Reactivity of OH• and eaq- from electron beam irradiation of aqueous solutions of EDTA and aminopolycarboxylic acids

Electron beam irradiation of aqueous solutions of EDTA, EDDA NN', NTA, IDA and Cu-EDTA was performed in the presence of scavengers for the hydroxyl radicals (methanol) or for the solvated electrons (hydrogen peroxide). Experiments showed that for each molecule, the G-value decreases as the radiation dose increases from 1 to 25 kGy, and for EDTA, when the initial concentration decreases from 10 to 0.1 mmol 1(-1). At pH 8 and for 5 kGy, the G-values of NTA, IDA, EDTA and EDDA NN' removal ascribed to OH. radicals are, respectively, 0.06, 0.06, 0.15 and 0.20 mumol J(-1), whereas for the solvated electrons the G-values were, respectively, 0.01, 0.01, 0.06 and 0.04 mumol J(-1). The rate constants of hydroxyl radicals and solvated electrons were determined by comparison with one competitor. For each active species (hydroxyl radical or solvated electron), the reactivity is connected to the number of nitrogen atoms and acetate groups. The rate constants of OH. radicals are above 1010 and 8.6 x 10(9) 1mol(-1) s(-1) for EDDA NN' and EDTA, respectively, 2.1 x 10(9) 1mol(-1) s(-1) for IDA and 6.1 x 10(8) 1mol(-1) s(-1) for NTA. The reactivity of solvated electrons is smaller and the rate constants are in the range 1.9 x 10(6) -3.7 x 10(6) 1mol(-1) s(-1) for NTA, IDA and EDDA NN' and equal 1.4 x 10(7) 1mol(-1) s(-1) for EDTA. The reactivity of the complex Cu-EDTA towards OH' does not differ to a large extent from EDTA whereas with e(aq)(-) the reactivity of Cu-EDTA is better than EDTA since k(e)-(/Cu)-EDTA reaches 2.2 x 10(9) 1mol(-1) s(-1). It follows that when both active entities (OH. and e(aq)(-)) are involved in the electron beam irradiation process, the removal of free aminopolycarboxylic acids is mainly due to OH. radicals. However, the complex Cu-EDTA is concerned by both e(aq)(-) and OH. radicals. (C) 2003 Elsevier Science Ltd. All rights reserved.