Antibiotics, antibiotic resistant bacteria and genes in wastewater effluents have received increased attention due to their possible contribution to growing rates of antibiotic resistance in human infections. Oxidation processes are being tested and applied (e.g. ozonation) for enhanced wastewater treatment to minimize the release of such contaminants of concern to the aquatic environment. Ferrate(VI) is a new water treatment chemical and has been demonstrated to be effective for oxidation of organic micropollutants and removal of phosphate by ferric-phosphate precipitation. In the present study, the reaction kinetics, transformation products, and changes of antibacterial activity during transformation of �-lactam antibiotics by ferrate(VI) oxidation were investigated. Amoxicillin, cloxacillin, penicillin G (penicillins), and cephalexin (cephalosporin) were selected. Ferrate(VI) shows an appreciable reactivity with the selected �-lactams (k for pH 7 = 110 - 770 M-1 s-1). The pH-dependent k-values could be well explained by considering the species-specific reactions between ferrate(VI) (HFeO4- and FeO42-) and �-lactams (thioether, amine, and/or phenol). Based on the kinetic results, the thioether-moiety is expected to be the main reaction site for penicillin G and cloxacillin. For cephalexin, the amine-moiety is an additional reaction site and for amoxicillin the amine- and phenol-moieties are additional reaction sites. A quantitative microbiological assay was used to measure the resulting changes in antibacterial potencies during ferrate(VI) oxidation. The results show that biologically-active transformation products are formed only for cephalexin (>20% of potency of the parent). For the other �-lactams, the transformation products showed much lower antibacterial potencies compared to the parents (<10%). HPLC/MS analysis shows that the thioether-moiety of �-lactams is transformed into sulfoxides ((R) and (S) optical isomers) and then further into sulfone. Thus, the structural transformations in the thioether-moiety are sufficient to deactivate the selected penicillins. Overall, this study demonstrates ferrate(VI) to be efficient in eliminating �-lactams during treatment of wastewater effluents with ferrate(VI).

Transformation of �-lactam antibiotics during water treatment with ferrate(VI): Reaction kinetics, transformation products, and changes of antibacterial activity

248th National Meeting (2014)

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