Degradation of tetracyclines in different water matrices by advanced oxidation/reduction processes based on gamma radiation

Background This study analyzes the efficacy of a gamma radiation advanced oxidation/reduction process (AORP) to treat waters contaminated with the antibiotics tetracycline (TC), chlortetracycline (CTC), and oxytetracycline (OTC). Results Study results indicate that: (1) radiolysis of the three TCs fits a pseudo‐first‐order kinetic model in which the radiation‐chemical yield decreases with higher absorbed dose; (2) the value of the dose constant depended on the dose rate, which ranged from 3.83 to 1.66 Gy min–1, and depended to a small extent on the medium pH between pH values of 2.0 and 10.0, since aqueous electrons and hydroxyl radicals both act in TC degradation; (3) the effectiveness of the process was slightly increased at low concentrations of H2O2; (4) the presence of Cl−, , , and humic acid influenced TCs degradation, which was higher at low concentrations of Cl−, and HA and markedly decreased at low concentrations of of and ; (5) the dose constant is lower in natural waters; (6) TOC values for ultrapure water, surface water, groundwater and wastewater showed that it is not possible to obtain complete TC mineralization at the absorbed doses; (7) the toxicity of byproducts formed during the radiolytic process was lower. Conclusions Gamma radiation, an oxidation/reduction procedure, is an effective treatment for removing TC, CTC and OTC from aqueous solutions. TC degradation takes place by both oxidation and reduction pathways, with a predominance of the latter, as demonstrated by the markedly reduced dose constant in the presence of aqueous electron scavengers.