Formation of N-Nitrosodimethylamine (NDMA) from Humic Substances in Natural Water

Abstract

N-nitrosodimethylamine (NDMA)formation in chloraminated Iowa River water (IRW) is primarily attributed to reactions with natural organic matter (NOM) generally classified as humic substances. Experiments were conducted to determine the contribution of various NOM humic fractions to the NDMA formation potential (NDMA FP) in this drinking water source. NOM was concentrated by reverse osmosis (RO) and humic fractions were obtained by a series of resin elution procedures. Mass balances showed that nearly 90% of the NDMA formation potential could be recovered in the NOM concentrate and in water reconstituted using additions of the various humic fractions. Generally, the hydrophilic fractions tended to form more NDMA than hydrophobic fractions, and basic fractions tend to form more NDMA than acid fractions when normalized to a carbon basis. Overall, the hydrophobic acid fraction was the dominant source of NDMA when both formation efficiency and water composition were considered. The amount of NDMA formed in a sample was found to correlate linearly with an oxidation-induced decrease in specific UV absorbance (SUVA) value at 272 nm. This is consistent with a mechanism in which precursors are formed as the direct consequence of the oxidation of NOM. The NDMA FP estimated using the slope of this relationship and the initial SUVA value compared closely to the value obtained by measuring the NDMA formed in solutions dosed with excess concentrations of monochloramine that presumably exhaust all potential precursor sources. However, the NOMA FP could not be correlated to the SUVA value of the individual humic fractions indicating that the relationship of the NDMA FP to SUVA value is probably a water-specific parameter dependent on the exact composition of humic fractions. It is hypothesized that either specific NDMA precursors are distributed among the various humic fractions or that the humic material itself represents a "generic" nonspecific precursor source that requires some degree of oxidation to eventually produce NDMA. The nonmonotonic behavior of NOM fluorescence spectra during chloramination and lack of correlation between NOM fluorescence characteristics and NDMA formation limited the usage of fluorescence spectra into probing NDMA formation.

Nitrosamines and water

“…On the other hand, Gerecke and Sedlak [53] and Chen and Valentine [52,61] have shown that chloramination of natural organic matter (NOM) is responsible for the formation of significant amounts of NDMA. According to Chen and Valentine [52], the oxidation of natural organic matter by chloramines is the ratedetermining step in formation of NDMA.…”

Characterization of dissolved organic matter for prediction of trihalomethane formation potential in surface and sub-surface waters

“…In previous studies, different wavelengths (e.g., 254 nm [44], 272 nm [45], 280 nm [46]) have been used to determine the SUVA value. Hur et al [47] reported that SUVA determined near to 250 nm is correlated with aromatic organic compounds.…”

N-nitrosamine removal by reverse osmosis for indirect potable water reuse – A critical review based on observations from laboratory-, pilot- and full-scale studies

“…These include both heterogeneous organic mixtures such as humic substances found in the natural environment [31] and some specific organic compounds containing the amine functional group such as dimethylamine, triethylamines, and dimethylaminobenzene ( Fig. 1).…”