Photodegradation of sulfadiazine in different aquatic environments: evaluation of influencing factors

Abstract

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 (t1/​2 = 6.76 h, at pH = 7.3; t1/​2 = 12.2 h, at pH = 6.3), in the pres­ence of hu­mic sub­stances (HS) (t1/​2 be­tween 1.76 and 2.42 h), as well as in the pres­ence of NaCl (t1/​2 = 1.00 h) or syn­thetic sea salts (t1/​2 = 0.78 h). Us­ing ˙OH and 1O2 scav­engers, it was pos­si­ble to in­fer that di­rect pho­tol­y­sis was the main pathway for SDZ pho­todegra­da­tion in ul­tra­pure wa­ter. Fur­ther­more, re­sults un­der N2 purg­ing con­firmed that 1O2 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 (t1/​2 be­tween 2.3 and 3.48 h), in which SDZ pho­todegra­da­tion was found to be much faster than in ul­tra­pure wa­ter (t1/​2 = 6.76 h).