Decomposition of dexamethasone by gamma irradiation: Kinetics, degradation mechanisms and impact on algae growth

Gamma-irradiation induced degradation of dexamethasone (DEX) in aqueous solution was investigated under different conditions. The results indicate that low-concentration DEX could be effectively decomposed during gamma irradiation. H2O2 and Fenton reagent were favorable for DEX radiolytic removal. However, DEX radiolysis was restrained in the presence of NO3-, CO32-, 2-propanol and tert-butanol. DEX radiolytic degradation was in accordance with the pseudo first-order reaction kinetics. The rate constant ratios of OH, eaq- and H towards DEX degradation could be calculated as kOH: keaq-: kH = 10:1.5:1. Besides, it is observed that radiolytic degradation of DEX restrained algae growth. Finally, LC-MS analysis was employed to identify the intermediates and Gaussian 03 software was used to optimize DEX geometry structure. On the basis of LC-MS analysis and Gaussian calculations, we attributed DEX radiolytic removal to OH oxidation, OH radical substitution and direct cleavage of DEX molecules.