Degradation and initial mechanism pathway of chloramphenicol by photo-Fenton process at circumneutral pH

Abstract

This paper describes the degradation of the antibiotic chloramphenicol by a photo-Fenton process under artificial and solar irradiation. Using artificial radiation, the role of different sources and concentrations of iron (salts of Fe2+ and Fe3+ and the iron complexes citrate (FeCit) and oxalate (FeOx)), initial pH, concentration of H2O2 and addition of oxalate at initial pH 6.0 were evaluated. The concentration of chloramphenicol was reduced to below the quantification limit of the equipment (<0.12 µmol L−1), as a result of 94% degradation after 40 min of reaction (equivalent to an accumulated UVA dose of 54 kJ m−2 furnished by two 8 W dark-light lamps). This occurred at pH 6.0, using 32 µmol L−1 FeOx and 44 µmol L−1 H2O2, and multiple additions of oxalate (before, and at 10 min of reaction, resulting in an excess of 192 µmol L−1). The same efficiency of chloramphenicol degradation was reached under solar irradiation using the same experimental conditions and accumulated UVA dose, but using a lower excess of oxalate (96 µmol L−1). In addition, three initial transformation products of chloramphenicol degradation were identified, one of them not yet being reported in the literature. These transformation products were probably formed by the attack of hydroxyl radicals on the aromatic ring or the benzylic carbon, according to a mechanism proposed in this study. Finally, on the basis of these results, the degradation under solar irradiation could represent a good alternative for degradation of chloramphenicol and its transformation products, since a solution with low toxicity in respect to the bacteria Vibrio fischeri was obtained, which is extremely advantageous due the reduction in energy costs.