Radiation-induced degradation of sulfonamides (SAs) antibiotics by gamma radiation: Effect of ferrous ion

In this study, the radiation-induced degradation of two sulfonamides (SAs): sulfadiazine (SD) and sulfamethazine (SMT), was investigated, focusing on the synergistic effect of ferrous ion (Fe²⁺). The initial concentration of SD and SMT solutions were 20 mg/L, which were irradiated in the presence of 0.4 mM Fe²⁺. The results showed that gamma radiation was effective in SAs degradation and the degradation reaction conformed to the pseudo first-order kinetics. However, the removal of TOC (Total Organic Carbon) and TN (Total Nitrogen) were not as effective as that of SAs degradation. TOC removal efficiency was less than 10 % at 1.0 kGy, while 80 % of SD and 90 % of SMT were removed. Sulfate (SO₄²⁻) and two small molecules of organic acids were detected. The possible pathways of SD and SMT degradation were investigated by density functional theory (DFT) and the analysis of intermediate products. The biodegradability of SAs-containing solution could be enhanced obviously by gamma radiation. More importantly, the comprehensive toxicity of the final intermediates was lower than that of SAs, based on the quantitative structure-activity relationship (QSAR) prediction.