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Published online 5 January 2006
Published in J Environ Qual 35:277-284 (2006)
DOI: 10.2134/jeq2005.0264
© 2006 American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America
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TECHNICAL REPORTS

Organic Compounds in the Environment

Leaching of N-Nitrosodimethylamine (NDMA) in Turfgrass Soils during Wastewater Irrigation

J. Gana,*, S. Bondarenkoa, F. Ernsta, W. Yanga, S. B. Riesb and D. L. Sedlakc

a Department of Environmental Sciences
b Agricultural Operations, University of California, Riverside, CA 92521
c Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720

* Corresponding author (jgan{at}ucr.edu)

Received for publication July 5, 2005.

   ABSTRACT
TOP
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
N-nitrosodimethylamine (NDMA) is a carcinogenic by-product of chlorination that is frequently found in municipal wastewater effluent. NDMA is miscible in water and negligibly adsorbed to soil, and therefore may pose a threat to ground water when treated wastewater is used for landscape irrigation. A field study was performed in the summer months under arid Southern California weather conditions to evaluate the leaching potential of NDMA in turfgrass soils during wastewater irrigation. Wastewater was used to irrigate multiple turfgrass plots at 110 to 160% evapotranspiration rate for about 4 mo, and leachate was continuously collected and analyzed for NDMA. The treated wastewater contained relatively high levels of NDMA (114–1820 ng L–1; mean 930 ng L–1). NDMA was detected infrequently in the leachate regardless of the soil type or irrigation schedule. At a method detection limit of 2 ng L–1, NDMA was only detected in 9 out of 400 leachate samples and when it was detected, the NDMA concentration was less than 5 ng L–1. NDMA was relatively persistent in the turfgrass soils during laboratory incubation, indicating that mechanisms other than biotransformation, likely volatilization and/or plant uptake, contributed to the rapid dissipation. Under conditions typical of turfgrass irrigation with wastewater effluent it is unlikely that NDMA will contaminate ground water.

Abbreviations: NDMA, N-nitrosodimethylamine


   INTRODUCTION
TOP
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 
THE SCARCITY of water supply in many arid regions, combined with the need for disposal of large volumes of wastewater, has led to an increased use of treated wastewater for ground water recharge or landscape irrigation (Sedlak et al., 2000; Levine and Asano, 2004). Although this practice has been employed for decades in many parts of the world, public health officials recently have begun to express concerns about the potential for wastewater-derived contaminants to contaminate potable water supplies (National Academy of Sciences, 1998). Most of the research to date has focused on compounds such as steroid hormones, pharmaceuticals, and personal care products (e.g., Kolpin et al., 2002). While some of these compounds may pose risks to aquatic organisms, none of the compounds have been shown to pose an unacceptable human health risk at the concentrations at which they occur in wastewater effluent. In contrast, N-nitrosodimethylamine (NDMA), a compound that is known for its high cancer potency (USEPA, 2005), is detected frequently in municipal wastewater effluent at concentrations up to approximately 1000 ng L–1 (Najm and Trussell, 2001; Mitch et al., 2003; California Department of Health Services, 2005a; Sedlak et al., 2005). Although a federal maximum contaminant level is not currently in place for NDMA in drinking water, regional regulatory authorities have adopted stringent limits for NDMA. For instance, the California Department of Health Services (CDHS) has set a reporting level of 10 ng L–1 for NDMA (California Department of Health Services, 2005b) while Ontario's Ministry of the Environment has set an Interim Maximum Acceptable Concentration (IMAC) of 9 ng L–1 for NDMA (Ministry of the Environment, 2003). As a result of such stringent guidelines, water-recycling programs are being scrutinized for their potential to introduce NDMA into ground water, particularly through practices such as use of treated wastewater for ground water recharge and landscape irrigation.

Earlier studies showed that NDMA has negligible affinity for soils but relatively long persistence in soil (Tate and Alexander, 1975, 1976; Oliver et al., 1979; Mallik and Tesfai, 1981; Kaplan and Kaplan, 1985; Gunnison et al., 2000; Yang et al., 2005). These characteristics suggest that NDMA may readily leach through soil and contaminate ground water if NDMA-containing wastewater is applied at the soil surface. The purpose of this study was to evaluate the leaching risk of NDMA during the use of treated wastewater for irrigating turfgrass soils. Treated wastewater was used to irrigate mature turfgrass plots in the summer months under the weather conditions typical of the arid southwestern regions of the United States, and leachate was monitored for about 4 mo for appearance of NDMA. Site-specific persistence of NDMA in turfgrass soils was independently determined through a laboratory incubation experiment to provide information on the role of degradation in NDMA dissipation from the test plots. The field study provides a more realistic understanding of NDMA than previous studies conducted with batch reactors or saturated columns (e.g., Dean-Raymond and Alexander, 1976; Gunnison et al., 2000) that did not adequately simulate processes that occur in the unsaturated vadose zone. In a companion study (Arienzo et al., 2006), NDMA loss pathways were characterized using 14C-NDMA in in situ lysimeters and the potential of prolonged wastewater irrigation in accelerating NDMA biodegradation was also investigated.


   MATERIALS AND METHODS
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 REFERENCES
 
Chemicals
NDMA was purchased as a neat liquid from Sigma-Aldrich (Milwaukee, WI) and used as received. The deuterium-labeled NDMA (d6-NDMA, 98%) was purchased from Cambridge Isotope Laboratories (Andover, MA) and used as a surrogate standard in NDMA analysis. Solvents and other chemicals were all gas chromatography (GC) or analytical reagent grade.

Source of Wastewater
Nitrified, filtered wastewater effluent, collected after chlorine disinfection, was obtained from a local wastewater treatment plant. The wastewater effluent was stored in a 22 712-L (6000-gallon) opaque polyethylene tank at the study site. Before the study, the stability of NDMA in the storage tank was determined using treated wastewater under outdoor conditions. Monitoring of NDMA levels for 28 d showed that NDMA in the wastewater was stable under the storage conditions (data not shown). A total of five tanks of treated wastewater were used for irrigation over a period of 113 d. During the study, triplicate samples were taken once a week from the tank and analyzed for NDMA concentrations. The overall concentration of NDMA in the received wastewater was high, and no additional NDMA was added in the water before it was used for irrigation.

Field Site and Soil Properties
The field study was performed in turfgrass plots located near the campus of the University of California, Riverside. The turfgrass plots were constructed in 1992 and transplanted with a hybrid Bermuda grass (Cynodon dactylon x transvaalensis) or creeping bentgrass [Agrostis stolonifera L. var. palustris (Huds.) Farw.] in 1993. Each plot was 3.7 x 3.7 m in dimension and was equipped with a separate sprinkler system with four pop-up sprinklers situated at the corners. At the time of construction, the top 89 cm was filled with soil, either a sandy loam or a loamy sand, while the bottom layer (7.6 cm) was paved with gravel. At the center of each plot, a cluster of five 208-L (55-gallon) steel drums were similarly filled with the soil and gravel. Leachate from each drum drained under gravity through a galvanized steel conduit pipe to an outlet at the edge of the field (at a lower elevation). Before the field study, soil cores were taken from both the Bermuda grass and the bentgrass plots and soil properties were characterized using standard methods (Table 1). Both soils, regardless of the turfgrass variety, contained little organic matter below the surface layer. Both soils were highly sandy, and may be considered highly conducive for water movement.


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  		Table 1. Basic physicochemical properties of soils from turfgrass plots used in the study.

 
Laboratory Incubation Experiment
Before the irrigation study the persistence of NDMA in the turfgrass soils was determined through a laboratory incubation experiment. Soil samples from both Bermuda grass and bentgrass plots were collected from the 0- to 10-, 10- to 20-, and 20- to 30-cm depths and were passed through a 2-mm sieve without air-drying. After the soil water content was adjusted to 12% (w/w), 50 g of soil (dry weight equivalent) was weighed into 125-mL glass serum bottles (Wheaton, Millville, NJ) and spiked with 2.5 mL of NDMA aqueous solution to achieve an initial concentration of 250 µg kg–1. The spiked bottles were closed by capping with aluminum seals and Teflon-lined butyl rubber septa, and manually mixed. To ascertain the role of microorganisms in NDMA degradation, one set of samples (sandy loam soil planted with Bermuda grass) were autoclaved twice and then similarly treated with NDMA. The sample bottles were then incubated in the dark at room temperature (21 ± 1°C) and triplicate samples were periodically removed for analysis of NDMA. Before extraction, soil samples were fortified with 0.1 mL of d6-NDMA in dichloromethane (10 mg L–1) as a surrogate, and then extracted by mixing in 50 mL dichloromethane on a shaker for 4 h. The solvent extract was filtered through a funnel containing 20 g anhydrous sodium sulfate, and the extract was concentrated to a final volume of about 1 mL under a stream of nitrogen. An aliquot of the final extract was used for analysis by gas chromatography–mass spectrometry (GC–MS). The recovery of NDMA spiked into the sample immediately before extraction was approximately 40%. However, as d6-NDMA was used as a surrogate standard, the low recovery did not affect the accuracy of the results. The detection limit of NDMA using the above protocol was 0.20 µg kg–1.

Irrigation Treatments and Leachate Collection
Eight Bermuda grass plots, four for each soil type, were used for the irrigation study. The field study was conducted 15 June–8 Oct. 2004. No precipitation occurred during the period of the study, and the test plots received water solely from irrigation. The daily air maximum, air minimum, and mean soil temperatures (measured at the 15-cm depth) were recorded at the study site (Fig. 1 ). The average daily air maximum, air minimum, and mean soil temperatures were 31.5, 15.8, and 22.8°C, respectively. The daily relative humidity (RH) was measured at the site and is shown in Fig. 2 . The average maximum, minimum, and mean RH values were 71, 29, and 52%, respectively. The warm and dry conditions, which are typical of southwestern U.S. regions during summer, were expected to result in high evapotranspiration rates for the turfgrass plots and a need for high irrigation inputs.



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  		Fig. 1. Daily maximum air temperature, minimum air temperature, and mean soil temperature at the 15-cm depth at the field site during the wastewater irrigation study.

 


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  		Fig. 2. Daily maximum, minimum, and mean relative humidity (RH) at the field site during the wastewater irrigation study.

 
Four treatments, each in two random plots, were considered in this study: two soil types (a sandy loam soil and a loamy sand soil), and two irrigation schedules. The two irrigation schedules were used to evaluate the potential effect of sunlight on NDMA leaching. Irrigation occurred at night (from 2230 h) or in the daytime (from 0730 h). The irrigation rate was frequently adjusted based on the actual evapotranspiration rate (ETo) measured at the site. The irrigation rate was maintained at 110 to 130% of ETo during the first 11 wk and was increased to 160% ETo thereafter to further increase the leachate flux. These irrigation rates were higher than normal and were used to create a worst-case scenario. The irrigation rates (in mm) averaged on a daily basis are shown in Fig. 3 . As irrigation occurred three times a week, the actual irrigation rate per irrigation event was from 8 to 31 mm, depending on the prevailing weather conditions.



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  		Fig. 3. Averaged daily irrigation rates of treated wastewater in turfgrass plots during the wastewater irrigation study.

 
Leachate from each plot was collected in an opaque polyethylene container with a small opening. Three times a week, the leachate samples were transferred into 1-L brown glass bottles and immediately transported to the laboratory. Samples were stored at 4°C if not immediately analyzed. Most samples were analyzed on the same day of sample collection. For quality control, 50% of the samples were also sent to the Department of Civil and Environmental Engineering, University of California, Berkeley, and 10% to the Water Quality Laboratories, Long Beach Water District, California, for confirmatory analysis of NDMA.

Analytical Procedures
The method used for analyzing NDMA in treated wastewater and leachate samples was similar to the method developed Mitch and Sedlak (2002). Briefly, a 1000-mL water sample was transferred to a 2-L glass separatory funnel and fortified with 0.1 mL of 10 mg L–1 d6-NDMA in methylene chloride. The sample was then vigorously mixed with 100 mL methylene chloride for 2 min. After phase separation, the methylene chloride phase was collected, and the remaining aqueous phase was extracted for two additional times with fresh solvent. The extracts were combined, passed through a layer of anhydrous sodium sulfate, and then concentrated to 0.1 to 0.2 mL on a rotary evaporator under vacuum. An aliquot of sample was injected into GC–MS for quantification of NDMA. Analysis of NDMA was performed on an Agilent 6890 GC (Agilent Technologies, Wilmington, DE) equipped with an Agilent 5973 MSD operating in electron-impact ionization mode. Separation was achieved on a DB-1701 capillary column (30 m x 0.25-mm i.d. x 0.25-µm film thickness) with a flow rate of 1.0 mL min–1 (helium). To prevent sample decomposition in the inlet, pulsed splitless injection was used with pressure at 25 psi for 0.5 min and the total splitless time was 0.51 min. The oven temperature was initially set at 45°C (2.5 min), ramped to 100°C at 50°C min–1, held for 2 min at 100°C, then ramped to 280°C at 50°C min–1, and finally held at 280°C for 1 min. The ion source and quadrupole were kept at 230°C and 150°C, respectively. The inlet temperature was 210°C, and transfer line between GC and MSD was maintained at 270°C. The mass spectra were obtained using selected ion monitoring (SIM) at 70 eV. The characteristic ions used for SIM were 74 and 42 for NDMA, and 80 and 46 for d6–NDMA. Under the above conditions, the retention time was 4.76 min for d6–NDMA and 4.79 min for NDMA. The response ratio between d6-NDMA and NDMA and peak areas were used to derive the concentration of NDMA. Leachate samples were generally clean and had few background peaks. The method detection limit for the above procedure was determined to be 2 ng L–1. Confirmatory analysis of NDMA was performed using similar analytical methods as described previously (WateReuse Foundation, 2005).


   RESULTS AND DISCUSSION
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
REFERENCES
 
Degradation of NDMA in Turfgrass Soils
Dissipation of NDMA in turfgrass soils over time was fitted to a first-order decay model to estimate the first-order degradation rate constant k (d–1) and half-life T1/2 (d) (Tables 2 and 3). Sterilization of soil samples by autoclaving resulted in significantly longer T1/2 compared to the nonsterile soils. This observation was consistent with previous studies (Oliver et al., 1979; Mallik and Tesfai, 1981; Yang et al., 2005; Sharp et al., 2005), suggesting that NDMA degradation in turfgrass soils was caused mainly by microorganisms. In nonsterile soils, NDMA showed moderate to long persistence, with T1/2 ranging from 13.5 to 36.5 d in the top 0- to 10-cm layer, and from 26.3 to 79.7 d in the 10- to 20- and 20- to 30-cm layers. The T1/2 for the 0- to 10-cm turfgrass soil was longer than in surface soils planted to tall fescue grass (5.6 d) or a groundcover (4.1 d) (Yang et al., 2005), suggesting that the type of vegetation or sampling time could also influence NDMA persistence in soil. The persistence observed in this study implies that degradation would not be an important attenuation mechanism for NDMA attenuation in the sandy turfgrass soils after wastewater irrigation.


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  		Table 2. First-order rate constants and correlation coefficient for NDMA degradation in different depth soils covered by Bermuda grass at 21 ± 1°C.

 

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  		Table 3. First-order rate constants and correlation coefficient for NDMA degradation in different depth soils covered by creeping bentgrass at 21 ± 1°C.

 
NDMA in Wastewater Effluent
The concentration of NDMA in the wastewater effluent was relatively high, with a mean concentration of 930 ng L–1 (Fig. 4 ). The level of NDMA varied significantly from batch to batch, with the lowest concentration in the second and fifth tanks (average concentration of 310 ng L–1), and the highest level in the first (1420 ng L–1) and third tanks (1220 ng L–1). In a recent study, Sedlak et al. (2005) analyzed NDMA in 21 secondary wastewater effluent samples before disinfection and found a median concentration of 46 ng L–1 and a maximum concentration of 380 ng L–1. After disinfection with chlorine the concentration of NDMA often increases (Najm and Trussell, 2001; Mitch et al., 2003; Sedlak et al., 2005), with concentrations as high as approximately 1000 ng L–1 reported at treatment plants in Los Angeles (WateReuse Foundation, 2005). Concentrations of NDMA in water delivered by full-scale landscape irrigation systems up to approximately 500 ng L–1 also have been observed (Pehlivanoglu and Sedlak, 2004). Although the concentrations of NDMA detected here were higher than expected for a wastewater treatment plant that employs nitrification, they were not outside the range of concentrations expected in wastewater effluent that is used for landscape irrigation.



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  		Fig. 4. Concentrations of N-nitrosodimethylamine (NDMA) in wastewater effluents used for irrigation during the wastewater irrigation study. Bars are mean of three replicates, lines are standard errors, and * indicates time when the tank was filled with a new batch of wastewater effluent.

 
Leaching of NDMA during Wastewater Irrigation
From 16 June through 12 Oct. 2004, leachate from each test plot was sampled and analyzed for a total of 50 times, at a frequency of 3 times per week. In most samples, NDMA was not detected (Fig. 5 and 6) . At a method detection limit (MDL) of 2 ng L–1, of the 200 samples taken from the daytime irrigated plots, only 4 samples, or 2%, gave positive NDMA detection (Fig. 5). When detected, NDMA concentrations were low, with the highest concentration at 5 ng L–1. Of the 200 samples taken from the nighttime irrigated plots, only 5 samples, or 2.5%, had positive detection of NDMA (Fig. 6). Similarly, even when detected, the NDMA level was very low, at ≤5 ng L–1. Analysis of split samples by external laboratories confirmed that no NDMA was present in the leachate. No significant difference was observed between the two irrigation schedules, or between the two soil types (Fig. 5 and 6). The lack of difference between the daytime and nighttime treated plots implies that despite the potential for NDMA to undergo photolysis in sunlight (Agency for Toxic Substances and Disease Registry, 1989; Mitch et al., 2003). The short exposure of NDMA to sunlight during daytime irrigation was not sufficient to cause significant photolysis of NDMA. Given that the NDMA concentration in the input water was always about two orders of magnitude higher than the limit of quantification of the analytical technique and that excessive irrigation rates were used, it may be concluded that NDMA has little potential for leaching to ground water when treated wastewater is used to irrigate turfgrass systems such as golf courses, parks, or lawns under conditions similar to those employed in this study. The lack of NDMA appearance in the leachate also implies that one or more attenuation mechanisms effectively removed NDMA from the soil profile, preventing it from reaching the leachate exit point at <100 cm below the surface.



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  		Fig. 5. Concentrations of N-nitrosodimethylamine (NDMA) in leachate water collected from the turfgrass plots irrigated with NDMA-containing wastewater during daytime.

 


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  		Fig. 6. Concentrations of N-nitrosodimethylamine (NDMA) in leachate water collected from the turfgrass plots irrigated with NDMA-containing wastewater during nighttime.

 
Probable NDMA Loss Pathways in Turfgrass Systems
NDMA is miscible with water and is negligibly adsorbed to soil, which suggests that NDMA should have a high leaching potential under the study conditions. In landscape soils planted with turfgrass, groundcover, or trees, the measured Kd for NDMA was only 0.45 to 0.64 L kg–1 (Yang et al., 2005). Consistent with these findings, an earlier study indicated that NDMA moved as fast as chloride when NDMA and chloride were leached through saturated soil columns (Dean-Raymond and Alexander, 1976). In another study, N-nitrosodipropylamine (NDPA), a compound with properties similar to those of NDMA, was also found to leach readily through small saturated soil columns (1.0-cm i.d. x 45 cm) (Saunders et al., 1979). However, one distinct difference between packed soil columns and the turfgrass plots used in this study is that the soil was always saturated with water in the packed columns, whereas in the turfgrass plots, except for a transient time period shortly after irrigation, the soil remained unsaturated. In unsaturated soils under open field conditions, for semivolatile compounds such as NDMA, chemical transport may occur in both the solution and gas phases and the chemical may volatilize readily at the soil–air interface into the atmosphere. Therefore, the absence of NDMA in leachate from the turfgrass plots may be due to one or more of the following loss mechanisms: (i) rapid NDMA degradation, (ii) plant uptake of NDMA from soil, and (iii) rapid gas phase diffusion in soil and volatilization at the surface.

Results from the degradation experiment and other studies consistently indicate that NDMA has moderate to long persistence in soil, with half-lives in excess of 5 d (Tate and Alexander, 1975; Oliver et al., 1979; Kaplan and Kaplan, 1985; Gunnison et al., 2000; Yang et al., 2005). Given the sandy texture and the limited distance from the surface to the leachate exit point, it was unlikely that degradation contributed significantly to the rapid NDMA removal. In previous studies, plants were found to be able to take up approximately 5% of the applied NDMA (Dean-Raymond and Alexander, 1976). The potential for turfgrass to absorb NDMA from soil, however, is unknown. As turfgrass has dense fibrous root systems, plant uptake could be a significant removal pathway for NDMA and should be further characterized.

Given its relatively low boiling point (152°C) and high vapor pressure (2.7 mm Hg at 20°C), volatilization could serve as another potentially important loss pathway that helped to negate NDMA leaching in the turfgrass soils. In the course of the field plot study, trays were placed on the surface of the plots to intercept irrigation water and NDMA concentrations were immediately determined. The results showed that NDMA concentrations in the water entering the turf soils were essentially equivalent to that in the tank (data not shown). This suggests that volatilization during the short travel of water from sprinklers to the plot surface, either as chemical vapor or aerosols, was insignificant. Volatilization loss, if any, would be possible only from the irrigated soil. Literature search for Henry's Law constant (KH) gave inconsistent KH values for NDMA. In the International Program on Chemical Safety's (IPCS) NDMA document, KH at 25°C was cited as 3.4 Pa m3 mol–1 (International Programme on Chemical Safety, 2002), which translates into a dimensionless KH' of 1.4 x 10–3. It is commonly assumed that for a compound with KH' ≥ 10–4, vapor phase diffusion dominates in unsaturated soil and the chemical's movement through unfilled soil pores can be very rapid (Jury et al., 1991). The vapor phase transport of NDMA in soil should be further facilitated by its weak adsorption to the solid phase (i.e., no retardation by the solid phase). However, in a report by the Agency for Toxic Substances and Disease Registry (ATSDR), KH of NDMA was listed at 2.63 x 10–7 atm m3 mol–1 (20°C) (Agency for Toxic Substances and Disease Registry, 1989). This value was calculated from NDMA's vapor pressure and water solubility rather than measured (Mirvish et al., 1976). This value would translate into a dimensionless KH' of only 1.1 x 10–5, which suggests a smaller role for gas phase diffusion in the transport of NDMA through unsaturated soils.

In the absence of reliable KH values, earlier studies experimentally showed that when present close to the surface, NDMA readily volatilized from soil (Oliver, 1979; Oliver et al., 1979). Oliver (1979) measured volatilization of NDMA, N-nitrosodieathylamine (NDEA), and NDPA from packed soil chambers. Volatilization was determined by trapping the vapor of 14C-labeled nitrosoamines on activated carbon tubes. When NDMA and NDPA were both applied onto the soil surface in dichloromethane, emission of NDMA appeared to be instantaneous, reaching about 80% within the first few hours. The amount of dichloromethane used for spiking the nitrosoamines was not given by the author, and it is therefore not possible to estimate the penetration depth of the applied material. However, it was noted that the soil was maintained at 70% of field capacity, or about 18% water content (w/w), and volatilization therefore occurred from moist soil (Oliver, 1979). In another treatment, 14C-NDEA was incorporated into the top 7.5-cm soil and volatilization was monitored, and the observed volatilization loss (21% in 2 d) decreased greatly when compared to the surface application. In a biometer flask incubation experiment, volatilization loss of >50% was observed for NDEA from sterilized soil (Oliver et al., 1979). Volatilization of NDMA after soil incorporation was not measured in this study. However, given NDMA's lower boiling point (152°C, compared to 176°C for NDEA), it may be expected that NDMA volatilization after soil incorporation would be more rapid than NDEA.

Volatilization of organic chemicals from soil depends on microclimatic conditions such as wind speed and barometric pressures. Volatilization of NDMA from unsaturated soils could be more significant under open field conditions than the relatively static conditions used in the laboratory studies. For example, Saunders et al. (1979) studied leaching of 14C-NDPA in small glass soil columns (1.0-cm i.d. x 32 cm) placed in field soil. The overall dissipation of NDPA occurred at a much slower rate (T1/2 = approximately 3 wk) than that observed for NDMA observed in the current study. However, very little 14C activity was found in the 20- to 30-cm layer, and no 14C activity was detected in the leachate that was collected at the bottom of the soil columns. The results suggest a significant role of gas phase diffusion and volatilization in the dissipation of NDPA in the vadose zone. In addition, under field conditions, water moves upward through capillaries and then evaporates at the surface, and the upward water transport can increase greatly due to active plant transpiration. It may be expected that in the turfgrass plots, the warm and dry conditions may have caused rapid upward water transport, and the water-miscible NDMA was carried along in the moving water. Once at the surface, NDMA could readily volatilize into the air. However, the above predictions must be substantiated with further experimental observations.

In conclusion, NDMA introduced through surface irrigation of treated wastewater was found to not leach through a <100-cm profile of turfgrass soil under field conditions. The limited NDMA leaching was likely a result of plant uptake of NDMA, rapid NDMA volatilization, or both. As the field irrigation study was performed under scenarios that were conducive to rapid leaching of NDMA, it may be concluded that most of the NDMA applied to the soil will not leach to ground water if treated wastewater is used to irrigate golf courses, parks, or other landscaped areas. Further research is needed to characterize the importance of plant uptake and volatilization in facilitating NDMA dissipation and preventing its leaching following wastewater irrigation.


   ACKNOWLEDGMENTS
 
This work was supported by WateReuse Foundation Award WRF-02-002. We would like to thank Steve Carr, Jennifer Bender, Tim Durbin, and Robert Cheng for their help in method development, project coordination, and sample analysis validation.


   REFERENCES
TOP
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 REFERENCES
 




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M. Arienzo, J. Gan, F. Ernst, S. Qin, S. Bondarenko, and D. L. Sedlak
Loss Pathways of N-Nitrosodimethylamine (NDMA) in Turfgrass Soils
J. Environ. Qual., January 5, 2006; 35(1): 285 - 292.
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