Photodegradation of N-nitrosodimethylamine under 365 nm Light Emitting Diode Irradiation

The photodegradation of NDMA has been extensively investigated under the irradiation of low-pressure or medium-pressure Hg lamps and xenon lamp. However, NDMA photolysis remains unknown under 365 nm ultraviolet light-emitting diode (UV-LED) irradiation. This study conducted a comprehensive investigation on NDMA photodegradation by 365 nm UV-LED illumination. The quantum yield of NDMA photolysis under 365 nm UV-LED irradiation was determined to be 0.0312 ± 0.0047. The influence of pH on NDMA photodegradation was found to be wavelength dependent. Compared with distilled and deionized water (DDW), tap water inhibited NDMA photodegradation, but secondary wastewater effluent did not. Based on the quantification of NDMA photolysis products and pH influence, the photooxidation of the excited NDMA in the nonprotonated form was proposed to be a major pathway for NDMA photodegradation under the irradiation of UV-LED lamp at 365 nm. This study further enhances our knowledge on NDMA photodegradation. PRACTITIONER POINTS: Quantum yield of NDMA photolysis at 365 nm was determined to be 0.0312 ± 0.0047. The influence of pH on NDMA photodegradation was wavelength dependent. NDMA photodegradation was inhibited in tap water compared with that in DDW. NDMA photodegradation in SWE was similar to that in DDW. Excited nonprotonated NDMA photooxidation is a major degradation pathway.

NDMA and NDMA precursor attenuation in environmental buffers prior to groundwater recharge for potable reuse

Natural attenuation of N-nitrosodimethylamine (NDMA) and NDMA precursors was evaluated in infiltration basins, a riverbed filtration system, and constructed wetlands operated as part of a managed aquifer recharge system. Initial NDMA concentrations up to 9.0 ng/L in infiltration basins (advanced purified, recycled water) before sunrise declined to non-detect (<1.5 ng/L) by 10:00 A.M due to natural photolysis (half-life of 33 to 86 min dependent on solar irradiance). NDMA fortified controls adjacent to the infiltration basin showed similar results, while concentrations in dark controls did not change over the basin's hydraulic retention time. NDMA precursor concentrations did not change significantly in the basin containing advanced-treated water from a potable reuse treatment plant, indicating that photolysis did not remove NDMA precursors nor did photolysis produce a significant amount of precursors. For the other environmental buffers evaluated, NDMA removal was variable through laboratory scale soil columns (22 cm height), in full-scale riverbed filtration system that pre-filters water prior to infiltration basin recharge, and in the constructed wetland. Variability in NDMA removal through the wetlands is attributed to high turbidity. In the case of the riverbed filtration system, variability is likely due to short exposure times to sunlight. For the soil columns, limited NDMA removal is attributed to inefficacy of soil aquifer treatment in removing NDMA over short travel times/distances. NDMA precursors were also ineffectively removed in these systems, with effluent concentrations occasionally exceeding influent concentrations. Overall, the removal of NDMA in environmental buffers utilized for planned or de facto indirect potable reuse is dependent on the system's capacity for photolysis, while NDMA precursors are more recalcitrant and unlikely to be removed in such systems without enhancement or sufficient hydraulic residence times.

Detection of N-nitrosodimethylamine (NDMA) and its formation potential in hospital wastewater

Hospital wastewaters contain high concentrations of pharmaceutical residues and other chemicals, and may present an important source for NDMA (N-nitrosodimethylamine) and its precursors in the aquatic environment. The present study evaluates the contribution of hospital wastewater to NDMA environmental load and identifies important sources within the hospital itself. For this purpose, wastewaters from five large hospitals in Israel were analyzed, and concentrations of NDMA were found in the range of 20.7-56.7 ng/L, which are similar to NDMA concentrations typically detected in domestic wastewater. The relative contribution of day surgery, oncology, laboratories, and central kitchen (in Sheba hospital) to the daily load of NDMA was calculated as 20.2%, 8.2%, 10%, and 43.2%, respectively. In addition, NDMA concentration in Sheba's mixed wastewater stream, measured throughout a complete working day, was highest at 14:00. This suggests the possible impact of lunchtime on NDMA concentration, and emphasizes the dominant contribution of central kitchen waste. Finally, formation potential of NDMA in the mixed stream was 7300 ng/L, in the upper range of domestic wastewater, but could be decreased by 70% during subsequent aerobic biological wastewater treatment.

Drinking water nitrosamines in a large metropolitan region in Brazil

Nitrosamines are a concerning group of carcinogens, which have gained increasing attention over the last years, frequently found in drinking and recycled water systems. In this work, an analytical method was developed for the detection and quantification of seven nitrosamines (NDMA, NMEA, NPYR, NDEA, NPIP, NDPA, and NDBA) in drinking water. The method is based on gas chromatography coupled with a single quadrupole mass spectrometer (GC-MS) with electron ionization (EI) mode. Sample enrichment and matrix cleanup by solid-phase extraction (SPE) were performed using the US EPA Method 521 cartridge packed with coconut-based charcoal. The simple method allowed reliable identification and quantification of nitrosamines in the water at nanogram per liter levels. The optimized method was validated at three concentration levels (20, 100, and 200 ng L-1) in ultrapure and drinking water samples. Average recoveries were 63-87% for ultrapure water and 38-79% for drinking water with relative standard deviations (RSD) below 10% for both matrices. Method detection limits were 1.23-3.14 ng L-1. The described method was applied to eighteen drinking water samples collected from 13 cities of the Metropolitan Region of Campinas (São Paulo, Brazil). NDMA was the most frequent nitrosamine detected (89% of samples) and had the highest concentration level found (67 ng L-1). The levels of nitrosamines found in drinking water samples are of considerable relevance since the selected area is a major urban center that has amply expanded industrial and agricultural activities over the last few decades. To the best of our knowledge, this is the first evaluation of nitrosamines in drinking water conducted in Brazil to date.

Spatial, temporal variability and carcinogenic health risk assessment of nitrosamines in a drinking water system in China

Nitrosamines, as a class of emerging frequently detected nitrogenous disinfection byproducts (N-DBPs) in drinking water, have gained increasing attention due to their potentially high health risk. Few studies focus on the occurrence variation and carcinogenic health risk of nitrosamines in drinking water systems. Our study aimed to investigate the spatial and temporal variability of nitrosamines in a drinking water system and to conduct a carcinogenic health risk assessment. Three types of water samples, including influent water, treated water and tap water, were collected monthly during an entire year in a drinking water system utilizing a combination of chlorine dioxide and chlorine in central China, and 9 nitrosamines were measured. The nitrosamine formation potentials (FPs) in influent water were also determined. N-nitrosodimethylamine (NDMA) was the most prevalent compound and was dominant in the water samples with average concentrations ranging from 2.5 to 67.4 ng/L, followed by N-nitrosodiethylamine (NDEA) and N-nitrosopiperidine (NPIP). Nitrosamine occurrence varied monthly, and significant seasonal differences were observed in tap water (p < .05). There were decreasing mean NDMA, NDEA and NPIP concentrations from influent water to treated water to tap water, but no significant spatial variability was observed within the water distribution system (p > .05). The average and 95th percentile total lifetime cancer risks for the three main nitrosamines were 4.83 × 10^-5 and 4.48 × 10^-4, respectively, exceeding the negligible risk level (10^-6) proposed by the USEPA. Exposure to nitrosamines in drinking water posed a higher cancer risk for children than for adults, and children aged 0.75 to 1 years suffered the highest cancer risk. These results suggest that nitrosamine occurrence in tap water varied temporally but not spatially. Exposure to drinking water nitrosamines may pose a carcinogenic risk to human health, especially to children.

Bench-scale column evaluation of factors associated with changes in N-nitrosodimethylamine (NDMA) precursor concentrations during drinking water biofiltration

Biofiltration has been observed to increase or decrease the concentrations of N-nitrosodimethylamine (NDMA) precursors in the effluents of full-scale drinking water facilities, but these changes have been inconsistent over time. Bench-scale tests comparing biofiltration columns side-by-side exposed to different conditions were employed to characterize factors associated with changes in NDMA precursor concentrations, as measured by application of chloramines under uniform formation conditions (UFC). Side-by-side comparisons of biofiltration media from different facilities fed with water from each of these facilities demonstrated that differences in source water quality were far more important than any original differences in the microbial communities on the biofiltration media for determining whether NDMA precursor concentrations increased, decreased or remained constant across biofilters. Additional tests involving spiking of specific constituents hypothesized to promote increases in NDMA precursor concentrations demonstrated that inorganic nitrogen species associated with nitrification, including ammonia, hydroxylamine and chloramines, and biotransformation of known precursors (i.e., municipal wastewater and the cationic polymer, polyDADMAC) to more potent forms were not important. Biotransformation of uncharacterized components of source waters determined whether NDMA precursor concentrations increased or decreased across biofilters. These uncharacterized source water component concentrations varied temporally and across locations. Where biotransformation of source water precursors increased NDMA precursor concentrations, ∼30-60% of the levels observed in column effluents fed with biofiltration influent water remained associated with the media and could be rinsed therefrom in either the dissolved or particulate form. Ozone pre-treatment significantly reduced NDMA precursor concentrations at one facility, suggesting that pre-oxidation could be an effective technique to mitigate the increase in NDMA precursor concentrations during biofiltration. Biofiltration decreased the concentrations of halogenated disinfection byproduct precursors.

Removal of wastewater and polymer derived N-nitrosodimethylamine precursors with integrated use of chlorine and chlorine dioxide

In this study, the effects of five different pre-oxidation scenarios (i.e., individual, simultaneous, and sequential applications of chlorine dioxide [ClO₂] and chlorine [Cl₂]) on the removal of N-nitrosodimethylamine (NDMA) formation potential (FP) from different water matrices (i.e., non-impacted natural waters, wastewater [WW]-impacted, and polymer-impacted waters) with subsequent chloramination were investigated. Practically relevant doses of ClO₂ and Cl₂ were applied for all scenarios to avoid the formation of disinfection by-products (DBPs) at regulatory levels. The removal efficiency of NDMA FP for all the oxidation scenarios (individual or simultaneous) was <20% in non-impacted natural water samples. In 20% WW-impacted waters, pre-oxidation with ClO₂ at pH 7.8 resulted in a significant reduction in NDMA FP (56-73%), whereas pre-oxidation with Cl₂ showed less removals (40-50%). For the integrated oxidation scenarios (i.e., simultaneous or sequential application), NDMA FP removals further increased (20-45%), especially, at pH 6.0 compared to individual application of oxidants in WW-impacted waters. The formation of NDMA in pre-oxidized water samples also decreased significantly under uniform formation condition (UFC). In polymer-impacted waters, integrated applications of Cl₂ and ClO₂ significantly improved the deactivation of polymer-derived NDMA precursors independent of oxidation time (10 vs. 60 min) and pH (6.0 vs. 7.8) compared to individual application of these oxidants. In addition, chlorite (ClO₂^-) formation was low and maintained well below 1 mg/L for integrated applications of Cl₂ and ClO₂, while chlorate (ClO₃^-) formation increased significantly as compared to application of ClO₂ only.

Deactivation of wastewater-derived N-nitrosodimethylamine precursors with chlorine dioxide oxidation and the effect of pH

In this study, the effect of chlorine dioxide (ClO₂) oxidation on the deactivation of wastewater (WW)-derived N-nitrosodimethylamine (NDMA) precursors was investigated under various conditions (i.e., ClO₂ application pH, dose and contact time). At pH 6.0, decreases in NDMA formation potentials (FPs) or occurrences (under uniform formation conditions [UFC]) were relatively low (<25%) with ClO₂ oxidation regardless of WW-impact. A negative removal was also observed after ClO₂ oxidation in some of the non-impacted waters. However, NDMA FP removals were significant (up to ~85%) under the same oxidation conditions in WW-impacted waters at pH 7.8. This indicates that the majority of WW-derived NDMA precursors can be deactivated with ClO₂ oxidation above neutral pH. This was attributed to the better oxidative reaction of ClO₂ with amines that have lone pair electrons to be shared at higher oxidation pH conditions. In addition, relatively short oxidation periods with ClO₂ (i.e., ≤10 min) or low Ct (concentration × time, ~10 mg ∗ min/L) values were sufficient for the deactivation of WW-derived NDMA precursors. ClO₂ oxidation was effective in freshly WW-impacted waters. Natural attenuation processes (e.g., sorption, biodegradation, etc.) can change the reactivity of WW-derived NDMA precursors for oxidation with ClO₂. The effect of ClO₂ on the removal of THM precursors was low (<25%) and independent of oxidation conditions. Given the low formation of regulated THMs and HAAs, ClO₂ oxidation presents a viable option for the simultaneous control of NDMA and regulated DBP formation during water treatment, especially for utilities treating WW-impacted water sources.

Carbon, Hydrogen, and Nitrogen Isotope Fractionation Trends in N-Nitrosodimethylamine Reflect the Formation Pathway during Chloramination of Tertiary Amines

Assessing the precursors and reactions leading to the carcinogenic N-nitrosodimethylamine (NDMA) during drinking water disinfection is a major challenge. Here, we investigate whether changes of ¹³C/¹²C, ²H/¹H, and ¹⁵N/¹⁴N ratios of NDMA give rise to isotope fractionation trends that can be used to infer NDMA formation pathways. We carried out compound-specific isotope analysis (CSIA) of NDMA during chloramination of four tertiary amines that produce NDMA at high yields, namely ranitidine, 5-(dimethylaminomethyl)furfuryl alcohol, N,N-dimethylthiophene-2-methylamine, and N,N-dimethylbenzylamine. Carbon and hydrogen isotope ratios of NDMA function as fingerprints of the N(CH₃)₂ moiety and exhibit only minor isotope fractionation during the disinfection process. Nitrogen isotope ratios showed that NH₂Cl is the source of the N atom of the nitroso group. The large enrichment of ¹⁵N in NDMA was indicative of the isotope effects pertinent to bond-cleavage and bond-formation reactions during chloramination of the tertiary amines. Correlation of δ¹⁵N versus δ¹³C values of NDMA resulted in trend lines that were not affected by the type of tertiary amine and treatment conditions, suggesting that the observed C and N isotope fractionation in NDMA may be diagnostic for NDMA precursors and formation pathways during chloramination.

The control of disinfection byproducts and their precursors in biologically active filtration processes

While disinfection provides hygienically safe drinking water, the disinfectants react with inorganic or organic precursors, leading to the formation of harmful disinfection byproducts (DBPs). Biological filtration is a process in which an otherwise conventional granular filter is designed to remove not only fine particulates but also dissolved organic matters (e.g., DBP precursors) through microbially mediated degradation. Recently, applications of biofiltration in drinking water treatment have increased significantly. This review summarizes the effectiveness of biofiltration in removing DBPs and their precursors and identifies potential factors in biofilters that may control the removal or contribute to formation of DBP and their precursors during drinking water treatment. Biofiltration can remove a fraction of the precursors of halogenated DBPs (trihalomethanes, haloacetic acids, haloketones, haloaldehydes, haloacetonitriles, haloacetamides, and halonitromethanes), while also demonstrating capability in removing bromate and halogenated DBPs, except for trihalomethanes. However, the effectiveness of biofiltration mediated removal of nitrosamine and its precursors appears to be variable. An increase in nitrosamine precursors after biofiltration was ascribed to the biomass sloughing off from media or direct nitrosamine formation in the biofilter under certain denitrifying conditions. Operating parameters, such as pre-ozonation, media type, empty bed contact time, backwashing, temperature, and nutrient addition may be optimized to control the regulated DBPs in the biofilter effluent while minimizing the formation of unregulated emerging DBPs. While summarizing the state of knowledge of biofiltration mediated control of DBPs, this review also identifies several knowledge gaps to highlight future research topics of interest.

A novel assay to measure tertiary and quaternary amines in wastewater: An indicator for NDMA wastewater precursors

This study examined the potential of using a novel bulk amine assay as an approximation for the tertiary and quaternary amine load in wastewaters and surface water samples, and this approximation was compared to N-nitrosodimethylamine (NDMA) formation potential using chloramines. An existing colorimetric method was examined and optimized for the detection of amines in environmental water samples. The method consists of liquid-liquid extraction followed by a catalyzed reaction to form a yet-undefined product that is known to be both a strong chromophore and fluorophore. Previous work verified that this reaction was effectively catalyzed by a number of compounds containing tertiary and quaternary amine moieties. Many tertiary and quaternary compounds are also efficient producers of NDMA under chloramination conditions, and a linear correlation was consequently derived from the bulk amine signals vs. NDMA formation potential in various wastewater samples (R² = 0.74; n = 24; p-value < 0.05). The results provide evidence that approximately 2% of the tertiary and quaternary amines measured can form NDMA and an estimated 0.01-1.3% of nitrogen in dissolved organic nitrogen originates from these bulk amines. The normalization of NDMA concentration by the amine measurement revealed that ozone effectively destroyed those tertiary and quaternary amine structures more likely to form NDMA in treated wastewater samples. This bulk amine assay illustrates that proxy measurements of tertiary and quaternary amines can be linked to the NDMA formation potential of a given sample, and this approach may prove useful as a characterizing tool for NDMA precursors in wastewater.

Relative Importance of Different Water Categories as Sources of N-Nitrosamine Precursors

A comparison of loadings of N-nitrosamines and their precursors from different source water categories is needed to design effective source water blending strategies. Previous research using Formation Potential (FP) chloramination protocols (high dose and prolonged contact times) raised concerns about precursor loadings from various source water categories, but differences in the protocols employed rendered comparisons difficult. In this study, we applied Uniform Formation Condition (UFC) chloramination and ozonation protocols mimicking typical disinfection practice to compare loadings of ambient specific and total N-nitrosamines as well as chloramine-reactive and ozone-reactive precursors in 47 samples, including 6 pristine headwaters, 16 eutrophic waters, 4 agricultural runoff samples, 9 stormwater runoff samples, and 12 municipal wastewater effluents. N-Nitrosodimethylamine (NDMA) formation from UFC and FP chloramination protocols did not correlate, with NDMA FP often being significant in samples where no NDMA formed under UFC conditions. N-Nitrosamines and their precursors were negligible in pristine headwaters. Conventional, and to a lesser degree, nutrient removal wastewater effluents were the dominant source of NDMA and its chloramine- and ozone-reactive precursors. While wastewater effluents were dominant sources of TONO and their precursors, algal blooms, and to a lesser degree agricultural or stormwater runoff, could be important where they affect a major fraction of the water supply.

Structural Modifications to Quaternary Ammonium Polymer Coagulants to Inhibit N-Nitrosamine Formation

Quaternary ammonium cationic polymers, such as poly(diallyldimethylammonium chloride) (polyDADMAC) and epichlorohydrin-dimethylamine (Epi-DMA), are commonly used by water utilities to enhance removal of particles and dissolved organic matter (DOM) from raw waters. Unfortunately, chloramination of waters treated with quaternary ammonium polymers leads to the formation of carcinogenic N-nitrosodimethylamine (NDMA). In this study, two approaches were developed to modify polyDADMAC and Epi-DMA to inhibit N-nitrosamine formation. The first approach involved treatment of polymers with methyl iodide (MeI), an alkylating agent, to convert polymer-bound tertiary amine groups to less chloramine-reactive quaternary ammonium groups. The second approach involved synthesis of polymers bearing less chloramine-reactive quaternary ammonium groups with dipropylamino (DPA) substituents. Treatment with MeI reduced NDMA formation from polymers by ∼75%, while synthesis of DPA-based polymers eliminated NDMA formation and formed N-nitrosodipropylamine, which is 10-fold less carcinogenic than NDMA, at 20-fold lower yields. Bench-scale jar tests demonstrated that both MeI-treated and DPA-based polymers achieved similar removal of particles and DOM as the original polyDADMAC and Epi-DMA at both low and high doses, but formed significantly less N-nitrosamines. This work demonstrates two approaches for modifying quaternary ammonium cationic polymers, which may enable water utilities to meet potential future regulations on N-nitrosamines while maintaining polymer usage to meet existing regulations.

Impact of Nitrification on the Formation of N-Nitrosamines and Halogenated Disinfection Byproducts within Distribution System Storage Facilities

Distribution system storage facilities are a critical, yet often overlooked, component of the urban water infrastructure. This study showed elevated concentrations of N-nitrosodimethylamine (NDMA), total N-nitrosamines (TONO), regulated trihalomethanes (THMs) and haloacetic acids (HAAs), 1,1-dichloropropanone (1,1-DCP), trichloroacetaldehyde (TCAL), haloacetonitriles (HANs), and haloacetamides (HAMs) in waters with ongoing nitrification as compared to non-nitrifying waters in storage facilities within five different chloraminated drinking water distribution systems. The concentrations of NDMA, TONO, HANs, and HAMs in the nitrifying waters further increased upon application of simulated distribution system chloramination. The addition of a nitrifying biofilm sample collected from a nitrifying facility to its non-nitrifying influent water led to increases in N-nitrosamine and halogenated DBP formation, suggesting the release of precursors from nitrifying biofilms. Periodic treatment of two nitrifying facilities with breakpoint chlorination (BPC) temporarily suppressed nitrification and reduced precursor levels for N-nitrosamines, HANs, and HAMs, as reflected by lower concentrations of these DBPs measured after re-establishment of a chloramine residual within the facilities than prior to the BPC treatment. However, BPC promoted the formation of halogenated DBPs while a free chlorine residual was maintained. Strategies that minimize application of free chlorine while preventing nitrification are needed to control DBP precursor release in storage facilities.

Natural attenuation of NDMA precursors in an urban, wastewater-dominated wash

N-Nitrosodimethylamine (NDMA) is a disinfection by-product (DBP) that is potentially carcinogenic and has been found to occur in drinking water treatment systems impacted with treated wastewater. A major gap in NDMA research is an understanding of the persistence of wastewater-derived precursors within the natural environment. This research sought to fill this knowledge gap by surveying NDMA precursors across the length of a wastewater effluent-dominated wash. Significant precursor reduction (17%) was found to occur from introduction into the wash to a point 9 h downstream. This reduction translates into a half-life of roughly 32 h for bulk NDMA precursors. Further laboratory experiments examining rates of photolysis, biodegradation and loss to sediments, illustrated that both photolytic and biological degradation were effective removal mechanisms for NDMA precursors. Loss to sediments that were acquired from the wash did not appear to reduce NDMA precursors in the water column, although a control conducted with DI water provided evidence that significant NDMA precursors could be released from autoclaved sediments (suggesting that sorption does occur). Microbial experiments revealed that microbes associated with sediments were much more effective at degrading precursors than microbes within the water column. Overall, this study demonstrated that natural processes are capable of attenuating NDMA precursors relatively quickly within the environment, and that utilities might benefit from maximizing source water residency time in the environment, prior to introduction into treatment plants.

Seasonal and spatial variability of nitrosamines and their precursor sources at a large-scale urban drinking water system

Nitrosamines are considered to pose greater health risks than currently regulated DBPs and are subsequently listed as a priority pollutant by the EPA, with potential for future regulation. Denver Water, as part of the EPA's Unregulated Contaminant Monitoring Rule 2 (UCMR2) monitoring campaign, found detectable levels of N-nitrosodimethylamine (NDMA) at all sites of maximum residency within the distribution system. To better understand the occurrence of nitrosamines and nitrosamine precursors, Denver Water undertook a comprehensive year-long monitoring campaign. Samples were taken every two weeks to monitor for NDMA in the distribution system, and quarterly sampling events further examined 9 nitrosamines and nitrosamine precursors throughout the treatment and distribution systems. NDMA levels within the distribution system were typically low (>1.3 to 7.2 ng/L) with a remote distribution site (frequently >200 h of residency) experiencing the highest concentrations found. Eight other nitrosamines (N-nitrosomethylethylamine, N-nitrosodiethylamine, N-nitroso-di-n-propylamine, N-nitroso-di-n-butylamine, N-nitroso-di-phenylamine, N-nitrosopyrrolidine, N-nitrosopiperidine, N-nitrosomorpholine) were also monitored but none of these 8, or precursors of these 8 [as estimated with formation potential (FP) tests], were detected anywhere in raw, partially-treated or distribution samples. Throughout the year, there was evidence that seasonality may impact NDMA formation, such that lower temperatures (~5-10°C) produced greater NDMA than during warmer months. The year of sampling further provided evidence that water quality and weather events may impact NDMA precursor loads. Precursor loading estimates demonstrated that NDMA precursors increased during treatment (potentially from cationic polymer coagulant aids). The precursor analysis also provided evidence that precursors may have increased further within the distribution system itself. This comprehensive study of a large-scale drinking water system provides insight into the variability of NDMA occurrence in a chloraminated system, which may be impacted by seasonality, water quality changes and/or the varied origins of NDMA precursors within a given system.