Nitrosamine Precursors and Wastewater Indicators in Discharges in

Chapter 7

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Nitrosamine Precursors and Wastewater Indicators in Discharges in the Sacramento-San Joaquin Delta Chih-Fen Tiffany Lee,* Stuart W. Krasner, Michael J. Sclimenti, Matthew Prescott, and Yingbo C. Guo Water Quality Section, Metropolitan Water District of Southern California, 700 Moreno Avenue, La Verne, California 91750-3303 *E-mail: [email protected].

Wastewater treatment plant (WWTP) discharges in the Sacramento-San Joaquin Delta were shown to be a source of N-nitrosodimethylamine (NDMA) and N-nitrosomorpholine (NMOR), as well as precursors for NDMA and N-nitrosopyrridine (NPYR). NDMA and NPYR were disinfection by-products, whereas NMOR was a wastewater contaminant. Nitrosamines were not found downstream of the WWTPs due to dilution with river water and/or sunlight photolysis, whereas NDMA precursor loadings in the river downstream of the WWTPs were at higher levels than at the upstream sites. The anticonvulsant primidone and the artificial sweetener sucralose were found to be good wastewater indicators and the percentage of treated wastewater in the Sacramento River (2-3%) and the San Joaquin River (2-14%) was determined by these. Moreover, the increase in NDMA precursor loadings in downstream sites was consistent with the wastewater volumetric contributions to river flow.

Introduction The Sacramento-San Joaquin Delta (Delta) is at the nexus of a California statewide water system, which provides a critical water supply (State Project Water [SPW]) to 23 million people in California. The Delta is at the confluence of the Sacramento and San Joaquin Rivers (Figure 1). The Delta empties into the Pacific © 2015 American Chemical Society Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Ocean via an estuary to the San Francisco Bay. Due to tidal activity, especially during droughts, there can be tidal actions in the San Joaquin River. There are nine wastewater treatment plants (WWTPs) discharging from 0.3 to 181 million gallons per day (MGD) into the Delta (1). The City of Stockton and Sacramento Regional operate the two largest WWTPs in the Delta. They discharge into the San Joaquin and Sacramento River, respectively (Figure 1). Wastewater discharges (effluent organic matter [EfOM]) contain emerging chemical contaminants, such as nitrosamines and their precursors, and pharmaceuticals and personal care products (PPCPs). EfOM is known to be one of the major sources of N-nitrosodimethylamine (NDMA) precursors (2). NDMA is a disinfection by-product (DBP) preferentially formed by chloramines (3). N-Nitrosomorpholine (NMOR) is also commonly detected in wastewater discharges, where it appeared to be a wastewater contaminant and not a DBP per se (4). Nitrosamines are known to be probable human carcinogens, and they have gained a lot of attention from health and regulatory agencies in the United States (U.S.) and internationally (5). Although there is no federal regulation for nitrosamines in drinking water, the California State Water Resources Control Board Division of Drinking Water (DDW) set a notification level of 10 ng/L each for NDMA and two other nitrosamines (6). The objective of this study was to evaluate the presence and fate of NDMA, other nitrosamines, their precursors, and selected PPCPs in the Delta, including seasonal and year-to-year variability.

Figure 1. Map of Sacramento –San Joaquin Delta (triangles = WWTPs). 120 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Experimental


Overview of Study The sampling sites in this study included locations upstream and downstream of the Stockton and Sacramento Regional WWTPs, and WWTP effluent or river water immediately adjacent to the discharge. Table 1 lists the sampling locations. There were a total of eight sampling events: both watersheds were sampled in six of them, covering summer, fall, and winter seasons over a two-year period; only the San Joaquin River and the Stockton WWTP were sampled in two additional events. The samples were analyzed for eight nitrosamines, including NDMA, NMOR, and N-nitrosopyrridine (NPYR). Certain PPCPs found in wastewater can be used as conservative indicators of wastewater impacts in drinking water supplies. The indicators used in this project were primidone (an anticonvulsant drug) (7, 8) and sucralose (an artificial sweetener - Splenda®) (9). The percentage of treated wastewater in the rivers was calculated as the ratio of the concentrations of these indicators in the rivers against their concentrations in the WWTP effluents. In addition, modeling of volumetric contributions of the WWTP discharges to the river flow was estimated using a simulation model.

Table 1. Sampling Locations in the Study Sampling Location San Joaquin River Watershed

Sacramento River Watershed

Upstream of Stockton WWTP

Upstream of Sacramento Regional WWTP

Stockton WWTP filter effluent

Sacramento Regional WWTP outfall (grab sample in Sacramento River by discharge)

Stockton WWTP plant effluent Downstream of Stockton WWTP

Downstream of Sacramento Regional WWTP

Study Sites Stockton WWTP The Stockton WWTP was a tertiary treatment plant. The advanced treatment units included oxidation ponds, wetlands, nitrifying biotowers, dissolved air floatation (DAF), and mix media filters. The effluent was chlorinated and ammonia was added (if needed; ammonia was present or not, depending on how well the biotowers nitrified the water to form chloramines). The tertiary processes provided additional treatment to clean up the wastewater, including removal of ammonia, algae, and a final filtering through sand, gravel, and anthracite coal to remove more organic material and fine suspended particles. 121 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Sacramento Regional WWTP The Sacramento Regional WWTP was a secondary treatment plant. Secondary treatment included a conventional aerobic biological treatment process and secondary clarification. The effluent was poorly nitrified. Chlorine was added, which should have reacted with the ammonia to form choramines.

Analytical Methods


Nitrosamines Standard method 6450B was used to measure eight nitrosamines: NDMA, N-nitrosomethylethylamine (NMEA), N-nitrosodiethylamine (NDEA), N-nitrosodi-n-proplyamine(NDPA), N-nitrosodi-butylamine (NDBA), NPYR, N-nitrosopiperidine (NPIP), and NMOR. Nitrosamines were extracted and concentrated using solid-phase extraction (SPE) with Ambersorb 572 resin and were analyzed using gas chromatography/mass spectrometry (GC/MS) with chemical ionization (10). Nitrosamine concentrations were determined by comparison of the area ratio of a unique product ion to one of the isotopically labeled internal standards (i.e., d6-NDMA, d14-NDPA, and 15N2-NDEA) against calibration curves made from method (SPE) standards. The minimum reporting level (MRL) for each nitrosamine was 2 ng/L.

Nitrosamine Precursors Nitrosamine precursors were determined using formation potential (FP) tests (11, 12). Nitrosamine FP tests were conducted in the presence of chloramines. Filtered (0.45-µm) samples were chloraminated on a reactivity basis (based on the amount of organic carbon) and held for 3 days at pH 8 at 25°C. The chlorine dose was based on the level of total organic carbon (TOC) (i.e., Cl2 = 3 x TOC, weight basis), and the amount of ammonia was calculated based on a chlorine-to-nitrogen (Cl2/N) weight ratio of 3:1. In the tests, ammonia was added before chlorine in order to form chloramines with no free chlorine contact time. Note, if ammonia was present in the sample, this was factored into how much more was added in the FP test. For poorly nitrified wastewaters, no ammonia was added in the FP test, and the resultant Cl2/N weight ratio was typically in the range of 1:1 to 2:1.

PPCPs PPCPs were concentrated using a SPE workstation with HLB cartridges (Waters, Milford, MA) and were analyzed using liquid chromatography/tandem MS (LC/MS/MS) with a 2.0-mm C18 reversed-phase high pressure LC (HPLC) column (13). For primidone, the MS was operated under an electrospray positive ion mode. PPCPs were identified by matching both the retention time and the 122 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

MS/MS transition in the samples with those in authentic standards. An isotope dilution technique was used for quantitation (14). The MRL for primidone was 2 ng/L.

Sucralose


Filtered (0.45-μm) water samples were injected directly onto the C18 HPLC column equipped with a 2.0-mm C18 guard column. The MS was operated under an electrospray negative ion mode. Sucralose was identified as were other PPCPs. An isotope dilution technique was used for quantitation with d6-sucralose. The MRL was 0.2 µg/L.

Hydraulic Flow Modeling The California Department of Water Resources (DWR) used the Delta Simulation Model II (DSM2) to study the complex hydraulic system in the Delta (15). DSM2 was a mathematical model for dynamic simulation of one-dimensional hydrodynamics, water quality, and particle tracking in a network of riverine or estuarine channels.

Results and Discussion N-Nitrosamines and Their Precursors in the Stockton WWTP Studies have shown that WWTPs may remove N-nitrosamines present in the wastewater (16). Studies in the U.S. showed that chloramination of treated wastewater can form N-nitrosamines above the background level (4). Moreover, studies in the U.S. showed that N-nitrosamine precursors were present in secondary or tertiary treated wastewater (2). In the Stockton WWTP, NDMA, NPYR and NMOR were detected in FP samples. Figure 2 shows the impact of the tertiary treatment process on N-nitrosamine FP. NDMA FP was over 1000 ng/L after secondary treatment; however, the concentration dropped significantly after the tertiary treatment began and remained fairly constant throughout the whole process. Similar trends were observed for NPYR FP and NMOR FP. In addition to measuring the N-nitrosamine FP, the amount of N-nitrosamines formed after chloramine addition at the WWTP was determined. Figure 3 shows there was no NDMA detected at or above the MRL in the WWTP filter effluent; however, the formation of NDMA spiked up at the WWTP effluent (interquartile range ~4-82ng/L, median ~18 ng/L) due to chloramine usage. Unlike NDMA, NMOR was present before chloramine addition, and its occurrence stayed the same after chloramine addition, as NMOR was a wastewater contaminant and not a DBP (4). Although NMOR was detected in some of the FP tests, its concentration in the FP test was often no different than that of the water before FP testing. Neither NDMA nor NMOR were detected downstream of the WWTP. This was likely due to dilution in the river water and/or sunlight photolysis (17). 123 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 2. Impact of tertiary treatment on N-nitrosamine FP at the Stockton WWTP.

Figure 3. NDMA and NMOR in the San Joaquin River and at the Stockton WWTP (bottom and top of the box = 25th to 75th percentile, line through the box = median, bottom and top of the whiskers = 10th to 90th percentile). 124 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Wastewater Indicators in WWTPs and Estimated Wastewater Effluent Figure 4 shows the concentrations of the wastewater indicators in the effluent of the Stockton WWTP. The interquartile range (25th to 75th percentile) of sucralose concentrations was 24 to 31 µg/L, which compared well with the typical range detected in other U.S. WWTP effluents of 20-30 µg/L (median = 27 µg/L) (9). The interquartile range of primidone concentrations, 109 to 136 ng/L, also fell within the typical range of other U.S. WWTPs of 100-200 ng/L (7). An effluent sample site was not available from the Sacramento Regional WWTP, so the sampling location was a depth sample in the Sacramento River near the discharge pipe (outfall); all samples were grab samples. The effluent sample was diluted to varying extents by river flow. The percent effluent in the sample was estimated based on either the sucralose or primidone concentration, assuming a similar level at the Sacramento Regional WWTP as that detected at the Stockton WWTP (Figure 4). These percentages were similar to estimates based on the ammonia level in the sample and the ammonia concentration in discharge records. The N-nitrosamine FP data from the Sacramento Regional WWTP discharge sample were corrected for dilution to provide an estimate of the levels likely present in the WWTP effluent as part of the effort to follow the fate of the precursors in the Sacramento River (Figure 5).

Figure 4. Concentrations of the wastewater indicators in the effluent of the Stockton WWTP. 125 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 5. Estimated percent WWTP effluent in Sacramento Regional WWTP outfall samples based on sucralose and primidone.

Impact of WWTP Effluents in the Sacramento and San Joaquin Rivers Figures 6 and 7 show the occurrence of NDMA precursors in the Sacramento and San Joaquin Rivers upstream and downstream of the WWTPs, and in the WWTP effluents during the six main sampling events. The percent effluent in the Sacramento Regional WWTP outfall sample was estimated based on primidone and then the NDMA FP in the WWTP effluent was back calculated. The San Joaquin WWTP effluent had 206-358 ng/L (median = 218 ng/L) and the Sacramento Regional WWTP effluent was estimated to have had 227-812 ng/L (median = 508 ng/L). In the Sacramento River, the NDMA precursor levels were higher downstream of the WWTP (9-22 ng/L [median = 17 ng/L]) than upstream (4-9 ng/L [median = 5 ng/L]), due to the wastewater discharge from the Sacramento Regional WWTP. In the San Joaquin River, in most cases, higher NDMA precursor levels were found downstream of the WWTP (e.g., 12-48 ng/L [median = 40 ng/L]) than upstream (e.g., 7-38 ng/L [median = 16 ng/L]). However, in some cases, the upstream location either had similar or higher levels of NDMA precursors than downstream. These events were due to “reverse river flow,” where the direction of the natural flow was reversed due to tidal action (the effect of the tidal flow into the Delta and the surrounding estuaries on the flow of the river). Sucralose and primidone had similar trends as the NDMA FP in the San Joaquin River during reverse river flow sampling events. 126 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 6. NDMA precursors in the Sacramento River and estimated in the Sacramento Regional WWTP effluent (based on primidone).

Table 2 shows an example of the impact of the Stockton WWTP discharge on the San Joaquin River. There was 35 µg/L of sucralose and 132 ng/L of primidone in the WWTP effluent. Higher levels of primidone (9.1 ng/L increase) and sucralose (2.7 µg/L increase) were observed at the downstream sample site due to the wastewater discharge from the Stockton WWTP. Based on these wastewater indicators, the downstream site was ~7-8% higher in EfOM than the upstream location (e.g., (5.3 µg/L of sucralose downstream – 2.6 µg/L of sucralose upstream)/35 µg/L of sucralose in the WWTP effluent)). In terms of the NDMA FP, there was a higher level downstream of the WWTP (20 ng/L increase).

Figure 7. NDMA precursors in the San Joaquin River and in the Stockton WWTP effluent (reverse flows during the November 2011 and July 2012 sample events). 127 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

Table 2. Concentrations of the Wastewater Indicators and NDMA FP in the San Joaquin River and in the Stockton WWTP Effluent (November 2012) NDMA FP

Primidone

Sucralose

ng/L

ng/L

µg/L

Upstream

25

9.5

2.6

WWTP

283

132

34.9

Downstream

45

18.6

5.3

10 %

7%

8%


Estimated % Effluent

Based on the wastewater indicators, it was predicted that the NDMA FP should have increased by ~20-23 ng/L, consistent with the observed increase. Note, there was a smaller WWTP upstream of the Stockton WWTP, which contributed to the presence of these contaminants in the upstream sample location. However, in this study, the focus was on the incremental contribution of the Stockton WWTP to the precursor loading in the river. Figure 8 shows the relationship of the wastewater indicators to NDMA FP in both river/WWTP systems. On a central tendency basis, the slope of the trend line was steeper for the Sacramento River/WWTP system. For example, 10 µg/L of sucralose corresponded to ~90 ng/L of NDMA FP in the San Joaquin River, whereas the same amount of sucralose corresponded to a higher level of NDMA FP (>150 ng/L) in the Sacramento River. This was probably due (in part) to the different treatment processes at the Sacramento Regional and Stockton WWTPs; the Sacramento Regional WWTP only had secondary treatment, whereas the Stockton WWTP had tertiary treatment. Tertiary treatment can remove NDMA precursors; however, tertiary treatment should have little effect on removing these wastewater indicators. Percentage of River Flow that Was Wastewater-Impacted DSM2 can calculate stages, flows, velocities, transport of individual particles, and mass transport processes for conservative and non-conservative constituents, including salts, water temperature, dissolved oxygen, and dissolved organic carbon. DMS2 was used to determine the volumetric fraction of WWTP effluent at certain locations, downstream of the WWTPs. 128 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 8. Relationship of the wastewater indicators to NDMA FP in the Sacramento and San Joaquin Rivers and at the corresponding WWTPs (Sacramento Regional WWTP outfall data plotted as measured, without correction for dilution of the WWTP effluent in the river).

129 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 9 shows the percent wastewater effluent in these two rivers as estimated by the model. The data from the model was a daily average of the river flow, whereas the data from our sampling events were based on grab samples. In the San Joaquin River, the percent WWTP effluent in the downstream location fluctuated from 2 to 14%, whereas the Sacramento River percentage remained steady at 2-4%. This was due to the higher river flow of the Sacramento River. The average annual river flow of Sacramento River was 23,469 cubic foot per second (cfs), whereas in the San Joaquin River it was 4,460 cfs.

Figure 9. Estimated percentage of WWTP effluent in downstream San Joaquin and Sacramento River sample sites (volume basis) from hydraulic flow modeling. 130 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.


Figure 10. Estimated percent of WWTP effluent in downstream Sacramento River and San Joaquin River sample sites based on the wastewater indicators

Figure 10 shows that both wastewater indicators had good agreement in the estimation of percent WWTP effluent in the downstream locations in these two rivers. Moreover, the estimations based on wastewater indicators matched well with the hydraulic flow-calculated contributions.

Conclusions Effluents from the two largest WWTPs in the Delta were shown to be an important source of NDMA precursors in a major source of drinking water for 23 million Californians. NDMA precursor loadings in the river were detected downstream of the WWTPs at higher levels than at the upstream sites, where the increase was consistent with the percent of river flow due to the WWTP discharge. However, due to river dilution and/or solar photolysis, the nitrosamines formed or present at the WWTP were not detected at or above the MRLs downstream of these WWTPs. The anticonvulsant primidone and the artificial sweetener sucralose were found to be good wastewater indicators, and the percentage of treated wastewater in the rivers was determined based on these indicators. In addition, the volumetric wastewater contribution to river flow was determined using a hydraulic simulation model, which matched the percent effluent estimations based on the wastewater 131 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

indicators. A good relationship was found between the level of NDMA precursors in the river/WWTP systems and the wastewater indicators, where the slope of the trend line was steeper for the river system with the WWTP with secondary treatment as compared to the system with the tertiary treatment process.

Acknowledgments


The authors gratefully acknowledge support from the staff of the California DWR and the City of Stockton, with special thanks going to Carol DiGiorgio (DWR) and Laura Lazzelle (City of Stockton).

References 1.

2.

3.

4.

5.

6.

7.

8.

9.

Guo, Y. C.; Krasner, S. W.; Fitzsimons, S.; Woodside, G.; Yamachika, N. Source, Fate, and Transport of Endocrine Disruptors, Pharmaceuticals, and Personal Care Products in Drinking Water Sources in California; National Water Research Institute: Fountain Valley, Ca., May 2010, pp 14−21 Krasner, S. W.; Westerhoff, P.; Chen, B.; Rittmann, B. E.; Nam, S.-N.; Amy, G. Impact of Wastewater Treatment Processes on Organic Carbon, Organic Nitrogen, and DBP Precursors in Effluent Organic Matter. Environ. Sci. Technol. 2009, 43 (8), 2911–2918. Mitch, W. A.; Sharp, J. O.; Trussell, R. P.; Valentine, R. L.; AlvarezCohen, L.; Sedlak, D. L. N-Nitrosodimethylamine as a Drinking Water Contaminant: A review. Environ. Eng. Sci. 2003, 20 (5), 389–404. Krasner, S. W.; Westerhoff, P.; Chen, B.; Rittmann, B. E.; Amy, G. Occurrence of Disinfection Byproducts in United States Wastewater Treatment Plant Effluents. Environ. Sci. Technol. 2009, 43 (21), 8320–8325. Krasner, S. W.; Mitch, W. A.; McCurry, D. L.; Hanigan, D.; Westerhoff, P. Formation, Precursors, Control, and Occurrence of Nitrosamines in Drinking Water: A review. Wat. Res. 2013, 47 (13), 4434–4446. California Environmental Protection Agency State Water Resources Control Board. NDMA and Other Nitrosamines - Drinking Water Issues;http://www.waterboards.ca.gov/drinking_water/certlic/ drinkingwater/NDMA.shtml [cited November 1, 2014]. Krasner, S. W.; Pastor, S. J.; Garcia, E. A. Measurement of the Pharmaceutical Primidone as a Conservative Tracer of Wastewater Influences in Drinking Water Supplies. In Proceedings of 2006 American Water Works Association (AWWA) Water Quality Technology Conference (WQTC); AWWA: Denver, CO, 2006. Guo, Y. C.; Krasner, S. W. Occurrence of Primidone, Carbamazepine, Caffeine, and Precursors for N-Nitrosodimethylamine in Drinking-Water Sources Impacted by Wastewater. J. Am. Water Resour. Assoc. 2009, 45, 58–67. Oppenheimer, J.; Eaton, A.; Badruzzaman, M.; Haghani, A.; Jacangelo, J. Occurrence and Suitability of Sucralose as an Indicator Compound of 132 Karanfil et al.; Recent Advances in Disinfection By-Products ACS Symposium Series; American Chemical Society: Washington, DC, 2015.

10. 11.


12.

13.

14.

15.

16.

17.

Wastewater Loading to Surface Waters in Urbanized Region. Water Res. 2011, 45, 4019–4027. APHA, AWWA, and WEF. Standard Methods for the Examination of Water and Wastewater, Method 6450, Nitrosamines; Washington DC, 2008. Krasner, S. W.; Sclimenti, M. J.; Guo, Y. C.; Hwang, C. J.; Westerhoff, P. Development of DBP and Nitrosamine Formation Potential Tests for Treated Wastewater, Reclaimed Water, and Drinking Water. In Proceedings of 2004 American Water Works Association (AWWA) Water Quality Technology Conference (WQTC); AWWA: Denver, CO, 2004. Krasner, S. W.; Sclimenti, M. J.; Mitch, W. A.; Westerhoff, P.; Dotson, A. Using Formation Potential tests to Elucidate the Reactivity of DBP precursors with Chlorine versus with Chloramines. Proceedings of 2007 American Water Works Association (AWWA) Water Quality Technology Conference (WQTC); AWWA: Denver, CO, November 18−22, 2007. Vanderford, B. J.; Pearson, R. A.; Rexing, D. J.; Snyder, S. A. Analysis of Endocrine Disruptors, Pharmaceuticals, and Personal Care Products in Water Using Liquid Chromatography/Tandem Mass Spectrometry. Anal. Chem. 2003, 75, 6265–6274. Vanderford, B. J.; Snyder, S. A. Analysis of Pharmaceuticals in Water by Isotope Dilution Liquid Chromatography/Tandem Mass Spectrometry. Environ. Sci. Technol. 2006, 40, 7312–7320. Department of Water Resources Bay-Delta. Delta Simulation Model II -DSM2;http://baydeltaoffice.water.ca.gov/modeling/deltamodeling/models/ dsm2/dsm2.cfm [cited November 1, 2014] Krauss, M.; Longrée, P.; Dorusch, F.; Ort, C.; Hollender, J. Occurrence and Removal of N-nitrosamines in Wastewater Treatment Plant. Water Res. 2009, 43 (17), 4381–4391. Chen, B.; Lee, W.; Westeroff, P.; Krasner, S. W.; Herckes, P. Solar Photolysis Kinetics of Disinfection Byproducts. Water Res. 2011, 44 (11), 3401–3409.

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Nitrosamine Precursors and Wastewater Indicators in Discharges in

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