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Journal of Environmental Radioactivity xxx (2012) 1e10

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Journal of Environmental Radioactivity

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Radionuclides from the Fukushima accident in the air over Lithuania:measurement and modelling approaches

G. Lujanien _e a,*, S. By�cenkien _e a, P.P. Povinec b, M. Gera b

a Environmental Research Department, SRI Center for Physical Sciences and Technology, Savanoriu 231, 02300 Vilnius, Lithuaniab Faculty of Mathematics, Physics and Informatics, Comenius University, Bratislava, Slovakia

a r t i c l e i n f o

Article history:Received 25 August 2011Received in revised form30 November 2011Accepted 5 December 2011Available online xxx

Keywords:Fukushima accidentAerosolsIodine-131Caesium-134,137Plutonium-238,239þ240

* Corresponding author. Tel.: þ370 5 2644856; faxE-mail address: [email protected] (G. Lujanien _e).

0265-931X/$ e see front matter � 2011 Elsevier Ltd.doi:10.1016/j.jenvrad.2011.12.004

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a b s t r a c t

Analyses of 131I, 137Cs and 134Cs in airborne aerosols were carried out in daily samples in Vilnius, Lith-uania after the Fukushima accident during the period of MarcheApril, 2011. The activity concentrationsof 131I and 137Cs ranged from 12 mBq/m3 and 1.4 mBq/m3 to 3700 mBq/m3 and 1040 mBq/m3, respectively.The activity concentration of 239,240Pu in one aerosol sample collected from 23 March to 15 April, 2011was found to be 44.5 nBq/m3. The two maxima found in radionuclide concentrations were related tocomplicated long-range air mass transport from Japan across the Pacific, the North America and theAtlantic Ocean to Central Europe as indicated by modelling. HYSPLIT backward trajectories and meteo-rological data were applied for interpretation of activity variations of measured radionuclides observedat the site of investigation. 7Be and 212Pb activity concentrations and their ratios were used as tracers ofvertical transport of air masses. Fukushima data were compared with the data obtained during theChernobyl accident and in the post Chernobyl period. The activity concentrations of 131I and 137Cs werefound to be by 4 orders of magnitude lower as compared to the Chernobyl accident. The activity ratio of134Cs/137Cs was around 1 with small variations only. The activity ratio of 238Pu/239,240Pu in the aerosolsample was 1.2, indicating a presence of the spent fuel of different origin than that of the Chernobylaccident.

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1. Introduction

On March 11, 2011 a strong earthquake followed by hightsunami and fires damaged three reactors and a fuel pond at theFukushima Dai-ichi Nuclear Power Plant (NPP) in Japan withreleases of radionuclides to the atmosphere and the sea. Accordingto the NISA (Nuclear and Industrial Safety Agency) report from1.3 � 1017 Bq to 1.5 � 1017 Bq of 131I and about 6.1 � 1015 to1.3 � 1016 Bq of 137Cs were released to the atmosphere (NISA, 2011;Chino et al., 2011). The consequences of this accident at thebeginning estimated as level 4 were raised to themaximum level of7 on the INES (International Nuclear and Radiological Event Scale)scale (IAEA, 2011), although the amount of discharged radioactivematerials comprised approximately 10% of the Chernobyl accidentonly. Measurements carried out at Tokushima (about 700 kmsouthwest from the Fukushima NPP) indicated the maximumactivity concentration of particulate 131I in the air of w3 mBq/m3

which was observed on 6 April (Fushimi et al., 2011).

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, G., et al., Radionuclides fromental Radioactivity (2012), do

Worldwide monitoring activities started immediately after theannouncement of large radionuclide releases from the FukushimaNPP. The particulate 131I activities of 4.4 mBq/m3 were detected on19e21 of March in Seattle (USA) (Diaz Leon et al., 2011). Accordingto the CTBTO (Comprehensive Test-Ben Treaty Organization) datathe first signs of diluted airborne activities appeared over Europeafter 12 days of the Fukushima accident (Wotawa, 2011). Theelevated levels of radionuclides on aerosols derived from theFukushima NPP were detected at several sampling stations in Spain(Lozano et al., 2011), Germany (Pittauerová et al., 2011), Greece(Manolopoulou et al., 2011), Russia (Bolsunovsky and Dementyev,2011). The most comprehensive radionuclide data over theEurope has been compiled by Masson et al. (2011).

Anthropogenic radionuclides were introduced into the terres-trial and marine environments primarily after the atmosphericnuclear weapon tests carried out by the United States and theformer Soviet Union from the 1940s to the early 1960s (Livingstonand Povinec, 2002). Another source of anthropogenic radionuclidesis related to nuclear accidents. The most severe of them was theChernobyl accident when among other radionuclides about1760 PBq of 131I, 47 PBq of 134Cs and 85 PBq of 137Cs were releasedinto the environment (IAEA, 2006). The consequences of the

the Fukushima accident in the air over Lithuania: measurement andi:10.1016/j.jenvrad.2011.12.004

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G. Lujanien _e et al. / Journal of Environmental Radioactivity xxx (2012) 1e102

Chernobyl accident on the environment and human health wereestimated as the worst in the nuclear accident history by its ratingto the highest level 7 on the INES scale. Until 12th March, 2011 thesecond largest accident was the Kyshtym accident which occurredon 29th September,1957, when due to problems in a cooling systemand followed explosion about 7.4� 105 TBq of radioactive materialswere released into the environment. As a result of this accident,more than 10,000 people received significant radiation doses (Huet al., 2010).

The aim of the present study has been to estimate activityconcentrations of Fukushima airborne radioactive aerosols overLithuania with special emphasis on particle transport fromFukushima to Europe (preliminary results were published byLujanien _e et al., 2011), and to compare the obtained results withdata gathered during the investigations of the Chernobyl accident.

2. Samples and methods

2.1. Sampling

The ground level air samples were collected in a forested area onthe outskirts of Vilnius (54�420N, 25�300E). Perchlorvinyl filters FPP-15 (w1 m2 surface) were exposed in a special building with blindwalls at the height of 1 m above the ground. High volume samplerswith flow rates from 2400m3/h to about 6000m3/h were used. Thesampling was carried out continuously. 131I, 137Cs and 134Cs weremeasured by gamma-ray spectrometry using a HPGe detector(relative efficiency of 42%, resolution of 1.9 keV at 1.33Mev). Theprecision of 137Cs measurements by gamma-spectrometry wasbetter than �7% at 2s level.

The radiochemical analyses of Am and Pu were performed onmonthly samples (total volume w2.0 � 106 m3) of aerosol ashes(about 30 g), which were dissolved in strong acids (HNO3, HCl, HFand HClO4). The TOPO/cyclohexane extraction and radiochemicalpurification using UTEVA, TRU and TEVA resins (100e150 mm)wereused for separation of Am and Pu isotopes. 242Pu and 243Am wereused as yield tracers in the separation procedure (Lujanien _e et al.,2006). The alpha-spectrometry measurements of Pu and Amisotopes deposited on stainless-steel discs were carried out withthe Alphaquattro (Silena) spectrometer. Accuracy and precision ofanalysis were tested using reference materials IAEA-135, NIST SRMNo 4350B and 4357, as well as in intercomparison exercises, orga-nized by the Risø National Laboratory (Denmark), and the NationalPhysical Laboratory (UK). The precision of Pu and Am measure-ments was better than �8% and �10%, respectively (at 2s level).

2.2. Modelling

The transport of radionuclides was simulated using a Lagrangianparticle model which calculates trajectories of particles that followthe instantaneousflow in the particle position (Závodský, 2011). Theoutput particle velocity is a sum of deterministic velocity and semi-random stochastic velocity, generated by the Monte Carlo tech-nique. The probability density function for the random component,which simulates the atmospheric turbulence, is dependent on thestate of the atmospheric boundary layer. The model also takes intoaccount the radioactive decay of particles (e.g. in the case of 131I), aswell as their scavenging by dry and wet deposition. For the mete-orological input, the Integrated Monitoring System e IMS ModelSuite Lagrangian dispersion model (MicroStep-MIS, 2011) has beenused. It calculates the spreading of radioactive materials withspecial regard to changes in atmospheric conditions, especiallychanges in wind direction. The meteorological input for thedispersionmodelwas a time sequence analysis of atmospheric statein GRIB format (WMO, 2009). The GFS global weather model was

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used in simulation time span from 12 March to 27 March, 2011. The3Dwind (u, v, vertical velocity) at upper airmodel levelswas neededto simulate dispersion due to large-scale winds.

A characterization of radionuclide activities with respect tocategorized air mass backward trajectories was carried out forestimation of potential location of the radioactivity source. Air massbackward trajectories were generated using the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT4) model(Rolph, 2011) with the Final Analyses (FNL, year 2011) and theGlobal Data Assimilation System (GDAS) meteorological databasesat the NOAA Air Resources Laboratory server (Rolph, 2011).

3. Results and discussion

3.1. Modelling of the Fukushima plume

For the assessment of contamination after the accident andprediction of radioactive particle transport the Lagrangian model-ling was applied. In order to describe the atmospheric processesrealistically, the vertical velocity, particle dissipation and turbu-lence during the particle trajectory were considered. A singlerelease of 1015 Bq of 137Cs, which occurred on March 12, 2011 fromdamaged Fukushima NPPwas analyzed. The initial plume height, asa result of initial vertical velocity and buoyancy, was kept to be at2000e3000 m. The meteorological data and simulated trajectoriesrevealed that the arrival times of particles released on 11 March,2011 and 12 March, 2011 were different, and the particles weretransported at different altitudes. It was also obvious that the jetstream affected the transport of emitted particles at upper atmo-spheric levels. Examples of the trajectories simulated using theLagrangian dispersion model show (Fig. 1) that the first signs ofFukushima released radionuclides could be detected in the Euro-pean countries (e.g. Island) on 20 March, 2011. The performedsimulation indicated that particles released on 11 March, 2011mainly appeared over Europe on 850 hPa on 13 April, 2011, at700 hPa on 30 March, 2011 and at 500 hPa on 20 March, 2011.Similar situation was observed for particles released on 12 March,2011which arrived to Europe at 700 hPa on 1 April, 2011, at 500 hPaon 21 March, 2011, and the particles at 850 hPa did not reach theEuropean territory. The particle arriving times are in a reasonableagreement with experimental radionuclide data obtained for Vil-nius (Lithuania), as discussed later.

3.2. Radionuclide data

The time course of 131I (aerosol component) and 137Cs concen-trations measured in MarcheApril of 2011 in Vilnius is shown inFig. 2, comparedwith the course of the cosmogenic 7Be. The activityconcentrations of 131I and 137Cs ranged from 2 to 3800 mBq/m3 andfrom 0.2 to 1070 mBq/m3, respectively. The first traces of 131I inaerosol filters in Vilnius were found on 23 March. A considerableincrease in the 131I activity concentrations (up to about 2.4 mBq/m3) was observed during the period of 28 Marche1 April. Thesecond maximumwas detected on 3e4 April, when up to 3.7 mBq/m3 of 131I was measured in the atmosphere. Activities of 137Cs inaerosol during this period increased up to 0.5mBq/m3 and 1.0 mBq/m3, respectively. In addition to 131I and 137Cs, traces of otherradionuclides were detected in the aerosol filters as well.Their concentrations in the most active sample collected on 3e4April 2011 14:00e06:50 UTC were: 132I e 0.12 � 0.01 mBq/m3,132Te e 0.13 � 0.01 mBq/m3, 129Te e 0.40 � 0.04 mBq/m3,129mTee0.75 � 0.25 mBq/m3 and 136Cs e 0.080 � 0.0080mBq/m3.

The variations in the activity concentrations of studied radio-nuclides can be due to the different arrival time of radioactiveparticles predicted by the Lagrangian modelling. The particles


Fig. 1. Particles spacing on 20 March, 2011 at 12:00 UTC (top) and on 27 March, 2011 at 18:00 UTC (bottom); shades of red indicate particles in the bottom layer, up to 3 km; black todark blue indicate the middle layer, up to 6 km height; and light blue indicates the upper layer; the trajectories were simulated using the Lagrangian dispersion model (time of theparticles release was on 12 March 2011). (For interpretation of the references to colour in this figure legend, the reader is referred to the web version of this article.)

G. Lujanien _e et al. / Journal of Environmental Radioactivity xxx (2012) 1e10 3

released on 11 March, 2011, and according to the prognosis theyshould appear over the Europe at 850 hPa on 13 April, 2011, werenot detected in Vilnius. The particles arriving at 700 hPa weredetected on 30 March, 2011, while the particles at 500 hPaappearing on 21 March, 2011, were detected in Vilnius on 22e23March. The particles released on 12 March, 2011 and which were

24 26 28 30 1 3 5 7 9 11 13

0500100015002000250030003500400045005000

March April 2011

137

Cs

R=-0.09 (n=29)

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I

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Fig. 2. Activity concentration of 131I, 137Cs and 7Be in aerosol samples as well asprecipitation amount in Vilnius in 2011.


expected over Europe at 700 hPa on 1 April, 2011 were not detectedat our sampling station, whereas a clear maximum in activityconcentrations of 131I, 134Cs and 137Cs was observed on 4 April, 2011.The particles that were supposed to be over Europe at 500 hPa on24 March, 2011 were detected with one day delay on 25 March,2011. It seems therefore that the Fukushima plumewhich arrived toEurope at high altitudes did not necessarily reach the near-surfacelevel.

On the other hand, meteorological conditions at the site(e.g. precipitation) could affect the activity concentrations. Theamount of precipitation given in Fig. 2 revealed that it could havea certain effect on changes in activity concentrations of studiedradionuclides. However, no correlationwas found between the 131I,137Cs and 7Be activity concentrations and the amount of precipi-tation (R ¼ �0.01, �0.09 and �0.07, respectively), indicating thatthe influence of precipitation was in general negligible. Nonethe-less, from data shown in Fig. 2 it can be seen that the increase in 131Iand 137Cs activity concentrations was accompanied by the rise of7Be activities. In addition, 131I and 137Cs activities well correlated(R¼ 0.69 and R¼ 0.75, respectively) with the activity concentrationof 7Be (Fig. 3).

The cosmogenic 7Be (half-life of 53.3 days) is mainly produced inthe lower stratosphere (w70%) and the rest in the upper tropo-sphere. It has been widely used to study vertical air mass transport


0 2000 4000 6000 8000

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I

R = 0.69 (n= 29)

Fig. 3. 137Cs and 131I activity concentrations plotted against the 7Be activity concen-tration in aerosol samples collected during the Fukushima plume episode.

24 26 28 30 1 3 5 7 9 11 13

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Fig. 4. Activity concentration of 137Cs and 134Cs/137Cs, 7Be/212Pb and 7Be/214Pb activityratios in aerosol samples in Vilnius in 2011.


(e.g. Lujanas and Lujanien _e, 2007). An increase in the 7Be activityconcentrations in summer and autumn season was explained bya vertically downward transport within the troposphere (Kochet al., 1996) and by a stratosphere-troposphere exchange (Jordanet al., 2003; Land and Feichter, 2003). The high 7Be activityconcentrations in the surface air were also interpreted by thedownward and upward atmospheric flows in the tropospherecaused by a pair of travelling anticyclone and extra tropical cyclonethat passes over Japan in spring and autumnwith a period of a fewdays (Yoshimori, 2005). It was supposed that the air of lowtemperature flows downward from convergence in the Rossbywaves to divergence in the surface anticyclone, and the warm airmoves upward from convergence in the surface cyclone to diver-gence in the Rossby waves. In these studies an increase in theactivity concentrations in the near-surface atmosphere was asso-ciated with downward movements of air masses. Thus, the positivecorrelation between the anthropogenic radionuclides and 7Be(Fig. 3) can be an indication of their arrival from the upper layers ofthe troposphere.

On the other hand, short-lived radon decay products, such as theterrigenous 210Pb, 212Pb and 214Pb can also be used as atmospherictracers to study air masses transport (Sheets and Lawrence, 1999).The main source of 212Pb (half-life of 10.6 h) in the air is 220Rn (half-life of 54 s) exhalation from the earth’s surface, therefore 212Pbactivity concentrations reflect local conditions (at height of about1 km), contrary to 222Rn (half-life of 3.82 d) progenies 214Pb(half-life of 26.8 min) and 210Pb (half-life of 22.3 y). The residencetimes of radon decay products in the ambient air were estimated tobe similar to that of 7Be (about 8 days). About 76% of the 214Pbactivity and 67% of the 212Pb activity were usually associated withaerosol particles in the 0.08e1.4-mm size range, though a small shiftin the aerosol size distribution was observed for 214Pb(Papastefanou, 2009). Seasonal variations of 212Pb and 210Pbisotopes were found to be distinctly different in the lower atmo-sphere while the behaviour of 214Pb was similar to that of 210Pb. Itwas concluded therefore that airborne concentrations of 212Pb,contrary to those of 210Pb could be strongly influenced by localemissions (Sheets and Lawrence, 1999). This behavior and shift inthe size distribution can be attributed to the variation in half-livesof Pb isotopes and their parents. Both parents are gaseous speciesbut their different half-life under particular local conditions such asexhalation, mixing height and intensity can result in their variousvertical and horizontal transports. 222Rn of longer half-life hasa higher potential to be more widely distributed vertically andhorizontally. On the other hand, due to different half-lives of Pbisotopes, they can serve for indication of events occurring on


different time scales. Kownacka (2002) reported that activityconcentrations of 210Pb were almost constantly distributed above1 km, and did not decrease with altitudes. An increase in 210Pb andother natural radionuclide concentrations in the stratosphere wasalso observed after the large volcanic eruptions. Abe et al. (2010)showed that distributions of the 7Be and 210Pb nuclides wereuniform in the range of a few hundred kilometers in the horizontaldirection and up to w1 km height, whereas 212Pb activity concen-trations varied greatly depending on the geographical location andaltitude of the observation site. The recent studies indicateda similar behavior of 7Be and 210Pb, and that they cannot be used asindependent tracers to study atmospheric processes. Although thebehavior of 212Pb and 214Pb is not fully understood yet, they can beused as independent atmospheric traces. A weak correlation wasfound in 7Be and 212Pb records (0.39), while no correlation wasobserved for 7Be and 214Pb (�0.16), indicating different sources ofPb isotopes. The 212Pb and 214Pb records may therefore indicatedifferent atmospheric processes. Most probably 212Pb is an indi-cator of horizontal transport at lower heights (up to 1 km),however, a weak correlation showed that this transport waslimited. On the other hand, 214Pb represents short time events atour site. An increase in the activity ratios of 7Be/212Pb and 7Be/214Pb,accompanied by an increase in 137Cs and 131I activity concentrationsobserved during the studied periodmay indicate that the dominantsource of Fukushima originated radionuclides at our site was athigher altitudes. Therefore, an increase in the 7Be/212Pb and7Be/214Pb activity ratios in this case can be used for an indication ofthe downward air mass transport.

The activity concentration of 137Cs as well as the 134Cs/137Cs,7Be/212Pb and 7Be/214Pb activity ratios in aerosol samples in thestudied episode after the Fukushima accident are presented inFig. 4. The 134Cs/137Cs activity ratio in Vilnius was close to 1 (N¼ 30,Mean ¼ 0.782, S.D. ¼ 0.345, Median ¼ 0.938). In samples collectedon 24March, and from 26 to 27March, the activity concentration of134Cs was below the detection limit. In the most active samplecollected on 3e4 April the 134Cs/137Cs activity ratio was equal to1.00 � 0.05.

Fig. 5 shows the wind speed and wind vectors indicating the jetstream at 500 hPa for 24e25 March which affected the transport ofthe Fukushima plume to Europe. The strong meanders on the jetstream resulted in the downward air mass transport, as it is indi-cated by an increase in the 7Be activity concentrations (Fig. 2), aswell as by an increase in the activity ratios of 7Be/212Pb and7Be/214Pb (Fig. 4). A similar increase in the activity concentrations of131I, 137Cs and 7Be, together with enhanced activity ratios of7Be/212Pb and 7Be/214Pb observed on 23, 24, 27 and 31 March, as


Fig. 5. The wind speed, wind vectors and relative humidity at 500 hPa for 24e25March and 3 April, 2011.



well as on 4 April, can be interpreted as a downward transport of airmasses carrying the Fukushima plume radionuclides from higherlayers of the troposphere (Figs. 2 and 4). The low relative humidityover the sampling site (Fig. 5) observed at 500 hPa on 4 April canserve as an additional confirmation of air flow from the upper levelsof the atmosphere.

A slightly different pattern of the radionuclide record observedfrom 28 to 31 March can be explained by the effect of precipitation(Fig. 2) that could remove the Fukushimaderived radionuclides and/or preferably wash out aerosol particles carrying cosmogenic 7Bedue to their different chemical composition and size distribution(Lujanien _e et al., 1998; Lujanien _e, 2000, 2003). Another possibleexplanation can be variations of the transport altitudes and arrivaltime of the Fukushima radioactive particles. The NOAA HYSPLITmodel (Draxler and Rolph, 2011) was used to assess the transportpattern and to explain the deviation in radionuclide activityconcentrations found in Vilnius. A large number of air mass back-ward trajectorieswere calculated over the time of interest. Themosttypical trajectories, capable to provide a proper interpretation of theobserved radionuclide variations (Fig. 6), show backward air masstransport starting at 500 (red triangles), 3000 (blue squares), and7000m (green circles) above the ground level (AGL). Trajectories arelabelled every 24 h by a filled symbol. The vertical projection of thetrajectories with time is shown in the panel below the map. The airmass backward trajectories calculated for 30 March can serve as anexample of complicated pathway of air masses (Fig. 6A). The back-ward trajectories were calculated for three 500, 3000 and 5000 mAGL for 315h. The airmasses at 500mwere caught up into a cyclonicsystem,while airmasses at 3000 and 5000mwere lifted and rapidlytransported over the North America to Europe. It seems thatradioactive particles have had a greater chance of being transportedat higher atmosphere levels. They can be removed in the lower layerof the atmosphere due to various reasons, e.g. rainfall characteris-tics, fog formation or growth of aerosol particles and their deposi-tion. Thus, there was a higher probability that activityconcentrations of radionuclides found on 28e31 March werediluted by clean air masses, and/or they were reduced by precipi-tation in the near-surface level and/or marine boundary layer(w1 km) during their long-range transport from Japan.

The air masses which arrived on 1e2 April were affected both bycyclone and anticyclone systems, and they brought rather clean airto Europe (Fig. 6B). During these days the activity concentrations of131I and 137Cs dropped to 150e190 mBq/m3 and 8e16 mBq/m3,respectively (Fig. 2), however, on 4 April they again rose up to2280e3690 mBq/m3 and 609e1026 mBq/m3, respectively. It shouldbe noted that an increase in radionuclide activities was detected inthe most European countries (Masson et al., 2011).

In order to explain the origin of the second maximum in theradionuclide courses (Fig. 2), the air mass backward trajectorieswere calculated for 1000, 3000 and 5000 m heights. The resultsshowed (i) a direct transfer from Fukushima across the PacificOcean, (ii) a transport through the North Pole, and (iii) a pathwaythrough the Greenland and Iceland (Fig. 6. C). The air masses at1000 and 5000 mwere rapidly transported, while the air masses at3000 m exhibited rather slow transport, and most probably theseair masses provided a transfer of contaminated air already presentover the Greenland. These results are in good agreement with theprognoses made by the CTBTO (Wotawa, 2011) explaining twomaxima of the Fukushima plume observed over Europe.

We can conclude that themeasured activityconcentrations at thesite of investigation resulted from a complicated air mass transport,arrival time, arrival height, meteorology and downward air masstransport. The downward transport was found to be an importantfactor affecting activity concentrations in the surface air. Higheractivities can be transported over long distances at higher altitudes


Fig. 6. Backward trajectories of air masses transport ending on 30 March, 1 April and 4 April, 2011 in Vilnius.


Please cite this article in press as: Lujanien _e, G., et al., Radionuclides from the Fukushima accident in the air over Lithuania: measurement andmodelling approaches, Journal of Environmental Radioactivity (2012), doi:10.1016/j.jenvrad.2011.12.004

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Fig. 7. Activity concentrations of 131I, 137Cs, 103Ru in aerosol samples in Vilnius in 1986.


with higher probability, due to the precipitation effect and rathershort residence time ofwater soluble aerosols in the boundary layer.

3.3. Comparison with the Chernobyl accident

The consequences of the Fukushima accident were estimated tobe close to the Chernobyl accident according to the given level 7 onthe INES scale (IAEA, 2011). The long-term radiological impact of theChernobyl accidenton the environment andhumansdue to releasedradioactivity, migration, resuspension of deposited radionuclideshas been studied over 20 years. During the accident, and the postChernobyl period, many measurements of gamma, beta and alpha-emitters in aerosol samples were carried out in Vilnius (Lujanaset al., 1994; Lujanien _e et al., 1997, 1999, 2009). A wide spectrum ofradionuclides and “hot particles”were detected in Vilnius followingthe Chernobyl accident, when activity concentrations were therehigher by 4 orders of magnitude as compared to the Fukushimaaccident. The maximum activities in Vilnius during the first weekafter the Chernobyl accident were 45.2 Bq/m3 for 131I (aerosolfraction) and 27.9 Bq/m3 for 137Cs. The 132Te and 103Ru activityconcentrations inAprileMay,1986 ranged from0.1Bq/m3 to51.0Bq/m3 and from 0.1 Bq/m3 to 20.3 Bq/m3, respectively (Fig. 7).

In the Chernobyl plume Zr, Nb, Ru and Ce isotopeswere detectedin the air as well. In addition, the presence of “hot particles” of0.37e22.2 mm in size carrying beta-emitters, and “hot particles” of0.7e2 mm containing alpha-emitters (233U, 234U, 235U, 238Pu, 239Pu,240Pu, 241Am, 242Cm, 244Cm) in 1986 were also found in aerosolfilters collected in Vilnius. The activity ratio of 238Pu/239,240Puvaried from 0.44 to 0.5 and the atom ratio of 240Pu/239Pu rangedfrom 0.41 to 0.42. The high activities detected in Vilnius after theChernobyl accident were explained by quite close location(480 km) of the site.

Furthermore, the Chernobyl accident resulted in contaminationof large areas of the Earth’s surface in Europe including six millionha of forested land of the Ukraine, Belarus and Russia (De Cort et al.,1998). The 137Cs surface deposition (Fig. 8) exceeded 1480 kBq/m2

(0.03% of the European territory). The prediction of 137Cs surfacedeposition after the Fukushima accident was made usinga numerical atmospheric chemistry/transport model Polyphemus/Polair3D, and compared with contamination of Europe after theChernobyl accident (Winiarek et al., 2011). The results indicatedobvious differences in the consequences of the Chernobyl andFukushima accidents, especially at the level of highly contaminatedterritories. However, a contamination of the marine environment


and a deposition to the bottom sediments were not taken intoaccount in this model. It is expected that the main radiologicalproblems will arise from contaminated seafood, while the atmo-spheric deposition will again trigger discussions on the impact oflow-level radiation doses on the public.

Areas with high Chernobyl 137Cs ground depositions locatedclose to Lithuania have been a source of the secondary contami-nation due to the forest fires and soil resuspension for a long time(Lujanien _e et al., 2009). The transport of aerosol particles, whichderived from resuspension and/or forest fires in 1997e2001 and2005e2006 was modelled using the HYSPLIT. The backwardtrajectories were calculated for 4 selected sectors for 72 h at theheights of 20, 500 and 1000 m AGL (Fig. 8). However, not allcalculated trajectories were possible to assign to a particular sector.Very complicated trajectories that did not match any sector wereassociated with sector 0.

In both studied periods a weak correlation between the 137Csactivity concentration and height (R ¼ 0.28 (20 m), 0.32 (500 m),and 0.31 (1000 m) in 1997e2001; and for 2005e2006 R ¼ 0.41(20 m), 0.49 (500 m), and 0.49 (1000 m)) was found for the Cher-nobyl sector, while for other sectors no correlation was observed. Adissimilar behaviour of Pu isotopes was explained by their differentvolatility as compared to Cs ones. This is again in good agreementwith results obtained in 2005e2006 (Fig. 9) where 239,240Puactivities ranged from 2 to 49 nBq/m3, with maxima observed inMay (29 and 49 nBq/m3, respectively), and they obviously derivedfrom soil resuspension. The 241Am activity concentrations variedfrom 1 to 25 nBq/m3 and the highest values were also detected inMay. Variations in the 241Am/239,240Pu activity ratios from 0.27 to0.65 were found in the analyzed samples with the average valueof 0.44.

The 238Pu/239,240Pu activity ratios in aerosol samples collected inVilnius during the Chernobyl accident were in the range 0.44e0.50,while the 240Pu/239Pu atom ratios in the same samples ranged from0.41 to 0.42. The 240Pu/239Pu atom ratios in monthly samples inVilnius in 1995e2003 varied from 0.14 to 0.40, whereas in samplescollected during forest fires the ratio was between 0.19 and 0.23. Inaddition, an exponential decrease in the 240Pu/239Pu atom ratiofrom 0.30 to 0.19 (mean values) was observed during 1995e2003.The characteristic 238Pu/239,240Pu activity ratio of global fallout is0.03, while that of the Chernobyl accident is 0.45 (Livingston andPovinec, 2002). The enhanced activity ratios of 238Pu/239,240Pu(from 1 to 3) have been measured in environmental samplesderived from industrial nuclear effluents. The highest ratio of238Pu/239,240Pu ¼ 25.3 was reported in October 1982 and wasattributed to discharges from the reprocessing plants at La Hagueand Sellafield (Martin and Thomas, 1988).

In order to check the presence of Pu isotopes in samplescollected after the Fukushima accident between 23 March and 15April, 2011 (N ¼ 30, sampling air volume of w2 � 106) all sampleswere combined together to form one sample and Pu isotopes wereseparated and measured by means of alfa-spectrometry (Fig. 10).The activity concentration of 239,240Pu in this integrated samplewasfound to be 44.5 � 2.5 nBq/m3, very close to the value measured inMay, 2005 (Fig. 9), and higher than the activity measured inAprileMay, 2006. The values measured in March, 2006(12.0 � 0.6 nBq/m3) and May, 2006 (29.2� 1.5 nBq/m3) could servetherefore as reference data for comparison. From the spectrumshown in Fig. 10 it can be seen that the activity of 238Pu is higherthan that of 239,240Pu (by a factor of 1.2).

The 238Pu/239,240Pu activity ratios in aerosol samples observed inMay 1986 at Tsukuba, Japan ranged from 0.04 to 0.33. The aero-dynamic diameter of particles carrying the Chernobyl derivedplutoniumwas estimated to be of 1.1e7 mm and the mean monthly239,240Pu activity concentration increased only by 0.03 mBq m�3


Fig. 8. An example of 72 h air mass backward trajectories ended at Vilnius sampling site at 19 UTC at 20, 500, 1000 m AGL on 29 January, 1997, on 06 June, 1999 and on 03 February,2001 for 4 analyzed sectors (modified after De Cort et al., 1998).

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

0

10

20

30

40

50 239,240

Pu

241

Am

2005-2006

239

,240

Pu

, 241

Am

, n

Bq

/m

3

0

1

2

3

4

137

Cs, µ

Bq

/m

3

137

Cs

Fig. 9. Activity concentrations of 239,240Pu and 241Am in monthly aerosol samples andmonthly average activity concentrations of 137Cs in 2005e2006 in Vilnius.

Fig. 10. Alfa-spectrum of Pu isotopes separated from aerosol samples collectedbetween 23 March and 15 April.


Please cite this article in press as: Lujanien _e, G., et al., Radionuclides from the Fukushima accident in the air over Lithuania: measurement andmodelling approaches, Journal of Environmental Radioactivity (2012), doi:10.1016/j.jenvrad.2011.12.004


(Hirose and Sugimura, 1990). This is approximately the same levelas observed in the aerosol samples collected in Vilnius.

The activity ratio of 238Pu/239,240Pu detected at the Fukushimasite was reported to be 2 (TEPCO, 2011). Assuming the backgroundratio equal to the global fallout determined on the basis of the long-term measurements at the Vilnius site (Lujanien _e et al., 2009) wecan estimate the contribution of the Fukushima plutonium bysimple calculations (Hirose and Sugimura, 1990) using thefollowing equation:

Fð%Þ ¼ 100$ðRM � RGÞ=ðRF � RGÞwhere F is the Fukushima originated 239,240Pu fraction, RM, RG and RFare the measured, global fallout and Fukushima derived ratios of238Pu/239,240Pu, respectively. According to these estimations thecontribution of the Fukushima derived 239,240Pu is 59% or 26.4nBq/m3.

The mean activity concentration of 137Cs found in Vilniusduring the studied period was 118 mBq/m3. The background 137Csactivity concentration can be estimated from the sample collectedone week before the accident and it was 0.7 � 0.1 mBq/m3. Fromthese estimations the mean Fukushima originated 239,240Pu/137Csratio could be 2$10�4. The activity ratio of 239,240Pu/137Cs in theChernobyl originated hot particles was 2$10�2. A fractionationduring the long-distance transport may have resulted in thevariation of the ratio at different locations (Pöllänen et al., 1997;Hirose and Sugimura, 1990). Further analyses (ICPMS and AMS)are in progress, which will help to explain Pu origin in thissample.

4. Conclusions

From the presented data on variations of activity concentrationsof studied radionuclides, from the analyses of meteorologicalsituation, and on the basis of the modelling exercises we canconclude that the complicated air mass transport, different arrivaltime, arrival height and downward air mass transport resulted intwo maxima of 131I and 137Cs activity concentrations in the near-surface atmosphere. An increase in the 131I and 137Cs activityconcentrations up to 3800 mBq/m3 and up to 1070 mBq/m3 wasobserved on 28 March e 1 April and up to 500 mBq/m3 and up to1000 mBq/m3 was found on 3e4 April, respectively. In addition to131I and 137Cs, traces of other radionuclides were detected, and 132I,132Te, 129Te, 129mTe and 136Cs among them. The comparison of theChernobyl and Fukushima accidents indicated the higher activityconcentration of radionuclides by 4 orders of magnitude anda broader spectrum of radionuclides in the Chernobyl plume ascompared to the Fukushima one. Large collected air volumesallowed us to determine for the first time in Europe the activityratio and concentration of Fukushima derived 238Pu and 239,240Puisotopes. Approximately twice higher Pu activity concentration asexpected, and 238Pu/239,240Pu ratio not typical either for globalfallout or the Chernobyl accident was found in the integratedaerosol sample.

Acknowledgements

This research was partially supported by the Structural Funds ofEU - the Research and Development Operational Program fundedby the ERDF (project No. 26240220004). The authors thankstudents of the Chemical Department of the Vilnius University fortechnical assistance. The authors gratefully acknowledge theNOAA Air Resources Laboratory (ARL) for the provision of theREADY website (http://www.arl.noaa.gov/ready.php) used in thispublication.


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