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Detection of anthropogenic gadolinium in treated wastewater in South East Queensland, Australia
water research 43 (2009) 3534–3540
Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
Detection of anthropogenic gadolinium in treated wastewater in South East Queensland, Australia Michael G. Lawrence*, Christoph Ort, Jurg Keller Advanced Water Management Centre, University of Queensland, St Lucia, Qld. 4072, Australia
article info
abstract
Article history:
The use of refractory gadolinium (Gd) complexes as paramagnetic contrast agents in
Received 14 November 2008
magnetic resonance imaging has resulted in point source release of anthropogenic Gd
Received in revised form
(GdAnth ) into the environment, and presents opportunities to trace the fate of wastewater in
15 April 2009
natural environments. We demonstrate an inductively coupled plasma mass spectrometry
Accepted 21 April 2009
(ICP-MS) technique that is capable of detecting GdAnth at concentrations as low as 48 fM,
Published online 3 May 2009
approximately six orders of magnitude lower than most other micropollutants, without the
Keywords:
wastewater at eight separate wastewater treatment plants in Brisbane, Australia, over a 3-
need for preconcentration. Further, we establish the ubiquitous presence of GdAnth in Micropollutants
month time period. In contrast, there is no evidence of GdAnth in tap water, or in four
Paramagnetic contrast agents
separate regional water supply dams in South East Queensland, Australia. It is, therefore,
ICP-MS
highly unlikely that other anthropogenic micropollutants sourced from urban wastewater would be present in the drinking water supply. ª 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
Brisbane, in South East Queensland (SEQ) is the site of the Western Corridor Recycled Water Project, the third largest recycled water project in the world with a capacity of 232,000 m3/day of purified recycled water for industrial and indirect potable reuse (Traves and Davies, 2008). The project commenced in 2006 in response to, and during the ‘‘Millennium Drought’’, recently acknowledged as the worst on record, (Queensland Government, 2007) in South East Queensland. In this project, secondary and tertiary treated wastewater from a number of wastewater treatment plants (WWTPs) is piped to three Advanced Water Treatment Plants (AWTPs) where it undergoes microfiltration, reverse osmosis, advanced oxidation and lime stabilisation prior to pumping to industrial users. It is planned that purified recycled water (PRW) will be returned to regional dams to replenish dwindling supplies.
The return of PRW to the drinking water supply is not without some community concern, in part due to the increasing prevalence in the literature of articles reporting the occurrence of WWTP effluent sourced micropollutants in the environment (see for example Schwarzenbach et al., 2006; Ternes and Joss, 2006 and references therein). As there is, theoretically, some risk of environmental or human health consequences as a result of indirect potable reuse of PRW, it is necessary to evaluate the prevalence of micropollutants in the environment. However, analytical detection limits impinge upon our ability to quantify their presence and evaluate their human health consequences (if any); it is, therefore, imperative that alternative strategies to detect and monitor micropollutants are pursued. Gadolinium (Gd) is a rare earth element (REE); stable Gdcomplexes have been utilised as paramagnetic contrast agents (CAs) since the late 1980s for patients requiring Magnetic Resonance Imaging (MRI). There are a number of
* Corresponding author. Tel.: þ61 7 3346 6252; fax: þ61 7 3365 4726. E-mail address: [email protected] (M.G. Lawrence). 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.04.033
water research 43 (2009) 3534–3540
different commercially available Gd CAs, which are typically variations of a linear or macro cyclic base structure. The compounds may be neutral or ionic with thermodynamic stability constants (log) in the range of 16–26. (Port et al., 2008) provides an excellent summary of the structural, chemical and pharmacological data for these molecules in their Table 1 and scheme 1. Gadolinium CAs are designed to be stable and non-reactive, are not metabolised, and are generally not considered to be toxic or to have any deleterious environmental consequences. Gadolinium CAs are used in relatively high doses (0.1–0.3 mmol/kg body weight, equating to 1–3 g Gd per average adult patient), and are excreted by the patient, primarily in urine, with a half-life of 6–12 h. Thus, high loads of Gd (relative to background concentrations) enter the urban water cycle. Bau and Dulski (1996) first demonstrated that Gd is present in natural waters receiving a portion of sewage effluent. The distribution of anthropogenic Gd (GdAnth ) is now known to be widespread (Bau et al., 2006; Knappe et al., 2005; Kulaksiz and Bau, 2007; Kummerer and Helmers, 2000; Lawrence et al., 2006c; Moller et al., 2000,2003; Morteani et al., 2006). Interestingly, the parameter GdAnth behaves as a refractory component that can be used as a conservative tracer of sewage effluent, at least on hydrological timescales of days to weeks (Kulaksiz and Bau, 2007; Moller et al., 2003), and even survives estuarine mixing. It is expected, although never previously confirmed, that wastewater in South East Queensland, Australia should also contain GdAnth . Previous research has indicated that Gd can be quantified in natural waters without preconcentration at sub picomolar concentrations (Lawrence et al., 2006b). In contrast, instrumental detection limits for high performance liquid chromatography–tandem mass spectrometry (LC–MSMS), are orders of magnitude higher. Anthropogenic Gd is potentially the most sensitive tracer of the input of micropollutants into natural waters. This paper has three purposes: (1) describe the technique used for measuring ultra-low trace levels of the REE in natural waters against which GdAnth can be evaluated, (2) demonstrate the ability to use GdAnth as a tracer of sewage effluent in SEQ, and (3) investigate whether GdAnth has already infiltrated the drinking water supply and, if not, provide baseline data prior to the commencement of releasing purified recycled water to the drinking water catchment.
smooth. Nonetheless, there are potentially large departures from the smooth pattern (anomalies) at Ce and Eu due to redox processes. The smaller aqueous phase anomalies of La, Gd, and Lu are believed to be due to the higher chemical stability of complexes of those elements in solution relative to their neighbouring REEs. This is a function of the higher stability of empty, half filled, and completely filled f-orbitals. As the REE pattern is smooth, it is an accepted geochemical practice to calculate the parameter Lnn , the expected shalenormalised concentration of any lanthanide (Lnn ) in order to quantify whether any particular element has anomalously high or low concentrations. Methods previously used for predicting Lnn include (i) linear (or geometric) extrapolation from either the heavy REE (HREE) or light REE (LREE), (ii) linear (or geometric) interpolation between a HREE and a LREE, or (iii) by modelling the shape of the REE pattern using a third order polynomial fit. For any calculation to have geochemical relevance, it is essential to exclude possibly anomalous REE (La, Ce, Eu, Gd, and Lu) from the calculation (Kulaksiz and Bau, 2007; Lawrence and Kamber, 2006). Of the previously applied calculations, the third order polynomial is the only method that makes no implicit assumption as to whether Gd behaves more like the LREE, or the HREE. Such a distinction is usually unimportant when all samples are of a similar type, however, this is not expected to be the case in this study where natural waters are compared with wastewater treatment plant effluent. For the current samples, the most consistent calculation results by calculating natural gadolinium Gdn from a third order polynomial fit of the remaining nine nonanomalous REE (Morteani et al., 2006). The Gd anomaly is defined by the ratio GdnðMeasuredÞ =Gdn . Anomalies calculated for freshwater sources in Australia that do not receive wastewater effluent (Lawrence et al., 2006b, 2006c), approach, but do not exceed 1.1, consistent with previous research e.g. (Bau et al., 2006). We arbitrarily define an anomaly of 1.1 as natural, whereas a value >1.1 (see WWTP A in Fig. 1) is interpreted as including both a natural and an anthropogenic component e.g. (Bau and Dulski, 1996). Once samples with positive Gd anomalies (>1.1) are identified, it is possible to calculate the actual concentration of GdAnth e.g. (Kulaksiz and Bau, 2007) using: ½GdAnth ¼ Gdn;Meas 1:1 Gdn ½GdMuQ
Materials and methods
2.1. Theory: Calculation of the Gd anomaly, and anthropogenic Gd Shale-normalised REE patterns are a log-linear representation of the measured concentrations of all REEs divided by their respective concentrations in a reference shale plotted against atomic number. For anthropogenically unaffected natural samples such as rocks and river water (see Reservoir A in Fig. 1) the shale normalised patterns are predominantly
(1)
where [GdMuQ] is the concentration of Gd in the normalising shale (Kamber et al., 2005).
2.2.
2.
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Sampling
Triplicate grab samples were collected from (i) tap water in Brisbane at various locations, (ii) from the surface water of four major regional water supply reservoirs, and (iii) from the effluent of eight wastewater treatment plants (WWTP A-H) over a 3-month period. Sample bottle cleaning and sampling protocols were developed whilst considering best-practice trace metal clean techniques (Bruland et al., 1979). Low density polyethylene (30 and 60 mL) sampling bottles were prepared for use by successive rinsing with MilliQ water, soaking with 1% Micro detergent solution for 1 week, rinsed in MilliQ, soaked in 4 N analytical grade hydrochloric acid (1 week), rinsed in MilliQ, soaked in 2 N quartz distilled nitric
3536
Table 1 – Rare earth element data (pM) for natural and waste water treatment plants (WWTPs) in SEQ. The three samples labelled as WWTP B were collected from a pipeline that combines the effluent from three separate WWTPs at varying proportions. In contrast, WWTP D, which was also sampled on multiple occasions, has a consistent anomaly. WWTP E, the largest population equivalent treatment plant, has the largest observed GdAnth signal. Sample (pmol/kg) W-2 (mmol/kg) BIR-1 (mmol/kg)
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
75.74 4.32
165.69 13.57
21.47 2.68
89.51 16.49
21.72 7.31
7.20 3.45
23.58 11.83
3.87 2.28
23.43 15.62
4.87 3.53
13.28 10.16
1.94 1.52
11.89 9.57
1.72 1.41
2145 2.23 0.74
2669 1.06 0.55
518 0.54 0.23
1907 1.96 1.54
390 1.93 0.74
530 1.16 0.58
224 0.52 0.48
28.3 0.11 0.07
146.5 0.58 0.28
29.7 0.07 0.08
79.5 0.23 0.19
11.2 0.06 0.07
70.5 0.30 0.30
10.9 0.07 0.06
Drinking water supply (n ¼ 3) Wivenhoe Dam 40.3 Somerset Dam 229.4 Hinze Dam 726.2 North Pine Dam 24.4 Mt Crosby Weir 50.4 Tap water 77.1
75.4 332.9 1273 34.6 79.4 71.4
12.2 68.8 218.7 6.9 15.0 13.2
60.6 295.1 954.7 12.6 67.6 62.4
15.9 66.8 229.5 10.7 21.4 12.3
5.4 17.9 49.2 3.8 5.0 2.0
16.0 64.3 233.1 11.1 21.9 15.5
2.4 8.9 34.6 1.8 3.6 2.2
15.2 53.1 212.2 11.6 22.4 15.7
3.2 11.0 45.6 2.7 5.0 4.6
8.4 31.2 128.5 7.9 13.9 13.8
1.3 4.6 19.1 1.3 2.1 2.0
9.1 27.9 123.2 8.0 14.3 11.7
1.4 4.6 18.7 1.2 2.4 2.0
Wastewater effluent (n ¼ 3) WWTP A1 14.9 WWTP A2 28.6 WWTP B1 2.4 WWTP B2 6.5 WWTP B3 20.9 WWTP C 23.9 WWTP D1 16.0 WWTP D2 23.0 WWTP D3 14.1 WWTP E 19.1 WWTP F 22.4 WWTP G 35.3 WWTP H 14.4
23.9 45.2 1.5 12.0 22.0 60.9 21.7 29.4 28.0 40.8 51.2 83.9 40.1
4.9 9.2 1.3 3.0 4.8 17.5 5.3 5.1 5.6 8.5 9.3 14.9 9.6
24.6 49.2 3.0 16.3 28.4 123.7 22.4 26.2 38.1 53.8 49.8 79.2 53.1
7.4 12.1 2.8 4.8 7.3 42.9 8.5 9.4 7.4 13.4 15.0 22.9 16.1
2.4 2.3 1.2 0.6 5.5 15.4 3.3 1.4 3.8 4.7 4.8 7.7 4.1
636.4 1574 119.6 354.8 379.1 381.0 263.6 235.8 305.9 1795 224.0 356.9 392.1
1.9 3.7 0.6 1.4 1.5 7.3 2.0 2.1 2.1 4.2 3.0 4.7 2.8
15.1 25.6 5.1 10.2 10.2 49.5 17.0 17.4 20.4 39.1 29.1 37.2 23.1
5.0 7.9 1.9 3.0 3.2 13.0 5.0 5.7 6.7 12.0 9.3 10.6 7.7
18.3 27.5 6.8 12.3 11.2 51.7 18.5 20.9 26.9 49.1 40.7 42.2 36.7
3.2 4.7 1.1 2.1 2.0 8.3 3.3 3.7 4.5 7.9 6.8 7.1 7.0
22.9 34.1 9.6 16.2 15.0 61.7 23.1 28.2 36.5 57.3 49.5 57.1 51.5
3.8 5.4 1.6 2.9 2.8 10.3 4.1 4.8 6.3 10.9 8.8 9.6 9.3
Gd anomaly (unitless)
GdAnth
1.07 1.09 1.08 1.07 1.05 1.04
0 0 0 0 0 0
57 99 32 50 46 9 22 19 27 88 15 13 30
623 1550 114 338 370 333 251 217 293 1772 207 325 378
water research 43 (2009) 3534–3540
SLRS-4 (pmol/L) Average blank (n ¼ 10) 3s
La
water research 43 (2009) 3534–3540
3537
Fig. 1 – Comparison of a natural rare earth element pattern (element concentrations are normalised to MuQ (Mud of Queensland, a sedimentary composite (Kamber et al., 2005), appropriate for Australia) Note that the typical ‘‘smooth’’ REE pattern in Reservoir A has a positive Eu anomaly, a feature related to the local lithology. Both REE patterns have negative Ce anomalies, probably due to the precipitation of cerium oxides in oxic water. The large positive Gd anomaly ðGdnðMeasuredÞ =Gdn Þ[99 observed at WWTP A is an anthropogenic feature that we attribute to the use of contrast agents in MRI. The parameter Gdn was calculated from a third order polynomial fit of the shale-normalised concentrations of the nonanomalous REEs as discussed in the text.
acid (1 week), rinsed 3 times in MilliQ, filled with MilliQ water and stored in double sealed Zip-Lock plastic bags until use. The water was discarded immediately prior to sample collection. Samples were carefully collected in 60 mL Terumo syringes, (rinsed 2 times with the sample) and a syringe filter (0.22-mm Millipore Millex–GV filters) fitted. The initial 2 mL of filtrate was discarded and the following w12 mL (3 times w4 mL) used to rinse out the residual MilliQ from the bottle) the remaining w40 mL was collected in the trace metal cleaned bottles. At all stages of sample collection, latex gloves were worn, and sample bottle lids were removed for the minimum possible time in an attempt to minimise potential sample contamination. Upon return to the laboratory, samples were immediately acidified with quartz sub-boiling double distilled nitric acid to pH 1.5, and spiked with 1 ppb Re as an internal standard prior to analysis. After collection, all further sample handling and analysis steps occurred in a trace metal clean laboratory.
2.3.
Analysis
Samples were analysed with a Thermo X-series ICP-MS housed in a clean facility at the University of Queensland. Reservoir, tap water, and finally, wastewater effluent samples were analysed after analysis of blanks and SLRS-4 dilutions to minimise the possibility of contamination. Instrumental conditions are similar to those previously described (Lawrence et al., 2006a). Briefly, the ICP-MS was tuned for maximum sensitivity using the high performance sample introduction system which was determined to have the best
signal to noise ratio, while maintaining oxide production below 2% (measured using CeO/Ce). The raw instrument data was corrected for variations in internal standard, external drift, and interfering oxides (Eggins et al., 1997). Instrument response was then calibrated against hotplate digests for the US Geological Survey (USGS) dolerite reference material W-2, using REE concentrations listed in Table 1. A similarly prepared hotplate digest of the USGS basalt reference material BIR-1 was used as a primary quality control. The National Research Council of Canada (NRCC) River Water Reference material (SLRS-4) was used as an external drift monitor, and secondary quality control.
2.4.
Evaluation of detection limits
MilliQ water blanks have detectable, consistent concentrations of the REE with absolute concentrations ranging from 62 fM (Tm) to 2.2 pM (La), and the shale-normalised REE patterns are smooth. Therefore, method detection limits were determined from ten individually prepared MilliQ water blanks. For all of the REE, the method detection limit, calculated as three times the standard deviation (3s, Table 1) is in the range 70–700 fM. As the REE patterns for the MilliQ blanks are smooth, it is possible to calculate Gdn . For any smooth REE patterns, if the ratio GdnðMeasuredÞ =Gdn exceeds 1.1, GdAnth can be calculated using Eq. (1). Specifically, as 3s for GdMeasured is 480 fM, the limit of quantification for GdAnth calculated from MilliQ blanks is, by definition, 48 fM. Similarly, it is possible to determine the limit of quantification by serial or sequential dilution of a known sample. We
3538
water research 43 (2009) 3534–3540
measured the REE concentration of MilliQ dilutions (both serial and sequential) of SLRS-4. As shown in Fig. 2, the entire REE pattern of SLRS-4 remains coherent at dilutions up to 510 times, and Gd is determined accurately, within analytical uncertainty, at 750 times dilution. The actual concentration of Gd in SLRS-4 is 0.225 nM, and using this method, it is possible to quantify Gd accurately at (0.225 nM/510) ¼ 440 fM, and GdAnth at concentrations as low as 44 fM. As different methods yield consistent concentrations, it imparts a high degree of confidence in our ability to determine GdAnth at this level. Nonetheless, it must be acknowledged that this is only the case when a REE pattern is measurable, with concentrations approaching the method detection limit. In a more general sense, the limit of quantification of is 10% of the measured Gd concentration. The limit of quantification of GdAnth of w48 fM compares favourably to the limits of quantification for analytical methods detecting representative pharmaceuticals in natural water bodies (e.g. Diazepam in river water) where the detection limit, taking into account a 1000-fold preconcentration, is 0.02 mg/L, giving equivalent detection limits of 70 nM (Zuccato et al., 2000). Thus, GdAnth can be detected at concentrations that are up to 6 orders of magnitude lower than most other micropollutants.
3.
Results and discussion
Rare earth element results are presented in Table 1 and Fig. 3. The shale-normalised REE patterns in Fig. 3A for tap water and the drinking water supply reservoirs in the Brisbane region are
typical of those previously reported for natural fresh water sources (Lawrence et al., 2006b). Further, there is no evidence that any sample has a Gd anomaly (in all cases, GdnðMeasuredÞ =Gdn < 1:1). As a result, the calculated GdAnth component in all cases is zero. In contrast, the WWTP effluents all have detectable Gd anomalies from 9 to 99, representing a maximum absolute excess of 1.7 nM at the largest population equivalent treatment plant (Fig. 3B). For that particular treatment plant, 99% of the detected Gd is anthropogenic in origin, consistent with the interpretation that MRI contrast agents are the source of the Gd anomaly. In each case the Gd anomaly, a ratio, is an indicator of how many times greater the measured value is over the natural concentration. The sample with the lowest anomaly (WWTP C, anomaly ¼ 9) has an GdAnth component of 330 pM. In contrast, WWTP B1, with the lowest GdAnth component of only 114 pM, has an anomaly of 32. The lowest concentration of total Gd measured was 119 pM, with 114 pM attributed to anthropogenic sources; this concentration is w2400 times higher than the detection limit, indicating the sensitivity of this technique. The Gd anomalies observed in South East Queensland are within range of previously reported values (Bau and Dulski, 1996; Bau et al., 2006; Knappe et al., 2005; Kulaksiz and Bau, 2007; Kummerer and Helmers, 2000; Lawrence et al., 2006c; Moller et al., 2000, 2003; Morteani et al., 2006), although well below the maximum reported anomaly (Bau and Dulski, 1996) of 2014 in Germany (GdAnth ¼ 7476 pM). Regardless, at every SEQ treatment plant, at every sampling time, GdAnth was
Fig. 2 – Shale (MuQ) normalised REE patterns for dilutions of the NRCC River water reference material SLRS-4 (dilution indicated in legend). Note that Eu is not quantifiable below 100 times dilution, but overall, the REE pattern is still quantifiable using a third order fit (Eu is excluded from the fit, along with other anomalous elements) at 510 times dilution. Although the REE pattern loses coherence beyond this limit, the absolute concentration of Gd is still determined within instrumental error (65%) at 750 times dilution. However, as the Gd anomaly is calculated from the remainder of the REE pattern, the limit of quantification is defined from the concentration from which the geogenic abundance can be confidently predicted. The REE pattern for the average blank (n [ 10) is shown as a solid black line, with error bars [ 1s represents the practical lowest measurable concentrations. As the REE pattern is consistent and (excluding Eu) smooth, it is possible to calculate the geogenic Gd concentration, and thus the anthropogenic component.
water research 43 (2009) 3534–3540
3539
Fig. 3 – Shale (MuQ) normalised REE patterns of (A) drinking water supply in South East Queensland, and (B) selected wastewater treatment plants. Note that WWTP B and D, both of which were sampled on multiple occasions, have remarkably consistent GdAnth concentrations. Every final treated effluent sample from all regional WWTPs had significant positive Gd anomalies, which range from 9 to 99. In contrast, no drinking water, or water supply reservoir sample had detectable concentrations of GdAnth .
detected. The ubiquitous occurrence of GdAnth in treated effluent from WWTPs is a significant outcome, as it confirms, in principle, that GdAnth may be used as a tracer for wastewater in South East Queensland waterways. The ICP-MS technique described is suitable for rapid and direct analysis of both fresh water and wastewater samples, with minimal pretreatment. Given the ubiquitous presence of GdAnth in wastewater, this parameter may be viewed as an ideal tracer. For example, the absence of GdAnth in tap water, and in the drinking water supply in SEQ can therefore be interpreted to indicate that the drinking water supply does not currently contain a detectable wastewater component. Specifically, for Somerset Dam, with the second highest
natural Gd component, an increase of just 6 pmol/kg would result in a detectable GdAnth component. The average WWTP GdAnth discharge was 550 pmol/kg, thus, if wastewater with this average GdAnth component was present above 1.1% by volume, it would have been detectable. For North Pine Dam, an increase of just 50 fmol/kg Gd, representing a contribution of 0.009% wastewater, it would have been detectable. These values would be lowered by a factor of 3 if the calculation was performed using the highest measured wastewater GdAnth component (detected in the largest population equivalent WWTP). In comparison, the refractory micropollutant, carbamazepine, is typically present in wastewater in Australia at 1 mg/L (Khan et al., 2004). When compared to published LODs
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water research 43 (2009) 3534–3540
of 0.01 mg/L (Clara et al., 2005), this represents detection at 1% wastewater dilution. Therefore, GdAnth potentially detects a wastewater contribution 50 times more easily than comparable SPE preconcentration, LC-MSMS techniques. As a result of this research, we have established baselines from which it is now possible to use GdAnth to monitor the effect of reservoir supplementation by the addition of purified recycled water from the Advanced Water Treatment Plants. We envisage that GdAnth , as a relatively easily measured parameter, may be further developed as a tracer to; evaluate hydrological models, act as a surrogate (or proxy) for the presence of other micropollutants of higher ecotoxicological or human health concern, and, help validate environmental risk assessments by allowing a direct measurement of the mixing and dilution of wastewater effluent in the environment.
4.
Conclusions
Anthropogenic Gd is a ubiquitous component of all measured wastewater effluents (8 separate WWTPs) in South East Queensland, Australia. Anthropogenic Gd is a useful proxy for wastewater contamination of natural waters. There is no evidence for anthropogenic Gd contamination of the drinking water supply dams (four reservoirs), or in tap water, prior to the commencement of a large-scale recycled water project in South East Queensland.
Acknowledgements The authors are funded by the ‘‘Chair in Water Recycling Agreement’’, jointly funded by the University of Queensland, Veolia Water Australia, and Water Secure.
references
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Available at www.sciencedirect.com
journal homepage: www.elsevier.com/locate/watres
Detection of anthropogenic gadolinium in treated wastewater in South East Queensland, Australia Michael G. Lawrence*, Christoph Ort, Jurg Keller Advanced Water Management Centre, University of Queensland, St Lucia, Qld. 4072, Australia
article info
abstract
Article history:
The use of refractory gadolinium (Gd) complexes as paramagnetic contrast agents in
Received 14 November 2008
magnetic resonance imaging has resulted in point source release of anthropogenic Gd
Received in revised form
(GdAnth ) into the environment, and presents opportunities to trace the fate of wastewater in
15 April 2009
natural environments. We demonstrate an inductively coupled plasma mass spectrometry
Accepted 21 April 2009
(ICP-MS) technique that is capable of detecting GdAnth at concentrations as low as 48 fM,
Published online 3 May 2009
approximately six orders of magnitude lower than most other micropollutants, without the
Keywords:
wastewater at eight separate wastewater treatment plants in Brisbane, Australia, over a 3-
need for preconcentration. Further, we establish the ubiquitous presence of GdAnth in Micropollutants
month time period. In contrast, there is no evidence of GdAnth in tap water, or in four
Paramagnetic contrast agents
separate regional water supply dams in South East Queensland, Australia. It is, therefore,
ICP-MS
highly unlikely that other anthropogenic micropollutants sourced from urban wastewater would be present in the drinking water supply. ª 2009 Elsevier Ltd. All rights reserved.
1.
Introduction
Brisbane, in South East Queensland (SEQ) is the site of the Western Corridor Recycled Water Project, the third largest recycled water project in the world with a capacity of 232,000 m3/day of purified recycled water for industrial and indirect potable reuse (Traves and Davies, 2008). The project commenced in 2006 in response to, and during the ‘‘Millennium Drought’’, recently acknowledged as the worst on record, (Queensland Government, 2007) in South East Queensland. In this project, secondary and tertiary treated wastewater from a number of wastewater treatment plants (WWTPs) is piped to three Advanced Water Treatment Plants (AWTPs) where it undergoes microfiltration, reverse osmosis, advanced oxidation and lime stabilisation prior to pumping to industrial users. It is planned that purified recycled water (PRW) will be returned to regional dams to replenish dwindling supplies.
The return of PRW to the drinking water supply is not without some community concern, in part due to the increasing prevalence in the literature of articles reporting the occurrence of WWTP effluent sourced micropollutants in the environment (see for example Schwarzenbach et al., 2006; Ternes and Joss, 2006 and references therein). As there is, theoretically, some risk of environmental or human health consequences as a result of indirect potable reuse of PRW, it is necessary to evaluate the prevalence of micropollutants in the environment. However, analytical detection limits impinge upon our ability to quantify their presence and evaluate their human health consequences (if any); it is, therefore, imperative that alternative strategies to detect and monitor micropollutants are pursued. Gadolinium (Gd) is a rare earth element (REE); stable Gdcomplexes have been utilised as paramagnetic contrast agents (CAs) since the late 1980s for patients requiring Magnetic Resonance Imaging (MRI). There are a number of
* Corresponding author. Tel.: þ61 7 3346 6252; fax: þ61 7 3365 4726. E-mail address: [email protected] (M.G. Lawrence). 0043-1354/$ – see front matter ª 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2009.04.033
water research 43 (2009) 3534–3540
different commercially available Gd CAs, which are typically variations of a linear or macro cyclic base structure. The compounds may be neutral or ionic with thermodynamic stability constants (log) in the range of 16–26. (Port et al., 2008) provides an excellent summary of the structural, chemical and pharmacological data for these molecules in their Table 1 and scheme 1. Gadolinium CAs are designed to be stable and non-reactive, are not metabolised, and are generally not considered to be toxic or to have any deleterious environmental consequences. Gadolinium CAs are used in relatively high doses (0.1–0.3 mmol/kg body weight, equating to 1–3 g Gd per average adult patient), and are excreted by the patient, primarily in urine, with a half-life of 6–12 h. Thus, high loads of Gd (relative to background concentrations) enter the urban water cycle. Bau and Dulski (1996) first demonstrated that Gd is present in natural waters receiving a portion of sewage effluent. The distribution of anthropogenic Gd (GdAnth ) is now known to be widespread (Bau et al., 2006; Knappe et al., 2005; Kulaksiz and Bau, 2007; Kummerer and Helmers, 2000; Lawrence et al., 2006c; Moller et al., 2000,2003; Morteani et al., 2006). Interestingly, the parameter GdAnth behaves as a refractory component that can be used as a conservative tracer of sewage effluent, at least on hydrological timescales of days to weeks (Kulaksiz and Bau, 2007; Moller et al., 2003), and even survives estuarine mixing. It is expected, although never previously confirmed, that wastewater in South East Queensland, Australia should also contain GdAnth . Previous research has indicated that Gd can be quantified in natural waters without preconcentration at sub picomolar concentrations (Lawrence et al., 2006b). In contrast, instrumental detection limits for high performance liquid chromatography–tandem mass spectrometry (LC–MSMS), are orders of magnitude higher. Anthropogenic Gd is potentially the most sensitive tracer of the input of micropollutants into natural waters. This paper has three purposes: (1) describe the technique used for measuring ultra-low trace levels of the REE in natural waters against which GdAnth can be evaluated, (2) demonstrate the ability to use GdAnth as a tracer of sewage effluent in SEQ, and (3) investigate whether GdAnth has already infiltrated the drinking water supply and, if not, provide baseline data prior to the commencement of releasing purified recycled water to the drinking water catchment.
smooth. Nonetheless, there are potentially large departures from the smooth pattern (anomalies) at Ce and Eu due to redox processes. The smaller aqueous phase anomalies of La, Gd, and Lu are believed to be due to the higher chemical stability of complexes of those elements in solution relative to their neighbouring REEs. This is a function of the higher stability of empty, half filled, and completely filled f-orbitals. As the REE pattern is smooth, it is an accepted geochemical practice to calculate the parameter Lnn , the expected shalenormalised concentration of any lanthanide (Lnn ) in order to quantify whether any particular element has anomalously high or low concentrations. Methods previously used for predicting Lnn include (i) linear (or geometric) extrapolation from either the heavy REE (HREE) or light REE (LREE), (ii) linear (or geometric) interpolation between a HREE and a LREE, or (iii) by modelling the shape of the REE pattern using a third order polynomial fit. For any calculation to have geochemical relevance, it is essential to exclude possibly anomalous REE (La, Ce, Eu, Gd, and Lu) from the calculation (Kulaksiz and Bau, 2007; Lawrence and Kamber, 2006). Of the previously applied calculations, the third order polynomial is the only method that makes no implicit assumption as to whether Gd behaves more like the LREE, or the HREE. Such a distinction is usually unimportant when all samples are of a similar type, however, this is not expected to be the case in this study where natural waters are compared with wastewater treatment plant effluent. For the current samples, the most consistent calculation results by calculating natural gadolinium Gdn from a third order polynomial fit of the remaining nine nonanomalous REE (Morteani et al., 2006). The Gd anomaly is defined by the ratio GdnðMeasuredÞ =Gdn . Anomalies calculated for freshwater sources in Australia that do not receive wastewater effluent (Lawrence et al., 2006b, 2006c), approach, but do not exceed 1.1, consistent with previous research e.g. (Bau et al., 2006). We arbitrarily define an anomaly of 1.1 as natural, whereas a value >1.1 (see WWTP A in Fig. 1) is interpreted as including both a natural and an anthropogenic component e.g. (Bau and Dulski, 1996). Once samples with positive Gd anomalies (>1.1) are identified, it is possible to calculate the actual concentration of GdAnth e.g. (Kulaksiz and Bau, 2007) using: ½GdAnth ¼ Gdn;Meas 1:1 Gdn ½GdMuQ
Materials and methods
2.1. Theory: Calculation of the Gd anomaly, and anthropogenic Gd Shale-normalised REE patterns are a log-linear representation of the measured concentrations of all REEs divided by their respective concentrations in a reference shale plotted against atomic number. For anthropogenically unaffected natural samples such as rocks and river water (see Reservoir A in Fig. 1) the shale normalised patterns are predominantly
(1)
where [GdMuQ] is the concentration of Gd in the normalising shale (Kamber et al., 2005).
2.2.
2.
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Sampling
Triplicate grab samples were collected from (i) tap water in Brisbane at various locations, (ii) from the surface water of four major regional water supply reservoirs, and (iii) from the effluent of eight wastewater treatment plants (WWTP A-H) over a 3-month period. Sample bottle cleaning and sampling protocols were developed whilst considering best-practice trace metal clean techniques (Bruland et al., 1979). Low density polyethylene (30 and 60 mL) sampling bottles were prepared for use by successive rinsing with MilliQ water, soaking with 1% Micro detergent solution for 1 week, rinsed in MilliQ, soaked in 4 N analytical grade hydrochloric acid (1 week), rinsed in MilliQ, soaked in 2 N quartz distilled nitric
3536
Table 1 – Rare earth element data (pM) for natural and waste water treatment plants (WWTPs) in SEQ. The three samples labelled as WWTP B were collected from a pipeline that combines the effluent from three separate WWTPs at varying proportions. In contrast, WWTP D, which was also sampled on multiple occasions, has a consistent anomaly. WWTP E, the largest population equivalent treatment plant, has the largest observed GdAnth signal. Sample (pmol/kg) W-2 (mmol/kg) BIR-1 (mmol/kg)
Ce
Pr
Nd
Sm
Eu
Gd
Tb
Dy
Ho
Er
Tm
Yb
Lu
75.74 4.32
165.69 13.57
21.47 2.68
89.51 16.49
21.72 7.31
7.20 3.45
23.58 11.83
3.87 2.28
23.43 15.62
4.87 3.53
13.28 10.16
1.94 1.52
11.89 9.57
1.72 1.41
2145 2.23 0.74
2669 1.06 0.55
518 0.54 0.23
1907 1.96 1.54
390 1.93 0.74
530 1.16 0.58
224 0.52 0.48
28.3 0.11 0.07
146.5 0.58 0.28
29.7 0.07 0.08
79.5 0.23 0.19
11.2 0.06 0.07
70.5 0.30 0.30
10.9 0.07 0.06
Drinking water supply (n ¼ 3) Wivenhoe Dam 40.3 Somerset Dam 229.4 Hinze Dam 726.2 North Pine Dam 24.4 Mt Crosby Weir 50.4 Tap water 77.1
75.4 332.9 1273 34.6 79.4 71.4
12.2 68.8 218.7 6.9 15.0 13.2
60.6 295.1 954.7 12.6 67.6 62.4
15.9 66.8 229.5 10.7 21.4 12.3
5.4 17.9 49.2 3.8 5.0 2.0
16.0 64.3 233.1 11.1 21.9 15.5
2.4 8.9 34.6 1.8 3.6 2.2
15.2 53.1 212.2 11.6 22.4 15.7
3.2 11.0 45.6 2.7 5.0 4.6
8.4 31.2 128.5 7.9 13.9 13.8
1.3 4.6 19.1 1.3 2.1 2.0
9.1 27.9 123.2 8.0 14.3 11.7
1.4 4.6 18.7 1.2 2.4 2.0
Wastewater effluent (n ¼ 3) WWTP A1 14.9 WWTP A2 28.6 WWTP B1 2.4 WWTP B2 6.5 WWTP B3 20.9 WWTP C 23.9 WWTP D1 16.0 WWTP D2 23.0 WWTP D3 14.1 WWTP E 19.1 WWTP F 22.4 WWTP G 35.3 WWTP H 14.4
23.9 45.2 1.5 12.0 22.0 60.9 21.7 29.4 28.0 40.8 51.2 83.9 40.1
4.9 9.2 1.3 3.0 4.8 17.5 5.3 5.1 5.6 8.5 9.3 14.9 9.6
24.6 49.2 3.0 16.3 28.4 123.7 22.4 26.2 38.1 53.8 49.8 79.2 53.1
7.4 12.1 2.8 4.8 7.3 42.9 8.5 9.4 7.4 13.4 15.0 22.9 16.1
2.4 2.3 1.2 0.6 5.5 15.4 3.3 1.4 3.8 4.7 4.8 7.7 4.1
636.4 1574 119.6 354.8 379.1 381.0 263.6 235.8 305.9 1795 224.0 356.9 392.1
1.9 3.7 0.6 1.4 1.5 7.3 2.0 2.1 2.1 4.2 3.0 4.7 2.8
15.1 25.6 5.1 10.2 10.2 49.5 17.0 17.4 20.4 39.1 29.1 37.2 23.1
5.0 7.9 1.9 3.0 3.2 13.0 5.0 5.7 6.7 12.0 9.3 10.6 7.7
18.3 27.5 6.8 12.3 11.2 51.7 18.5 20.9 26.9 49.1 40.7 42.2 36.7
3.2 4.7 1.1 2.1 2.0 8.3 3.3 3.7 4.5 7.9 6.8 7.1 7.0
22.9 34.1 9.6 16.2 15.0 61.7 23.1 28.2 36.5 57.3 49.5 57.1 51.5
3.8 5.4 1.6 2.9 2.8 10.3 4.1 4.8 6.3 10.9 8.8 9.6 9.3
Gd anomaly (unitless)
GdAnth
1.07 1.09 1.08 1.07 1.05 1.04
0 0 0 0 0 0
57 99 32 50 46 9 22 19 27 88 15 13 30
623 1550 114 338 370 333 251 217 293 1772 207 325 378
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SLRS-4 (pmol/L) Average blank (n ¼ 10) 3s
La
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Fig. 1 – Comparison of a natural rare earth element pattern (element concentrations are normalised to MuQ (Mud of Queensland, a sedimentary composite (Kamber et al., 2005), appropriate for Australia) Note that the typical ‘‘smooth’’ REE pattern in Reservoir A has a positive Eu anomaly, a feature related to the local lithology. Both REE patterns have negative Ce anomalies, probably due to the precipitation of cerium oxides in oxic water. The large positive Gd anomaly ðGdnðMeasuredÞ =Gdn Þ[99 observed at WWTP A is an anthropogenic feature that we attribute to the use of contrast agents in MRI. The parameter Gdn was calculated from a third order polynomial fit of the shale-normalised concentrations of the nonanomalous REEs as discussed in the text.
acid (1 week), rinsed 3 times in MilliQ, filled with MilliQ water and stored in double sealed Zip-Lock plastic bags until use. The water was discarded immediately prior to sample collection. Samples were carefully collected in 60 mL Terumo syringes, (rinsed 2 times with the sample) and a syringe filter (0.22-mm Millipore Millex–GV filters) fitted. The initial 2 mL of filtrate was discarded and the following w12 mL (3 times w4 mL) used to rinse out the residual MilliQ from the bottle) the remaining w40 mL was collected in the trace metal cleaned bottles. At all stages of sample collection, latex gloves were worn, and sample bottle lids were removed for the minimum possible time in an attempt to minimise potential sample contamination. Upon return to the laboratory, samples were immediately acidified with quartz sub-boiling double distilled nitric acid to pH 1.5, and spiked with 1 ppb Re as an internal standard prior to analysis. After collection, all further sample handling and analysis steps occurred in a trace metal clean laboratory.
2.3.
Analysis
Samples were analysed with a Thermo X-series ICP-MS housed in a clean facility at the University of Queensland. Reservoir, tap water, and finally, wastewater effluent samples were analysed after analysis of blanks and SLRS-4 dilutions to minimise the possibility of contamination. Instrumental conditions are similar to those previously described (Lawrence et al., 2006a). Briefly, the ICP-MS was tuned for maximum sensitivity using the high performance sample introduction system which was determined to have the best
signal to noise ratio, while maintaining oxide production below 2% (measured using CeO/Ce). The raw instrument data was corrected for variations in internal standard, external drift, and interfering oxides (Eggins et al., 1997). Instrument response was then calibrated against hotplate digests for the US Geological Survey (USGS) dolerite reference material W-2, using REE concentrations listed in Table 1. A similarly prepared hotplate digest of the USGS basalt reference material BIR-1 was used as a primary quality control. The National Research Council of Canada (NRCC) River Water Reference material (SLRS-4) was used as an external drift monitor, and secondary quality control.
2.4.
Evaluation of detection limits
MilliQ water blanks have detectable, consistent concentrations of the REE with absolute concentrations ranging from 62 fM (Tm) to 2.2 pM (La), and the shale-normalised REE patterns are smooth. Therefore, method detection limits were determined from ten individually prepared MilliQ water blanks. For all of the REE, the method detection limit, calculated as three times the standard deviation (3s, Table 1) is in the range 70–700 fM. As the REE patterns for the MilliQ blanks are smooth, it is possible to calculate Gdn . For any smooth REE patterns, if the ratio GdnðMeasuredÞ =Gdn exceeds 1.1, GdAnth can be calculated using Eq. (1). Specifically, as 3s for GdMeasured is 480 fM, the limit of quantification for GdAnth calculated from MilliQ blanks is, by definition, 48 fM. Similarly, it is possible to determine the limit of quantification by serial or sequential dilution of a known sample. We
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measured the REE concentration of MilliQ dilutions (both serial and sequential) of SLRS-4. As shown in Fig. 2, the entire REE pattern of SLRS-4 remains coherent at dilutions up to 510 times, and Gd is determined accurately, within analytical uncertainty, at 750 times dilution. The actual concentration of Gd in SLRS-4 is 0.225 nM, and using this method, it is possible to quantify Gd accurately at (0.225 nM/510) ¼ 440 fM, and GdAnth at concentrations as low as 44 fM. As different methods yield consistent concentrations, it imparts a high degree of confidence in our ability to determine GdAnth at this level. Nonetheless, it must be acknowledged that this is only the case when a REE pattern is measurable, with concentrations approaching the method detection limit. In a more general sense, the limit of quantification of is 10% of the measured Gd concentration. The limit of quantification of GdAnth of w48 fM compares favourably to the limits of quantification for analytical methods detecting representative pharmaceuticals in natural water bodies (e.g. Diazepam in river water) where the detection limit, taking into account a 1000-fold preconcentration, is 0.02 mg/L, giving equivalent detection limits of 70 nM (Zuccato et al., 2000). Thus, GdAnth can be detected at concentrations that are up to 6 orders of magnitude lower than most other micropollutants.
3.
Results and discussion
Rare earth element results are presented in Table 1 and Fig. 3. The shale-normalised REE patterns in Fig. 3A for tap water and the drinking water supply reservoirs in the Brisbane region are
typical of those previously reported for natural fresh water sources (Lawrence et al., 2006b). Further, there is no evidence that any sample has a Gd anomaly (in all cases, GdnðMeasuredÞ =Gdn < 1:1). As a result, the calculated GdAnth component in all cases is zero. In contrast, the WWTP effluents all have detectable Gd anomalies from 9 to 99, representing a maximum absolute excess of 1.7 nM at the largest population equivalent treatment plant (Fig. 3B). For that particular treatment plant, 99% of the detected Gd is anthropogenic in origin, consistent with the interpretation that MRI contrast agents are the source of the Gd anomaly. In each case the Gd anomaly, a ratio, is an indicator of how many times greater the measured value is over the natural concentration. The sample with the lowest anomaly (WWTP C, anomaly ¼ 9) has an GdAnth component of 330 pM. In contrast, WWTP B1, with the lowest GdAnth component of only 114 pM, has an anomaly of 32. The lowest concentration of total Gd measured was 119 pM, with 114 pM attributed to anthropogenic sources; this concentration is w2400 times higher than the detection limit, indicating the sensitivity of this technique. The Gd anomalies observed in South East Queensland are within range of previously reported values (Bau and Dulski, 1996; Bau et al., 2006; Knappe et al., 2005; Kulaksiz and Bau, 2007; Kummerer and Helmers, 2000; Lawrence et al., 2006c; Moller et al., 2000, 2003; Morteani et al., 2006), although well below the maximum reported anomaly (Bau and Dulski, 1996) of 2014 in Germany (GdAnth ¼ 7476 pM). Regardless, at every SEQ treatment plant, at every sampling time, GdAnth was
Fig. 2 – Shale (MuQ) normalised REE patterns for dilutions of the NRCC River water reference material SLRS-4 (dilution indicated in legend). Note that Eu is not quantifiable below 100 times dilution, but overall, the REE pattern is still quantifiable using a third order fit (Eu is excluded from the fit, along with other anomalous elements) at 510 times dilution. Although the REE pattern loses coherence beyond this limit, the absolute concentration of Gd is still determined within instrumental error (65%) at 750 times dilution. However, as the Gd anomaly is calculated from the remainder of the REE pattern, the limit of quantification is defined from the concentration from which the geogenic abundance can be confidently predicted. The REE pattern for the average blank (n [ 10) is shown as a solid black line, with error bars [ 1s represents the practical lowest measurable concentrations. As the REE pattern is consistent and (excluding Eu) smooth, it is possible to calculate the geogenic Gd concentration, and thus the anthropogenic component.
water research 43 (2009) 3534–3540
3539
Fig. 3 – Shale (MuQ) normalised REE patterns of (A) drinking water supply in South East Queensland, and (B) selected wastewater treatment plants. Note that WWTP B and D, both of which were sampled on multiple occasions, have remarkably consistent GdAnth concentrations. Every final treated effluent sample from all regional WWTPs had significant positive Gd anomalies, which range from 9 to 99. In contrast, no drinking water, or water supply reservoir sample had detectable concentrations of GdAnth .
detected. The ubiquitous occurrence of GdAnth in treated effluent from WWTPs is a significant outcome, as it confirms, in principle, that GdAnth may be used as a tracer for wastewater in South East Queensland waterways. The ICP-MS technique described is suitable for rapid and direct analysis of both fresh water and wastewater samples, with minimal pretreatment. Given the ubiquitous presence of GdAnth in wastewater, this parameter may be viewed as an ideal tracer. For example, the absence of GdAnth in tap water, and in the drinking water supply in SEQ can therefore be interpreted to indicate that the drinking water supply does not currently contain a detectable wastewater component. Specifically, for Somerset Dam, with the second highest
natural Gd component, an increase of just 6 pmol/kg would result in a detectable GdAnth component. The average WWTP GdAnth discharge was 550 pmol/kg, thus, if wastewater with this average GdAnth component was present above 1.1% by volume, it would have been detectable. For North Pine Dam, an increase of just 50 fmol/kg Gd, representing a contribution of 0.009% wastewater, it would have been detectable. These values would be lowered by a factor of 3 if the calculation was performed using the highest measured wastewater GdAnth component (detected in the largest population equivalent WWTP). In comparison, the refractory micropollutant, carbamazepine, is typically present in wastewater in Australia at 1 mg/L (Khan et al., 2004). When compared to published LODs
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of 0.01 mg/L (Clara et al., 2005), this represents detection at 1% wastewater dilution. Therefore, GdAnth potentially detects a wastewater contribution 50 times more easily than comparable SPE preconcentration, LC-MSMS techniques. As a result of this research, we have established baselines from which it is now possible to use GdAnth to monitor the effect of reservoir supplementation by the addition of purified recycled water from the Advanced Water Treatment Plants. We envisage that GdAnth , as a relatively easily measured parameter, may be further developed as a tracer to; evaluate hydrological models, act as a surrogate (or proxy) for the presence of other micropollutants of higher ecotoxicological or human health concern, and, help validate environmental risk assessments by allowing a direct measurement of the mixing and dilution of wastewater effluent in the environment.
4.
Conclusions
Anthropogenic Gd is a ubiquitous component of all measured wastewater effluents (8 separate WWTPs) in South East Queensland, Australia. Anthropogenic Gd is a useful proxy for wastewater contamination of natural waters. There is no evidence for anthropogenic Gd contamination of the drinking water supply dams (four reservoirs), or in tap water, prior to the commencement of a large-scale recycled water project in South East Queensland.
Acknowledgements The authors are funded by the ‘‘Chair in Water Recycling Agreement’’, jointly funded by the University of Queensland, Veolia Water Australia, and Water Secure.
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