm, involving passive sampling techniques. The results showed that the risk threshold for irgarol concerning seawater organisms is exceeded. On the other hand, the risk to predators and especially humans through consumption of fish is very low, due to the low bioconcentration potential of the substances assessed.

Nonalcoholic fatty liver disease is a hepatic disorder with deposition of fat droplets and has a high risk of progression to steatosis-related hepatitis and irreversible hepatic cancer. Metronidazole (MNZ) is an antiprotozoal and antimicrobial agent widely used to treat patients infected with anaerobic bacteria and intestinal parasites; however, MNZ has also been shown to induce liver tumors in rodents. To investigate the effects of MNZ on steatosis-related early-stage hepatocarcinogenesis, male rats treated with N-nitrosodiethylamine following 2/3 hepatectomy at week 3 were received a control basal diet, high fat diet (HFD), or HFD containing 0.5% MNZ. The HFD induced obesity and steatosis in the liver, accompanied by altered expression of Pparg and Fasn, genes related to lipid metabolism. MNZ increased nuclear translocation of lipid metabolism-related transcription factor peroxisome proliferator-activated receptor gamma in hepatocytes, together with altered liver expression of lipid metabolism genes (Srebf1, Srebf2, Pnpla2). Furthermore, MNZ significantly increased the number of preneoplastic liver foci, accompanied by DNA double-strand breaks and late-stage autophagy inhibition, as reflected by increased levels of γ-H2AX, LC3, and p62. Therefore, MNZ could induce steatosis-related hepatocarcinogenesis by inducing DNA double-strand breaks and modulating autophagy in HFD-fed rats.

In Egypt, antibiotic sensitivity analysis for Helicobacter pylori is not routinely performed. We aimed to identify the clarithromycin and metronidazole resistance directly from gastric biopsies for better guide treatment regimens. This cross-sectional descriptive study included 75 adult dyspeptic patients referred to the upper endoscopy unit in Suez Canal University Hospital, Ismailia, Egypt. Gastric biopsies were taken for rapid urease test (RUT) and cultured on brucella agar with antibiotic supplements. Genomic DNA was extracted directly from the specimen, and PCR was performed for direct detection of H. pylori. Also, to explore clarithromycin and metronidazole resistance, mutations in the 23S rRNA gene and the rdxA gene were investigated. We found that 60 samples were positive to RUT (80%), and only 4 samples were positive by culture. UreC gene was detected in 45 specimens. Meanwhile, 26 isolates were contained mutations at positions 2142 and 2143. Amplification of the metronidazole rdx gene was performed by conventional PCR. Out of 45 isolates, DNA sequence analysis of PCR product showed the wild type (ACA) in 9 isolates, while the mutant type (ATA) was detected in 28 isolates. We found a significant proportion of clarithromycin and metronidazole resistance among H. pylori infected patients in our region.

The single and binary adsorptions of metronidazole (MNZ) and dimetridazole (DTZ) on activated carbon (F400) and activated carbon felt (ACF) were studied in this work. The adsorption capacities of both materials towards antibiotics were determined at pH = 7 and 25 °C. The π-π dispersive interactions controlled the adsorption mechanism of both antibiotics. The Prausnitz-Radke isotherm interpreted quite well the single adsorption equilibrium data of DTZ and MNZ on F400 and ACF. DTZ presented higher affinity for both adsorbents because the DTZ had higher electronic density and smaller molecular size than those of MNZ. The capacity of F400 for adsorbing DTZ or MNZ was higher than that of ACF because the ACF presented higher microporosity and surface area, which was unavailable for adsorbing DTZ and MNZ due to pore restriction. The binary equilibrium data on F400 and ACF were interpreted reasonably well with the extended Langmuir multicomponent isotherm and Sheindorf-Rebuhn-Sheintuch isotherm, respectively. The competitive adsorption of MNZ and DTZ was antagonistic, but not cooperative. In the binary adsorption, both antibiotics were adsorbed simultaneously, competed for the same adsorption sites, and both carbon materials presented higher selectivity towards DTZ than MNZ. Moreover, if one antibiotic was adsorbed first, then another antibiotic could be adsorbed on unoccupied sites or by displacing the antibiotic already adsorbed. The results revealed that the binary adsorption equilibrium was independent on the way of contacting the antibiotics.

The efficiency of the following systems: photolysis (UV-C only), photocatalysis with titanium-dioxide (UV-C/TiO₂), photocatalysis with granular-activated carbon (UV-C/GAC), and by adsorption on GAC, was assessed under different initial contaminant concentrations, i.e., 0.1–100 mg L⁻¹. The experiments were conducted in a batch photocatalytic reactor (1.9 L and 32 W UV power). It was found that UV-C/TiO₂ and UV-C/GAC systems showed fairly equal removal efficiencies under lower MNZ concentrations (0.1–5 mg L⁻¹) compared to higher concentrations at similar catalyst loading of 2.5 g L⁻¹. A decline in removal rate (based on first-order reaction) was observed with respect to increase in initial MNZ concentration in all systems. MNZ removal by adsorption on GAC was much lesser compared to UV-C only, UV-C/TiO₂, and UV-C/GAC systems. The adsorption data well correlated with the Freundlich model indicated that the adsorption was on the heterogeneous surface of the catalyst. The effectiveness of the systems were evaluated by calculating electrical energy consumed per order (E EO). The lowest E EO value was found to be for UV-C/TiO₂ (0.03 kWh m⁻³ order⁻¹) for the degradation of 0.1 mg L⁻¹ of MNZ compared to UV-C/GAC (0.06 kWh m⁻³ order⁻¹), UV-C only (0.15 kWh m⁻³ order⁻¹), and adsorption (0.44 kWh m⁻³ order⁻¹). The total organic carbon and nitrogen ion analyses have confirmed the mineralization of MNZ via aliphatic carboxylic acid compounds in the photocatalytic system. Overall, the photocatalytic system seems to be an energy-efficient treatment option for the removal of MNZ and similar other micropollutants.

Herein, the efficient degradation of a highly consumed antibiotic known as metronidazole (MNZ) in aqueous solutions using Co/g-C₃N₄/Fe₃O₄ nanocomposite under visible light irradiation was accomplished. Initially, the photocatalyst (Co/g-C₃N₄/Fe₃O₄) was synthesized by a simple hydrothermal method and then characterized by several analytical techniques, namely EDS, SEM, XRD, UV–vis DRS, and FTIR. The efficiency of the synthesized photocatalyst with regard to the degradation of the studied antibiotic (MNZ) under visible light irradiation was fully evaluated. The influential operational parameters affecting the efficiency of the degradation process such as pH (2–10), nanocomposite dosage (0.2–1 g/L), MNZ concentration (5–20 mg/L), and irradiation time (0–80 min) were optimized. The results revealed that the maximum degradation efficiency for MNZ was obtained under the following conditions: irradiation time of 60 min, pH = 8, MNZ concentration of 5 mg/L, and photocatalyst dosage of 0.7 g/L. In addition, the degradation of MNZ followed the pseudo-first-order kinetic model. The best rate constant (k) value was determined to be 0.0102 min⁻¹ with the correlation coefficient (R²) of 0.992. According to the results of the quenching tests, it was found out that hydroxyl radicals (OH°) were the main species responsible for the MNZ degradation. Furthermore, the applied photocatalyst (Co/g-C₃N₄/Fe₃O₄) exhibited a high level of recovery and stability after five cycles of reuse. Co/g-C₃N₄/Fe₃O₄/Vis system exhibited an excellent performance in the treatment of wastewater and real water samples. Finally, it was concluded that the synthesized nanocomposite could be potentially used as a promising and suitable photocatalyst in the degradation of other antibiotics.

In this study, ZnCo₂O₄/g-C₃N₄/Cu is synthesized as a new and highly effectual solar light-driven heterogeneous photocatalyst. The prepared photocatalyst is characterized using FT-IR, XRD, XPS, DRS, FESEM, TEM, EDS, and elemental mapping techniques. The performance of ZnCo₂O₄/g-C₃N₄/Cu is studied towards the metronidazole (MNZ) degradation under solar light irradiation. The kinetics of MNZ degradation and efficacy of the operational parameters comprising the initial MNZ amount (10–30 mg L⁻¹), photocatalyst dosage (0.005–0.05 g L⁻¹), pH (3–11), and contact time (5–30 min) on the MNZ degradation process are investigated. Surprisingly, the ZnCo₂O₄/g-C₃N₄/Cu nanocomposite presents a privileged photocatalytic performance towards the MNZ degradation under solar light irradiation. The enhanced photocatalytic activity of this photocatalyst can be ascribed to the synergistic optical effects of ZnCo₂O₄, g-C₃N₄, and Cu. The value of band gap energy for ZnCo₂O₄/g-C₃N₄/Cu is estimated to be 2.3 eV based on the Tauc plot of (αhν)² vs. hν. The radical quenching experiments confirm that the superoxide radicals and holes are the principal active species in the photocatalytic degradation of MNZ, whereas the hydroxyl radicals have no major role in such degradation. The as-prepared photocatalyst is simply isolated and recycled for at least eight runs without noticeable loss of the efficiency. Using the natural sunlight source, applying a very low amount of the photocatalyst, neutrality of the reaction medium, short reaction time, high efficiency of the degradation procedure, utilizing air as the oxidant, low operational costs, and easy to recover and reuse of the photocatalyst are the significant highlights of the present method. It is supposed that the current investigation can be a step forward in the representation of an efficacious photocatalytic system in the treatment of a wide range of contaminated aquatic environments.

One of the most important wastewater treatment processes is microelectrolysis, which is extensively used in the primary treatment of pharmaceutical wastewater. In this study, microelectrolysis, as a pretreatment method for the refractory metronidazole pharmaceutical wastewater (MPW) of choice, was improved using the Fenton process and used to remove the chemical oxygen demand (COD) and improve the biochemical capability of MPW. The results showed that the highest COD removal of 40.8% was obtained in the presence of optimized significant factors and the BI (BI = biochemical oxygen demand over five days/COD) of MPW increased from 0.10 to 0.31. In addition, the ultraviolet–visible (UV–Vis) spectroscopy demonstrated that metronidazole in MPW was effectively removed during the combined processes. All these results showed that microelectrolysis combined with Fenton oxidation for MPW was an effective treatment process to achieve higher COD removal and biodegradability improvement. Finally, the breakthrough curves at different flow rates were measured to prove the feasibility of the combined process under optimal conditions.

AgClₓBr₁₋ₓ composites with different halogen molar ratios (Cl/Br) were prepared by a facile ultrasound-assisted ion-exchange method. The formation of close contact between AgCl and AgBr facilitated the transportation of photoexcited charge carriers and contributed to the enhanced visible-light-driven photocatalytic degradation of different kinds of antibiotics. The AgClₓBr₁₋ₓ composites had a sphere-like morphology and tunable band gaps from 2.95 to 2.57 eV depending on Cl/Br mole ratios. Besides, the AgClₓBr₁₋ₓ composite was optimized by varying halogen mole ratios (Cl/Br) to achieve the highest photocatalytic activity. Results indicated that AgCl₀.₇₅Br₀.₂₅ showed the best photocatalytic degradation performance, which was about 2.36 and 2.78 times that of the single AgCl towards ciprofloxacin (CIP) and metronidazole (MNZ) degradation, respectively. Meanwhile, a possible photocatalytic degradation mechanism was discussed, and results indicated that the holes (h⁺) and •OH were the dominant active species in the AgCl₀.₇₅Br₀.₂₅ system.