Impact of Hydrogen Peroxide on the UVC Photolysis of Diclofenac and Toxicity of the Phototransformation Products

Abstract

The aim of this study was to investigate the effect of hydrogen peroxide on the UVC photolysis of diclofenac (DCF) in aqueous solution. The experimental results confirmed very high effectivity of UVC direct photolysis of diclofenac. Moreover, it was found that H2O2/UV only slightly improved photodegradation; however, the addition of hydrogen peroxide into the reaction system affected the mechanism of DCF decomposition. Kinetics of the DCF reaction with ⋅OH radicals in the UV/H2O2 process was determined. For both processes, namely, photolysis and UV/H2O2, an in-depth analysis focused on the formation of phototransformation products of DCF (TPs) was performed. To the best of our knowledge, such comprehensive comparison of diclofenac photodegradation via UVC photolysis and UV/H2O2 has not been presented so far. Although there were no significant differences with regard to the rate of diclofenac degradation by photolysis and UV/H2O2, different oxidation products were found to be associated with the two considered processes. Furthermore, the H2O2/UV treatment increased toxicity towards Vibrio fischeri, while direct UVC photolysis had no significant effect on toxicity. The increase in toxicity can be attributed to the breakdown of DCF and formation of much more toxic TPs in the course of the H2O2/UVC process.

Enhanced Removal and Toxicity Decline of Diclofenac by Combining UVA Treatment and Adsorption of Photoproducts to Polyvinylidene Difluoride

“…Diclofenac is classified by the EU Directive 93/67/EEC as “harmful to aquatic organisms” [ 54 , 55 ] and due to its low log K ow of 4.51 as toxic [ 56 ]. The EC 50 toxicity towards Vibrio fischeri was determined to be 19.7 mg L −1 (with a confidence interval of 17.9 to 22.2) which is comparable to literature value (15.78 mg L −1 [ 56 ]).…”

“…The toxicity unit (TU = 100/EC 50% , EC 50% is the effect concentration at which 50% of effect occurs; the higher the TU, the higher the toxicity) and G L level (dilution level at which the inhibition is below 20% for the first time; the higher the G L level, the higher the toxicity) at 90 min of UVA irradiation doubles compared to an untreated diclofenac solution. The evaluation of the toxicity of diclofenac treated with UVA light is controversial discussed [ 52 , 56 , 57 , 58 ]. But the conditions (concentration of diclofenac, UVA light wavelength, UVA light intensities, additives in water, tested biological organism) do differ and lead to different transformation products and concentrations of these products.…”

Comparison of Different Advanced Oxidation Processes (AOPs) and Photocatalysts for the Degradation of Diclofenac

“…In our setup it was used a lamp that emits at longer wavelength, thus, it is likely that the hydrogen peroxide participates in the degradation process since the beginning. In addition, Ledakowicz reported that H 2 O 2 in quantity of millimoles and above prevents the radiation from reaching the substrate, as the photons are almost completely absorbed by the oxidant itself, so increasing its concentration does not lead to a greater conversion due to the fixed amount of photons provided by the lamp [45] …”

“…In addition, Ledakowicz reported that H 2 O 2 in quantity of millimoles and above prevents the radiation from reaching the substrate, as the photons are almost completely absorbed by the oxidant itself, so increasing its concentration does not lead to a greater conversion due to the fixed amount of photons provided by the lamp. [45]…”

Removal of Diclofenac by UV-B and UV-C Light-Emitting Diodes (LEDs) Driven Advanced Oxidation Processes (AOPs): Wavelength Dependence, Kinetic Modelling and Energy Consumption

“…While it is not the focus of this work, in this regard, several studies have carefully identified the DCF degradation by-products using liquid chromatography-mass spectroscopy (LC-MS) often associated with the ecological structure activity relationship (ECOSAR) simulation, where the latter allows the estimation to aquatic organisms by using the structure activity relationships of the by-product. The research available extensively covers the by-products formed during UV [18,30,44], UV/ H 2 O 2 [18,30], UV/FC [17], and water chlorination [52]. In general, it can be concluded that predicted chronic ecotoxicity towards fish, daphnids and algae is reduced [44]; however, some intermediates possess higher toxicity than DCF itself [17].…”