Free radical destruction of N-nitrosodimethylamine in water

Absolute rate constants for the reactions of the hydroxyl radical, hydrated electron, and hydrogen atom with N-nitrosodimethylamine (NDMA) in water at room temperature have been determined using electron pulse radiolysis and transient absorption spectroscopy (.OH and e-aq) and EPR free induction decay attenuation (.H) measurements. Specific values of (4.30 ± 0.12, x 108, (1.41 ± 0.02) x 1010, and (2.01 ± 0.03) x 108 M-1 s-1 were measured, respectively. DMPO spin-trapping experiments demonstrated that the hydroxyl radical reaction with NDMA occurs by hydrogen atom abstraction from a methyl group, and the rate constant for the subsequent reaction of this radical transient with dissolved oxygen was measured as (5.3 ± 0.6) × 106 M-1 s-1. This relatively slow rate constant implies that regeneration of the parent nitrosoamine from the oxidized transient could occur in natural waters containing dissolved organic compounds. The reaction of the hydrated electron with NDMA was to form a transient adduct anion, which could subsequently transfer this excess electron to regenerate the parent chemical. Such regeneration reactions would significantly reduce the effectiveness of any applied advanced oxidation technology remediation effort on NDMA-contaminated natural waters.