N-nitrosodimethylamine (NDMA) formation during ozonation of N,N-dimethylhydrazine compounds: Reaction kinetics, mechanisms, and implications for NDMA formation control.
Compounds with N,N-dimethylhydrazine moieties ((CH3)2N-N-) form N-nitrosodimethylamine (NDMA) during ozonation, but the relevant reaction chemistry is hitherto poorly understood. This study investigated the reaction kinetics and mechanisms of NDMA formation during ozonation of unsymmetrical dimethylhydrazine (UDMH) and daminozide (DMZ) as structural model N,N-dimethylhydrazine compounds. The reaction of ozone with these NDMA precursor compounds was fast, and kO3at pH 7 was 2 × 106M-1s-1for UDMH and 5 × 105M-1s-1for DMZ. Molar NDMA yields (i.e., Δ[NDMA]/Δ[precursor] × 100) were 84% and 100% for UDMH and DMZ, respectively, determined at molar ozone dose ratio ([O3]0/[precursor]0) of ≥4 in the presence of tert-butanol as hydroxyl radical (OH) scavenger. The molar NDMA yields decreased significantly in the absence of tert-butanol, indicating OH formation and its subsequent reaction with the parent precursors forming negligible NDMA. The kOHat pH 7 was 4.9 × 109M-1s-1and 3.4 × 109M-1s-1for UDMH and DMZ, respectively. Reaction mechanisms are proposed in which an ozone adduct is formed at the nitrogen next to N,N-dimethylamine which decomposes via homolytic and heterolytic cleavages of the -N+-O-O-O-bond, forming NDMA as a final product. The heterolytic cleavage pathway explains the significant OH formation via radical intermediates. Overall, significant NDMA formation was found to be unavoidable during ozonation or even O3/H2O2treatment of waters containing N,N-dimethylhydrazine compounds due to their rapid reaction with ozone forming NDMA with high yield. Thus, source control or pre-treatment of N,N-dimethylhydrazine precursors and post-treatment of NDMA are proposed as the mitigation options.
School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
Sungeun
S
Lim
School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
Woongbae
W
Lee
School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
Soyoung
S
Na
School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea.
Jaedon
J
Shin
School of Earth Sciences and Environmental Engineering, Gwangju Institute of Science and Technology (GIST), Gwangju, 500-712, Republic of Korea. Electronic address: yhlee42@gist.ac.kr.
Yunho
Y
Lee
D004127:Dimethylhydrazines; D004128:Dimethylnitrosamine / Q000737:chemistry*; D006861:Hydrogen Peroxide / Q000737:chemistry*; D007700:Kinetics; D010126:Ozone / Q000737:chemistry
D004127:Dimethylhydrazines; D010126:Ozone; D006861:Hydrogen Peroxide; D004128:Dimethylnitrosamine
Daminozide; Hydroxyl radical; N-nitrosodimethylamine (NDMA); Ozone; Unsymmetrical dimethyl hydrazine