Mechanism of NDMA formation during ferrate or permanganate reactions with aqueous solutions of dimethylamine (DMA)

Abstract

Nitrosamines, mainly N-nitrosodimetylamine (NDMA), N-nitrosomethylethylamine (NMEA) and N-nitrosodiethylamine (NDEA) are mutagenic compounds and are suspected to be carcinogenic towards humans. American Environmental Protection Agency (US EPA) classified them into group B2 - i.e., compounds which are probably carcinogenic to humans. US-EPA also determined concentrations of these compounds in potable water (oral exposure) at the levels of 7 ng 1 -1 (NDMA), 20 ng l -1 (NMEA) and 2 ng l -1 (NDEA), associated with the risk of 10 -5 . The reactions of permanganate (KMnO 4 ) or ferrate (K 2 FeO 4 ) with dimethylamine, as possible paths of NDMA formation, have been investigated. The influence of nitrite (in the reaction mixture) on both, the efficiency of NDMA formation and determination of sources of nitroso group in an NDMA molecule, were aims of these experiments. The primary goal of these investigations was to check whether nitrosating mechanism of DMA, that occurs during the reaction of strong oxidants with DMA, is responsible for NDMA formation.The results of the permanganate-DMA reaction show that by adding nitrite to the reaction mixture the amount of NDMA formed significantly increases. On the other hand, no correlation between the nitrite concentration and the amount of NDMA formed was observed. The results obtained for ferrate differ from these for permanganate. The addition of nitrite to reaction mixture decreases the amount of NDMA formed. However, the addition of nitrite in the amount of up to 75% of the amount required to reduce ferrate to Fe 2 O 3 has led to a negligible drop in NDMA formation rate. A significant decrease of NDMA formation rate (about 50% of reference sample, i.e. without nitrite addition) has been observed in the experiment, in which 100% of the amount of nitrite required for the reduction of ferrate was added. The addition of nitrite to the reaction mixture (for both oxidants) is not necessary for NDMA formation, since NDMA is also formed without an external source of nitrite. The formation of nitrite during DMA oxidation with both oxidants explains this phenomenon. The addition of labeled nitrite ( 15 N) to reaction mixtures containing DMA and permanganate or ferrate resulted in formation of higher amounts of NDMA with molecular mass of 75 Da (compared with the natural isotopic composition of nitrogen). The fragmentation analysis of the NDMA molecule has shown that the presence of isotope 15 N in nitroso group of NDMA is responsible for the molecular mass increase. This means that the presence of nitrite in the reaction is the source of nitrogen in the NDMA molecule. Thus the mechanism of nitrosation of DMA is responsible for NDMA formation during permanganate or ferrate reaction with aqueous solution of DMA.