Hydroxyl radical involvement in the decomposition of hydrogen peroxide by ferrous and ferric-nitrilotriacetate complexes at neutral pH.

The relative rates of degradation of three hydroxyl radical probe compounds (atrazine, fenuron and parachlorobenzoic acid (pCBA)) by Fe(III)/H(2)O(2) (pH = 2.85), Fe(III)NTA/H(2)O(2) (neutral pH), Fe(II)/O(2), Fe(II)NTA/O(2), Fe(II)/H(2)O(2) and Fe(II)NTA/H(2)O(2) (neutral pH) have been investigated using the competitive kinetic method. Experiments were carried out in batch and in semi-batch reactors, in the dark, at 25 °C. The data showed that the three probe compounds could be degraded by all the systems studied, and in particular by Fe(II)NTA/H(2)O(2) and Fe(III)NTA/H(2)O(2) at neutral pH. The relative rate constants of degradation of the three probe compounds obtained for all the systems tested were identical and equal to 1.45 ± 0.03 and 0.47 ± 0.02 for k(Atrazine)/k(pCBA) and k(Fenuron)/k(pCBA), respectively. These values as well as the decrease of the rates of degradation of the probe compounds upon the addition of hydroxyl radical scavengers (tert-butanol, bicarbonate ions) suggest that the degradation of atrazine, fenuron and pCBA by Fe(II)NTA/O(2), Fe(II)NTA/H(2)O(2) and Fe(III)NTA/H(2)O(2) is initiated by hydroxyl radicals.