Radioactive isotopes in atmospheric aerosols over ...

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Mar 11, 2011 - aerosols over Russia and the Sea of Japan following nuclear accident at Fukushima. Nr. 1 Daiichi Nuclear Power Station in. March 2011.
Radioactive isotopes in atmospheric aerosols over Russia and the Sea of Japan following nuclear accident at Fukushima Nr. 1 Daiichi Nuclear Power Station in March 2011 Andrey S. Neroda, Vasily F. Mishukov, Vladimir A. Goryachev, Denis V. Simonenkov & Anna A. Goncharova Environmental Science and Pollution Research ISSN 0944-1344 Environ Sci Pollut Res DOI 10.1007/s11356-013-2472-5

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Author's personal copy Environ Sci Pollut Res DOI 10.1007/s11356-013-2472-5

RESEARCH ARTICLE

Radioactive isotopes in atmospheric aerosols over Russia and the Sea of Japan following nuclear accident at Fukushima Nr. 1 Daiichi Nuclear Power Station in March 2011 Andrey S. Neroda & Vasily F. Mishukov & Vladimir A. Goryachev & Denis V. Simonenkov & Anna A. Goncharova

Received: 13 June 2013 / Accepted: 16 December 2013 # Springer-Verlag Berlin Heidelberg 2014

Abstract Artificial radionuclides, such as iodine-131 (131I), cesium-134 (134Cs), and cesium-137 (137Cs), as well as natural isotopes of beryllium-7 (7Be) and potassium-40 (40K) have been registered in atmospheric aerosols over Vladivostok selected from 11 March to 17 June 2011. Additionally, 134Cs and 137Cs were detected in atmospheric aerosols over Tomsk selected from 16 March to 17 June 2011. Artificial radionuclides were also discovered in atmospheric wet depositions sampled in Vladivostok from 3 to 17 May 2011. Moreover, these radionuclides have been registered in atmospheric aerosols over the sea surface of the Sea of Japan selected from 3 to 31 May 2011 during an expedition of the “Nadezhda” sailing ship. From 18 March to 15 April, an increase in concentrations of atmospheric aerosols over Vladivostok from 108.8 to 321.5 μg/m3 has been registered. It was accompanied by increased activity concentrations of 134Cs, 137Cs, and the Responsible editor: Philippe Garrigues A. S. Neroda (*) : V. F. Mishukov : V. A. Goryachev : A. A. Goncharova V.I.Il’ichev Pacific Oceanological Institute, FEB RAS, 43, Baltiyskaya Street, Vladivostok 690041, Russia e-mail: [email protected]

131

I. During the period from 18 March to 15 April, activity concentrations of 137Cs and 134Cs in atmospheric aerosols increased 100 times compared with the minimum detectable concentration (MDC) level and peaked in the weekly sample gathered from 8 to 15 April (145.0 and 105.3 μBq/m3, respectively). Variability of concentrations of natural isotopes of 7 Be and 40K was not greater than 1 order of magnitude throughout the sampling period. Maximal values of 137Cs and 134 Cs concentrations (1,281.5 ± 141 and 384.4 ± 42.3 μBq/m3, respectively) in Tomsk were reached in samples taken from 1 to 2 April. For the atmospheric aerosol samples from the Sea of Japan, the largest concentration of 131I (392.3 ±215.7 μBq/m3) was detected from 13 to 19 May, while all other samples had much lower concentration values. Synoptic analysis of back trajectories movement of air masses showed that the radioactive cloud came to Vladivostok from the regions of Siberia and northeastern part of China. Synoptic analysis for Tomsk showed that during the period of maximal activity concentrations (1–9 April), air masses were arriving from the European part of Russia and north of Kazakhstan. Keywords Artificial radioactive isotopes . Fukushima reactor accident . Aerosols . Atmosphere . Transport

V. F. Mishukov e-mail: [email protected] V. A. Goryachev e-mail: [email protected]

Introduction

A. A. Goncharova e-mail: [email protected]

On 11 March 2011, at 1446 hours local time (JST), an earthquake has occurred with an epicenter near the eastern coast of Honshu Island (Japan), at the distance of about 70 km from the nearest point on the Japanese shoreline. The Great East Japan Earthquake triggered extremely destructive tsunami waves which resulted in a number of nuclear accidents at Fukushima

D. V. Simonenkov V.E. Zuev Institute of Atmospheric Optics SB RAS, 1, Academician Zuev Square, Tomsk 634021, Russia e-mail: [email protected]

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Nr. 1 Daiichi Nuclear Power Station. The Fukushima 1 nuclear accidents have resulted in a release of some radioactive elements, including radioactive iodine-131, cesium-134, and cesium 137. According to Tokyo Electric Power Company, high concentrations of 131I, 134Cs, and 137Cs near the power station persisted up to 3 months after the accident. Maximal concentrations were 2,239 Bq/m3 for 131I on 22 March 2011 and 81 Bq/m3 for 137Cs on 14–15 April 2011 (TEPCO 2011). According to the Nuclear and Industrial Safety Agency (NISA) report, about 1.3×1017 to 1.5×1 017 Bq of 131I and about 6.1×1015 to 1.3×1016 Bq of 137Cs were released to the atmosphere (NISA 2011; Chino et al. 2011). Table 1 describes the half-life periods, the values of radionuclide permissible volumetric activity in the air and its permissible mass (specific) activity in the water. Table 1 shows the Tokyo Electric Power Company (TEPCO) and NISA reports that airborne radioactivity near the power station exceeded the permissible values, especially for 131I, within 3 months. Due to the intensive processes related to transfer and turbulent exchange in the atmosphere, the artificial radionuclides might reach the adjacent waters and the neighboring countries, inducing the change of radiological environment and deterioration of ecological situation both for land and marine ecosystems. As reported by the National Institute of Health (2011), the two radionuclides, namely, 131I and 137Cs, which usually emit to the environment after the accidents at nuclear power stations, expose people to the highest risk of cancer diseases. Primarily, the artificial radionuclides in the air were found in Las Vegas (USA) on 18 March 2011 using air cartridges (131I) and in Anaheim (131I, 134Cs, 137Cs), San Francisco (131I, 134 Cs, 137Cs), Las Vegas (131I), and Seattle (131I, 134Cs, 137Cs) using air filters. After 20 March 2011, the maximum concentration of 131I was registered in Dutch Harbor (Alaska) as ∼103,600±8,510 μBq/m3 on air cartridge and as ∼25,600± 1,480 μBq/m3 on air filter. The maximum concentrations of 134 Cs (∼5,330±407 μBq/m3) and 137Cs (∼4,670±296 μBq/ 3 m ) were registered in Nome (Alaska) on 24 March on air filters (United States Environmental Protection Agency 2011). In Chapel Hill, the US East Coast, the highest concentrations of 131I were registered on 2 April 2011 and amounted to

3,990 μBq/m3 (MacMullin et al. 2012). The heavy increase of 131I was registered in Helsinki (Finland) on 22 March 2011, with its peak concentration on 31 March 2011 (∼1,661 μBq/ m3) (STUK 2011). Following Fukushima Nuclear Power Plant (NPP) accident, artificial radionuclides in aerosol samples were detected at sampling stations throughout Europe including Germany (Pittauerová et al. 2011) and Greece (Manolopoulou et al. 2011). One Russian paper reported the presence of Fukushima-originated radionuclides in melted snow and rainwater in samples taken near Krasnoyarsk (Central Russia) (Bolsunovsky and Dementyev 2011). The most comprehensive radionuclide data over the Europe has been compiled by Masson et al. (2011). For comparison, the concentration of 137Cs in the air near Thessaloniki (Northern Greece) 9 days after Chernobyl accident reached 2 Bq/m3, and its dry deposition on the land surface was 24 kBq/m2 (Papastefanou et al. 1988). This paper is intended to study the influence of Fukushima nuclear accident on the composition of aerosols in Russia and over the water area of the Sea of Japan as well as to identify the mechanisms of transboundary transport of radionuclides in the atmosphere. It is worth mentioning that a significant amount of artificial radionuclides including 137Cs has been injected to the environment after nuclear weapon tests conducted by the USA and the Soviet Union during the 1950s and early 1960s (Beck 2011). A significant part of the 137Cs fallout is still present in soils around test sites due to its long (30 years) half-life. We will show that old sources like nuclear weapons tests or industrial accidents might have a secondary polluting effect on aerosol samples taken in one of our sampling sites in the aftermath of Fukushima nuclear accident.

Materials and methods Atmospheric aerosols were collected in Russian cities (Vladivostok and Tomsk) and in the Sea of Japan. Atmospheric aerosol samples in the Vladivostok and the Sea of Japan were taken using a Japanese-made sampler (Kimoto Company, Japan) by a procedure approved in the international

Table 1 Half-life periods and values of permissible volumetric activity (by Russian standards) of several radionuclides in the breathing air and permissible mass activity in water (Ministry of Health of Russia 1999) 40

K

Half-life periods

Permissible volumetric activity, Bq/m3 Permissible mass activity in water, Bq/kg

1.28+ 09 years 31 22

7

137

134

131

53.3days 2,000 4,900

30 years 27 11

2.06 years 19 7.2

8.04days 7.3 6.3

Be

Cs

Cs

I

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program SEAREX (Uematsu et al. 1983). In Vladivostok, the air sampler was located on the top of the building of V.I.Il’ichev Pacific Oceanological Institute, FEB RAS, Vladivostok, Russia (coordinates: 1=43°20′ N, φ=131°92′ E; elevation, 50 m). The sampling started at 1218 hours local time, 11 March 2011, for the purpose of dust storm monitoring. In the Tomsk, Russia (coordinates: l=56°28′41″ N, φ=85°3′14″ E) sampling started at 1535 hours local time, 16 March 2011. Atmospheric aerosol samples in the Sea of Japan were taken during 3–31 May 2011 expedition of the Nadezhda sailing ship. The expedition route of the Nadezhda sailing ship is shown in Fig. 1. Atmospheric aerosols in the Vladivostok and the Sea of Japan were taken using Pallflex membrane filters and at similar flow rates. Atmosphere aerosol was collected in Tomsk using AFA-XP-20 filters (S=∼38.5 cm2) daily. Before and after the sampling, the filters were brought to a constant weight in a desiccator and then weighed. The air volume passed through the filters was average 3,500 m3 per weekly sample (Vladivostok), 150 m3 per daily sample (Tomsk), and 2,000 m3 per 3–4-day sample (the Sea of Japan). Wet depositions were collected using the Aerochem Metrics (model 301) wet/dry bucket collector. The gamma-spectrometric analysis of the aerosol samples was performed in the Laboratory of Nuclear Oceanology, V.I.Il’ichev Pacific Oceanological Institute, Far Eastern Branch, Russian Academy of Sciences, using a gamma spectrometer

Fig. 1 Route an expedition of the Nadezhda sailing ship, May 2011

with a detector of High Purity Germanium GEM150 with a digital multichannel analyzer (DSPEC 2.0; ORTEC, USA). Relative efficiency of registration on 1.33 MeV level was 150 % with a resolution of 1.9 keV. Minimally detectible concentrations of artificial isotopes ranged from 1 to 10 μBq/ m3, depending on the sample mass and air volume pumped. For all radionuclides, the estimation of decay was fixed for the middle of the respective sampling period. Gamma Vision-32 software (ORTEC) was used for spectrum analysis. We analyzed the origin of incoming air masses to the sampling site by computing the 72-h kinematic back trajectories starting at 0, 3, 6, 9, 12, 15, 18, and 21 UTC each day from 11 March to 17 June for Vladivostok and Tomsk. For the Sea of Japan, back trajectories were built with 1-h intervals for points along the ship’s route. They were evaluated for the altitude of 100 m using the Hybrid Single Particle Lagrangian Integrated Trajectory (Hysplit, version 4.9) model with the GDAS1 (Global Data Assimilation System) global analysis meteorological data provided by NCEP (National Weather Service’s National Center for Environmental Prediction) database as developed by the NOAA’s Air Resources Laboratory (ARL) (Draxler 1999). Precision of an individual air trajectory calculated using this method depends on the temporal and spatial resolution of meteorological parameters, their measurement accuracy, as well as any kind of simplifications in the model itself (Stohl 1998; Brankov et al. 1998). It was shown that a spatial error in

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the location of trajectory points is about 20 % of their traveled distance (Stohl 1998). By using a larger number of trajectories, we can reduce the influence of random spatial errors. We then used trajectory cluster analysis to obtain the aggregate information about possible directions of aerosol transport (Dorling et al. 1992; Sirois and Bottenheim 1995). K-means clustering (MacQueen 1967) is one of the simplest unsupervised learning algorithms that solve the well-known clustering problem. There are several ways to define distance (measure of similarity) between trajectories. The most commonly used one is Euclidean distance, and the clustering method based on it is implemented in NOAA Hysplit software package. Another way to measure distance is measuring the angular distance that is more appropriate if the most important trajectory parameter is its direction and not the wind speed (Sirois and Bottenheim 1995).

Results and discussion Tables 2 and 3 show the concentrations of artificial radionuclides in the atmosphere aerosols and wet precipitation in the suburbs of Vladivostok, Tomsk, and over the water area of the Sea of Japan. From 25 March to 15 April, an increase in concentrations of atmospheric aerosols over Vladivostok from 121 to 322 μg/ m3 has been registered. It was accompanied by increased activity concentrations of 134Cs, 137Cs, and the 131I. Maximal activity concentrations of 131I over Vladivostok (1,047.0 μBq/ m3) was reached in samples taken from 1 to 8 April. Measurements carried out at Tokushima (about 700 km southwest from the Fukushima NPP) indicated the maximum concentration of particulate 131I (12,000.8 μBq/m3) in the air which was observed on 6 April (Fushimi et al. 2011). The filter efficiency for iodine depends on the chemical structure of iodine. The gaseous iodine such as I2, HOI, and CH3I cannot be collected by using a normal glass filter. Only a small fraction of iodine ion and chemical compounds of iodine which are attached on aerosol is cached by our glass filter (Fushimi et al. 2011). Since we did not sample the gaseous fraction of iodine, we cannot know the total activity concentration of 131I. In Vladivostok during the period from 1 to 29 April, activity concentrations of 137Cs and 134Cs in atmospheric aerosols was above the minimum detectable activity (MDC) level and peaked in the weekly sample gathered from 8 to 15 April (145.0 and 105.3 μBq/m3, respectively). Variability of concentrations of natural isotopes of 7Be and 40K was not greater than 1 order of magnitude throughout the sampling period. From 1 to 22 April 2011, an increase in activity concentrations of 137Cs and 134Cs in atmospheric aerosols was seen in the city of Tomsk, while maximal values of 137Cs and 134Cs concentrations (169.6 and 50.9 μBq/m3, respectively) were reached in samples taken from 1 to 8 April (for the sum of daily filters from 1 to 8 April). However, individual analysis of daily filters in Tomsk shows more than a 1,000-times increase

in activity concentrations compared to MDC (1,281.5 and 384.4 μBq/m3 for 137Cs and 134Cs, respectively). Concentration of 137Cs and 134Cs peaked from 1 to 2 April. It leaves the possibility that daily concentrations of 131I, 137Cs, and 134Cs in Vladivostok could have been higher. Analysis of activity concentrations of Tomsk samples took place later when no 131 I could be detected. For the atmospheric aerosol samples from the Sea of Japan, the largest concentrations of 131I (392.3и35.4 μBq/m3) were detected near the continent from 13 to 19 May and from 19 to 22 May, respectively. The maximal concentrations of 137Cs (34.4 μBq/m3) and 137Cs were detected from 28 to 31 May near south of Primorsky Krai, Russia. Figure 2 shows changes in the artificial radionuclide concentrations in aerosols and the total amount of wet precipitation during the sampling period. It could be noted that there was no precipitation during the early sampling period when maximal concentration was detected. Rains started from 15 to 22 April, leading to a decrease in concentrations of 134Cs and 137Cs. In the dry week between the two rainy periods (20 May to 3 June), the concentrations of 134Cs increase again up to 18 μBq/m3. Maximal concentration of 134Cs in the solid part of wet precipitation was 68 and 93 mBq/g for 137Cs. At the same time period, the mean mass concentrations of 134Cs in aerosols were 27.5 and 45.1 mBq/g for 137Cs. From 1 to 15 April 2011, the average mass concentrations of 134Cs and 137Cs in aerosols were 347 and 494 mBq/g, respectively (134Cs/137Cs ratio of ∼0.70), without any wet precipitation. From 15 April to 20 May when the total amount of wet precipitation was 126.1 mm, the average level of the said isotopes’ concentrations decreased to 149 mBq/g (134Cs) and 198 mBq/g (137Cs), respectively (134Cs/137Cs ratio of ∼0.75). The next peaks of artificial radionuclides from 6 to 13 May and from 20 May to 3 June are also accompanied by a decrease in wet precipitation. Similar situation was evidenced in Tomsk where after the steady rains from 1 to 8 April 2011 (Table 2), there was a decrease in 134Cs and 137Cs concentrations from 50.9 to 30.0 and from 169.6 to 110.2, respectively, during the period from 8 to 15 April 2011. The ratio of 134Cs/137Cs in our measurements performed in Vladivostok from 18 March to 22 April 2011 was close to 1. That complies with the information provided by TEPCO monitoring service, the company operator of Fukushima 1 nuclear power plant, and the results obtained by other researchers. As reviewed by Thakur et al. (2013), the 134Cs/137Cs ratio in the data of various organizations and researchers varied from 0.63 to 1.19. As shown in Table 2, the average ratio 134Cs/137Cs in Tomsk from 1 to 15 April 2011 is less than the same ratio for Vladivostok (∼0.73). Detailed analysis of backward trajectories showed that a part of 137Cs activity concentration could be of local origin. Tomsk is located 16 km away in southwestern direction from the Siberian Group of Chemical Enterprises (Tomsk-7) that contains several nuclear reactors and chemical

Author's personal copy Environ Sci Pollut Res Table 2 Radioactivity of 131I, 137Cs, and 134Cs in aerosols per cubic meter of atmosphere air and in wet deposition in Vladivostok (2σ, twice the standard deviation) Concentrations, μBq/m3 Date

131

Point

137

I±2σ

134

Cs±2σ

Cs±2σ

Aerosols

Rainfall

(μg/m3)

(mm)

11–18 March 2011

Vladivostok

0.9 in Vladivostok and ∼0.58 in Tomsk. Among the eight samples taken during the 2011 Sea of Japan expedition, only three samples showed any 134Cs radioactivity. These were the samples taken in the periods 6–9 May, 22–25 May, and 28–31 May with 134Cs activity

Date

137

134

Cluster 1 (%)

Cluster 2 (%)

Cluster 3 (%)

1 to 2 April 2011 2 to 3 April 2011 3 to 4 April 2011 4 to 5 April 2011 5 to 6 April 2011 6 to 7 April 2011 7 to 8 April 2011 8 to 9 April 2011

1,281.5 153.8 158.8 – 225.0