Biotransformation of Nitrosamines and Precursor Secondary Amines under Methanogenic Conditions

Abstract

b S Supporting Information ' INTRODUCTION Nitrosamines (NISA) are an emerging group of disinfection byproducts and suspected carcinogens. 1 Among all nitrosamines, N-nitrosodimethylamine (NDMA), N-nitrosomethylethylamine (NMEA), N-nitrosopyrrolidine (NPYR), N-nitrosodiethylamine (NDEA), N-nitrosodi-N-propylamine (NDPA), and N-nitrosodi-N-butylamine (NDBA), are of particular interest because they are listed in the Unregulated Contaminant Monitoring Regulation (UCMR 2) 2 as well as the recently proposed Contaminant Candidate List 3 (CCL 3) by the U.S. Environmental Protection Agency. 3 Secondary amines (SAN) are well-known nitrosamine precursors that can yield corresponding nitrosamines via Nnitrosation, 4 during disinfection, 1,5,6 or at different stages of water and wastewater treatment. 7,8 Recent studies have reported the presence of nitrosamines and their precursors in both the influent and effluent of municipal wastewater treatment plants throughout the U.S. and Canada. 7,9 Aerobic degradation and mineralization of nitrosamines, particularly NDMA, has been observed in mixed microbial cultures. 10,11 Biodegradation of nitrosamines has also been reported for indigenous soil bacteria under aerobic conditions. 12,13 A recent study showed that aerobic NDMA biotransformation was cometabolic, achieved by various monooxygenases, such as soluble methane monooxygenase, propane monooxygenase and toluene-4-monooxygenase. 14,15 Aerobic, cometabolic NDMA biotransformation takes place either through the cleavage of the N-N bond (denitrosation) 14 or by α-hydroxylation of the methyl group followed by a demethylation. 16 NDMA biodegradation under anaerobic conditions has also been reported for indigenous soil microorganisms and biofilm reactors; however, the rate and extent of biodegradation under anaerobic conditions were significantly lower than under aerobic conditions. 17,18 Biotransformation of secondary amines via demethylation has also been reported under both aerobic and anaerobic conditions. 19 Methanogens are also known to utilize secondary amines, such as DMA, and convert them to methane. 20,21 Recently, Padhye et al. 9 showed that nitrosamines, particularly NDMA, are abundant in municipal primary and waste activated sludge at concentrations up to 10-fold higher than those found in municipal wastewater. Considering that many of the NISA are hydrophilic and have a low affinity to sorb on sludge solids, high NISA concentrations found in municipal sludge were therefore attributed to the in situ formation of NISA through nitrosation of nitrogen-bearing, sludge-associated organic compounds, such as quaternary ammonium compounds and cationic polymers. 9,22,23 Moreover, it was shown that NISA present in municipal sludge were partially removed during anaerobic digestion. 9 The study

Characterization of the microbial community structure and nitrosamine-reducing isolates in drinking water biofilters

“…Removal ratios ranged from 38.1% to 85.4%, listed here in decreasing order: NDMA (85.4%), NDPA (78.8%), NDEA (47.7%), Npyr (48.5%), and NDBA (38.1%). In previous studies, many isolates belonging to different genera have shown a biodegradation capacity for NDMA at high concentrations, and propane monooxygenases (PrMO), soluble methane monooxygenases (sMMO) and toluene monooxygenases (TMO) enhanced the biodegradation of NDMA as the nitrogen source (Fournier et al, 2006(Fournier et al, , 2009Sharp et al, 2005Sharp et al, , 2007Sharp et al, , 2010Tezel et al, 2011). When cultures were grown on media with added organics (i.e., propane, methane or toluene) as the carbon source, the degradation rates increased.…”

“…When cultures were grown on media with added organics (i.e., propane, methane or toluene) as the carbon source, the degradation rates increased. In addition to the biodegradation of NDMA, a few reports (Carissa and Jonathan, 2013;Tezel et al, 2011) focused on the biotransformation of other nitrosamines. Multiple nitrosamines at high concentrations have been biodegraded as the nitrogen source by an isolate reported by Carissa and Jonathan (2013), growth of cells on propane as the sole carbon source greatly enhanced degradation rates.…”

“…3a, b, e) in this study scaled consistently with the linear functional groups and mass (Supplementary Table B). Tezel et al (2011) reported that nitrosamines with symmetric, long-chain alkyl groups were less likely to be biodegraded by an uncharacterized mixed methanogenic culture than nitrosamines with asymmetric, shorter alkyl chains. The removal ratios of linear nitrosamines were higher than those of cyclic nitrosamines that were more recalcitrant.…”

“…The half-life data presented by Drewes et al (2006) also shows a similar order of degradation from fastest to slowest: NDPA, NDMA, NPip, NDEA, Npyr. On the contrary, Tezel et al (2011) found that biotransformation of NDEA, NDPA and NDBA was intractable under fermentative and methanogenic conditions. The discrepancy in NDPA's relative position in our study could potentially be attributed to increased volatility and/or an abiotic mechanism that either complements or out-competes baseline biotransformation.…”

“…Biological treatment, though slow under environmental conditions, is thought to be an important mechanism for the removal of these nitrosamines and those originating from industrial discharge in DWTPs, and it could also avoid the risks of chemically treating in groundwater (Gunnison et al, 2000;Zhou et al, 2009;Patterson et al, 2012). With the biodegradation of precursors and nitrosamines formed in the pre-oxidation processes, the nitrosamine formation potential might decrease after disinfection (Tezel et al, 2011;Mitch et al, 2003). For the practical operation of DWTPs, the screening and isolation of microbial strains capable of reducing nitrosamine levels is urgently required.…”