Kinetic studies and characterization of photolytic products of sulfamethazine, sulfapyridine and their acetylated metabolites in water under simulated solar irradiation

Sulfapyridine (SPY), sulfonamide (SA) typically used in human therapies, and veterinary SA sulfamethazine (SMZ), are amongst the two SAS most frequently detected in effluent wastewater and surface water respectively. Within this context, this study reports the behaviour of both SAs and their acetylated metabolites, AcSPY and AcSMZ, under artificial irradiance conditions in both high performance liquid chromatography (HPLC) water and in reclaimed wastewater, in order to compare the influence of dissolved organic matter (DOM) and also inorganic matter in the photolysis kinetics. Estimated degradation rate constants (k) ranged from 0.063 h−1 (SPY) to 2.808 h−1 (AcSPY), both in HPLC water, with corresponding half-lives (t1/2) of 10.93 h and 0.25 h, respectively. A total of 10 different photodegradation products were identified during the photolytic transformation of SPY and 7 for SMZ, through ultra-performance liquid chromatography-quadrupole time of flight mass spectrometry analyses (UPLC-QqTOF-MS), which allowed for exact mass measurements. Regarding the acetylated metabolites, 3 photoproducts were generated for AcSMZ and one for AcSPY. The desulfonated products of each of the four analytes under study were the most relevant photodegradation products identified.

► The photodegradation kinetics of selected sulfonamides has been investigated.
► The behaviour of acetylated metabolites under irradiation has been studied for the first time.
► Effects of dissolved organic matter on the photodegradation kinetics have been evaluated.
► New photodegradation products for the different sulfonamides have been identified.
► The molecular structures and masses of photolytic products were accurately calculated.