Degradation of diclofenac using Advanced Oxidation Processes and identification of its degradation products by LC-HRMS

Abstract

The anthropogenic pollution of water is becoming a severe problem because of the increasing wastewaters generated by the industry and the population day by day. In this context, pharmaceuticals are products of special concern. Indeed, pharmaceuticals are used to improve the quality of life of humans and animals, but the effect of their accumulation in the aquatic system can be dangerous. This study is focused on diclofenac, which is a non-steroidal anti-inflammatory drug (NSAID) and is one of the priority substances that, according to the European Union, must be monitored in order to determine the risk for the environment. The main concern of these pollutants is the persistence in the environment as they are not biodegradable and, therefore, they are not completely eliminated by classical wastewater treatments. Advanced Oxidation Processes (AOPs) are a useful alternative to traditional water treatments. To perform the degradation of diclofenac, the most promising AOPs are direct photolysis with UV radiation and the combination with hydrogen peroxide. For this reason, in this work, the diclofenac was treated with UV/H2O2 and UV photolysis, achieving removals higher than 95% with UV/H2O2 and higher than 90% for UV. Experimental data fit well pseudo-first-order kinetics. Experiments were also done with only H2O2 and with solar light but the percentage of diclofenac removal in both cases was very low. Another related problem is the low concentration of these compounds in the superficial waters, and for this reason are called micropollutants. Thus, analytical technologies with high sensitivity are needed to detect these compounds in the environment and to allow the identification of their degradation products. Therefore, liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) has been used, in this work, to identify the degradation products. Fourteen intermediates have been detected and degradation pathways have been tentatively proposedFinally, an estimation of the toxicity of the final products of the experiment with the computerized predictive system ECOSAR was carried out, because the transformation products can be more detrimental than the main product.