Photodegradation of sulfadiazine in different aquatic environments - Evaluation of influencing factors.

The presence of antibiotics, such as sulfadiazine (SDZ), in the aquatic environment contributes to the generation of antimicrobial resistance, which is a matter of great concern. Photolysis is known to be a major degradation pathway for SDZ in surface waters. Therefore, influencing factors affecting SDZ photodegradation in different aquatic environments were here evaluated in order to have a better knowledge about its persistence in the environment. Photodegradation of SDZ was found to be more efficient at higher pH (t = 6.76 h, at pH = 7.3; t = 12.2 h, at pH = 6.3), in the presence of humic substances (HS) (t between 1.76 and 2.42 h), as well as in the presence of NaCl (t = 1.00 h) or synthetic sea salts (t = 0.78 h). Using ˙OH and O scavengers, it was possible to infer that direct photolysis was the main pathway for SDZ photodegradation in ultrapure water. Furthermore, results under N purging confirmed that O was not relevant in the phototransformation of SDZ. Then, the referred observations were used for the interpretation of results obtained in environmental matrices, namely the final effluent of a sewage treatment plant (STPF), fresh and brackish water (t between 2.3 and 3.48 h), in which SDZ photodegradation was found to be much faster than in ultrapure water (t = 6.76 h).