Effect of Different Lead and Cadmium Salts on the Photolytic Degradation of Two Typical Fluoroquinolones under Natural Sunlight Irradiation

This study investigated the effects of different lead and cadmium salts (Pb(NO3)2, Cd(NO3)2, PbCl2, and CdCl2) on the photolytic degradation of two typical fluoroquinolones (levofloxacin (LVF) and norfloxacin (NOR)) under natural sunlight irradiation. Their half-life time and photolytic kinetic constants (k) were calculated at different molar ratios. The results indicated that the photolytic degradation curves of LVF and NOR followed apparent first-order kinetics. After 42 days of sunlight irradiation, approximately 48.3–69.4% of NOR was decomposed when the initial concentration increased from 0.006 to 0.06 mmol/L. In comparison, only 9.8–43.4% of LVF was decomposed. The k of NOR ranged from 0.79 × 10−3 to 1.30 × 10−3 h−1, and the k of LVF increased from 6.82 × 10−4 to 1.61 × 10−4 h−1. Compared with the control, the Pb2+ and Cd2+ participation tended to enhance the LVF and NOR photodegradation. The effects of Cd2+ on the photodegradation efficiency were more significant than those of Pb2+. It was inferred that the presence of aqueous NO3− obviously suppressed the NOR degradation, but Cl− had slight effects on these two fluoroquinolones’ photodegradation. These results are of importance toward the understanding of the persistence of FQs under natural sunlight irradiation in surface waters.