Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone

STOTEN-24290; No of Pages 7 Science of the Total Environment xxx (2017) xxx–xxx

Contents lists available at ScienceDirect

Science of the Total Environment journal homepage: www.elsevier.com/locate/scitotenv

Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone Deivis Plausinaitis a,⁎, Aleksandr Prokopchik b, Algimantas Karaliunas b, Leonid Bohdan c, Yuliya Balashevska c a b c

Department of Physical Chemistry, Vilnius University, Naugarduko str. 24, LT-03225, Lithuania Company LOKMIS, Visoriu str. 2, LT-08300 Vilnius, Lithuania Central Analytical Laboratory for RAW Characterization, Center for Individual and Environmental Radiation Monitoring “EcoCenter”, Shkilna str. 6, 07270 Chernobyl, Ukraine

H I G H L I G H T S

G R A P H I C A L

A B S T R A C T

• The distribution of lanthanides in natural waters around Chernobyl was determined. • The normalized distribution of lanthanides increases from La towards Lu. • There are clear concentration anomalies of Ce, Eu, and Er. • The Er anomaly exceeded the average by 13 times.

a r t i c l e

i n f o

Article history: Received 14 July 2017 Received in revised form 6 October 2017 Accepted 8 October 2017 Available online xxxx Editor: D. Barcelo Keywords: Anthropogenic lanthanides Rare earth elements Erbium Anomalies Chernobyl

a b s t r a c t This study focused on measurement of lanthanides in surface water (SW) and ground water (GW) samples from the Chernobyl Exclusion Zone. Results showed that the total lanthanide concentration in SW ranges from 500 to 1100 ng L−1 and is about 10 times lower than the GW concentration. The normalized patterns of lanthanide concentrations increase from lighter elements to heavier lanthanides. Concurrently, concentration anomalies of Ce, Eu, and Er are visible. The Er anomaly is the most noticeable and exceeds the theoretical calculation by about 13 times. The Ce and Eu anomalies are likely related to the variety of oxidation states of these elements. Meanwhile, the cause of the Er anomaly is not completely clear, but is likely related to the Chernobyl Nuclear Power Plant accident, since increased concentrations correlate with the distribution of contamination in the zone. 137Cs activity measurements partially confirm this hypothesis. Simultaneously, there is a relationship between the positive Er anomaly and increase in 235U concentrations. However, there is no reliable information in the literature that indicates that Er was used in the Chernobyl Nuclear Power Plant before the reactor accident. © 2017 Elsevier B.V. All rights reserved.

1. Introduction The determination of rare earth elements is gaining an increasingly important role in modern environmental research, and is related to the increased application of these metals in science and technology, ⁎ Corresponding author. E-mail address: [email protected] (D. Plausinaitis).

such as electronics, chemical industries, and the creation of new alloys (U.S. Environmental Protection Agency, 2012; Du and Graedel, 2013). In modern medicine, lanthanides are often used for diagnostic purposes (Kümmerer and Helmers, 2000). For this reason, the concentration of lanthanides may be increasing in living environments, such as natural waters or soil (Zhang et al., 2001; Hatje et al., 2016), and there are several cases of increasing concentrations of certain lanthanides (Byrne and Sholkovitz, 1996). For example, in samples from the Rhine River,

https://doi.org/10.1016/j.scitotenv.2017.10.066 0048-9697/© 2017 Elsevier B.V. All rights reserved.

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

2

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx

anomalously high concentrations of La, Sm, and Gd were detected, and related to anthropogenic activity (Kulaksız and Bau, 2013; Klaver et al., 2014). Increased concentrations of Gd in the San Francisco Bay Area have been associated with its use for medical diagnostic purposes (Hatje et al., 2016). Iwashita et al. (2011) reported anomalous concentrations of Yb and Lu in precipitation water samples. Lanthanide isotopes detection can be used to determine nuclear activity (Labrecque et al., 2016). Since lanthanides are fission products of U and Pu, they can be found with other radioactive isotopes (IAEATECDOC-1340, 2003). In addition, contamination of the environment with lanthanides has further increased due to a number of nuclear facility accidents worldwide. This increase is also related to the fact that lanthanides are used in nuclear reactor designs (U.S. Department of Energy, 1993; Remeikis and Jurkevicius, 2004). For example, a mixture of U and Er oxides drastically improves the technical and economic parameters of power distribution and the safety of Water–Water Energetic Reactors (Barchevtsev et al., 2002a, 2002b). Spectroscopic techniques are commonly employed for lanthanide determination, such as atomic absorption spectroscopy or inductively coupled plasma optical emission spectroscopy (ICP-OES) (DeKalb and Fassel, 1979). ICP mass spectroscopy (MS) is one of the most suitable methods for this purpose. However, difficulties emerge when detecting lanthanides from plasma-generated compounds. The most common interfering compounds of lanthanide isotopes are hydrides (MH+), oxides (MO+), and hydroxides (MOH+) (Rauta et al., 2003; Dressler et al., 2007). The impacts of interfering masses can be reduced in several ways. Primarily, the concentration of the elements can be calculated using the isotope with the lowest potential interference. For example, 147 Sm is a more appropriate isotope for the determination of Sm concentration than 154Sm due to the interference of Ba compounds (e.g., 138Ba16O and 137Ba16OH). Another method of reducing the influence of interference is to use high-resolution MS (Hatje et al., 2016) or MS with a reaction cell (Ardini et al., 2010). In addition, more precise measurements of lanthanide isotopes can be performed using ion chromatography coupled with ICP-MS (Perna et al., 2002). In this study, using ICP-MS, we determined the concentrations and distribution patterns of lanthanides in various water sources in the Chernobyl Exclusion Zone. After the accident at the fourth unit of the Chernobyl Nuclear Power Plant, a large amount of nuclear fuel particles was released into the environment. At the same time, large amounts of lanthanides were dispersed into the surrounding area (Gudiksen et al., 1989). During the initial radioactive contamination, the largest share of short-lived isotopes present included 141Ce, 144Ce, 154Eu, and 155Eu, and their concentrations have decreased significantly since the accident. Monitoring activity for these nuclides has been carried out up to the present time (LaRosa et al., 1992; Jaracz et al., 1995; Carbol et al., 2003; Bossew et al., 2004). However, insufficient data has been collected on the pollution of the Chernobyl Exclusion Zone by other lanthanides.

2. Materials and methods 2.1. Sampling location The main objective of this study was to measure lanthanide concentrations in surface water (SW) and ground water (GW) from the Chernobyl Exclusion Zone. These sample mediums were selected due to the ability to use natural waters to accurately represent the total area of contamination. Fig. 1 presents a map of a section of the Chernobyl Exclusion Zone, including the sample site locations. Samples were taken from natural (Lake Azbuchin) and artificial (Lake Glubokoje, and Pripyat and Semichod backwaters) lakes, which are located around the plant within the 10-km Exclusion Zone. Other samples were taken from water boreholes in the 10-km Exclusion Zone. Table 1 lists the locations of all samples and the total background radiation at these sites.

2.2. Preparation of samples and calibration solutions After rinsing with sample volume several times, 5-L polyethylene bottles were used to collect samples. Samples were immediately acidified by adding 10 mL of ultrapure HNO3 to each bottle to reduce the formation of precipitation. To ensure reliable quantification, all lanthanide samples were pre-concentrated before the ICP-MS measurement. The preconcentration of all samples was carried out 15 times via the slow evaporation of water. To avoid clogging the ICP-MS injector, before measuring the samples, all samples were filtered through a 2-μm pore size filter. After the initial pre-concentration of the samples, precipitate formed in the GW samples. The precipitate of each GW sample was placed in a separate PTFE vessel together with filter paper. After adding 10 mL of ultrapure HNO3 to each vessel, dissolution was carried out using a microwave digestion system (Berghof Speedwave, Germany). The procedure resulted in the formation of clear liquid, which was diluted 10 times before the ICP-MS measurement. The ICP-MS was calibrated using two standard stock solutions. Lanthanide standard solutions of 5, 20, and 50 μg L−1 were prepared immediately before use via the stepwise dilution of a 50-mg L−1 stock solution purchased from Sigma-Aldrich (rare earth element mix for ICP; Buchs, Switzerland). For the detection of the other elements, the multi-element Calibration Standard 2A (Agilent Technologies, Japan) was used and 10-, 30-, and 100-μg L− 1 standard solutions were prepared. All standards were diluted with a 0.2% HNO3 solution made from concentrated HNO3 by dilution with deionized water (18 MΩ∙cm). Concentrated HNO3 was purchased from Merck (Nitric acid 65%, Suprapur®, Darmstadt, Germany). 2.3. Methods All measurements were performed using a quadrupole-type ICP-MS (Agilent 7700x; Agilent Technologies, Japan). The ICP-MS system was controlled and data were processed using the Agilent 7700 Series ICPMS MassHunter Workstation software. The operating conditions for the ICP-MS were as follows: Rf power: 1500 W; sampling depth: 7.00 mm; number of acquisition points per mass: 3; integration time per acquisition point: 0.1 s; and cooling, carrier, and makeup gas flows: 15.0, 0.8, and 0.3 L min−1, respectively. The measurements were performed by obtaining the mass spectra for masses 6–246 (excluding forbidden masses). Recording broad spectra facilitates the estimation of potential interference of masses. To assess the impact on the results of the interfering ions in each mass measurement, we took the measurements in two modes, the ICP-MS mode with the reaction cell containing He gas, and that without it. During the method optimization process, the mass spectrum was registered in a standardized multi-element calibration solution containing 100 μg L−1 of Ba and without lanthanides. The He gas flow into the reaction cell was adjusted so that minimal MO+ ions were formed at the time of measurement to change the main mass signal as little as possible. We tested the 135th and 151st mass signals (i.e., possible 135Ba16O ion formation). The optimal He flow was 3.4 mL min−1 and in this case, the 135 Ba16O signal decreased by 95 times while the 135Ba signal decreased by 18 times. In the next step of the method optimization, we evaluated the residual impacts of potential interferences. According to the literature, the greatest influence on the determination of lanthanides is the formation of BaO+ and BaOH+, especially in the determination of Eu concentrations (Dulski, 1994; Dressler et al., 2007). The influence of the remaining interference was determined according to the ratio of 151st mass signal (151M) between the sum of 134th (134M) and 135th (135M) signals (i.e., possible 135Ba16O and 134Ba16O1H formation):

151

M=

134

Mþ

135


M ¼ 1:41  10−3 :

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx

3

Fig. 1. Map of the central area of the Chernobyl Exclusion Zone showing the water sampling locations. Descriptions of the samples are presented in Table 1.

Based on this experiment, in further measurements, 0.141% of the sum of the signals 134M and 135M was subtracted from the obtained 151st mass signal. For the calculation of other lanthanide concentrations, the influence of polyatomic interferences was not taken into account, as there were minimal differences between lanthanide concentrations in water samples. Since this research focused particularly on the determination of Er concentrations, we also evaluated the potential interference of this lanthanide. The total Er concentration was calculated based on 166Er. The most likely interference for the 166th mass signal is related to lanthanide compounds such as 165Ho1H, 150Nd16O, 150Sm16O, and 149 Sm16O1H. Other interferences can arise due to the formation of Te argides 126Te40Ar and 130Te36Ar. Therefore, we evaluated the possibility

of interference by comparing the 166th mass signal to the mass signals of these isotopes. During the spectra scan of the 166th mass, we recorded a 20 kcps signal. Meanwhile, the signals of interfering atoms were 1493 cps (150th mass), 551 cps (149th mass), 2894 cps (130th mass), and 6 cps (126th mass). These signals were much lower than that of the 166th signal and did not significantly impact the calculation of Er concentration. The element concentration calculations were performed with the stable isotopes shown in Table 2. These isotopes were selected because they are free from isobaric interference and are sufficiently abundant for quantitative measurements using ICP-MS. The minimum detection limits (MDLs) were calculated as the standard deviation of the integrated blank signal multiplied by 3, while the minimum quantitation limits

Table 1 Sampling dates and locations and background radiation levels at the sampling sites. Sample name

Sampling date

Location name

Geographic coordinates

SW1 SW2 SW3 SW4 SW5 SW6 SW7 GW8 GW9 GW10 GW11

28.10.2015 28.10.2015 28.10.2015 28.10.2015 28.10.2015 28.10.2015 28.10.2015 09.09.2015 09.09.2015 09.09.2015 09.09.2015

Pripyat backwater, river station Pripyat backwater, river port Semichod backwater, boat station Semichod backwater, dam No.1 Lake Azbuchin Headrace canal Lake Glubokoe, dam Borehole No. 1/1, Red Forest Borehole No. K13, Red Forest Borehole No. K8, filtration fields Borehole No. 168/Q2, filtration fields

N 51.40844°, E 30.06496° N 51.41025°, E 30.09035° N 51.41579°, E 30.05602° N 51.42138°, E 30.06496° N 51.40593°, E 30.11885° N 51.38579°, E 30.11095° N 51.43344°, E 30.09881° N 51.38366°, E 30.07744° N 51.39094°, E 30.06261° N 51.39918°, E 30.08644° N 51.39500°, E 30.09972°

137

Cs activity (MDL), Bq kg−1

0.67 (0.03)

15.74 (0.05) 3.77 (0.04)

Background radiation, μSv h−1 0.569 1.483 3.536 0.765 0.653 4.114 16.327 25.936 1.278 1.763 2.164

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

4

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx

Table 2 Detection limits and sensitivities of selected ICP-MS methods. Isotope

MDL, ng L−1

MQL, ng L−1

Sensitivity, CPS / (ng L−1)

139

13.9 21.8 4.1 0.6 0.3 0.6 0.3 0.4 1.4 0.4 0.4 1.0 1.0 0.5

38.3 59.4 11.8 1.8 0.8 1.8 0.9 1.3 4.0 1.3 1.2 2.9 3.0 1.5

14.9 22.3 17.0 19.2 19.0 21.8 41.4 33.5 29.0 33.3 32.6 38.9 38.9 15.5

La Ce 141 Pr 146 Nd 147 Sm 151 Eu 157 Gd 159 Tb 163 Dy 165 Ho 166 Er 169 Tm 172 Yb 175 Lu 140

A high-purity Ge detector GCD-60200 (BSI, Riga, Latvia) with a relative efficiency of 60% and a 0.9-L Marinelli beaker was used to acquire and analyze the gamma spectra.

(MQLs) were multiplied by 10. The standard solutions were measured in one series with samples that enabled good performance of the ICPMS calibration procedure and calculation sensitivities (Table 2). 3. Results and discussion 3.1. Lanthanide distribution The lanthanide concentration measurement results in SW and GW are presented in Table 3. The total average lanthanide concentration (ΣLN) in SW was 697 ng L−1 while that in GW was 7376 ng L−1, about 10 times higher than the SW concentration. This difference could be explained by the various characteristics of natural water, such as pH and salinity (ionic strength), which can cause colloidal particle formation (Noack et al., 2014). The lanthanide concentrations in the samples from the Chernobyl Exclusion Zone were higher than those in SW from elsewhere in Europe. For example, the ΣLN in the Danube River and River Thames were 218 and 406 ng L− 1, respectively, while the ΣLN in rivers in south-central Poland (i.e., Bobrza and Silnica) ranged from approximately 120 to 330 ng L−1 (Kulaksız and Bau, 2011; Migaszewski and Galuszka, 2016). In addition, Savenko et al. (2014) reported that the concentrations of the majority of lanthanides (Ce, Pr, Nd, Dy, Ho, Er, Tm, Yb, and Lu) in the Volga River were similar to the mean values in global continental runoff. Meanwhile, the overall lanthanide concentration in lakes and ponds in the Chernobyl Exclusion Zone ranged from 500 to 1100 ng L−1. This difference could be explained in part by the fact that the studied samples were collected from closed (i.e., standing) water bodies in which the ion concentrations could be naturally higher.

To determine the lanthanide distribution and eliminate the Oddo– Harkins effect (Cantrell and Byrne, 1987), the concentrations were normalized to the post-Archean Australian shale (PAAS) distribution (Taylor and McLennan, 2009). The normalized concentrations increased slightly in the row from lighter (LLN) towards heavier (HLN) elements (Fig. 2). This tendency generally replicated data from ocean water (Garcia-Solsona et al., 2014) and freshwater samples (Kulaksız and Bau, 2013). In SW samples from the Chernobyl Exclusion Zone, the ratio of shale-normalized (subscript: SN) Ho to Nd concentrations (i.e., HoSN/NdSN) ranged from 1.07 to 2.74, while that of TmSN/NdSN ranged from 1.88 to 7.87. These were very similar to values determined between ErSN and NdSN demonstrated by Hatje et al. (2016). In the lanthanide distribution, profile dominance of HLN is associated with higher complex stability than LLN complexes (Byrne and Sholkovitz, 1996); therefore heavy elements tend to form less sediment. The lanthanide distribution profile of the GW samples differed slightly from that of SW. This might be related to the area's (Ukrainian Shield) soil specificity (Viehmanna et al., 2015). Another possible explanation is related to the probability of the presence of nanoparticles in our samples. Klaver et al. (2014) tested the same SW samples using two methods, directly and after an ultrafiltration procedure. The authors observed an increasing tendency from LLNSN towards HLNSN in shale-normalized concentrations in the ultra-filtrated samples. Meanwhile, a low peak at MLNSN was visible in the distribution of lanthanides in the unfiltered samples. We observed a comparable trend in borehole water samples GW8, GW9, and GW11 (Fig. 2B). To verify and estimate the impact of the formation of micro- and nanoparticles on lanthanide distribution, we re-investigated the GW samples. Precipitates formed in the GW samples after the concentration procedure. Fig. 3 presents the lanthanide distributions of these precipitates. The maximum MLNSN decreased compared to the composition of the GW liquid phase (Fig. 2B). This gives reason to suspect that the discrepancies between the distribution profiles of SW and GW may be the result of the formation of micro- and nanoparticles in the solution, where the greater part of heavier lanthanides was concentrated in these particles.

3.2. Er anomaly All SW samples had anomalous Ce, Eu, and Er concentrations (Fig. 2). The most unexpected of these recorded anomalies was the relatively high Er concentrations. As noted above, few studies have examined the occurrence of lanthanides in the Chernobyl Exclusion Zone. Sahoo et al. (2001) presented the normalized distribution of lanthanides in soil samples from the Bryansk region (Russia), which was also contaminated after the Chernobyl accident. However, anomalous concentrations of lanthanides were not observed in this data.

Table 3 Lanthanide concentrations (ng L−1) in surface and ground water. Element

SW1

SW2

SW3

SW4

SW5

SW6

SW7

GW8

GW9

GW10

GW11

La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu ∑LN

41.9 267.8 12.0 53.5 10.0 8.8 15.8 2.0 13.6 3.1 117.4 1.5 10.0 2.9 560.2

123.8 523.5 31.8 129.4 26.1 12.7 34.2 3.5 21.1 4.0 167.3 2.9 26.0 7.4 1113.7

93.7 411.1 17.2 70.8 14.4 8.8 21.6 2.7 18.8 5.7 164.0 5.2 62.6 16.4 913.0

37.9 167.4 11.3 52.6 14.2 8.2 16.9 2.2 16.2 4.1 65.2 3.9 35.9 8.8 444.9

31.8 249.7 9.1 43.0 8.4 9.1 13.1 1.3 9.8 3.4 121.2 4.1 51.1 13.3 568.4

99.5 342.9 19.9 80.1 17.4 8.8 23.0 2.8 19.8 4.6 94.0 3.7 34.6 8.7 759.8

30.0 295.2 5.2 16.4 4.5 6.3 6.4 0.8 4.1 0.8 143.6 0.6 3.5 0.6 518.2

1841.9 5793.2 702.1 2546.9 448.2 114.6 479.1 66.3 403.6 71.5 241.5 23.6 146.9 19.8 12,899.0

847.3 1761.4 189.4 811.6 172.9 51.5 192.4 25.7 164.9 28.9 174.4 10.2 70.7 10.6 4511.7

463.1 1040.7 243.6 1281.4 344.3 94.5 301.3 38.1 309.6 87.6 547.2 108.0 1360.5 314.7 6534.6

890.2 1627.3 242.4 1133.6 285.4 82.1 371.0 49.9 333.5 67.0 227.5 27.0 193.0 29.7 5559.6

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx

5

adjacent elements at normalized concentrations (Hatje et al., 2016). The main requirement of this method is that the concentrations of the adjacent elements should not be abnormal. The concentrations of Ho and Tm in this study were suitable for this calculation (Fig. 2A), and we calculated the theoretical (Er*) and PAAS-normalized (ErSN*) Er concentration after performing the interpolation between normalized Ho and Tm concentrations (HoSN and TmSN). We evaluated the magnitude of the Er anomaly as the ratio of Er/Er* between the measured ErSN and theoretical ErSN* = (HoSN × TmSN)0.5 concentration of Er: Er=Er ¼ ErSN =ðHoSN  TmSN Þ0:5 :

Fig. 2. Lanthanide sample patterns normalized to PAAS from (A) surface water (SW) and (B) ground water (GW) in the Chernobyl Exclusion Zone. Sample descriptions are presented in Table 1. Bold lines represent the average patterns of the corresponding sample types.

To evaluate the magnitude of the detected anomaly, we calculated the theoretical Er concentrations. A few methods that can be used to estimate the theoretical concentration of several lanthanides (e.g., La and Gd or Ce (Kulaksız and Bau, 2013)) are presented in the literature. One method involves the calculation of the mean value between two

Fig. 3. Lanthanide patterns of ground water (GW) precipitates normalized to PAAS. The bold lines represent the average pattern.

Table 4 presents the concentration anomaly values. The positive Er anomaly was not high in the GW samples and varied from 1.2 (GW11, filtration field borehole) to 2.3 (GW9, Red Forest borehole), with an average of 1.5 (RSD: 0.338). Meanwhile, anomalies observed in SW samples varied from 3.6 (SW4, Semichod backwater) to 46.6 (SW7, Lake Glubokoe), with an average of 13.2 (RSD: 1.14). One possible reason for this anomaly could be related to the Chernobyl Nuclear Power Plant accident in 1986. As shown in a map of the area based on 239 + 240Pu contamination (2000 data) by Kashparov et al. (2003), some of the highest radioactivity levels were recorded in the so-called northern and western traces. Lake Glubokoe and Pripyat pond are located in the area with the highest contamination, where the largest concentration anomaly of Er was detected (samples SW1, SW2, and SW7). After determining the gamma spectra for all samples, we observed the 137Cs activities (Table 1). Samples SW3, SW6, and SW7 had 137Cs activities of 0.67 (MDL: 0.03), 15.74 (MDL: 0.05), and 3.77 (MDL: 0.04) Bq kg− 1, respectively. The Cs activities of the other samples were below the MDL and are not presented. As shown by Shestopalov (1996) in a 137Cs distribution map of the 30-km Exclusion Zone, these water bodies fall into one of the highest contamination areas (4–7.5 MBq m−2). Our sample SW7 (Lake Glubokoe) also had enhanced 137 Cs activity. Furthermore, the area around this sample exhibited some of the highest total background radiation in the area (Table 1). This led to the initial conclusion that the emergence of Er anomalies in SW around Chernobyl may be associated with the spread of nuclear fuel particles after the fourth unit accident. This conclusion is partially confirmed by our observed correlation between Er anomalies and 235U concentrations (Fig. 4). Based on the first approximation between Er/Er* and 235U/238U (235U concentration ratio to 238U), a linear relationship could be observed (correlation: r2 = 0.91) when the concentration of 235 U increased in water samples (indication of anthropogenic U), the Er anomaly increased. However, this correlation was not perfect, probably due to the heterogeneity of natural water samples. For this reason, data for SW1 and SW6 were not included in Fig. 4. Mochizuki et al. (2016) showed that U concentrations in natural waters were significantly dependent on pH. This phenomenon was mainly related to the stability of UO22 + and Ca2 + carbonate complexes (Dong and Brooks, 2006), which could promote the formation of colloidal particles in solution. As previously mentioned, Hf and lanthanides such as Gd and Er are used in nuclear energy applications as neutron absorbers (Davydova et al., 1991; Fedosov, 1993; Men'kin et al., 1997; Barchevtsev et al., 2002a, 2002b). In the cores of reactors, such absorbers can be used in two ways, primarily as control rods to regulate the power of a reactor and, more recently, as so-called “burnable poison” in nuclear fuel (Schlieck et al., 2001; Barchevtsev et al., 2002a, 2002b). Er2O3 has been used in RBMK reactors as a nuclear fuel additive with Er (natural isotope distribution) concentrations of 0.41% by weight (Men'kin et al., 1997). However, no information could be found supporting that nuclear fuel or control rods containing Er were used in Chernobyl's fourth reactor. We cannot exclude the possibility that a new type of nuclear fuel rod could have been used for experimental purposes, and this

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

6

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx

Table 4 Ce, Eu, and Er concentration ratios between the measured and theoretical (asterisk) values in SW and GW samples.

Er/Er* Ce/Ce* Eu/Eu*

SW1

SW2

SW3

SW4

SW5

SW6

SW7

GW8

GW9

GW10

GW11

12.2 2.8 0.6

10.8 1.9 0.8

6.7 2.4 0.6

3.6 1.9 0.6

7.2 3.4 0.3

5.1 1.8 0.3

46.6 5.4 0.1

1.3 1.2 1.2

2.3 1.0 1.1

1.3 0.7 1.2

1.2 0.8 1.0

information could be classified. Therefore, the anomalous Er concentration increase in SW around Chernobyl remains unexplained. 3.3. Ce and Eu anomalies By applying the aforementioned methodology, the concentration anomalies of Ce and Eu were calculated as the ratio between the theoretical and measured values and those normalized to PAAS. The Ce anomaly was estimated from normalized La and Pr concentrations:

Ce=Ce ¼ CeSN =ðLaSN  PrSN Þ0:5 : The average anomaly of Ce in SW was 2.8 (RSD: 0.47), and the highest anomaly of 5.4 was observed in Lake Glubokoe (Table 4). In the GW samples, minimal Ce anomalies were observed (average: 0.9 (RSD: 0.22)). At the same time, a negative Eu anomaly was estimated based on the normalized concentrations of Sm and Tb:

Eu=Eu ¼ EuSN =ðSmSN  TbSN Þ

0:5

:

The Gd concentration was not suitable for this purpose because it was somewhat anomalously increased (Fig. 2). Based on these calculations, the Eu concentration in SW was decreased an average of 0.48 (RSD: 0.51) parts from the theoretical value. In GW samples, the anomaly of Eu was insignificant. The positive Ce anomaly was most likely related to the Ce3+/Ce4+ balance effect (Byrne and Sholkovitz, 1996). The same can be said regarding the reduced Eu concentrations, which may be related to the ability of Eu to be in two oxidation states, +2 and +3. Therefore, to verify whether the Ce and Eu concentrations could have changed as a result of a nuclear accident, more precise studies should be performed, such as using ion chromatography techniques connected to ICP-MS. 4. Conclusions In this study, lanthanide concentrations in SW and GW samples from the Chernobyl Exclusion Zone were determined. The total lanthanide concentration in GW was approximately 10 times greater than in the

Fig. 4. Comparison of the 235U ratio to 238U and Er anomaly in the SW samples. Linear correlation: r2 = 0.91.

SW (i.e., 7376 ng L−1 versus 697 ng L−1, respectively). The results of this investigation showed that shale-normalized lanthanide concentration patterns exhibited an increasing trend from lighter towards heavier elements. This trend was more visible in SW. Moreover, clear concentration anomalies of Ce, Eu, and Er were observed. The increased Er concentrations were the most conspicuous of the lanthanides, which exceeded the average level by 13.2 times. The greatest Er anomalies were found in water bodies that experienced the greatest contamination after the Chernobyl Nuclear Power Plant accident according to contamination maps of the Exclusion Zone. A linear relationship between 235 U concentrations and Er anomalies was established. These results suggest that the Er anomalies could be related to the spread of nuclear fuel particles after the reactor accident. However, this conclusion was not endorsed by an analysis of literary data, as we were unable to confirm whether Er was used as a nuclear fuel additive in the reactor before the accident. Therefore, the Er anomaly remains unexplained. Further experimental investigations are needed to estimate the distribution of lanthanides in SW sediment in the Exclusion Zone. Since such samples are less influenced by ambient pH and temperature fluctuations, the anomalies could be determined more accurately. Finally, another possible direction of future research is the precise analysis of lanthanide isotopes after chromatographic separation. Acknowledgments The authors would like to acknowledge the company LOKMIS, which partially supported this work under the project Nuclear Waste Characterization Research. Furthermore, the authors would like to acknowledge the Ukrainian state specialized enterprise “EcoCenter” for the opportunity to measure actual samples and personally thank Serhii Kirieiev, the head of “EcoCenter” for his help and support. References Ardini, F., Soggia, F., Rugi, F., Udisti, R., Grotti, M., 2010. Conversion of rare earth elements to molecular oxide ions in a dynamic reaction cell and consequences on their determination by inductively coupled plasma mass spectrometry. J. Anal. At. Spectrom. 25, 1588–1597. Barchevtsev, V., Ninokata, H., Artisyuk, V., 2002a. Potential to approach the long-life core in a light water reactor with uranium oxide fuel. Ann. Nucl. Energy 29, 595–608. Barchevtsev, V., Artisyuk, V., Ninokata, H., 2002b. Concept of erbium doped uranium oxide fuel cycle in light water reactors. J. Nucl. Sci. Technol. 39 (5), 506–513. Bossew, P., Gastberger, M., Gohla, H., Hofer, P., Hubmer, A., 2004. Vertical distribution of radionuclides in soil of a grassland site in Chernobyl exclusion zone. J. Environ. Radioact. 73, 87–99. Byrne, R.H., Sholkovitz, E.R., 1996. Marine chemistry and geochemistry of the lanthanides. Handb. Phys. Chem. Rare Earths 23 (158), 497–594. Cantrell, K.J., Byrne, R.H., 1987. Rare earth element complexation by carbonate and oxalate ions. Geochim. Cosmochim. Acta 51 (3), 597–605. Carbol, P., Solatie, D., Erdmann, N., Nyle'n, T., Betti, M., 2003. Deposition and distribution of Chernobyl fallout fission products and actinides in a Russian soil profile. J. Environ. Radioact. 68, 27–46. Davydova, G.B., Kvator, V.M., Fedosov, A.M., 1991. The use of burnable poison in RBMK reactors. Atom. Energ. 71 (4), 344–345. DeKalb, E.L., Fassel, V.A., 1979. Optical atomic emission and absorption methods. Handbook on the Physics and Chemistry of Rare Earths. 4, pp. 405–440. Dong, W., Brooks, S.C., 2006. Determination of the formation constants of ternary complexes of uranyl and carbonate with alkaline earth metals (Mg2+, Ca2+, Sr2+, and Ba2+) using anion exchange method. Environ. Sci. Technol. 40, 4689–4695. Dressler, V.L., Pozebon, D., Matusch, A., Becker, J.S., 2007. Micronebulization for trace analysis of lanthanides in small biological specimens by ICP-MS. Int. J. Mass Spectrom. 266, 25–33. Du, X.Y., Graedel, T.E., 2013. Uncovering the end uses of the rare earth elements. Sci. Total Environ. 461-462, 781–784.

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066

D. Plausinaitis et al. / Science of the Total Environment xxx (2017) xxx–xxx Dulski, P., 1994. Interferences of oxide, hydroxide and chloride analyte species in the determination of rare earth elements in geological samples by inductively coupled plasma-mass spectrometry. Fresenius J. Anal. Chem. 350, 194–203. Fedosov, A.M., 1993. Influence of burnable absorbers on the dehydration effect of an RBMK reactor. Atom. Energ. 75 (1), 67–69. Garcia-Solsona, E., Jeandel, C., Labatut, M., Lacan, F., Vance, D., Chavagnac, V., Pradoux, C., 2014. Rare earth elements and Nd isotopes tracing water mass mixing and particleseawater interactions in the SE Atlantic. Geochim. Cosmochim. Acta 125, 351–372. Gudiksen, P.H., Harvey, T.F., Large, R., 1989. Chernobyl source term, atmospheric dispersion, and dose estimation. Health Phys. 57 (5), 697–706. Hatje, V., Bruland, K.W., Flegal, A.R., 2016. Increases in anthropogenic gadolinium anomalies and rare earth element concentrations in San Francisco Bay over a 20 year record. Environ. Sci. Technol. 50 (8), 4159–4168. IAEA: Vienna, 2003. Manual for Reactor Produced Radioisotopes (IAEA-TECDOC-1340). Iwashita, M., Saito, A., Arai, M., Furusho, Y., Shimamura, T., 2011. Determination of rare earth elements in rainwater collected in suburban Tokyo. Geochem. J. 45 (3), 187–197. Jaracz, P., Mirowski, S., Trzcińska, A., 1995. Calculations and measurements of 154Eu and 155 Eu in ‘fuel-like’ hot particles from Chernobyl fallout. J. Environ. Radioact. 26 (1), 83–97. Kashparov, V.A., Lundin, S.M., Zvarych, S.I., Yoshchenko, V.I., Levchuk, S.E., Khomutinin, Y.V., Maloshtan, I.M., Protsak, V.P., 2003. Territory contamination with the radionuclides representing the fuel component of Chernobyl fallout. Sci. Total Environ. 317, 105–119. Klaver, G., Verheul, M., Bakker, I., Petelet-Giraud, E., Négrel, P., 2014. Anthropogenic rare earth element in rivers: gadolinium and lanthanum. Partitioning between the dissolved and particulate phases in the Rhine River and spatial propagation through the Rhine-Meuse Delta (the Netherlands). Appl. Geochem. 47, 186–197. Kulaksız, S., Bau, M., 2011. Anthropogenic gadolinium as a microcontaminant in tap water used as drinking water in urban areas and megacities. Appl. Geochem. 26, 1877–1885. Kulaksız, S., Bau, M., 2013. Anthropogenic dissolved and colloid/nanoparticle-bound samarium, lanthanum and gadolinium in the Rhine River and the impending destruction of the natural rare earth element distribution in rivers. Earth Planet. Sci. Lett. 362, 43–50. Kümmerer, K., Helmers, E., 2000. Hospital effluents as a source of gadolinium in the aquatic environment. Environ. Sci. Technol. 34 (4), 573–577. Labrecque, Ch., Lebed, P.J., Lariviere, D., 2016. Isotopic signature of selected lanthanides for nuclear activities profiling using cloud point extraction and ICP-MS/MS. J. Environ. Radioact. 155-156, 15–22. LaRosa, J.J., Cooper, E.L., Ghods-Esphahani, A., Jansta, V., Makarewicz, M., Shawky, S., Vajda, N., 1992. Radiochemical methods used by the IAEA's laboratories at Seibersdorf for the determination of 90Sr, 144Ce and Pu radionuclides in environmental samples collected for the International Chernobyl project. J. Environ. Radioact. 17 (2–3), 183–209. Men'kin, L.I., Tokarev, V.I., Trubina, V.K., Timokhin, A.N., Kuznetsov, V.R., Nikolaev, V.A., Kupalov-Yaropolk, A.I., Ivanov, A.V., 1997. Reactor and postreactor tests on RBMK elements containing uranium-erbium fuel. Atom. Energ. 83 (6), 887–889.

7

Migaszewski, M.Z., Galuszka, A., 2016. The use of gadolinium and europium concentrations as contaminant tracers in the Nida River watershed in south-central Poland. Geol. Q. 60 (1), 67–76. Mochizuki, A., Hosoda, K., Sugiyama, M., 2016. Characteristic seasonal variation in dissolved uranium concentration induced by the change of lake water pH in Lake Biwa, Japan. Limnology 17, 127–142. Noack, C.W., Dzombak, D.A., Karamalidis, A.K., 2014. Rare earth element distributions and trends in natural waters with a focus on groundwater. Environ. Sci. Technol. 48, 4317–4326. Perna, L., Bocci, F., Heras, L.A., Pablob, J.D., Betti, M., 2002. Studies on simultaneous separation and determination of lanthanides and actinides by ion chromatography inductively coupled plasma mass spectrometry combined with isotope dilution mass spectrometry. J. Anal. At. Spectrom. 17, 1166–1171. Rauta, N.M., Huangb, L.Sh., Aggarwala, S.K., Lin, K.Ch., 2003. Determination of lanthanides in rock samples by inductively coupled plasma mass spectrometry using thorium as oxide and hydroxide correction standard. Spectrochim. Acta B 58, 809–822. Remeikis, V., Jurkevicius, A., 2004. Evolution of the neutron sensor characteristics in the RBMK-1500 reactor neutron flux. Nucl. Eng. Des. 231, 271–282. Sahoo, S.K., Yonehara, H., Kurotaki, K., Shiraishi, K., Ramzaev, V., Barkovski, A., 2001. Determination of rare earth elements, thorium and uranium by inductively coupled plasma mass spectrometry and strontium isotopes by thermal ionization mass spectrometry in soil samples of Bryansk region contaminated due to Chernobyl accident. J. Radioanal. Nucl. 247 (2), 341–345. Savenko, A.V., Brekhovskikh, V.F., Pokrovskii, O.S., 2014. Migration of dissolved trace elements in the mixing zone between Volga River water and Caspian seawater: results of observations over many years. Geochem. Int. 52 (7), 533–547. Schlieck, M., Berger, H.D., Neufert, A., 2001. Optimized gadolinia concepts for advanced incore fuel management in PWRs. Nucl. Eng. Des. 205, 191–198. Shestopalov, V.M., 1996. Atlas of Chernobyl Exclusion Zone Kiev. Ukrainian Academy of Science, Ukraine. Taylor, S.R., McLennan, S.M., 2009. Planetary Crusts: Their Composition, Origin and Evolution. Cambridge University Press. U.S. Department of Energy: Washington, D.C. 20585, 1993. DOE Fundamentals Handbook, Nuclear Physics and Reactor Theory. Vol. 2 of 2 (DOE-HDBK-1019/1-93). https:// energy.gov/sites/prod/files/2013/06/f2/h1019v2.pdf. U.S. Environmental Protection Agency, Office of Research and Development: Cincinnati, OH, 2012. Rare Earth Elements: A Review of Production, Processing, Recycling, and Associated Environmental Issues. (EPA/600/R-12/572). https://nepis.epa.gov/Exe/ ZyPDF.cgi/P100EUBC.PDF?Dockey=P100EUBC.PDF. Viehmanna, S., Baua, M., Hoffmannb, J.E., Münker, C., 2015. Geochemistry of the Krivoy Rog Banded Iron Formation, Ukraine, and the impact of peak episodes of increased global magmatic activity on the trace element composition of Precambrian seawater. Precambrian Res. 270, 165–180. Zhang, F., Yamasaki, S., Kimura, K., 2001. Rare earth element content in various waste ashes and the potential risk to Japanese soils. Environ. Int. 27, 393–398.

Please cite this article as: Plausinaitis, D., et al., Erbium concentration anomaly as an indicator of nuclear activity: Focus on Natural waters in the Chernobyl exclusion zone, Sci Total Environ (2017), https://doi.org/10.1016/j.scitotenv.2017.10.066