Photodegradation of the pharmaceuticals atorvastatin, carbamazepine, levofloxacin, and sulfamethoxazole in natural waters

Abstract

The photochemical behaviour of the four pharmaceuticals, atorvastatin, carbamazepine, levofloxacin, and sulfamethoxazole in sunlit surface water was investigated. These compounds, which have been observed or have the potential to be in surface waters, were susceptible to direct and indirect photodegradation. Several photoproducts are identified using authentic standards, and structures of other degradation products are proposed based on mass spectral information from this and previous studies. The same degradation compounds are formed from direct and indirect photolysis, suggesting the same photoproducts are formed by alternate pathways. The natural water constituents nitrate, dissolved organic matter (DOM), and bicarbonate influence the elimination rates of the pharmaceuticals differently. Since direct photolysis appears important in limiting the persistence of levofloxacin and sulfamethoxazole, the presence of humic matter decreases degradation rates. The same constituent has an opposite and positive effect on the elimination rates of atorvastatin and carbamazepine and thus, photosensitization reactions or photooxidants generated from DOM photolysis are important. Products resulting from direct and indirect photolysis also seem to be susceptible to photodegradation, suggesting they will not persist in sunlit aqueous systems.