Anthropogenic 129I in precipitation and surface waters in Ireland

Nuclear Instruments and Methods in Physics Research B 268 (2010) 1232–1235

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Anthropogenic

129

I in precipitation and surface waters in Ireland

S.M. Keogh a, A. Aldahan b,e, G. Possnert c, L. León Vintró a, P.I. Mitchell a,*, K.J. Smith d, P. McGinnity d a

School of Physics, University College Dublin, Belfield, Dublin 4, Ireland Department of Earth Sciences, Uppsala University, SE-75120 Uppsala, Sweden c Tandem Laboratory, Uppsala University, SE-75120 Uppsala, Sweden d Radiological Protection Institute of Ireland, Clonskeagh Square, Dublin 14, Ireland e Department of Geology, United Arab Emirates University, Al Ain, UAE b

a r t i c l e

i n f o

Article history: Available online 7 October 2009 Keywords: Anthropogenic 129 I Water Ireland

a b s t r a c t The 129I content in precipitation, lake and river waters sampled in Ireland in 2005–2006 has been determined by accelerator mass spectrometry. In the case of lake and river waters, the data reveal little if any geographic dispersion with a mean (n = 14) concentration of 4.6 ± 1.2(1r)  108 atoms L 1. In contrast, concentrations of 129I in precipitation show significant variations both in time and space, with concentrations ranging from a low of 1.9  108 atoms L 1 to a high of 303  108 atoms L 1. These variations in precipitation are attributed to temporal changes in on-going discharges of 129I from west European reprocessing plants in conjunction with the trajectories of airstreams prevailing over Ireland at the time of sampling. Ó 2009 Elsevier B.V. All rights reserved.

1. Introduction Iodine-129 (T1/2 = 1.57  107 y) is produced naturally by the spontaneous fission of uranium in the lithosphere, and by cosmic-ray spallation reactions with xenon isotopes in the upper atmosphere. The natural inventory of 129I has been estimated to be 230 kg, most of which resides in the deep oceans [1]. Iodine129 is also anthropogenically produced during fission processes associated with civil and military nuclear activities. An estimated 50–150 kg of 129I were released to the atmosphere during the main period (1945–1964) of above-ground nuclear weapons testing [2,3] and a further 6 kg were released in the aftermath of major nuclear accidents such as the Windscale fire (1957) and Chernobyl (1986) [4,5]. However, the most significant contribution to the mobile 129I inventory in the environment comes from spent nuclear fuel reprocessing operations and, in particular, the liquid and gaseous releases from two major European reprocessing facilities, namely NDA’s plant at Sellafield (UK) and AREVA’s plant at Cap de La Hague (France), which now account for >90% of total global releases [6]. It has been estimated that, by 2004, 1371 kg of 129I had been discharged into the NE Irish Sea from the Sellafield plant, with an additional 182 kg released directly to the atmosphere in gaseous form [7–9]. By the end of the same year, 3119 kg of 129I had been released from the La Hague plant as liquid discharges into the Eng* Corresponding author. Tel.: +353 1 7162222; fax: +353 1 2837275. E-mail address: [email protected] (P.I. Mitchell). 0168-583X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2009.10.141

lish Channel, with an additional 68 kg released in gaseous form [6,9]. Releases from a third European reprocessing facility, the Marcoule plant in southern France, also contributed to the direct atmospheric releases of 129I prior to its shut-down in 1997, with an estimated 68 kg of 129I released over the period 1988– 1997 [6]. Airborne releases from these facilities, and the fraction of their liquid 129I releases volatilised from the ocean surface have been shown to be the main source of 129I deposited over Europe, and explain the enhanced 129I concentrations observed in European surface waters [9–15]. It follows that likely sources of 129I in Irish terrestrial waters and precipitation include atmospheric washout of 129I present in gaseous discharges from these plants and volatilisation of 129I from seawater contaminated by liquid discharges, mainly from Sellafield. Given the proximity of the latter to Ireland and the fact that current annual liquid and gaseous discharges of 129 I from this source remain substantial, there is a clear need to establish ambient baseline data for Ireland against which future releases, either routine or accidental, can be assessed. In relation to liquid discharges from Sellafield to the NE Irish Sea, following a recent survey, there is now a substantial database on 129I concentrations in seawater and biota in coastal waters surrounding Ireland [16]. However, prior to the present study, there were no data on levels of 129I present in precipitation and terrestrial waters in Ireland, and delivered via the atmospheric pathway. Here, for the first time, we report data on the concentrations of 129I in precipitation and freshwaters sampled at various locations throughout Ireland in the period 2005–2006. We also interpret

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S.M. Keogh et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 1232–1235

the data utilising relevant meteorological data and air parcel backtrajectory analysis.

2. Methodology One litre samples of lake and river water (including tap water) were collected at 13 geographically well-spaced locations throughout Ireland (Fig. 1) in the period December 2005 – April 2006 and stored in a cool and dark cabinet prior to analysis for 129I. In addition, samples of rainwater from an established network of stations throughout the country were made available to us by the Irish Meteorological Service (Met Eireann) and the Radiological Protection Institute of Ireland, who routinely collect such samples for total beta activity and selected radionuclides, but not 129I. These samples were taken within a similar period of time as the surface water samples already referred to, and were collected with the aid of a circular 1 m2 surface funnel draining into a polyethylene bottle. The chemical extraction of iodine from water is usually based on the solubility of I2 in carbon tetrachloride (CCl4) after the method of Buraglio et al. [17]. However, we chose to use chloroform (CHCl3) instead of CCl4 because of its lower toxicity. Full details of the procedure are given elsewhere [18]. Suffice that 2 mg of soluble iodine carrier (analytical grade KI) were added to each sample and the solution reduced to iodide (I ) by the addition of 2 ml of 0.1 M NaHSO3. Following this, the solution was acidified to pH 2 using concentrated HNO3, converting iodide to molecular iodine (I2). Iodine was extracted into CHCl3 and the extraction repeated to ensure efficient recovery. Iodine was then back-extracted into

21 12

1

20 19 11

10

2 18

8

a 10 ml solution of 0.1 M NaHSO3. Finally, iodine was precipitated as silver iodide (AgI) from the aqueous phase by the addition of a few drops of 50% H2SO4 and 1.2 ml of 0.01 M AgNO3. Each sample of AgI precipitate was primed for AMS measurement by mixing 1 mg of precipitate with high purity niobium powder in a ratio of 1:2 and pressing into a small hollow copper target holder. The targets were then analysed for 129I content by AMS at the Tandem Laboratory, Uppsala University. Specifically, 129I/127I quotients in the samples were recorded using a 5 MV Pelletron tandem accelerator. Sample absolute 129I content was then calculated using NIST’s standard iodine reference material, SRM 4949C, at a background 129I/127I level of <5  10 13. Natural AgI (iodargyrite) was used for the estimation of machine background, which proved to be <10 14. 3. Results and discussion 129 I concentrations recorded in lake and river waters throughout Ireland are summarised in Table 1. Although no significant geographic trend is evident from the dataset (Fig. 1), it is the case that the two highest values recorded were for streams close to the east coast. The mean concentration was determined to be 4.6  108 atoms L 1, with a range of 2.1–9.2  108 atoms L 1, which is similar, for example, to the concentration range of 2.2–4.9  108 atoms L 1 reported for the River Fyrisån in Uppsala, Sweden, in the period 1998–1999 [19]. Concentrations in the same order have also been reported for both rivers and lakes elsewhere throughout Europe [14,20]. In absolute terms, the levels recorded in Irish natural waters are between one and two orders of magnitude higher than those reported for locations outside of Europe, at some remove from the direct influence of discharges from European reprocessing plants, and four to five orders of magnitude higher than the expected natural concentrations, estimated to be about 104 atoms L 1 [19]. Clearly, as for other European countries, the main source of 129I to Irish surface waters is direct or indirect atmospheric deposition of 129I that was initially discharged from the reprocessing facilities at Sellafield and La Hague. Two samples of tap water taken from Dundrum in south Dublin were also analysed in the course of this study and shown to have 129 I concentrations of 2.2 and 2.9  108 atoms L 1, respectively. As one should expect, these concentrations are very similar to those recorded in Irish surface waters. In contrast to surface waters, 129I concentrations in rainwater sampled throughout Ireland in the period December 2005 – May

9 3

17

Table 1 Measured to ± 2r. Site

15

6 16

14

13

7

1 2 3 3 3 4 5 6 7 8 9 10 11 12

4

5 = 109 atoms L-1

100 km Fig. 1. Map of Ireland showing the locations of precipitation (j) and surface water (h) sampling sites throughout the island and the corresponding recorded 129I concentrations (note: in the case of Dublin rainfall, only the lowest concentration recorded is shown for reasons of scale).

a

129

I concentrations in surface waters in Ireland. Uncertainties are given

Location Waterfoot Stream, Co. Antrim Boyne River, Co. Louth Dublin City Dublin Citya Dublin Citya Bunclody, Co. Wexford River Lee, Co. Cork River Shannon, Co. Limerick River Suir, Co. Tipperary Dunmore, Co. Galway Balinfield Lake, Co. Westmeath Temonbarry, Co. Longford River Erne, Co. Cavan Lake Gartan, Co. Donegal

Tap water samples.

Date of sampling

129 I (108 atoms L

12/05 12/05 12/05 12/05 12/05 04/06 12/05 12/05 12/05 04/06 04/06 04/06 04/06 04/06

8.4 ± 0.3 3.4 ± 0.1 9.2 ± 0.3 2.9 ± 0.1 2.2 ± 0.1 4.8 ± 0.2 3.0 ± 0.1 3.4 ± 0.1 2.1 ± 0.1 3.7 ± 0.3 5.7 ± 0.3 5.3 ± 0.4 6.8 ± 0.4 4.1 ± 0.3

Mean (n = 14) Range

4.6 ± 4.4 2.1–9.2

1

)

1234 Table 2 Measured

S.M. Keogh et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 1232–1235

129

I concentrations in precipitation over Ireland. Uncertainties are given to ± 2r.

Site

Location

Sampling period

129

3 3 3 3 13 14 15 16 17 18 19 20 21

Dublin City Dublin City Dublin City Dublin City Cork City Valentia, Co. Kerry Shannon airport, Co. Limerick Kilkenny City Birr, Co. Offaly Mullingar, Co. Westmeath Belmullet, Co. Mayo Clones, Co. Monaghan Malin Head, Co. Donegal

22/12/05–28/12/2005 15/02/06–28/02/2006 01/03/06–16/03/2006 01/04/06–20/04/2006 14/04/06–21/04/2006 01/03/06–31/03/2006 07/04/06–14/04/2006 16/04/06–01/05/2006 04/05/2006 30/04/06–01/05/06 01/04/06–21/04/2006 21/04/06–28/04/2006 01/04/06–01/05/2006

134 ± 2 303 ± 2 108 ± 6 39 ± 3 13.4 ± 0.9 4.0 ± 0.6 6.4 ± 1.2 8.7 ± 0.6 9.7 ± 0.6 1.9 ± 0.3 4.3 ± 0.5 7.8 ± 0.9 5.8 ± 0.5

Mean (n = 13) Range

50 ± 174 1.9–303

a

Dublin (26/12/05)

c

Mullingar (30/04/06)

I (108 atoms L

1

)

b

Dublin (13/03/06)

d

Cork (21/04/06)

Fig. 2. NOAA HYSPLIT model back-trajectories for air parcels arriving at (a) Dublin 26/12/05; (b) Dublin 13/03/06; (c) Mullingar 30/04/06; (d) Cork Airport 21/04/06. Note that for (a) and (b) back-trajectories are computed at 2-h intervals spanning the 24-h period ending at 14:00 UTC on the date given. For (c) and (d) back-trajectories are computed for a single 24-h interval ending at 14:00 UTC on the date given.

2006 were found to vary by at least two orders of magnitude, being in the range 1.9–303  108 atoms L 1 (Table 2). The three samples containing the highest concentrations of 129I (108–303  108 atoms L 1) were collected at Dublin, suggesting an enhancement in 129I levels over this region during the sampling periods involved. Careful scrutiny of meteorological records indicates that the prevailing winds in Dublin were generally speaking from the east/northeast during each of these periods. This would suggest the possibility that an air-mass labelled with enhanced levels of 129 I in gaseous form had travelled from the vicinity of Sellafield across the Irish Sea and that 129I had subsequently been deposited in the Dublin area via precipitation. To test this hypothesis, an air parcel back-trajectory analysis was performed using the National Oceanic and Atmosphere Administration (NOAA) Hybrid Single-Particle Lagrangian Inte-

grated Trajectory (HYSPLIT) atmospheric transport/dispersion model [21], together with meteorological data spanning the relevant sampling periods. The HYSPLIT backward trajectory shows an aereal view of the path(s) an air parcel(s) took in order to reach its destination at a particular sampling point and date. A selection of some trajectories are shown in Fig. 2. Our modelling results confirm that, for the three cases where elevated concentrations in excess of 100  108 atoms L 1 were recorded, air parcels that were over Dublin during periods of rainfall at the time of sampling had previously passed over the vicinity of Sellafield (Fig. 2a) or La Hague (Fig. 2b). Indeed, for the period in which the highest concentration (303  108 atoms L 1) was recorded, easterly trajectories crossing the Sellafield region prevailed for >50% of the days. In contrast, for the period corresponding to the lowest measured 129I concentration recorded in Dublin (39  108 atoms L 1),

S.M. Keogh et al. / Nuclear Instruments and Methods in Physics Research B 268 (2010) 1232–1235 Table 3 Concentrations of Hemisphere.

129

I in precipitation at selected locations in the Northern

Location Germany (Bavaria) Norway (Bergen) Sweden (Kvidinge) Italy Spain Switzerland (Zurich) USA Ireland

Sampling period

129

2003–04 2003 2001–02 1998–99 1996–97 1994–97 1995–97 2005–06

4.8–50 16–41 10–57 1.1–9.4 0.47–50 2.2–445 0.07–0.67 1.9–303

I (108 atoms L

Reference 1

) [22] [13] [13] [19] [24] [25] [23] Present work

1235

atmospheric deposition of 129I that was initially discharged from the reprocessing facilities at Sellafield and La Hague. Concentrations of 129I in precipitation reveal significant variations both in time and space, with concentrations ranging from a low of 1.9  108 atoms L 1 to a high of 303  108 atoms L 1. These variations in precipitation are attributed to temporal variations in ongoing atmospheric discharges of 129I from west European reprocessing plants in conjunction with trajectories of airstreams prevailing over Ireland at the time of sampling. Modelling results using an atmospheric transport/dispersion model support this interpretation.

Acknowledgements trajectories were mainly from a westerly direction, and had not traversed the vicinity of either reprocessing facility. Nevertheless, it is apparent that this concentration is significantly higher than that recorded at any of the other sampling stations throughout the island, all of which are sited at some considerable remove from the east coast and the presumed influence of waters labelled with 129 I discharged in liquid form from Sellafield. These latter (i.e., non-east coast) concentrations were in the range 1.9–13.4  108 atoms L 1, which is comparable to 129I concentrations in precipitation recorded for other countries throughout Europe (Table 3). For example, Swedish rainwater sampled at Kvidinge (56°N) during 2001 and 2002 showed concentrations of between 10 and 57  108 atoms L 1 [13], while concentrations recorded in Upper Bavaria in the period 2003–2004 were in the range 4.8–50  108 atoms L 1 [22]. Farther afield, however, recorded concentrations would appear to be at least an order of magnitude lower [23]. As for the Dublin station, back-trajectory analyses were carried out for each of the other sampling locations over the relevant sampling periods. With one exception (i.e., Valentia), lower 129I concentrations (1.9–6.4  108 atoms L 1) were recorded during periods in which trajectories were from a northerly or westerly direction (Fig. 2c). In contrast, for periods in which trajectories were from an easterly or south-easterly direction (but not passing directly over either of the two reprocessing plants), 129I concentrations were somewhat higher (7.8–13.4  108 atoms L 1) (Fig. 2d). In the case of Valentia, easterly trajectories traversing Sellafield and La Hague were observed for the period 20–24 of March 2006 (representing 16% of the sampling timespan). However, scrutiny of the meteorological records indicates that precipitation only occurred on the last of these days (12 mm), with the bulk of the precipitation (151 mm) taking place outside this period. Although the source of most of the 129I present in Irish precipitation and surface waters appears to be a combination of 129I released directly to the atmosphere from the reprocessing plants at Sellafield and La Hague, and 129I in seaspray or 129I volatilised from seawater labelled by the same sources, our data would appear to indicate that the former is the dominant mechanism at the present time. 4. Conclusions Our data show that 129I concentrations in Irish river and lake waters, with a mean concentration of 4.6 ± 1.2 (1r)  108 atoms L 1, are considerably enriched above pre-anthropogenic levels. Clearly, the main source of 129I to Irish surface waters is

We gratefully acknowledge the award of an international collaboration grant from Enterprise Ireland, which enabled one of us (SMK) to undertake a three-month sabbatical at Uppsala University (Grant No. IC/2005/36/). The authors also acknowledge the NOAA Air Resources Laboratory (ARL) for the provision of the HYSPLIT transport and dispersion model (http://www.arl.noaa.gov/ ready.html) used in this study.

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