radioactive contamination of the coastal seawater following the fukushima 1 nuclear power plant ( f1npp ) accident was the most significant artificial radioactive liquid release into the sea ever known , on a short time and space scale basis ( buesseler et al .
2005 ) . the amount of radionuclides discharged from the f1npp immediate after the accident was estimated to be 510 pbq to the atmosphere and 36 pbq to the sea , the latter being caused by direct leakages of the contaminated cooling water ( estournel et al . 2012 ; kawamura et al .
the seawater contamination has become severe by ( 1 ) a deposition from an atmospheric contamination plume , ( 2 ) direct , artificial releases of highly contaminated waters into the sea , and ( 3 ) the transport of radiopollutants into the sea by surface water leaching through contaminated soil or by river systems .
the first case was most serious during mid - march 2011 , and the second from late march to early april 2011 .
the contaminated seawater may be diluted or has been transported offshore by currents . along the coast , however , a significant portion of the radioactive cs and other radioactive substances are believed to have been absorbed by coastal organisms or bound to suspended particles , causing a deposition of radiopolluted sediments on the sea bottom .
the concentration of radionuclides reached the maximum in mid - april 2011 , but it thereafter declined exponentially .
however , in addition to the inflow through the river systems , artificial release of radionuclides from f1npp is reported to have continued at least until 2012 ( kanda 2013 ) . among the radionuclides discharged by the accident ,
the effects of cs and cs are most serious because of their high levels and long decay periods .
these radionuclides are considered to most substantially contribute to the contamination of marine organisms due to the contaminated seawater .
marine macroalgae ( so - called seaweeds ) grow by absorbing nutrient salts and other minerals directly from seawater at the surface of their thalli .
cs is soluble in seawater , and algal cells are thought to absorb cs through certain k transporters ( kanter et al .
2010 ; zhu and smolders 2000 ) , resulting in cs  accumulation within the cells .
the concentration factors ( cfs ) of marine macroalgae for cs were reported to vary considerably from species to species ( coughtrey and thorne 1983 ; pentreath 1976 ; tateda and koyanagi 1994 ) , but iaea ( 2004 ) recommended the value of 50 .
marine macroalgae may also capture the ions in phycocolloids such as alginate , fucan , agar , and carrageenan , although the affinity of cs for these phycocolloids is not well - established ( morris et al .
marine macroalgae are primary producers in coastal ecosystems , and diverse benthic animals as well as fishes feed on them . therefore , the radioactive contamination of marine macroalgae will be transferred to consumer animals through the food chain , and may become concentrated by biological accumulation . prior to the accident , the concentrations of cs in the surface water of the pacific ocean were in the range of 14  bq  m ( ikeuchi 2003 ; nakanishi et al . 2010 ; povinec et al .
2004 ) , which mainly resulted from global fallout due to atmospheric nuclear weapon tests .
tateda and koyanagi ( 1994 ) have reported the background concentrations of cs in representative green , red and brown marine macroalgae , e.g. ulvapertusa kjellman , neodilseayendoana tokida , saccharinareligiosa ( miyabe ) c.e .
saunders ( = laminariareligiosa miyabe ) , sargassumhorneri ( turner ) c. agardh , s. thunbergii ( mertens ex roth ) kuntze , in the range of ca . 0.03037 
later , morita et al . ( 2010 ) have compared the level of sr and cs in undariapinnatifida collected from three representative areas ( nagasaki pref .
, kanagawa pref . and niigata pref . ) in japan and in saccharinalongissima ( miyabe ) c.e .
saunders ( = laminarialongissima miyabe ) from hokkaido during a 19982008 period and reported cs levels of 0.030.08 and 0.050.09  bq  kg wet weight for u. pinnatifida and s. longissima , respectively .
( 2010 ) also compared concentrations of sr and cs in some additional kelp and sargassum species and reported cs concentrations of 0.020.34  kg wet weight .
several agencies have conducted investigations to measure the radioactive quantities of major fishery organisms after the f1npp accident .
some algal taxa have been included in the target species , e.g. , pyropia ( porphyra ) , saccharina ( laminaria ) , eisenia , gloiopeltis , monostroma , but the number of species was rather limited , and rather biased in respect to phylogenetic diversity , habitat , and life history ( e.g. , intertidal vs. subtidal , annual vs. perennial ) .
in addition , measurement protocols were not standardized among the investigations , and the detection levels were sometimes rather high ( e.g. ,  >  20  bq  kg  for fresh specimens : http://www.jfa.maff.go.jp/e/inspection/index.html ) depending on the available facilities .
therefore , it was difficult to compare the data to clarify the general fate of radioactive contamination in marine macroalgae , and to discuss the differences in the cfs for radionuclides among the taxa . in the present study , we aimed to monitor the level of radionuclides including cs , cs and k based on a standardized protocol using high - purity germanium detectors and to undertake multi - seasonal sampling as much as possible .
specimens were seasonally collected by snorkeling at nagasaki , fukushima pref . , ca . 50  km distant from the f1npp ( fig .  1 )
additional specimens were collected at the following localities : hironocho , hisanohama , shioyazaki and soma ( fukushima pref . ) ; iwanuma ( miyagi pref . ) ; kamogawa and katsuura ( chiba pref . ) ; and iwaya ( hyogo pref . ) ( fig .  1 ) .
the list of the specimens is shown in table  1 ( measurements made at kobe university ) and table  2 ( measurements made at iwaki meisei university).fig . 
1locations of the collection sites of the specimens investigated in the present studytable  1list of samples examined at kobe university , and the results of cs , cs and k measurements for dried samples when not specially notedsample codecollection datetaxonomylocalitynote ( sample preparation and nature of samples ) 
 cs 
 cs 
 kclassorderspeciesbq kg 
 errordetect .
limitk0019 july 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimafertile thalli , directly dried320.5716.070.012346.1422.700.0091,132.70310.810.282k0022 may 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 shioyazaki , iwaki , fukushimafrozen5,406.7068.220.0295557.9093.100.0202,494.30375.950.309k0032 may 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimafrozen3,009.5097.100.0542897.80122.560.0422,780.801013.300.942k0049 july 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried487.5458.310.051567.8374.200.046n.d.n.d.1.381k0052 may 2011phaeophyceaefucales 
 sargassum 
 thunbergii 
 shioyazaki , iwaki , fukushimafrozen4,151.9060.110.0264239.9081.190.0202,507.50384.800.315k0062 may 2011phaeophyceaeectocarpales s.l . 

scytosiphon 
 lomentaria 
 nagasaki , iwaki , fukushimafrozen4,544.9069.540.0314616.0093.950.021n.d.n.d.0.376k0082 may 2011phaeophyceaefucales 
 sargassum 
 muticum 
 shioyazaki , iwaki , fukushimafrozen3,991.3098.260.0494282.40132.040.0381,981.80808.570.760k0092 may 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 shioyazaki , iwaki , fukushimafrozen4,231.90138.520.0704340.20182.550.062n.d.n.d.1.409k0102 may 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 shioyazaki , iwaki , fukushimafrozen7,433.50133.330.0607371.20173.950.0471,152.20799.520.800k0119 july 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimajuvenile thalli , directly dried529.9248.560.160569.0860.430.142n.d.n.d.3.396k0129 july 2011phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimabasal portion , directly dried457.6522.240.053501.0629.900.0442,867.30411.991.061k0132 may 2011ulvophyceaeulvales 
 ulva 
 linza 
 shioyazaki , iwaki , fukushimafrozen5,516.50128.990.0735433.80165.310.038n.d.n.d.0.944k0146 may 2011rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 nagasaki , iwaki , fukushimafrozen691.8623.500.015767.3732.900.012371.85260.950.257k0156 may 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimafrozen4,690.0071.890.0314810.3096.650.0232,957.80462.110.383k0169 july 2011rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 nagasaki , iwaki , fukushimadirectly dried318.4828.830.106352.4036.170.090n.d.n.d.2.073k0179 july 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimafrozen606.5066.730.200576.9385.960.199n.d.n.d.5.182k0189 july 2011phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimatip portion , directly dried340.7721.650.018321.1526.710.0164,783.70525.791.280k0199 july 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried426.8737.520.136425.3245.340.097n.d.n.d.2.638k0209 july 2011phaeophyceaefucales 
 sargassum 
 yamadae 
 nagasaki , iwaki , fukushimadirectly dried499.6225.710.064498.7433.710.0611,871.40446.751.295k0239 july 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimafertile thalli , frozen278.3816.890.045292.4021.880.0381,987.90355.520.976k02417 may 2011phaeophyceaefucales 
 sargassum 
 muticum 
 iwaya , awaji isl . ,
, hyogodirectly driedn.d.0.000.007n.d.0.000.0051,955.90188.090.176k0296 september 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly dried681.8620.680.043773.2230.830.0342,115.40278.580.703k0306 september 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.220202.8543.480.158n.d.n.d.4.519k0316 september 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimajuvenile thallus , directly dried193.7025.070.097230.3136.710.0864,214.10860.982.389k0326 september 2011phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimaold sporophyll , directly dried255.0231.380.121224.3436.260.108n.d.n.d.2.716k03514 october 2011rhodophyceaegigartinales 
 hypnea 
 asiatica 
 nagasaki , iwaki , fukushimadirectly dried114.0428.880.045161.9628.910.0392,423.001144.601.108k03614 october 2011ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried36.564.750.00643.056.670.0071,013.10194.790.177k03714 october 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried57.644.200.00567.416.090.0051,120.30158.440.137k03814 october 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly dried51.429.670.01464.2910.740.0131,380.30372.980.348k03914 october 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimamature thalli , directly dried105.994.780.004114.006.660.004995.04126.900.109k04014 october 2011rhodophyceaegigartinales 
 neodilsea 
 yendoana 
 nagasaki , iwaki , fukushimadirectly dried53.926.210.00968.468.430.0071,550.90264.190.233k04114 october 2011phaeophyceaefucales 
 sargassum 
 yamadae 
 nagasaki , iwaki , fukushimadirectly dried200.1714.010.013229.2017.540.0121,522.60401.820.380k04214 october 2011rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried59.915.330.00786.657.680.006761.02184.220.170k04314 october 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimajuvenile thalli , directly dried59.576.330.00869.158.250.0081,742.10259.790.226k04514 october 2011rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 nagasaki , iwaki , fukushimadirectly dried121.407.230.006111.819.180.0082,772.70244.740.192k0462 may 2011seawatershioyazaki , iwaki , fukushimaseawater9.542.250.0048.413.210.003n.d.n.d.0.096k0472 may 2011seawaternagasaki , iwaki , fukushimaseawater11.272.150.0039.743.430.003n.d.n.d.0.094k0489 july 2011meltwater ( dripping)nagasaki , iwaki , fukushimafrom undaria 
 pinnatifida 
 39.483.100.00342.214.050.003340.4597.780.091k0499 july 2011meltwater ( dripping)nagasaki , iwaki , fukushimafrom scytosiphon 
 lomentaria 
 344.718.630.005383.0912.010.005n.d.n.d.0.120k0509 july 2011meltwater ( dripping)shioyazaki , iwaki , fukushimafrom sargassum 
 thunbergii 
 402.978.860.005436.7212.140.004502.65116.140.108k0519 july 2011meltwater ( dripping)shioyazaki , iwaki , fukushimafrom eisenia 
 bicyclis 
 697.8711.190.006809.5016.200.005440.83113.320.106k0525 december 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimajuvenile thalli , directly dried54.387.130.00969.8412.270.0092,512.00310.200.232k0535 december 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimamature thalli , directly dried96.848.520.007106.1112.000.0102,258.50275.400.210k0545 december 2011rhodophyceaegigartinales 
 neodilsea 
 yendoana 
 nagasaki , iwaki , fukushimadirectly dried45.307.300.01040.5813.320.0121,082.40281.800.249k0565 december 2011rhodophyceaecorallinales 
 calliarthron sp.nagasaki , iwaki , fukushimadirectly dried25.565.170.00734.108.950.007n.d.n.d.0.197k0575 december 2011rhodophyceaeceramiales 
 dasya 
 sessilis 
 nagasaki , iwaki , fukushimadirectly dried219.4322.280.022234.5929.330.0214,101.20705.210.592k0585 december 2011phaeophyceaefucales 
 sargassum 
 yamadae 
 nagasaki , iwaki , fukushimadirectly dried70.497.930.00782.2211.740.0102,037.50297.700.234k0595 december 2011rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried100.859.720.01092.0711.750.009468.71261.310.248k0605 december 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried67.147.070.00778.8210.210.0081,793.10259.950.209k0615 december 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried57.128.510.01159.3413.530.0112,279.10351.170.283k0625 december 2011phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.048197.2041.700.042n.d.n.d.1.285k0635 december 2011rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 nagasaki , iwaki , fukushimadirectly dried51.7710.060.00853.6511.710.011592.87309.570.296k0647 march 2012phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimadirectly dried133.8723.470.031187.5830.540.0232,015.00856.600.831k0657 march 2012rhodophyceaebangiales 
 bangia 
 fuscopurpurea 
 nagasaki , iwaki , fukushimadirectly dried160.518.980.009226.2213.800.009936.70256.600.240k0667 march 2012ulvophyceaeulvales 

ulva 
 linza 
 nagasaki , iwaki , fukushimadirectly dried66.2510.300.01685.1614.600.0151,865.00443.300.408k0677 march 2012phaeophyceaefucales 
 sargassum 
 thunbergii 
 nagasaki , iwaki , fukushimadirectly dried106.376.400.007137.039.240.0061,654.00208.100.178k0687 march 2012phaeophyceaeectocarpales s.l . 

scytosiphon 
 lomentaria 
 nagasaki , iwaki , fukushimadirectly dried82.487.860.008115.5910.550.0092,442.00285.500.237k0697 march 2012rhodophyceaebangiales 
 pyropia 
 yezoensis 
 nagasaki , iwaki , fukushimadirectly dried24.474.780.00851.069.610.0081,195.00252.300.230k0707 march 2012phaeophyceaeectocarpales s.l . 

petalonia 
 fascia 
 nagasaki , iwaki , fukushimadirectly dried53.688.590.01384.3712.500.0143,159.00446.900.381k0717 march 2012ulvophyceaeulvales 
 monostroma 
 nitidum 
 nagasaki , iwaki , fukushimadirectly dried46.999.580.01769.7110.990.0131,614.00412.700.400k0727 march 2012phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly
dried76.485.710.006105.778.000.0051,064.00184.900.164k0737 march 2012phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly dried93.276.470.008101.188.320.0081,512.00258.000.243k0747 march 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly
dried33.694.580.00562.916.440.0051,642.00178.600.148k0757 march 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly dried26.963.950.00537.925.430.0052,999.00193.900.140k0769 april 2012phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimadirectly dried17.432.090.00321.752.400.0031,996.70101.660.082k0779 april 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried42.634.350.00660.715.650.006862.87172.480.164k0789 april 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly dried21.711.830.00228.452.480.0021,588.5089.130.073k0799 april 2012phaeophyceaefucales 
 sargassum 
 thunbergii 
 nagasaki , iwaki , fukushimadirectly dried67.572.970.00390.224.190.0031,293.001016.600.088k0809 april 2012phaeophyceaedesmarestiales 
 desmarestia 
 ligulata 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.007n.d.0.000.0071,743.30203.490.186k0819 april 2012phaeophyceaeectocarpales s.l . 

scytosiphon 
 lomentaria 
 nagasaki , iwaki , fukushimadirectly dried48.662.990.00371.764.170.0031,603.20115.510.099k0829 april 2012rhodophyceaerhodymeniales 
 lomentaria 
 hakodatensis 
 nagasaki , iwaki , fukushimadirectly dried157.823.960.003221.716.000.003897.3395.590.086k0839 april 2012rhodophyceaebangiales 
 pyropia 
 yezoensis 
 nagasaki , iwaki , fukushimadirectly dried38.643.260.00449.653.920.004967.23130.020.120k0849 april 2012rhodophyceaeceramiales 
 pterosiphonia 
 pinnulata 
 nagasaki , iwaki , fukushimadirectly dried253.767.220.007360.9510.610.0062,149.90190.200.169k0859 april 2012rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried29.802.240.00344.042.910.002982.3087.270.077k0869 april 2012phaeophyceaeectocarpales s.l . 

colpomenia 
 sinuosa 
 nagasaki , iwaki , fukushimadirectly dried222.639.120.010302.9912.390.0093,865.90282.480.243k0889 april 2012phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried10.051.890.00315.282.590.0031,988.00103.710.084k0899 april 2012phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly dried53.892.750.00377.913.900.003983.2995.030.085k0909 april 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly dried7.841.170.0028.581.530.0021,051.4076.610.007k0919 april 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimajuvenile thalli , directly dried8.302.890.00518.212.960.0041,905.00142.120.123k0929 april 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimasporophyll , directly dried16.731.980.00322.492.540.0032,767.40104.090.077k09310 april 2012phaeophyceaefucales 
 sargassum 
 yamadae 
 yoshio , katsuura , chibadirectly driedn.d.0.000.003n.d.0.000.0031,184.00102.980.091k09410 april 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 yoshio , katsuura , chibadirectly driedn.d.0.000.002n.d.0.000.0021,745.1093.140.076k09510 april 2012phaeophyceaedictyotales 
 padina 
 arborescens 
 yoshio , katsuura , chibadirectly driedn.d.0.000.006n.d.0.000.0061,579.40183.420.166k09610 april 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 yoshio , katsuura , chibadirectly driedn.d.0.000.003n.d.0.000.0031,991.1094.590.075k09710 april 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 kamogawa , chibadirectly driedn.d.0.000.003n.d.0.000.0031,652.3095.390.079k09810 april 2012phaeophyceaelaminariales 
 ecklonia 
 cava 
 kamogawa , chibadirectly driedn.d.0.000.003n.d.0.000.0032,714.60119.120.092k09910 april 2012phaeophyceaefucales 
 sargassum 
 fusiforme 
 kamogawa , chibadirectly driedn.d.0.000.002n.d.0.000.0023,236.6091.820.061k10010 april 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 kamogawa , chibadirectly driedn.d.0.000.003n.d.0.000.0031,922.90103.420.084k10123 may 2012phaeophyceaefucales 
 sargassum 
 horneri 
 terashima , iwanuma , miyagidirectly dried67.1226.240.02976.0523.030.0221,701.70723.220.711k10223 may 2012ulvophyceaeulvales 
 ulva 
 prolifera 
 terashima , iwanuma , miyagidirectly dried370.1320.460.023485.8727.160.0221,268.70663.950.655k10323 may 2012phaeophyceaefucales 
 sargassum 
 horneri 
 matsukawaura , soma , fukushimadirectly dried55.552.550.00381.233.750.0031,619.5097.970.081k10423 may 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 soma port , soma , fukushimadirectly driedn.d.0.000.012n.d.0.000.011449.78329.170.329k10523 may 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 matsukawaura , soma , fukushimadirectly dried21.803.160.00426.033.990.0041,015.10157.700.148k10623 may 2012phaeophyceaedesmarestiales 
 desmarestia 
 ligulata 
 soma port , soma , fukushimadirectly driedn.d.0.000.0056.255.010.0051,261.70154.200.141k10723 may 2012phaeophyceaefucales 
 sargassum 
 muticum 
 soma port , soma , fukushimadirectly driedn.d.0.000.00913.298.600.0082,181.51287.910.260k10823 may 2012rhodophyceaeceramiales 
 delesseria 
 serrulata 
 soma port , soma , fukushimadirectly dried14.264.030.00525.174.340.0041,723.80145.100.128k1099 april 2012ulvophyceaeulvales 
 monostroma 
 nitidum 
 nagasaki , iwaki , fukushimadirectly dried25.733.510.00727.325.020.006703.11180.500.173k11023 may 2012rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 matsukawaura , soma , fukushimadirectly dried12.963.270.006n.d.0.000.005825.74168.620.160k11123 may 2012rhodophyceaegigartinales 
 schizymenia 
 dubyi 
 matsukawaura , soma , fukushimadirectly driedn.d.0.000.004n.d.0.000.003721.71108.010.101k11223 may 2012rhodophyceaegigartinales 
 schizymenia 
 dubyi 
 matsukawaura , soma , fukushimadirectly dried19.686.730.00717.977.140.007882.64216.670.210k11323 may 2012rhodophyceaecorallinales 
 gelidium 
 elegans 
 matsukawaura , soma , fukushimadirectly dried60.914.660.00690.926.230.0061,165.70177.930.167k11523 may 2012phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 matsukawaura , soma , fukushimadirectly dried49.352.500.00354.703.310.0031,428.5099.270.008k1169 december 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 hirono , futaba , fukushimadirectly dried36.733.030.00454.464.980.0040.000.000.209k1179 december 2012rhodophyceaegigartinales 
 chondrus 
 giganteus 
 hirono , futaba , fukushimadirectly dried13.611.840.00222.892.220.0020.000.000.132k1189 december 2012phaeophyceaeectocarpales s.l . 

petalonia 
 fascia 
 hirono , futaba , fukushimadirectly dried33.092.670.00348.983.810.0040.000.000.200k1199 december 2012rhodophyceaegigartinales 
 neodilsea 
 longissima 
 hirono , futaba , fukushimadirectly dried13.662.150.002n.d.0.000.000.000.139k12210 december 2012phaeophyceaefucales 
 sargassum 
 yamadae 
 nagasaki , iwaki , fukushimadirectly dried17.051.790.00222.022.630.0031,299.0088.130.075k12310 december 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.00726.196.810.006769.50208.600.202k12410 december 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.00310.493.040.0031,996.00106.000.086k12510 december 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly dried19.623.960.00421.564.080.0052,457.00160.100.135k12810 december 2012phaeophyceaedictyotales 
 spatoglossum 
 pacificum 
 nagasaki , iwaki , fukushimadirectly dried41.532.920.00468.915.620.0042,484.00147.100.121k13010 december 2012rhodophyceaebangiales 
 pyropia 
 yezoensis 
 nagasaki , iwaki , fukushimadirectly dried12.212.800.00426.863.840.005657.28148.700.143k13110 december 2012ulvophyceaeulvales 
 ulva 
 prolifera 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.0088.047.580.008848.51236.560.229k13210 december 2012ulvophyceaecladophorales 
 chaetomorpha 
 moniligera 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.007n.d.0.003,770.30247.200.214k13310 december 2012rhodophyceaegigartinales 
 chondrus 
 ocellatus 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.0036.683.580.004677.03112.570.106k13410 december 2012rhodophyceaegigartinales 
 grateloupia 
 turuturu 
 nagasaki , iwaki , fukushimadirectly dried10.322.490.0039.464.220.0041,163.40128.020.116k13510 december 2012rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried10.642.140.0029.841.870.003604.9481.660.076k13810 december 2012rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 nagasaki , iwaki , fukushimadirectly dried64.958.000.01492.3312.250.0135,190.10427.400.376k13910 december 2012rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.0078.516.270.006688.58198.650.193k14010 december 2012rhodophyceaegigartinales 
 plocamium 
 cartilagineum 
 nagasaki , iwaki , fukushimadirectly dried22.163.920.00759.696.300.006514.62206.470.204k14110 december 2012rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 nagasaki , iwaki , fukushimadirectly dried41.824.620.00547.815.450.0063,859.40213.110.174k1429 december 2012phaeophyceaefucales 
 sargassum 
 thunbergii 
 hisanohama , iwaki , fukushimadirectly dried345.965.950.004592.6798.320.0041,401.50112.600.098k1439 december 2012rhodophyceaegigartinales 
 chondrus 
 giganteus 
 hisanohama , iwaki , fukushimadirectly dried38.552.440.00359.743.620.0031,149.1097.590.086k1449 december 2012rhodophyceaegigartinales 
 chondrus 
 giganteus 
 hisanohama , iwaki , fukushimadirectly dried18.333.510.00436.823.470.0041,257.70122.810.110k1459 december 2012phaeophyceaefucales 
 sargassum 
 muticum 
 hisanohama , iwaki , fukushimadirectly dried123.974.210.004209.896.760.0041,503.301290.700.113k1469 december 2012phaeophyceaefucales 
 sargassum 
 fusiforme 
 hisanohama , iwaki , fukushimadirectly dried21.491.860.00334.703.370.0034,206.90116.520.078k1479 december 2012phaeophyceaeectocarpales s.l . 

colpomenia 
 sinuosa 
 hisanohama , iwaki , fukushimadirectly dried219.974.880.004363.657.700.0033,025.40122.480.093k1489 december 2012phaeophyceaelaminariales 
 saccharina 
 japonica 
 hisanohama , iwaki , fukushimadirectly dried33.552.710.00360.8735.820.0033,479.60118.900.086k1499 december 2012phaeophyceaelaminariales 
 saccharina 
 japonica 
 hisanohama , iwaki , fukushimadirectly dried34.032.820.00354.743.610.0033,218.60122.460.091k1509 december 2012rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 hisanohama , iwaki , fukushimadirectly dried42.054.270.00558.606.180.0053,937.10186.640.147k15116 march 2013phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.00310.643.110.0032,250.80108.280.085k15216 march 2013phaeophyceaefucales 
 sargassum 
 yamadae 
 nagasaki , iwaki , fukushimadirectly dried9.692.300.0057.914.560.004840.94140.740.132k15316 march 2013ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried9.791.870.00319.123.240.0031,453.10117.820.103k15416 march 2013phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.007.181.840.0031,274.5091.320.079k15516 march 2013phaeophyceaefucales 
 sargassum 
 thunbergii 
 nagasaki , iwaki , fukushimadirectly dried13.922.350.00320.902.880.0031,738.20124.220.106k15616 march 2013rhodophyceaegigartinales 
 ahnfeltiopsis 
 flabelliformis 
 nagasaki , iwaki , fukushimadirectly dried16.713.770.00822.807.530.0071,349.40230.510.217k15816 march 2013rhodophyceaerhodymeniales 
 lomentaria 
 hakodatensis 
 nagasaki , iwaki , fukushimadirectly
dried34.773.080.00460.474.430.004993.42130.860.121k15916 march 2013phaeophyceaedictyotales 
 pachydictyon 
 coriaceum 
 nagasaki , iwaki , fukushimadirectly dried26.234.940.00738.115.350.0071,494.50229.910.216k16016 march 2013ulvophyceaecladophorales 
 cladophora sp.nagasaki , iwaki , fukushimadirectly dried50.885.230.00675.116.100.0061,029.20190.050.179k16116 march 2013ulvophyceaeulvales 
 ulva 
 prolifera 
 nagasaki , iwaki , fukushimadirectly dried44.664.580.00667.055.660.0061,218.00182.820.172k16216 march 2013ulvophyceaecladophorales 
 chaetomorpha 
 moniligera 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.00410.233.070.0043,397.30168.280.134k16416 march 2013rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried11.312.130.00216.852.180.002902.5385.450.076k16516 march 2013rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.003n.d.0.000.003534.66105.280.100k16616 march 2013rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.004n.d.0.000.004601.26125.920.120k16716 march 2013rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.0037.421.970.003503.2785.200.081k16916 march 2013rhodophyceaegigartinales 
 polyopes 
 affinis 
 nagasaki , iwaki , fukushimadirectly dried27.534.410.00448.014.060.004533.00133.370.128k17016 march 2013rhodophyceaegigartinales 

polyopes 
 affinis 
 nagasaki , iwaki , fukushimadirectly dried12.202.420.00413.513.600.003377.65107.940.105k17116 march 2013phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly dried13.122.580.00636.355.030.005931.90180.170.172k17316 march 2013rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 nagasaki , iwaki , fukushimadirectly dried12.142.480.00415.773.920.0044,277.60152.070.110k17416 march 2013phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly dried6.702.110.003n.d.0.000.0291,352.80100.010.086k17516 march 2013phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly dried5.292.100.00311.272.960.0031,808.80102.710.084k17616 march 2013ulvophyceaecladophorales 
 cladophora 
 albida 
 nagasaki , iwaki , fukushimadirectly dried62.135.300.006113.198.750.0061,573.60205.120.190k17716 march 2013rhodophyceaegigartinales 
 mazzaella 
 japonica 
 nagasaki , iwaki , fukushimadirectly driedn.d.0.000.0048.242.330.004771.82109.990.103k17816 march 2013ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried32.053.560.00560.485.130.0051,362.20161.870.148k17916 march 2013ulvophyceaeulvales 
 ulva 
 pertusa 
 hirono , futaba , fukushimadirectly dried26.064.600.00758.175.740.0061,016.70201.460.192k18016 march 2013rhodophyceaegigartinales 
 chondrus 
 giganteus 
 hirono , futaba , fukushimadirectly dried8.032.000.00313.813.090.003537.8890.530.086k18316 march 2013rhodophyceaebangiales 
 pyropia 
 yezoensis 
 hirono , futaba , fukushimadirectly driedn.d.0.000.00511.262.880.004759.90146.330.139k18416 march 2013ulvophyceaeulvales 
 ulva 
 prolifera 
 hirono , futaba , fukushimadirectly dried78.646.220.008139.628.750.007828.08230.720.224k18516 march 2013phaeophyceaeectocarpales s.l . 

petalonia 
 fascia 
 hirono , futaba , fukushimadirectly driedn.d.0.000.00521.693.260.0041,394.70138.480.125k18616 march 2013rhodophyceaegigartinales 
 neodilsea 
 longissima 
 hirono , futaba , fukushimadirectly dried7.082.590.00314.363.250.0031,756.70113.020.096k18716 march 2013rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 hirono , futaba , fukushimadirectly dried14.632.890.00518.173.360.005437.27148.110.145k18816 march 2013rhodophyceaegigartinales 
 gloiopeltis 
 furcata 
 hirono , futaba , fukushimadirectly dried9.042.420.00524.573.710.005542.12143.030.138k18916 march 2013phaeophyceaeralfsiales 
 analipus 
 japonicus 
 hirono , futaba , fukushimadirectly dried22.102.300.00336.363.020.0031,113.901017.400.910k19016 march 2013rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 hirono , futaba , fukushimadirectly dried29.822.840.00349.954.250.0033,051.80126.980.097k19116 march 2013phaeophyceaelaminariales 
 undaria 
 pinnatifida 
 hirono , futaba , fukushimadirectly driedn.d.0.000.00311.932.670.0021,313.6089.820.077values of detection limit in bq  kg .
error means overall error estimated by the analyzing software from systematic errors in the system together with the standard deviation of the countingtable  2list of samples examined at iwaki meisei university , and the results of cs and cs measurementssample codecollection datetaxonomylocalitynote ( sample preparation and nature of samples ) 
 cs 
 csclassorderspeciesbq kg 
 errordetect .
limitimu0012 may 2011phaeophyceaedictyotales 
 spatoglossum 
 pacificum 
 shioyazaki , iwaki , fukushimafrozen5,2001381569,430179133imu0022 may 2011phaeophyceaefucales 
 sargassum 
 yamadae 
 shioyazaki , iwaki , fukushimafrozen1,21025.225.81,98031.519.9imu0036 may 2011phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimafrozen3,9101161446,020138108imu0046 may 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimafrozen3,67096.51075,98011989.2imu0056 may 2011rhodophyceaegigartinales 
 grateloupia 
 lanceolata 
 nagasaki , iwaki , fukushimafrozen2,9201231594,390146144imu0069 july 2011phaeophyceaedictyotales 
 dictyota 
 dichotoma 
 nagasaki , iwaki , fukushimafrozen55672.11671,13088.2148imu0079 july 2011phaeophyceaeectocarpales s.l . 

scytosiphon 
 lomentaria 
 nagasaki , iwaki , fukushimafrozen59053.498.51,08068.3101imu0099 july 2011phaeophyceaedesmarestiales 
 desmarestia 
 ligulata 
 nagasaki , iwaki , fukushimafrozen1547.7011.32559.9811.5imu0109 july 2011phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimafrozen67616.021.01,24021.117.5imu0119 july 2011rhodophyceaegigartinales 
 chondrus 
 ocellatus 
 nagasaki , iwaki , fukushimafrozen28864.117433363.7164imu0129 july 2011rhodophyceaegigartinales 
 grateloupia 
 sparsa 
 nagasaki , iwaki , fukushimafrozen56950.01021,03058.881.1imu0139 july 2011rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimafrozen17413.223.333917.422.9imu0149 july 2011rhodophyceaerhodymeniales 

gastroclonium 
 pacificum 
 nagasaki , iwaki , fukushimafrozen73343.870.21,19053.164.5imu01514 october 2011phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimafrozen26762.317247066.2147imu0164 july 2012phaeophyceaeralfsiales 
 analipus 
 japonicus 
 nagasaki , iwaki , fukushimadirectly dried54.26.3013.887.87.5213.7imu0174 july 2012phaeophyceaedictyotales 
 dictyota 
 dichotoma 
 nagasaki , iwaki , fukushimadirectly dried1138.2014.81509.3114.7imu0184 july 2012phaeophyceaeectocarpales s.l . 

tinocladia 
 crassa 
 nagasaki , iwaki , fukushimadirectly dried27.38.3124.438.79.6227.0imu0214 july 2012phaeophyceaefucales 
 sargassum 
 confusum 
 nagasaki , iwaki , fukushimadirectly dried15.53.8010.630.04.209.20imu0224 july 2012phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimadirectly dried17.73.7510.337.44.7511.1imu0234 july 2012phaeophyceaefucales 
 sargassum 
 thunbergii 
 nagasaki , iwaki , fukushimadirectly dried14.32.817.5931.33.608.00imu0244 july 2012phaeophyceaelaminariales 

undaria 
 pinnatifida 
 nagasaki , iwaki , fukushimadirectly driedn.d.010.823.04.2511.2imu0254 july 2012phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly driedn.d.010.823.73.929.39imu0264 july 2012phaeophyceaelaminariales 
 eisenia 
 bicyclis 
 nagasaki , iwaki , fukushimadirectly dried14.83.238.6919.03.679.52imu0274 july 2012ulvophyceaeulvales 
 ulva 
 pertusa 
 nagasaki , iwaki , fukushimadirectly dried15.33.7610.523.74.3211.0imu0284 july 2012ulvophyceaecladophorales 
 chaetomorpha 
 moniligera 
 nagasaki , iwaki , fukushimadirectly dried17.13.9911.026.54.9312.7imu0294 july 2012ulvophyceaecodiales 
 codium 
 lucasii 
 nagasaki , iwaki , fukushimadirectly driedn.d.048.010918.34.50imu0304 july 2012ulvophyceaebryopsidales 
 bryopsis 
 plumosa 
 nagasaki , iwaki , fukushimadirectly dried72.48.3219.086.78.9619.5imu0314 july 2012rhodophyceaecorallinales 
 corallina 
 pilulifera 
 nagasaki , iwaki , fukushimadirectly dried36.23.567.2963.94.637.87imu0324 july 2012rhodophyceaecorallinales 
 calliarthron 
 yessoense 
 nagasaki , iwaki , fukushimadirectly dried14.73.539.8222.13.839.45imu0334 july 2012rhodophyceaegigartinales 
 chondracanthus 
 intermedius 
 nagasaki , iwaki , fukushimadirectly dried38.96.0414.954.26.6414.7imu0344 july 2012rhodophyceaegigartinales 
 chondrus 
 ocellatus 
 nagasaki , iwaki , fukushimadirectly dried23.24.0710.340.64.8710.4imu0354 july 2012rhodophyceaegigartinales 
 ahnfeltiopsis 
 paradoxa 
 nagasaki , iwaki , fukushimadirectly dried27.935.98.2247.04.549.15imu0364 july 2012rhodophyceaeceramiales 
 chondria 
 crassicaulis 
 nagasaki , iwaki , fukushimadirectly dried69.07.6916.41058.8115.4imu0374 july 2012rhodophyceaeceramiales 
 laurencia 
 okamurae 
 nagasaki , iwaki , fukushimadirectly dried1297.2911.32399.599.84imu03810 december 2012phaeophyceaefucales 
 sargassum 
 horneri 
 nagasaki , iwaki , fukushimadirectly dried16.34.6913.6n.d.016.0imu03910 december 2012phaeophyceaefucales 
 sargassum 
 siliquastrum 
 nagasaki , iwaki , fukushimadirectly dried60.57.0416.21188.3713.1imu04010 december 2012phaeophyceaelaminariales 
 saccharina 
 japonica 
 nagasaki , iwaki , fukushimadirectly dried26.25.2313.847.56.2213.9values of detection limit in bq  kg .
error means overall error estimated by the analyzing software from systematic errors in the system together with the standard deviation of the counting locations of the collection sites of the specimens investigated in the present study list of samples examined at kobe university , and the results of cs , cs and k measurements for dried samples when not specially noted values of detection limit in bq  kg . n.d .
error means overall error estimated by the analyzing software from systematic errors in the system together with the standard deviation of the counting list of samples examined at iwaki meisei university , and the results of cs and cs measurements values of detection limit in bq  kg . n.d . means not detectable ( blow the detection limit ) .
error means overall error estimated by the analyzing software from systematic errors in the system together with the standard deviation of the counting for the measurements at kobe university , sorted specimens were identified based on their morphology , preliminarily air - dried overnight using a fan at room temperature , and then dried in an oven at 90100  c for 8  h. the weight ratios of wet / dry samples were roughly 10 , and this value was used in the comparisons of literature data based on wet samples , and concentration factors .
dried specimens were preliminarily broken into fragments manually , and powdered using a blender ( waring j - spec 7011buj , conair corp . , stamford , ct , usa ) .
powdered specimens were packed in u-8 sample cups ( 56  mm  and 68  mm high ) and used for measurement .
( 2014 ) . in tables  1 and 2 ,  error  is the overall error estimated by the analyzing software from systematic errors in the system together with the standard deviation of the counting .
seawaters collected at the coasts of nagasaki and shioyazaki in may 2011 were filled in u-8 sample cups and used for measurements without evaporation . for the measurements at iwaki meisei university ,
sorted specimens were identified based on their morphology , washed with fresh water and pre - dried at room temperature .
dried specimens were desiccated in an oven at 60  c for 48  h , powdered using a blender , and packed in u-8 sample cups .
cs and cs were measured using a gem40p4 - 76 germanium detector ( seiko eg & g , tokyo , japan ) following the manufacturer s instructions .
the first collections ( may 2011 ) of the macroalgal specimens were kept frozen at 20  c until drying . however , this protocol resulted in some loss of radioactivity in meltwater ( dripping ) .
accordingly , in order to assess the loss of radioactivity during thawing , some specimens ( collected in july 2011 ) were either frozen before drying or directly dried , and the radioactivity was compared between these drying protocols . in addition , the radioactivity of the meltwater obtained from the thawed specimens was also measured . in some radioactivity measurements , such as for macroalgal samples , we could not obtain a sufficient amount of samples that allow us to ensure statistical reliance of the measurement .
in other cases , the total volume of collected samples was not large enough to fill the u-8 sample cup , resulting in rather low detection signals .
for all these experiments , only data are presented with notification that the precision of data was not statistically tested .
in some radioactivity measurements , such as for macroalgal samples , we could not obtain a sufficient amount of samples that allow us to ensure statistical reliance of the measurement .
in other cases , the total volume of collected samples was not large enough to fill the u-8 sample cup , resulting in rather low detection signals .
for all these experiments , only data are presented with notification that the precision of data was not statistically tested .
the cs : cs ratios of examined specimens were plotted according to time series ( fig .  2 ) .
0.6 after two years , which agreed well with the expected value by natural decay ( 0.79 after one year , and 0.64 after two years).fig . 
dotted line indicates the theoretical expected value by the spontaneous decay of cs and cs evolution of cs / cs ratio of the specimens examined .
dotted line indicates the theoretical expected value by the spontaneous decay of cs and cs results of the measurements at kobe university ( cs , cs and k ) and iwaki meisei university ( cs and cs ) are listed in table  1 and table  2 , respectively . on 2
may and 6 may 2011 ( shioyazaki and nagasaki , about 50  km from f1npp ) , specimens of most macroalgal species , i.e. , ulvapertusa , u. linza linnaeus , scytosiphonlomentaria ( lyngbye ) link , eiseniabicyclis ( kjellman ) setchell , undariapinnatifida , sargassummuticum ( yendo ) fensholt , and s. thunbergii , showed cs levels greater than 3,000  bq  kg  ( figs .  3 , 4 ) . the highest cs level was 7,371.20    173.95  bq  kg in undariapinnatifida ( fig .  3 ;
exceptionally , gloiopeltisfurcata ( postels & ruprecht ) j. agardh showed a relatively lower value of 767.37    32.90  bq  kg
4 ) measured 8.41    3.21 and 9.74    3.43  bq l , respectively . in control samples from awaji island in may 2011 ,
cs levels were below the detectable level of 0.0010.002 in undariapinnatifida , sargassummuticum , and ulvapertusa ( table  1).fig . 
3quantities of cs and cs of diverse marine macroalgae and seawater collected in may 2011 at shioyazaki , iwaki , fukushima pref .
4quantities of cs and cs of diverse marine macroalgae and seawater collected in may 2011 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae and seawater collected in may 2011 at shioyazaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae and seawater collected in may 2011 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university cs levels remarkably declined at nagasaki within the following 56  months . in july 2011 , cs ranged from ca .
.  5 ) , declined to 40200  bq  kg  in october 2011 ( fig . 
6 ) and became lower than 100  bq  kg in most samples in july 2012 ( fig . 
however , cs was still detectable in the range of 10100  bq  kg in many samples in march 2013 , 24  months after the date of highest records ( fig . 
5quantities of cs and cs of diverse marine macroalgae collected in july 2011 at nagasaki , iwaki , fukushima pref .
6quantities of cs and cs of diverse marine macroalgae collected in october 2011 at nagasaki , iwaki , fukushima pref .
7quantities of cs and cs of diverse marine macroalgae collected in july 2012 at nagasaki , iwaki , fukushima pref .
8quantities of cs and cs of diverse marine macroalgae and seawater collected in december 2012 at nagasaki , iwaki , fukushima pref .
9quantities of cs and cs of diverse marine macroalgae and seawater collected in march 2013 at nagasaki , iwaki , fukushima pref . , japan quantities of cs and cs of diverse marine macroalgae collected in july 2011 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae collected in october 2011 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae collected in july 2012 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae and seawater collected in december 2012 at nagasaki , iwaki , fukushima pref .
asterisks show data by the measurement at iwaki meisei university quantities of cs and cs of diverse marine macroalgae and seawater collected in march 2013 at nagasaki , iwaki , fukushima pref . , japan the progression of cs levels differed in different taxa . in the green alga ulvapertusa , which has very short lifetime ( ephemeral species ) ,
cs levels clearly declined during the summer of 2011 , but remained in the range of 10110  bq  kg  from winter 2011 to spring 2013 ( fig . 
k was somewhat higher in may 2011 samples , but was rather constant in the other samples ( ca .
11 ) and sargassumhorneri ( data not shown ) showed similar patterns of cs progression : they showed rapid decline in the first year , and continuously declined until march 2013 .
the k level of undariapinnatifida of the specimens from chiba pref . and hyogo pref .
10evolution of cs , cs and k quantities in the annual green alga ulva 
 pertusa at nagasaki , iwaki , fukushima pref .
11evolution of cs , cs and k quantities in the annual brown alga undaria 
 pinnatifida at nagasaki , iwaki , fukushima pref . , japan evolution of cs , cs and k quantities in the annual green alga ulva 
 pertusa at nagasaki , iwaki , fukushima pref . , japan evolution of cs , cs and k quantities in the annual brown alga undaria 
 pinnatifida at nagasaki , iwaki , fukushima pref . ,
13 ) , which are important elements of algal beds in the area , also showed similar progressions in cs levels , although the level of k ( ca .
1,5002,000  bq  kg ) was generally higher than in ulvapertusa ( fig . 
the k levels of eiseniabicyclis and sargassumyamadae of the specimens from chiba pref . were 1,6501,750 and 1,180  bq  kg , respectively , and were comparable to those in fukushima pref .
14 ) showed a clear decrease in cs levels in 2011 , but it was also still in a detectable range of ca .
k levels were in the range of 8001,000  bq  kg , which was comparable to ulva ( green alga ) and considerably lower than undaria , eisenia and sargassum ) ( brown algae).fig . 
12evolution of cs , cs and k quantities in the perennial brown alga eisenia 
 bicyclis at nagasaki , iwaki , fukushima pref . , japanfig . 
13evolution of cs , cs and k quantities in the perennial brown alga sargassum 
 yamadae at nagasaki , iwaki , fukushima pref .
14evolution of cs , cs and k quantities in the perennial red alga ahnfeltiopsis 
 paradoxa at nagasaki , iwaki , fukushima pref . , japan evolution of cs , cs and k quantities in the perennial brown alga eisenia 
 bicyclis at nagasaki , iwaki , fukushima pref . , japan evolution of cs , cs and k quantities in the perennial brown alga sargassum 
 yamadae at nagasaki , iwaki , fukushima pref . , japan evolution of cs , cs and k quantities in the perennial red alga ahnfeltiopsis 
 paradoxa at nagasaki , iwaki , fukushima pref .
cs concentrations in seawater off the eastern japan coast prior to the accident were in the same order of magnitude as other surface oceanic waters , between 1 and 3  bq  m for cs ( nakanishi et al . 2010 ) .
after the accident , measured concentrations in a 30  km perimeter around the plant exceeded 10  bq l ( or 10,000,000  bq  m ) ( bailly du bois et al .
2012 ) . the cs levels in seawater at the coast of iwaki ( shioyazaki and nagasaki )
one month after the mass discharge of high concentration contaminated water in april measured ca .
the coast around shioyazaki and nagasaki was estimated to have been exposed up to ca .
60  bq l  for about two weeks ( 15 april1 may 2011 ) according to the estimated geographical distribution of the cs in bailly du bois et al .
the influence of the radioactive liquid effluents escaping directly from the nuclear power plant was particularly significant from 26 march to 8 april 2011 in the vicinity of the plant .
the perennial brown alga eiseniabicyclis also showed a similar pattern , but in the red alga ahnfeltiopsisparadoxa the levels stayed about the same during december 2012 and march 2013 .
in contrast , the concentration of k was relatively stable throughout the period , in accordance with the assumption that it is not of anthropogenic origin because the levels were comparable to those of the specimens from chiba pref . and hyogo pref .
given that the seawater cs levels were in the range of 1060  bq  l at shioyazaki and nagasaki in april 2011 [ according to our data and those by bailly du bois et al .
( 2012 ) ] , and that seaweeds collected in may 2011 contained an average cs level of ca .
5,000  bq  kg , the seaweeds are considered to have accumulated cs in their tissues by 850 folds compared to their environment ( 80500 folds in dry samples , given the wet / dry mass ratio of 10 ) .
these cf values must be certainly underestimated because some part ( or a large part ) of the algal tissue of the specimens collected in early may 2011 ( 2 may and 6 may 2011 ) had already been grown up before the exposure to the highly radiopolluted seawater . in general , the growth rate of seaweeds differs depending on the species ; even in rather fast growing species , such as ulva spp . and
undariapinnatifida , their growth period is longer than one month ; and many species grow up in 34  months .
the above cf values of ca . 850 agree well with the known cf values of ca .
3050 in marine macroalgae ( iaea 2004 ) . considering the underestimation in our data as mentioned above
this could be caused if the local concentration of cs in polluted seawater during the seaweed growth period ( e.g. , during later april 2011 ) were higher than that on the collection dates after may 2011 .
the cs levels of the specimens directly dried after collection ( air - dried and then heated ; e.g. , k001 , k004 in table  1 ) , and those frozen before drying ( frozen , thawed , air - dried and then heated ; e.g. , k017 , k023 ) were roughly comparable .
meltwater from the frozen algal tissues ( k048k051 ) contained significantly higher concentrations of cs compared to the thawed tissue , although the levels were rather variable depending on the taxa ( ca .
the cs concentrations in meltwater was much higher than that in ambient seawater , which was below the detection level of ca .
1  bq  l in early july 2011 , and was comparable to that in fresh algal tissues , which was estimated from the present measurements of directly dried specimens .
thus , we concluded that the measurements based on dried specimens after the freezing process may underestimate the cs concentrations in fresh algal tissues .
we showed that the radioactive cs levels in marine macroalgae decline rather rapidly during the summer of 2011 .
this may be ascribed to the fact that the marine macroalgae grow and turnover rapidly during this period .
the growth periods of a number of annual taxa [ e.g. , scytosiphonlomentaria , monostromanitidum wittrock , ulva spp . , pyropia ( porphyra ) spp .
] are less than six  months irrespective of their life history patterns ( see below ; fig . 
many taxa have life histories with alternation of heteromorphic sporophytes and gametophytes [ e.g. , undariapinnatifida , scytosiphonlomentaria , monostromanitidum , pyropiayezoensis ( roth ) c. agardh ] and their macroscopic generations disappear during summer and autumn ( bold and wynne 1985 ; graham and wilcox 2000 ; hori 1993 , 1994 ) . in these cases , even though the thallus tissues had absorbed a large amount of radionuclides during development ( i.e. , late march 
april 2011 ) , they were replaced by new tissues , resulting in lower or null radionuclide concentrations before summer and autumn 2011.fig .  15schematic presentation of growth period ( phenology ) of representative marine macroalgae at iwaki and its vicinity schematic presentation of growth period ( phenology ) of representative marine macroalgae at iwaki and its vicinity some of the taxa with heteromorphic life history have perennial macroscopic thalli , and these thalli persist during summer ( e.g. , eiseniabicyclis , saccharinajaponica )
. however , they show intercalary growth with a growth zone in the transitional zone between blade and stipe , and the older parts of the thalli ( blade ) become gradually lost from the tip within several months ( bold and wynne 1985 ) . many others , e.g. , ulva spp . , dictyotadichotoma ( hudson ) j.v .
gloiopeltisfurcate , and ahnfeltiopsisparadoxa , have life histories with alternation between isomorphic macroscopic generations . however , the growth period of a generation is generally less than 6  months as mentioned above .
a few taxa , e.g. , codium spp . and sargassum spp . , lack alternation of generations in their life history . among them , sargassumhorneri is a winter - spring annual , and s. yamadae is a perennial species growing during a spring 
therefore , most of the macroalgae ( and the tissues constituting their thalli ) collected later than autumn 2011 grew by absorbing ambient nutrients including cs after a rapid decline of the radionuclide concentrations in seawater .
however , it is noteworthy that the levels of cs as well as cs have remained more or less stable since winter 2012 , and were still detectable in spring 2013 in most marine macroalgae ( ca .
8140  bq  kg  for  cs in dried specimens ) . considering the cf values of cs in marine macroalgae ,
i.e. , 850 in our study and 50 in the iaea report , the cs level in ambient seawater of marine macroalgae habitats was considered to have retained at the minimum the level of ca . 0.020.3  bq  l  ( based on cf 50 ) .
the detection limit of cs and cs in seawater differs remarkably depending on analytical facilities : ca .
0.0008  bq l , http://www1.kaiho.mlit.go.jp/kankyo/press/press20121106.pdf ; 0.025  bq l , http://www.env.go.jp/guide/budget/h25/h25-gaiyo/011.pdf ; and 1.2  bq l , http://radioactivity.nsr.go.jp/ja/contents/8000/7638/24/278_i_0531.pdf .
it has been suggested that marine macroalgal metal loads can be used as markers to track the geographical distributions of the metal concentrations in coastal seawaters , e.g. , ulva spp .
( caliceti et al . 2002 ; haritonidis and malea1999 ) , undariapinnatifida ( yamada et al .
similarly , the bio - monitoring of coastal cs using seaweeds must be very useful because marine macroalgae in general are shown to avidly accumulate cs in their tissues ( cf  =  ca .
850 ) , whereas they grow rather rapidly and , hence , turnover rapidly , so that they exert no influence of bioconcentration through the food chain .
 accumulations of radionuclides in marine macroalgae ( seaweeds ) resulting from the fukushima 1 nuclear power plant ( f1npp ) accident in march 2011 have been monitored for two years using high - purity germanium detectors . 
 algal specimens were collected seasonally by snorkeling at nagasaki , iwaki , fukushima prefecture ( pref . ) , japan , ca . 
 50  km perimeter from the f1npp . 
 additional collections were done at soma , hironocho , hisanohama and shioyazaki in fukushima pref . as well as at chiba pref . and hyogo pref . 
 as controls . 
 in may 2011 , specimens of most macroalgal species showed 137cs levels greater than 3,000  bq  kg1 at shioyazaki and nagasaki . 
 the highest 137cs level recorded 7371.20    173.95  bq  kg1  in undariapinnatifida ( harvey ) suringar on 2 may 2011 , whereas seawater collected at the same time at shioyazaki and nagasaki measured 8.41    3.21 and 9.74    3.43  bq  l1 , respectively . 
 the concentration factor of marine macroalgae was estimated to be ca . 
 850 , depending on taxa and considering a weight ratio of wet / dry samples of ca . 10 . 
 137cs level declined remarkably during the following 56  months . 
 in contrast , the 137cs level remained rather stable during the following 1216  months , and maintained the range of 10110  bq  kg1 . 
 contamination was still detectable in many samples in march 2013 , 24  months after the most significant pollution . 
Introduction
Materials and methods
Statistical problems
Results
Discussion