THE HAZARD OF N-NITROSAMINES FORMATION DURING SHORT CHAIN SECONDARY AMINES (DMA, MEA AND DEA) REACTIONS WITH CATALYZED AND NON-CATALYZED HYDROGEN PEROXIDE

摘要

The aim of the paper is the evaluation of the possibility of N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA) and N-nitrosodiethylamine (NDEA) formations as a result of dimethylamine (DMA), methylethylamine (MEA) and diethylamine (DEA), respectively, reactions with hydrogen peroxide and the Fenton reagent as well as influence of several parameters like pH, contact time and oxidant/amine ratio on N-nitrosamines formation. In 2002 Mitch et al.and Choi et al. reported that N-nitrosodimethylamine is formed during the disinfection of water or wastewater treatment plant effluents containing dimethylamine and ammonia with chlorine. Andrzejewski et al. proved that NDMA could be formed during reaction of DMA with chlorine dioxide or ozone. Experiments on dimethylamine, methylethylamine and diethylamine, respectively, reactions with hydrogen peroxide and the Fenton reagent were carried out in batch conditions at room temperature. Finally, in several experiments, the high purity water spiked with DMA was replaced with natural groundwater enriched with DMA. Water samples were withdrawn during the experiment and subsequently analyzed with HPLC-IE with UV-Vis detector at 230 nm in order to determine nitrosamines concentration as well as the main products of reactions. Formation of nitrosamines was also confirmed by GC-LRMS technique. The DMA concentration changes during reaction of DMA with hydrogen peroxide and the Fenton reagent were analyzed according GC-FID analytical procedure developed by Sacher et al. The aldehydes as well as nitrites and nitrates concentrations were also analyzed with GC-ECD and HPLC-IE-CD techniques respectively. N-nitrosamines are formed as a result of the reaction of non-catalyzed hydrogen peroxide with secondary amines only at pH higher than 11. The increase of reaction time as well as increase of H_2O_2/amine ratio results with significant increase of amine/nitrosamine conversion even to single percents. The formic acid was found as the main product of reaction of DMA with hydrogen peroxide; however DMA to formic acid molar conversion rate did not exceed 10%. When DMA was replaced with MEA or DEA, only NMEA formation was observed, however conversion rate of MEA to NMEA was significantly lower compared to results obtained for DMA. The mechanism of N-nitrosamines formation with H_2O_2is different to that described by Mitch and Choi. The presence of nitrites and nitrates in a post-reaction mixture suggests that NDMA is formed as result of DMA reaction with nitrites and the mechanism, probably, is similar to that observed previously for CIO_2 and ozone reaction with secondary amines. No oxidation of DMA by mean of the Fenton chemistry was observed. Both for the classical Fenton and Fenton-like oxidation no NDMA were found and no traces of formic acid were observed in post-reaction mixture. No changes in DMA concentration before and after Fenton oxidation of DMA were observed as well.