Study On Photolytic Behavior Of Diclofenac In Aqueous Environment

In recent years, pharmaceuticals are a novel class of pollutant whose presence is pseudo-persistent inthe aquatic environment due to an incomplete degradation in the sewage treatment plant pharmaceutical,making them of acute concern. Personal Care Products (PPCPs) have been found polluting a wide range ofaquatic environments including groundwater, surface water and drinking water. Accordingly, this emergingtrend of environmental pollution and their metabolites have the potential to have an adverse impact onaquatic environments. The behavior and fate of pharmaceuticals in aquatic environments remain poorlyunderstood, and therefore study of these phenomena would be valuable. Photodegradation is one of themain abiotic degradation pathways of PPCPs in the aqueous environment. Diclofenac (DCF) is a syntheticnon-steroidal anti-inflammatory drug (NSAID), mostly used as its sodium salt in medical care as anantiarthritic, analgesic and antirheumatic. This paper investigated the photodegradation kinetics,photodegradation mechanisms, photodegradation pathways and photoproducts and studied the effects ofaqueous environmental factors on on photodegradation of diclofenac under simulated sunlight.Photodegradation mechanisms of diclofenac were investigated. The results indicated that thephotodegradation pathways of diclofenac proceed via pseudo first-order kinetics well. Quenchingexperiments demonstrates that the photodegradation of diclofenac by simulated sunlight is the sum of thedegradation by direct photodegradation and self-sensitization in the aquatic environment (directphotodegradation contributed to the main degradation of DCF with little contributed of self-sensitization).Toxicity test indicated that the generation of some more toxic products of diclofenac than diclofenac. Threeintermediates were detected by HPLC-MS, which were8-hydroxy-9,9a-dihydro-4aH-carbazol-1-yl) aceticacid,8-hydroxy-9,9a-dihydro-4aH-carbazol-1-yl) acetal dehyde and8-chloro-9,9a-dihydro-4aH-carbazol-1-yl) acetic acid. Moreover, we speculated degradation pathway for pure diclofenac undersimulated sunlight.Hydrolytic stability of diclofenac was investigated. The results indicated that the hydrolysis ofdiclofenac belongs to acidic hydrolysis. The hydrolysis rate was found to increase with increasingtemperature and the presence of metals ions could promote the hydrolysis of diclofenac. This paper studies the effect of aquatic environmental factors on photodegradation of diclofenac under simulated sunlight. Thephotodegradation rate was found to increase with increasing temperature. The rate constant graduallyincreased when the pH increased from3to5and decreased as the pH increased from5to8, finally,increased when the pH further increased from8to12. Different forms of nitrogen inhibited thephotodegradation of diclofenac due to the absorption wavelength overlaps the absorbance wavelengthregion of diclofenac. The addition of HCO3is anticipated to scavenge hydroxyl radicals that can inhibit thephotolysis of diclofenac. Halide ions inhibited the photodegradation of diclofenac. On the one hand,chloride ions are likely to act as scavengers of³DCF^*, on the other hand, can form reactive oxygen species,moreover, the absorption wavelength overlaps the absorbance wavelength region of diclofenac. Metal ionsinhibited the photodegradation of diclofenac. The mechanisms of inhibting effect of metal ions ondiclofenac photodegradation were proposed as followed:(1) the absorption wavelength overlaps theabsorbance wavelength region of diclofenac,(2) complex hydrated metal cations was formed with metalions and H₂O, The hydrated metal cations lower the transmittance of system, moreover, hydrated metalcations can form reactive oxygen species,(3) precipitation was formed with metal ions and OH^-. Thedegradation rate was found to decrease with increasing surfactant concentration. The result can beattributed to the strong absorption of surfactant in an overlapping wavelength range as the absorbance ofdiclofenac, moreover, formed micelles of Tween-80and solubilization of diclofenac by sodium dodecylbenzene sulphonate. Acetone promote the photodegradation of diclofenac due to formed³DCF^*and H₂O₂promote the photodegradation of diclofenac due to formed hydroxyl radicals. Pigment inhibited thephotodegradation of diclofenac due to the overlapping absorption spectra with diclofenac and their colour.Humic acid inhibited the photodegradation of diclofenac due to the overlapping absorption spectra,scavengers of³DCF^*and formed³HA^*.Photodegradation rate of diclofenac in different waters and in the presence of different forms ofnitrogen changes with different PE values in the aquatic environment under simulated sunlight wereinvestigated. The results show that different forms of nitrogen coexist in the aquatic environment had anobvious antagonistic action. The experimental approach using Box-Behnken design and response surfacemethodology to determine how these components interact to control diclofenac degradation is described.The photodegradation of diclofenac in the absence/presence of nitrate, Fe (â…¢) and chloride under simulated sunlight has been studied. A simple linear model is given that very well describes the results obtained andthe predicted values of photodegradation rate were in good agreement with experimental values. Thephotodegradation of diclofenac in the absence/presence of cetyltrimethyl ammonium bromide, crystalviolet and humic acid under simulated sunlight has also been studied. A simple linear model is given thatvery well describes the results obtained and the predicted values of photodegradation rate were in goodagreement with experimental values also.