Photolysis of sulfamethoxypyridazine in various aqueous media: Aerobic biodegradation and photoproducts identification by LC-UV-MS/MS

In recent years, interest is growing continuously in the occurrence, fate, and possible effects of pharmaceutical compounds residues in the environment. Sulfonamides are one of the most frequently used antibiotics in human and veterinary medicines worldwide especially in Asia and Africa. Therefore
mitigation processes are of interest. Photodegradation and biodegradation are the potentially significant removal mechanisms for pharmaceuticals in aquatic environments.
The photolysis of sulfamethoxypyridazine (SMZ) using a medium pressure Hg-lamp was evaluated in three different media: Millipore water pH 6.1 (MW), effluent from sewage treatment plant pH 7.6 (STP), and buffered demineralized water pH 7.4 (BDW). Identification of transformation products (TPs) was performed by LC-UV-MS/MS. The biodegradation of SMZ using two tests from the OECD series was studied: Closed Bottle test (CBT; OECD 301 D), and Manometric Respirometry test (MRT; OECD 301 F).
The results showed that SMZ was removed completely within 128 min of irradiation in the three media, but they differ only in the degradation rate. However, no dissolved organic carbon (DOC) removal was observed in BDW and little DOC removal was observed in MW and STP, thus indicating the formation of nearly abundant TPs. Analysis by LC-UV-MS/MS resulted in the detection of up to six TPs of photolysis in MW, but only one of them was detected in STP and BDW. The observed difference may be due to pH or buffer salts differences. The hydroxylation of SMZ represents the main photodegradation pathway. In biodegradation tests, it was found that SMZ was not readily biodegradable in both CBT and MRT so it may pose a risk to the environment.
Advanced oxidation process for SMZ and biodegradation tests for photodegradation samples will be performed. Further research on SMZ and its TPs, including environmental samples analysis, as well as toxicity tests are strongly recommended to know its environmental impact.