Effects of environmental factors on nitrofurantoin photolysis in water and its acute toxicity assessment

Photochemical transformation of the uricosuric drug benzbromarone in aqueous solutions exposed to UV irradiation

As one of benzophenone-derived drugs, benzbromarone (BBM) has been widely used to reduce blood uric acid, treat gout, and gouty arthritis. Understanding the transformation and fate of BBM in natural and engineered systems is critical for its ecological risk assessment. In this study, we systematically investigated the photochemical behavior of BBM in aqueous solutions under laboratory UV254 irradiation. UV-vis spectra show that an aqueous solution of BBM is capable of absorbing UV photons at 200-400 nm. Spectroscopic titration indicates that BBM with a pKa value of 4.83 ± 0.17 is present mainly as the phenolate form under circumneutral conditions. BBM undergoes rapid direct photolysis when exposed to UV254 irradiation and the quantum yields were determined to be 0.0105 and 0.0196 mol E-1 for phenol and phenolate forms, respectively. The heavy atom effect of bromine and spin-orbit coupling effect of aromatic ketone make dibromophenol and carbonyl moieties the critical chromophores accounting for the high photoreactivity of BBM. Laser flash photolysis and electron paramagnetic resonance studies suggest that the photolysis of BBM is initiated by ultrafast photodebromination and Norrish I cleavage. The high yield of bromide determined by ion chromatograph highlights the importance of photodebromination. Due to the light screening effect of wastewater components, the photolysis of BBM in hospital wastewater is inhibited. Photo-induced modification of the dibromophenol moiety of BBM likely generates photoproducts showing toxicity to luminescent bacteria. Overall, our results reveal that photochemical reaction under UV irradiation plays an important role in the attenuation of BBM in engineered water.

Photostability evaluation of manidipine tablets and structural determination of its photoproducts

Manidipine (MP) is a dihydropyridine drug, which is treated for the reduction of high blood pressure. The aim of this study is to clarify the photochemical behavior of MP in the case of ultraviolet light (UV) irradiation for MP tablets (Calslot® tablets). The tablets and its altered forms (powders and suspensions) were UV-irradiated using a black light, and residual amounts of active pharmaceutical ingredients (APIs) were monitored by high-performance liquid chromatography (HPLC). Due to the photoproducts of MP were detected in HPLC chromatograms, the elucidation of their chemical structures was carried out utilizing electrospray ionization tandem mass spectrometry (LC-ESI-MS/MS). As a result, APIs in Calslot® tablets were almost completely photodegraded in the case that Calslot® tablets were suspended in an aqueous media along with the generation of some MP photoproducts. LC-ESI-MS/MS analysis clarified the chemical structures of three MP photoproducts, indicating that they were a pyridine analogue, benzophenone and a hydrolysate. Benzophenone was a main MP photoproduct. It was possible that MP might be firstly oxidized to form its pyridine analogue, followed by the oxidation of a dimethyl methylene moiety. This moiety seemed to be eliminated as a benzophenone, and the cleavage of an ester bond of the residual moiety resulted in the generation of a hydrolysate. Finally, toxicological potencies of MP and its photoproducts were predicted in silico toxicity evaluation, suggesting some of biological effects of the photoproducts might be altered compared with MP.

Kinetics of the photolysis of pyridaben and its main photoproduct in aqueous environments under simulated solar irradiation

The photolytic fate of pyridaben and its main photolysis product was investigated in different aqueous solutions. Results showed that the photolysis of pyridaben followed pseudo first-order kinetics or the hockey-stick model. In buffer solutions, the half-life of pyridaben was the shortest at pH 4, while the degradation rate within 24 h was the highest at pH 9. Humic acids (HA) at concentrations of 1-20 mg L^-1 favored the photolysis of pyridaben while fulvic acids (FA) did not have a significant effect. Nitrate at low concentrations (0.01 mM) accelerated the photolysis and Fe(iii) at high concentrations (0.01 and 0.1 mM) significantly inhibited the photolysis. The photolysis rate of pyridaben in rainwater, tap water, and river water was significantly higher than that in distilled water. The half-lives in distilled water, rainwater, tap water, river water, and pond water were 2.36, 1.36, 1.61, 1.77, and 2.68 h, respectively. Ultra-high-performance liquid chromatography/high-resolution mass spectrometry identified M328 as a photolysis product. The degradation of M328 followed pseudo first-order kinetics in distilled water, buffer solutions and aqueous solutions fortified with HA. The half-lives of M328 were in the range of 7.07-13.95 h. These results are essential for further environmental risk assessment of pyridaben.