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Contribution of N-Nitrosamines and Their Precursors to Domestic Sewage by Greywaters and Blackwaters Teng Zeng, and William A. Mitch Environ. Sci. Technol., Just Accepted Manuscript • DOI: 10.1021/acs.est.5b04254 • Publication Date (Web): 23 Oct 2015 Downloaded from http://pubs.acs.org on October 24, 2015
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Contribution of N-Nitrosamines and Their Precursors to
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Domestic Sewage by Greywaters and Blackwaters
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Teng Zeng1,2, William A. Mitch1,2,*
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Stanford, California 94305, United States
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Water Infrastructure (ReNUWIt), 473 Via Ortega, Stanford, California 94305, United States
Department of Civil and Environmental Engineering, Stanford University, 473 Via Ortega,
National Science Foundation Engineering Research Center for Re-Inventing the Nation’s Urban
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AUTHOR EMAIL ADDRESS:
[email protected] 10
CORRESPONDING AUTHOR FOOTNOTE:
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William A. Mitch: Email:
[email protected], Phone: 650-725-9298, Fax: 650-723-7058
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ABSTRACT
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N-nitrosamines and their precursors are significant concerns for utilities exploiting
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wastewater-impacted water supplies, particularly those practicing potable reuse of wastewater.
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Previous efforts to identify specific precursors in municipal wastewater accounting for N-
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nitrosamine formation have met with limited success. As an alternative, we quantified the
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relative importance of greywater (i.e., shower, kitchen sink, bathroom washbasin and laundry)
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and blackwater (i.e., urine and feces) streams in terms of their loadings of ambient specific and
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total N-nitrosamines and chloramine-reactive and ozone-reactive N-nitrosamine precursors to
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domestic sewage. Accounting for the volume fractions of individual greywater and blackwater
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streams, laundry water represented the most significant source of N-nitrosamines and their
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precursors, followed by shower water and urine. Laundry water was particularly important for
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ozone-reactive N-nitrosamine precursors, accounting for ~98% of N-nitrosodimethylamine
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(NDMA) precursors and ~70% of precursors for other uncharacterized N-nitrosamines. For the
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other greywater streams, consumer products contributed additional N-nitrosamines and
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precursors, but the remarkable uniformity across different products suggested the importance of
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common macroconstituents. Consumption of a standard dose of the antacid, ranitidine,
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substantially increased NDMA and its chloramine-reactive precursors in urine. Nevertheless,
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nearly 40% of the American population would need to consume ranitidine daily to match the
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NDMA loadings from laundry water.
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INTRODUCTION
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To meet increasing water demands, utilities are exploring the use of source waters impacted
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by municipal wastewater discharges or even the potable reuse of highly treated municipal
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wastewater effluents.1 In addition to the occurrence of N-nitrosamines in municipal wastewater,2,
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N-nitrosamines are probable human carcinogens with low nanogram-per-liter drinking water
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concentrations associated with a 10-6 lifetime excess cancer risk.9 The U.S. Environmental
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Protection Agency (USEPA) is considering regulation of N-nitrosamines as a group,10 and
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California has established a drinking water notification level of 10 ng/L for N-
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nitrosodimethylamine (NDMA) and two other N-nitrosamines.11 Thus, N-nitrosamines are a
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significant concern for wastewater-impacted water supplies.5, 6
application of chloramines or ozone during treatment also promotes their formation.4-8 Several
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Characterization of specific N-nitrosamine precursors and formation pathways has been a
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research focus over the past decade.5, 6 Chloramination of secondary and tertiary amines forms
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N-nitrosamines at comparable yields (i.e., ~2%).5, 12 Although secondary (e.g., dimethylamine)
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and tertiary amines (e.g., trimethylamine) are human metabolites occurring in urine and feces,13,
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significantly to N-nitrosamine formation in chloraminated wastewater effluents.4, 12 A subset of
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tertiary amine-based moieties form NDMA at yields up to 90% upon chloramination and have
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been hypothesized as an important source of NDMA precursors because some of these structures
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occur in pharmaceuticals that may be microconstituents of domestic sewage (e.g., ranitidine and
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methadone).15-17 Chloramination of quaternary ammonium compounds forms N-nitrosamines at
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an order of magnitude lower yields than secondary and tertiary amines,18 but they have been
both are removed during activated sludge treatment, such that they do not contribute
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hypothesized to serve as N-nitrosamine precursors due to their occurrence as macroconstituents
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of domestic sewage based upon their widespread usage as major ingredients of consumer
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products (e.g., shampoos18) and of treatment polymers (e.g., cationic coagulation polymers19, 20).
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Efforts to identify specific precursors accounting for a significant fraction of N-nitrosamine
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formation during chloramination have met with less success. While ranitidine has been detected
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in U.S. wastewater treatment plant effluents with a mean concentration of 120 ng/L,21 it was
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detected in only one out of 84 samples (at the 10 ng/L method reporting limit) in a nationwide
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survey of wastewater-impacted streams.22 Methadone has been detected in a range of wastewater
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effluents, but only accounted for a maximum of 3% of NDMA formation in wastewater-
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impacted surface waters and a median of 13% of NDMA formation in one wastewater sample.17
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On the other hand, ozonation of certain hydrazine, sulfamide, hydrazone and carbamate-
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containing industrial chemicals can form NDMA at high yields.23 While efforts to attribute
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NDMA formation during ozonation to specific industrial chemicals have achieved some success
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in particular watersheds (e.g., anti-yellowing agents in Japan24, 25 and the fungicide, tolylfluanide,
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in Germany26, 27), the dependence of such findings on the types of industrial discharges likely
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render these precursors highly site-specific. Given the matrix complexity of wastewater, it is
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likely that a wide array of compounds contribute to N-nitrosamine formation. However, the
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relative importance of specific precursors during chloramination or ozonation remains unclear.
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As an alternative to identifying specific precursors, the goal of this work was to compare the
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loadings of N-nitrosamines and their precursors from different greywater and blackwater streams
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to domestic sewage, including greywaters from tub showers, kitchen sinks, bathroom washbasins
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and washing machines, and blackwaters from urine and feces. Particular emphasis was placed on
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evaluating whether N-nitrosamine precursors derived from consumer products. Specifically, we
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quantified the ambient specific and total N-nitrosamine levels in four greywater and two
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blackwater streams. We also quantified the levels of chloramine-reactive and ozone-reactive N-
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nitrosamine precursors in these streams. Weighting these data by the percentage of domestic
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sewage constituted by each stream, we estimated the fractional contributions of individual
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streams to the overall loading of N-nitrosamines and their precursors to domestic sewage.
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MATERIALS AND METHODS
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Chemicals and reagents are described in the Supporting Information (see Text S1). Sample collection and processing
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Greywater samples were collected from tub showers, kitchen sinks, bathroom washbasins and
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washing machines by residents at two single-family houses on separate occasions. In order to
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capture the variation in commercial formulations available on the market, at least five market-
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leading brands of personal care (i.e., shampoos or handsoaps) or household cleaning products
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(i.e., dishsoaps or detergents) were used for washing or cleaning activities (see Tables S1-S6 for
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a product list). Each greywater and consumer product combination was evaluated once. For the
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amount of consumer products applied and consumer practices (e.g., shower duration), the
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residents followed their personal preferences. In contrast to previous studies measuring N-
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nitrosamine formation from consumer products mixed with ultrapure water,18 we sought to gauge
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the importance of consumer products relative to other components within the context of the
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complex mixture generated under realistic usage conditions.
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Shower water samples were collected from a stoppered tub after two daily showers where one
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shampoo product was used along with the same type of bar soap. Kitchen water samples were
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collected from a stoppered kitchen sink after manual washing of various loads of plates, bowls
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and cutlery with one liquid dishwashing product. Bathroom washbasin water samples were
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collected in a stoppered bathroom washbasin after six handwashings with one handsoap product.
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Laundry water samples were collected from the effluent of an Electrolux front-load washing
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machine (model #EIFLW55HIW0, normal 52 min wash cycle set to warm water, medium soil
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and high spin) washing a medium-size load of old, mixed white and colored clothes with one
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detergent product but without any fabric softener product. One separate laundry water sample
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was collected with mixed white and colored clothes washed with one fabric softener product but
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without any detergent. Two additional laundry water samples were collected with white and
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colored clothes washed separately without any detergent or fabric softener. For each greywater
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stream, control samples without the application of consumer products were also collected (e.g.,
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handwashings without using any handsoap). All samples were collected in high-density
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polyethylene jars and returned to Stanford University within 24 h of collection, filtered through
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0.7-µm pre-combusted glass fiber filters, and stored at 4 °C in the dark until use. While filtration
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may remove particle-associated N-nitrosamines,4,
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relevance to wastewater effluents.
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dissolved N-nitrosamines are of greater
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Urine and fecal water samples were obtained from five adult volunteers who had no known
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gastrointestinal symptoms and had balanced meals at regular times. Sample collection and
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handling protocols were reviewed and approved by the Stanford University Institutional Review
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Board (Protocol Number 32245). Five volunteers who indicated no pharmaceutical use
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contributed one set of first-voided morning urine and feces samples. In addition, two of these
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volunteers consumed one Zantac® 150 tablet (contains 150 mg of ranitidine) at bedtime and then
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contributed first-voided morning urine and feces samples. Urine samples were collected using
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sterilized SAFE-D-Spense containers, while feces samples were collected using sterilized
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Commode specimen collection systems. All samples were returned to Stanford University within
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6 h of collection. Whole urine samples were diluted into 6 L of tap water exhibiting a chloramine
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residual to simulate a single urinal flush, filtered through 0.7-µm glass fiber filters, and stored at
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-20 °C in the dark until use. Whole feces samples were homogenized with tap water in a
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weight:volume ratio of 1:1 in a Waring laboratory blender, mixed with ~12 L of tap water to
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simulate a single toilet flush, and centrifuged at 8,000 g for 10 min. The supernatant (i.e., fecal
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water) was sequentially filtered through 2.7-µm and 0.7-µm glass fiber filters and stored at -20
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°C in the dark until use. Greywater and blackwater samples were analyzed for basic water quality
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parameters (see Text S2 for additional details), and each sample was split and chloraminated or
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ozonated in duplicate.
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Chloramination and ozonation tests
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Previous research on chloramine-reactive precursors has mostly employed formation potential
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tests, but the extreme chloramination conditions may overestimate the importance of precursors
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that may not lead to meaningful N-nitrosamine formation under typical treatment conditions.
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Instead, we employed Uniform Formation Condition (UFC) tests mimicking practical
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chloramination conditions (designated as the “NH2Cl” samples). When needed, ultrapure water
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was added to the sample to target a constant final volume of 500 mL for the analysis of specific
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N-nitrosamines or 1 L for the analysis of total N-nitrosamines (TONO). The overall dilution of
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matrix components (e.g., dissolved organic carbon (DOC), nitrogen species, etc.) was maintained
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consistent across chloramination and ozonation tests (see Text S3 for additional descriptions).
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These dilution factors were accounted for such that the N-nitrosamine concentrations are
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reported as the concentrations in the raw greywater samples or in the urine or fecal water
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samples after dilution into 6 L or 12 L of tap water, respectively. Chloramination was initiated by
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adding an aliquot of freshly-prepared preformed monochloramine solution into the sample
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(buffered at pH 8.0 with 4 mM borate) to achieve an initial concentration of 5 mgCl2/L.
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Chloraminated samples were held in the dark for 3 d at room temperature (typically 23±1 °C)
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and the residual chloramines (typically 1.0±0.4 mgCl2/L) were quenched with ~31 mg/L ʟ-
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ascorbic acid. We further applied ozone reactivity tests on a second set of samples (designated as
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the “O3” samples). Ozonation was initiated by mixing an aliquot of ozone solution with the
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sample to achieve an initial ratio of 0.8 mg ozone per mg DOC. This ozone dose was chosen
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based on a literature review of typical doses employed for trace organic contaminant removal,
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pathogen inactivation, and membrane fouling control.7, 29-34 Ozonated samples were held in the
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dark at room temperature until no ozone residual was detectable.
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Chloraminated and ozonated samples were analyzed following a modified USEPA Method
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521 protocol for nine specific N-nitrosamines, including NDMA, N-nitrosomethylethylamine
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(NMEA),
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butylamine, N-nitrosopyrrolidine (NPYR), N-nitrosopiperidine (NPIP), N-nitrosomorpholine
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(NMOR) and N-nitrosodiphenylamine. Samples were also analyzed for TONO using a
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chemiluminescence method.8, 35, 36 A third set of untreated samples (designated as the “Raw”
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samples), along with tap water blanks, were processed and analyzed following the same protocol
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to quantify the background levels of N-nitrosamines. Specific and total N-nitrosamine
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concentrations in raw, chloraminated and ozonated tap water samples were below the method
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reporting limits (i.e.,
