Degradation of antineoplastic cytarabine in aqueous solution by gamma radiation

The aim of this study was to determine the effectiveness of gamma radiation to degrade cytarabine in aqueous solution. The effect of dose rate, initial cytarabine concentration, medium pH, and the presence of H2O2, Cl-, CO32-, NO3-, NO2- and organic matter was studied. Furthermore, the influence of the chemical composition of water on cytarabine degradation was evaluated by using different water matrix (ultrapure water, surface water, groundwater, and wastewater) and the variations in total organic carbon concentration and toxicity were also studied. Results show that cytarabine radiolysis fits pseudo-first order kinetics. The dose constants determined in this study ranged from 0.002 x 10(-2) to 1.32 x 10(-2) Gy(-1), whereas the initial radiation-chemical yield ranged from 0.033 to 0.94 mu mol J(-1). Cytarabine degradation in the presence of Cl-, CO32-, NO3-, NO2- and humic acid showed a decrease in dose constants with the increase in present species concentration, largely due to competition of cytarabine with Cl-, CO32-, NO3-, NO2- and humic acid by the reactive species generated, mainly HO center dot radicals. Cytarabine degradation was slightly improved by the presence of small amounts of H2O2, which acted as promoter of HO center dot radicals. However, the dose constant decreased at high concentrations of H2O2 (concentrations above 1 mM) due to inhibition of HO center dot radicals by recombination reactions. The effectiveness of gamma radiation was markedly reduced in wastewater due to inhibition of the reactive species by the high organic matter and anion content of the water. This study shows that it is not possible to completely mineralize organic matter in ultrapure water, surface water, groundwater, or wastewater at the radiation closes used (C) 2011 Elsevier B.V. All rights reserved.