Degradation of Ketoprofen, Tenoxicam, and Meloxicam Drugs by Photo-Assisted Peroxidation and Photo-Fenton Processes: Identification of Intermediates and Toxicity Study

The non-steroidal anti-inflammatory pharmaceuticals ketoprofen, meloxicam, and tenoxicam were degraded by photo-assisted peroxidation (hv/H2O2) and photo-Fenton processes under simulated solar radiation (sunlight) and UV-C. Preliminary studies showed that the processes under UV-C and sun-photo-Fenton radiation showed similar degradation results. The sun-photo-Fenton was less sensitive to the concentration variation of the H2O2 oxidant. Given that, in general, the highest percentages of degradation were achieved using the sun-photo-Fenton system and that this radiation resembles solar radiation, this process was selected for further studies. From the results of a factorial design 23, in duplicate, the highest degradation condition within the studied levels was 400 mg L−1 of [H2O2], 1.75 mg L−1 of [Fe], and pH at 3–4 range. The kinetic degradation curve, monitored by the chemical oxygen demand (COD), could be represented by the pseudo-first-order model, and after 120 min the COD concentrations reached values below 2% of the initial demand. Degradation products from the three drugs were identified by high-performance liquid chromatography with coupled mass spectrometry (UCLAE-EM) and verified the toxicity of Escherichia coli and Salmonella enteritidis bacteria and of lettuce seeds (Lettuce Veneranda), indicating the formation of compounds that have lower molecular mass and can be more easily degraded, using this process as one of the stages of a system of treatment.