Natural and Fukushima-derivedradioactivity in macroalgae and mussels along the Japanese shoreline
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Natural and Fukushima-derived radioactivity in macroalgae and mussels along the Japanese shoreline Z.Baumann 1,N.Casacuberta 2,*,H.Baumann 1,P.Masqu′e 2,and N.S.Fisher 1
1School
of Marine and Atmospheric Sciences,Stony Brook University,Stony Brook,NY 11794-5000,USA 2Institut de Ci`e ncia i Tecnologia Ambientals &Departament de F′?sica,Universitat Aut`o noma de Barcelona,08193,
Bellaterra,Spain
*now at:ETH-Zurich,Laboratory of Ion Beam Physics,HPK G26,Schafmattstrasse 20,8093Zurich,Switzerland
Correspondence to:Z.Baumann (zo?a.baumann@https://www.wendangku.net/doc/ff16450555.html,)
Received:1January 2013–Published in Biogeosciences Discuss.:13February 2013Revised:8May 2013–Accepted:14May 2013–Published:13June 2013Abstract.Following the failure of the nuclear power plant in Fukushima Prefecture in March 2011,peer-reviewed pub-lications describing radioactivity levels in organisms inhab-iting coastal environments are scarce.This paper reports on elevated levels of 134Cs and 137Cs in macroalgae and mus-sels (up to ～800Bq kg ?1dry wt.)in June 2011.Cs concen-trations in biota sampled in early June 2011were higher in areas south of Fukushima than sampled in the last third of the month north of Fukushima.Activity concentrations from 134+137Cs in organisms south of Fukushima were compara-ble to or lower than those from the naturally occurring 40K in the same samples.While 210Pb and 210Po concentrations were generally lower than these other radionuclides,210Po as an α-emitter is more signi?cant from a radiological view-point than γ-emitters as it can in?ict greater biological dam-age.By applying known bioconcentration factors of Cs in biota,measured biota concentrations of Cs were also used to estimate Cs concentrations in coastal seawater to be in the range of 102–103Bq m ?3.These estimates show that,3months after the accident and maximal release of radioactive Cs,levels of Cs persisted in coastal waters,although at lev-els that were two orders of magnitude lower than at the time of release.These June coastal seawater Cs levels were four orders of magnitude above Cs concentrations off Japan prior to the Fukushima disaster.
1
Introduction
Following the devastation caused by the earthquake and
tsunami on 11March 2011,the Japanese public was anxious
regarding radioactivity release from the damaged Fukushima Daiichi nuclear power plant (NPP).Radioactivity released onto land led to contamination in vegetable produce,dairy,and meat products,and similarly release into the coastal ocean led to contamination of seafood.Recognizing public concerns,the Ministry of Agriculture,Forestry and Fisheries (MAFF)initiated a monitoring program that set allowable radioactivity levels in seafood to 500Bq kg ?1wet weight (wet wt.,later lowered to 100Bq kg ?1wet weight)for ra-dioactive cesium (i.e.,sum of 134Cs and 137Cs)(MAFF).Post-Fukushima academic studies have either attempted to predict consequences of the fallout for human and animal
health (Kryshev and Sazykina,2011;Garnier-Laplace et al.,
2011;Murakami and Oki,2012)or focused on estimat-ing the quantities of released radioactivity and their atmo-spheric and oceanic dissipation (Buesseler et al.,2011,2012;Tsumune et al.,2011;Yoshida and Kanda,2012;Masson et al.,2011).However,peer-reviewed studies of radioactive
concentrations in post-Fukushima marine animals and plants
remain surprisingly scarce.Apart from detailed radioactiv-ity measurements in small ?sh and crustaceans collected off-shore during an international survey in June 2011(Bues-seler et al.,2012),peer-reviewed reports of radioactivity in economically important coastal organisms (e.g.,macroal-gae,bivalves)are missing.However,TEPCO (Tokyo Electric Power Company),MEXT (Ministry of Education,Culture,
Published by Copernicus Publications on behalf of the European Geosciences Union.
Fig.1.Sampling locations for mussels and macroalgae along the east coast of Honshu Island of Japan.
Sports,Science,and Technology)and MAFF have used the Internet as an outlet for continuous publication of radioactiv-ity measurements in sediments,water and biota.While there is undeniably a value to a stream of data published on the web page,this approach is missing key information on methodol-ogy and therefore missing quality assurance(MEXT;MAFF; TEPCO,2013).
The goal of this study was to quantify June2011levels of Fukushima-derivedγ-emitting cesium isotopes(i.e.,134Cs, 137Cs)in mussels and macroalgae,collected from coastal lo-
cations north and south of the Fukushima NPP(Fig.1).A second goal was to put these levels in the context of natu-rally occurring radioactivity due toγ-andβ-emitting potas-sium(40K)and210Pb andα-emitting polonium(210Po)iso-topes present in these organisms,which is directly relevant to assessing any increased radioactive dose for seafood con-sumers.2Material and methods
2.1Sample collection
Samples of green(Ulva sp.)and brown(species were not identi?ed)macroalgae as well as mussels(Mytilus gal-loprovincialis;average shell length45.0±3.8mm)were collected by hand along several Paci?c beaches south (2June2011)and north of Fukushima NPP(21June2011) (Fig.1).Collection times were different for the northern and southern locations due to logistical capabilities.South-ern sampling sites,i.e.,Isohara port(36.81?N,140.76?E), Nakoso beach and port(36.86?N,140.79?E and36.83?N, 140.80?E,respectively),and the Cape Misaki(36.94?N, 140.91?E),were approximately70km south of Fukushima NPP,while northern sites,Odonohama(38.28?N,141.05?E) and Shichigahama(38.29?N,141.07?E)beaches,were ap-proximately30km north of Fukushima NPP.Samples were sealed in plastic bags and shipped to Stony Brook University in New York in coolers with dry ice(?50?C).
2.2Sample preparation
In the laboratory,mussel shells were separated from soft tissue,since only the latter was assumed to have accumu-lated radioactive Cs(Ke et al.,2000).Mussel tissue and macroalgae were placed into individual plastic containers and stored at?80?C for24h prior to freeze-drying.All samples were then placed inside fast-freeze?asks and con-nected to a Labconco FreeZone Benchtop Freeze Dry Sys-tem that was cooled to?52?C,and pressurized to0.12mbar (Buesseler et al.,2012).After freeze-drying,samples were ground with a ceramic mortar and pestle to obtain homoge-neously distributed samples that varied in dry weight(dry wt.)from3.1to79.1g.Samples were stored in straight-side polypropylene120mL jars(Nalgene),which had been ef?ciency-calibrated to their speci?c geometry.
2.3134Cs,137Cs and40K analysis
We used a planar,low energy germanium detector(Canberra model GLP3830)and Genie2000software(Canberra)to measure and analyze the spectrum ofγemissions in our sam-ples.Average counting time was27h,and the average count-ing uncertainties were4%for134Cs and137Cs,and8%for 40K.The detector ef?ciency was determined as previously
described by Buesseler et al.(2012)for individual radioiso-topes with varying geometries as follows:1.7–3.5%for 134Cs(at604.7keV peak),1.6–3.2%for137Cs(at661.7keV peak),and0.8–1.7%for40K(at1461keV peak).Calcula-tions of134Cs,137Cs,and40K concentrations in the samples assumed negligible self-absorption ofγrays for these iso-topes,given that they all emit at energies>200keV(Hurtado et al.,2007).Correction for coincidence summing was omit-ted as a low ef?ciency planar detector was used for sample analyses.Measured134Cs and137Cs were decay-corrected to
Biogeosciences,10,3809–3815,https://www.wendangku.net/doc/ff16450555.html,/10/3809/2013/
Table1.Dry-weight-based concentrations of134Cs,137Cs,40K and210Po in macroalgae and mussels sampled in June2011along the east coast of Japan.Activities were decay-corrected to the date of sample collection,except for40K given its very long half-life(1.25×109yr).σis the propagated counting error(Bq kg?1).
Sample NPP?Location Lat.Long.134Cs±σ137Cs±σ134Cs:137Cs±σ210Po±σ210Pb±σ40K±σtype?N?E Bq kg?1Bq kg?1Bq kg?1Bq kg?1Bq kg?1 Brown N Shichigahama38.29141.07108 5.1103 5.1 1.050.0716.3 3.2 1.70.284255 algae Beach
Odonohama38.28141.0580 5.487 5.80.920.0929.6 3.6 4.60.388068
Beach
124 6.2143 6.60.870.0610.3 2.20.90.1118973
127 4.4152 4.80.830.0423.7 4.48.30.4136956 S Nakoso Port36.94140.91239 4.7282 5.10.850.0217.8 3.2 2.20.2129644 Green N Shichigahama38.29141.0766584 4.90.780.0718.1 2.7 5.10.451152 algae Beach
Odonohama38.28141.0560 2.273 2.40.820.04115 6.9 5.40.350926
Beach
S Cape Misaki36.94140.91369 5.1435 5.60.850.0227221.78.80.542624 Mussels N Odonohama Beach38.28141.0551 2.159 2.20.870.0514.0 2.9 1.30.135321 S Cape Misaki36.94140.91393 5.6463 6.10.850.0228.8 3.6 4.50.330022
3728.84179.10.890.03300217.70.833436?North(N)or south(S)relative to the Fukushima nuclear power plant(NPP)
the date of sample collection(taking into consideration their
half-lives of2.07and30.08yr,respectively).
2.4Analyses of210Pb and210Po
Small sub-samples(0.5–1.0g)were spiked with known
amounts of209Po(0.07Bq)and stable Pb(0.1mg)as in-
ternal tracers of the radiochemical analysis.After the addi-
tion of tracers,sub-samples were acid-digested at80–90?C
on a hot plate for10–12h using65%HNO3(30–40mL)
and a few drops of H2O2.Digested samples were?ltered
(Albet Quantitative Filter Paper ashless hardened DP1507),
non-digested residuals discarded,and samples reconstituted
to80mL of1N HCl after evaporation to dryness.Samples
were heated to70?C and ascorbic acid added to reduce
Fe(III).The polonium isotopes were plated onto silver disks
at70?C for8h while stirring.Polonium emissions were
counted by alpha particle spectrometry using silicon surface
barrier and PIPS detectors(EG&Ortec and Canberra).Upon
plating and to assure the complete removal of polonium,the
solutions were converted to9M HCl and passed through ion
exchange columns(resin type Dowex1X8,100–200mesh).
Aliquots of each sample were taken before and after this step
to determine the chemical yield for Pb by atomic absorp-
tion spectrometry.The solutions were re-spiked with209Po
and stored for several months to attain suf?cient growth of 210Po from210Pb.After4–6months,polonium isotopes were plated again onto silver disks and counted.Activities of both 210Pb and210Po at the time of sample collection were cal-culated after appropriate in-growth and decay corrections
(Church et al.,2012).3Results and discussion
3.1Cesium in macroalgae and mussels
All samples of post-Fukushima mussels and macroalgae
contained134Cs(range:51–393Bq kg?1dry wt.)and137Cs
(range:60–463Bq kg?1dry wt.,Table1).Measured137Cs
concentrations in mussels and macroalgae prior to the
Fukushima accident(background)were two to three or-
ders of magnitude lower.For example,brown macroal-
gae collected off the Japanese coast in2007–2008had 137Cs concentrations of0.038–0.058Bq kg?1wet wt.(or 0.14–0.21Bq kg?1dw assuming a wet/dry ratio of0.27;
Morita et al.,2010;Carvalho,2011),and mussels(Mytilus
edulis)collected from the south-western Korean Sea in1988
had0.04Bq kg?1dry wt.In the case of the shorter lived 134Cs isotope(half-life=2.07yr),no other sources than the Fukushima accident could have produced the detected 134Cs levels in mussels and algae.In addition,the ratio of 134Cs:137Cs in our macroalgae samples was approximately 1(mean±SD=0.85±0.003and0.88±0.10for the north-ern and southern sampling locations,respectively),consis-tent with ratios found in marine plankton(Buesseler et al., 2012)and similar to measured concentrations in the water following the radioactive discharge from the Fukushima NPP (Buesseler et al.,2011;MEXT;Aoyama et al.,2012). Furthermore,our analyses revealed consistently lower ra-diocesium levels(i.e.,the sum of137Cs and134Cs)in samples from northern locations than those in the southern locations. However,even in the more contaminated southern loca-tions none of the samples exceeded the500Bq kg?1wet wt. safety limit.Differences in Cs contamination between the two regions were greatest for mussels.M.galloprovincialis from the site north of the Fukushima NPP contained7.5 times less radiocesium than southern samples(north:mean
https://www.wendangku.net/doc/ff16450555.html,/10/3809/2013/Biogeosciences,10,3809–3815,2013
Table2.Estimates of134Cs and137Cs concentrations in coastal seawater at the locations north and south of the Fukushima NPP based on concentration factors(CFs;L kg?1)derived from the literature(IAEA,2004).Ranges are provided based on the maximum and minimum concentration values for the biota.
Biota Seawater
134Cs137Cs134Cs137Cs
Sample NPP a Dry/wet CF Bq kg?1dry wt.×102Bq m?3
type conversion
factor
Brown algae
N 0.273480–12787–152 6.4–10.1 6.9–12.1
Green algae0.186060–6673–84 1.8– 2.0 2.2– 2.5 Mussels0.166051b59b 1.4b 1.6b
Brown algae
S 0.2734239b282b19.0b22.4b
Green algae0.1860369b435b11.1b13.1b Mussels0.1660372–393417–4359.9–10.511.1–11.6
a North(N)or south(S)relative to the Fukushima nuclear power plant(NPP).
b Indicates one value instead of a range when concentrations were available for only one sample.
of110Bq kg?1dry wt.;south:mean of822Bq kg?1dry wt.). Green macroalgae from northern locations contained on av-erage141Bq kg?1dry wt.of radiocesium,which was5.7 times less than in the southern sample(804Bq kg?1dry wt.), while brown macroalgae from the south contained approx-imately twice as much radiocesium as northern samples. Given that Cs uptake by macroalgae is proportional to the Cs concentrations in water(Gutknecht,1965),we conclude that radiocesium levels were indeed higher in coastal waters south of Fukushima than in waters north of Fukushima at the time of sampling,likely due to the19-day lag between sam-pling at these locations.Indeed,MEXT-online reports show a～30%decline in137Cs seawater concentration at Dai-ichi within this time interval(i.e.,2–21June2011).Some of the difference in137Cs concentrations in biota collected at these two time points(i.e.,the137Cs concentration difference be-tween biota collected north on21June2011vs.those col-lected south on2June2011)can be accounted for by the general decline of radioactivity at its discharge.Any further difference could be accounted for by the southward shore current along the Paci?c coast of Honshu(Buesseler et al., 2012).
Cs concentrations in biota can be combined with published concentration factors(CFs,i.e.,the wet tissue to water activ-ity ratio;L kg?1)to estimate Cs concentrations in the water, assuming that the organisms were in equilibrium with ambi-ent water(IAEA,2004).Given that the biological half-lives of Cs in green and brown macroalgae and in mussels are5–8 and8days,respectively(Gutknecht,1965;Dahlgaard,1981), it would appear that the assumption of equilibrium was met. However,for longer biological half-life values(e.g.,as re-ported by Dahlgaard and Nolan,1989,for Cs in https://www.wendangku.net/doc/ff16450555.html,lis –17.5d),assumption of equilibrium could lead to a greater error.
While CFs might be useful in approximating the concen-tration levels in the water,it is important to realize that these approximations come with an increased chance of error.For example,CFs of137Cs in various brown macroalgae varied up to100%and in mollusks up to67%in a study follow-ing radioactive waste disposal in Arctic seas(Fisher et al., 1999).The variation of CF values of137Cs in green mussels –Perna viridis–has been also related to body size,water pumping rate,and salinity(Ke et al.,2000).Due to observed variability of137Cs CFs in algae and mussels,which however is smaller for an individual species,estimates of137Cs con-centrations in seawater based on literature CFs are therefore expected to fall within fourfold of directly measured values. By applying our measured Cs concentrations in mussels and using a Cs wet wt.CF for mussels as60(IAEA, 2004),we estimate total ambient radiocesium levels in northern and southern coastal sampling sites in June2011 to have ranged from2.9×102Bq m?3to22.1×102Bq m?3, respectively(Table2).Estimates for seawater134Cs con-centrations using our mussel concentrations of134Cs were1.4×102north of Fukushima NPP and9.9×102–10.5×102Bq m?3south of Fukushima NPP(Table2). Reported CF values for green and brown algae are60and 34,respectively(IAEA,2004).Using these CFs and a dry to wet weight ratio of0.18for green algae and0.27 for brown algae(Carvalho,2011),we estimate seawa-ter134Cs concentrations of 1.8×102–2.0×102Bq m?3 north of Fukushima and11×102Bq m?3south of Fukushima based on green algae measurements(Table 2).Brown-algae-based measurements estimated134Cs concentrations of 6.4×102–10.1×102Bq m?3north of Fukushima and19×102Bq m?3south of Fukushima (Table2).Green-algae-based estimates of137Cs in seawater north of Fukushima are 2.2×102–2.5×102Bq m?3and
Biogeosciences,10,3809–3815,https://www.wendangku.net/doc/ff16450555.html,/10/3809/2013/
13.1×102Bq m?3south of Fukushima,while brown-algae-
based estimates of134Cs in seawater north of Fukushima
are 6.9×102–12.1×102Bq m?3and22.4×102Bq m?3
south of Fukushima(Table2).These estimated137Cs con-
centrations in coastal seawater are generally about2orders
of magnitude lower than the maximum137Cs concentrations
recorded by TEPCO and presented by MEXT in mid-April
at30km offshore Fukushima(～200000Bq m?3;Buesseler
et al.,2011).It is practically impossible to relate our lower
estimates at northern locations to those reported by MEXT,
because137Cs detection limits declared in these reports were
high(i.e.,6Bq L?1or6×103Bq m?3).Therefore,any
Cs at concentrations lower than6×103Bq m?3would not
have been detected.137Cs concentrations predicted by us for
the southern location on2June2011are at least sevenfold
lower than15×103Bq m?3reported online for seawater
collected on2June2011near our sampling site(MEXT). 134Cs concentrations measured in coastal seawater Onahama (Aoyama et al.,2012),near the southern sampling site in the
present study,show up to threefold higher than the maximum
CF-estimated values in the present study(Table2).This
agreement between our CF-estimation of seawater Cs and
an actual measurement is consistent with an up to fourfold
error(see above).
3.240K,210Pb and210Po in macroalgae and mussels Naturally occurring radioisotopes40K,210Pb and210Po were detected for all samples.Highest concentrations of40K were present in brown macroalgae(i.e.,842–1369Bq kg?1dry wt.;Table1),lower in green macroal-gae(i.e.,426–511Bq kg?1dry wt.;Table1),and in low-est in mussel soft tissue(300–353Bq kg?1dry wt.;Table1). Concentrations of210Pb varied by an order of magnitude for brown algae(0.9±0.10–8.3±0.40Bq kg?1dry wt.; Table1),but were similar for green algae(5.1±0.36–8.8±0.48Bq kg?1dry wt.;Table1).210Pb in mussels varied by sixfold(Table1).Concentrations of210Po were similar among brown algae samples and ranged from10to30Bq kg?1dry wt.with an average of19.5±7.4Bq kg?1dry wt.(Table1),but they were variable among the green algae and mussels.210Po concentration in green algae ranged from18.1to272Bq kg?1dry wt.,and from1
4.0to300Bq kg?1dry wt.for mussels.
The variability in the40K and210Po levels for brown
macroalgae(Table1)is not unusual(Thompson et al.,
1982;U?g ur et al.,2002;Goddard and Jupp,2001).Thomp-
son et al.(1982)showed that for just one species of
a brown macroalgae,Fucus vesiculosus,collected from
the Irish Sea,40K concentrations varied twofold.Another
study showed that40K concentrations can vary within al-
gal divisions(Goddard and Jupp,2001).In that study 40K concentrations showed a44-fold variation and ranged from100to4400Bq kg?1dry wt.in green algae,and125–5400Bq kg?1dry wt.in brown algae(Goddard and Jupp,2001).Published210Po concentrations for green algae are scarce,but one study reported210Po concentration of 15Bq kg?1dry wt.,which falls within the range of210Po concentration in green algae in this study(Carvalho,2011). As in the present study,variability for210Po concentrations in mussels has been reported.For example,210Po concen-trations showed26-fold(52–1300Bq kg?1dry wt.)variation for Mytilus galloprovincialis from various coastal locations of the Aegean Sea(U?g ur et al.,2002).Wildgust et al.(1998) suggested that variation of210Po concentrations in organisms could be linked to environmental conditions such as salinity or temperature,and to biological parameters such as the re-productive cycle phase.The ratios of210Po:210Pb for green and brown macroalgae?t within the range of previously re-ported ratios,but for mussels210Po:210Pb ratios are lower in this study(Carvalho,2011).
From a human-health perspective,it is important to assess levels of natural radionuclides such as40K,210Po and210Pb as these radionuclides are always present in seafood.Because 40K is the dominantγ-emitter in the ocean and in marine
biota,its evaluation as a potential radioactive dose contribu-tor is important.The dose attributable to40K is however pre-dominantly due to itsβemissions(UNSCEAR,1993).210Po releasesα-particles with its decay,andαemissions are20 times more damaging to cells thanγandβemissions(Eck-erman et al.,2012).In fact210Po has been shown as the ra-dionuclide producing by far the greatest radioactive dose in marine biota,as it also is the greatest radioactive dose con-tributor to seafood consumers(Aarkrog et al.,1997).There-fore even though its radioactivity is lower,doses from the naturally occurring210Po in biota,including those from the Japanese shore(Table1),can be of greater radiological im-portance than134+137Cs.
4Summary
This is the?rst report in the peer-reviewed literature on the levels of anthropogenic and natural radioactivity in the biota from coastal Japan following the Fukushima NPP failure. At the time of sample collection in June2011,concentra-tions of Fukushima-derived137Cs and134Cs were elevated, and when combined(i.e.,134+137Cs)they did not exceed the 500Bq kg?1wet wt.recommended safety level for seafood consumption.Biota concentrations of Cs were higher in the southern locations than in the north,likely due to the19-day lag between sampling and the southward?ow of coastal currents(Buesseler et al.,2012).Concentrations of individ-ual(i.e.,210Po and40K)natural radionuclides showed lev-els that were20-fold lower or5-fold higher than those of 134+137Cs.A concentration-factor-based approach estimated that radioactive Cs concentrations in coastal waters at the northern location in the second half of June could be in the range of2.9×102–22.2×102Bq m?3,and at the southern
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locations earlier on were either similar or up to14-fold higher.
Acknowledgements.We thank J.A.George for help in collecting the samples,C.Heilbrun for technical assistance,C.Weintraub-Weissman,H.Reddy, D.Li and M.Castrillejo for laboratory assistance.This project was funded by the Gordon and Betty Moore Foundation through Grant GBMF3007to Ken Buesseler. PM was funded through the ICREA Academia prize of the Generalitat de Catalunya and the project CTM2011-15152-E of the Spanish Government
Edited by:H.Nies
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