Appl Radrat Isot Vol 43, No 5, pp 651-657, Int .I Rodm Appl Instrum Part A Pnnted m Great Bntam All nghts reserved
1992 Copynght
0883-2889/92 S5 00 + 0 00 0 1992 Pergamon Press plc
Study on the Environmental Behavior of Chernobyl-derived Radionuclides in Kyushu Island, Japan N. MATSUOKAl*,
M. OKAMURA’,
E. HIRAI’
and Y. TAKASHIMA’
’ Kyushu Environmental Evaluation Assoclatlon, I-10-1, Matsukadal, Hlgashl-ku, Fukuoka 813, Japan and 2Department of Chemistry, Faculty of Science, Kyushu Umverslty 33, Hakozakl, Hlgashl-ku, Fukuoka 812, Japan (Recetved 15 July 1991, m revlsedform 20 August 1991)
The envlronmental behavior of Chernobyl-derived radlonuchdes m Kyushu Island was mvestlgated for one month after the accident The radloactlvlty level m alrborne dusts was two orders of magnitude lower than that observed m Western Europe The dlstributlon of 13’I m axborne dusts slufted to a larger particle Size compared with other radlonuchdes The radlonuchde concentration m seaweeds varied dependmg on the geographical situation where the samphng was done The blologlcal half-lives m red algae were calculated to be 17 4d and 32 9 d for “‘I and ““Ru , respectively The concentration factors m red algae were estimated to be 3 x 10” and 5 x 10” for ‘7’1 and ‘03Ru, respectively The cookmg effect of 13’1 m seaweeds and the committed effective dose eqmvalent through ingestion of seaweed were also evaluated
Introduction The Chernobyl accident on 26 April 1986, caused serious environmental contammatlon with radlonuchdes m the Northern Hemisphere (Juzdan et al., 1986). In Western Europe, the concentration of 13’Cs m surface air after the accident had increased to two orders of magmtude higher than that m 1963, Just after the moratormm on atmospheric nuclear exploslon tests, and the “‘Cs deposlted by the accident was estimated to be equivalent to the annual deposltlon of 13’Cs m 1963 (Thomas and Martin, 1986). In Japan, 8000 km away from Chernobyl, various radlonuchdes began to be detected m surface an samples within a week after the accident (Aoyama et al., 1986) and the monthly deposltlon of 13’Cs m May 1986 was about the same level as that m 1963 (Aoyama et al, 1991), and furthermore the total deposltlon of 13’Cs by the accident was estimated to be 10 times larger than that from the 26th Chmese nuclear explosion test m October 1980 (Hlguchl et al, 1988) Many sclentlsts have investigated the worldwide impact of environmental contammatlon by the accident, and a great deal of information has been obtained on the behavior of radlonuchdes m the environment. However, few mvestlgatlons have focused on the marme environment, especially marme products. Marme products such as seaweeds are dally foods m Japan,
*Author
for correspondence 651
so research on the contammatlon level of seaweeds 1s very important for evaluating the radiation to which the Japanese population was exposed. Kyushu Island, located in the southern part of Japan, received less radloactlve fallout from the accident than the northern part of Japan (Hlguchl et al, 1988) However, significant amounts of radlonuchdes were observed m Kyushu Island, and continuous measurements were conducted for over a month after the accident m our laboratory. In this paper, we describe the results for seaweeds, airborne dust and ram samples
Experimental To measure radlonuchdes m airborne dust, air was passed through a glass fiber filter (TOY0 GBlOOR, with warranted collection efficiency for particles with a diameter of 0.3 pm of 99 99%) at a flow-rate of 1 m3 mln-’ by a high-volume air sampler (Shlbata HVC-1000) The samphng of airborne dust was carried out on a daily basis (24 h) at a height of 1 m above ground-level from 7 May to 6 June 1986, at Fukuoka. Collection of airborne dust was carried out several times by a high-volume air sampler equipped with a five-stage Andersen cascade lmpactor to evaluate distribution of radlonuclides by particle size. The filter sample was cut mto pieces and compressed mto a disk with a diameter of 48 mm and a thickness of 5 mm, and then subJected to gamma-ray spectroscopy
N
652
MATSIJOKA et al
with a high-resolution pure germanmm detector The measurement time was from 2 to 3 h The detector was calibrated usmg an “*Eu standard solution and a potassium chloride powder, for relative and geometrical effictenctes, respectively The gamma-ray spectrum was analyzed by a computer, and the determmation limit was set at the confidence level of 95% Rainwater was collected at the ttme of each rainfall using a 0 5 m* receptor Iodine- 13 1 was enrtched by the AgI coprectpttation method usmg a 1 L portion of rainwater collected The AgI prectpttate was dried and the acttvity was measured by gamma-ray spectroscopy The restdual portton of the rainwater was reduced to a volume of 100 mL by a rotary evaporator and subjected to gamma-ray measurement Seaweeds were collected m May and June 1986 at two different sues, Shikanoshima, 10 km northwest and Kadokawa Bay, 180 km southeast of Fukuoka (Fig 1). The seaweed samples were pretreated m three different ways In the first case, the seaweed was washed only wtth fresh sea water. In the second case, after being washed with fresh sea water, tt was washed again with tap water In the third case, after bemg washed wtth fresh sea water and tap water, it was boiled m tap water for 30 mm A seaweed sample treated m each way was dried at 110°C for 6 h and ground to powder. Acttvity was measured m the same way as for airborne dust
Results and Discussion The variations of radtonuchde concentrations m airborne dust at Fukuoka after the accident are shown m Ftg 2 In European countries, the effect of
Be-7 T
I-131 __i__
Te-132 a
Ru-103 -*_
Ru-106 _. .
1
Rainfall -
Japan .&
Kyushu Island
I
A
I
0
130-E
Fig
100 km
1 Sampling locations 0, Airborne dust and ram, 0, seaweeds
the accident began to be detected at the end of April (ApSimon er al, 1987). In Astan countries and North America, however, the effect began to appear only after 3 May (Aoyama et al, 1986, Chung and Lo, 1986, Costa and Kuroda, 1989) We started to collect airborne dust on 7 May, so the early effect of the Chernobyl accident m Kyushu was not clearly specified by the atrborne dust samples. However, fatrly htgh concentrations of 13’I and ““Ru were
G-134
Cs-136
Cs-137
MO-99
G-141
Ba-140
J :rl
(A)
1
50
7
12
17
22
27
1
6
June
May
Fig 2 Variations of radionuchde concentrations Fukuoka
(A) ‘Be, “‘I, 13*Te,‘03Ru
12
7 May
17
22
27
6
1
June
in airborne dust after the Chernobyl accident at and lo6Ru, (B) ‘34Cs, lz6Cs, “‘Cs, WMo, ““Ce and “‘Ba
Chernobyl-derived Table
I
Concentratmns
of “‘I and “‘Ru Fukuoka
m ram, May
Radloactwty (Bq L-‘) Period Id May 13-14 May 19-20 Mav 27-31 Ma;
radionuchdes at Kyushu Is
1986, at
DeposItIon m ram (Bq mm2)
Ramfall (mm)
‘,‘I
‘O3RU
104 60 5 45 0 29 5
2 02 0 95 1 47 0 50
0 0 0 0
17 34 13 86
131,
111I
210 54 5 66 2 14 8
177 20 6 59 2; 4
observed m the composite ram samples collected from 1 to 6 May at Fukuoka (Table 1). In this period major precipitations occurred on 1 May (35.5 mm), 3 May (15.5 mm) and 6 May (40 0 mm), so it could be considered that the radioactive air mass reached Fukuoka by 6 May and probably on 3 May as observed m other places m Japan. The concentration level of radioactivity m the airborne dust at Fukuoka was one order of magmtude lower than that at Fukui, Japan. The contamtnation level m Japan, however, was one or two orders of magnitude lower than m West Germany, which received a great deal of fallout (UNSCEAR, 1988) Fukui is located m the central part of Japan, 570 km northeast of Fukuoka, and faces the Japan Sea The level at Fukuoka was comparable to that at Tsukuba, which is also located m the central part of Japan, but faces the Pacific Ocean (Aoyama et al., 1986) We observed 34.8 Bq kg-’ wet wt of r3’I concentration m grass sampled at Fukuoka on 9 May 1986, which was one order of magnitude higher than that m Taiwan, located 1500 km southwest of Fukuoka (Chung and Lo, 1986). According to the above facts, it seemed that the mam stream of radioactive air mass from Table 2 Part&
Chernobyl passed over the central part of Japan, and mountains above 1500 m high prevented the passage of airborne dust from the Japan Sea side to the Pacific Ocean side (Higuchi et al., 1988) The major radionuchdes m the airborne dust samples were I” I and lo3Ru until the middle of May, but ro3Ru, lo6Ru, ‘34Cs and 13’Cs became significant m early June The level of radioactivity m the airborne dust was decreased after rainfall. Here it must be noticed that gaseous 13’I was not evaluated m our measurement As the existence of gaseous 13’I was revealed by other mvestigators (Hoffmann et al, 1987, Noguchi and Murata, 1988) it would be reasonable to postulate the existence of gaseous 13’1 as well as particulate 13’1 at Fukuoka The size distributions of radionuclides m the airborne dust samples are summarized m Table 2 For all radionuchdes, most of the radioactivtty was distributed m size fracttons smaller than 2.0 pm AMAD (actrvity median aerodynamic diameter) was obtamed from cumulative particle size distributions of radionuchdes, as shown m Fig 3 (ICRP, 1966). The AMADs for radioactive Cs, radioactive Ru and r3*Te were m the range between 0 57 and 0.85 pm, while those for “’ I were between 0 94 and 1.15 pm. The AMAD for 13’I was distmctly shifted to a larger size This would be explained by the mteraction of gaseous 13’I with airborne aerosols durmg transport from Chernobyl to Japan (Jost et al., 1986, Noguchi and Murata, 1988) The size distribution of particulate 13’1was considered to be influenced to a certain extent by gaseous 13’I attached to airborne aerosols at the sampling site In Japan, MMD (mass median diameter) of airborne aerosols is usually from 1 to 2 pm.
we dlstnbutlons of radlonuchdes m surface an at Fukuoka after the Chernobyl accident m 1986 Radloactwty
Penod 30 Apnl 6 May
Part& we (urn)
‘O6RU
“4CS
“‘CS
“2Te
0 10 0 30 0 72 2 34 681 0 80
ND ND ND ND 1 93
ND 0 IO 0 17 0 56 1 33
0 0 0 I 2 0
0 0 0 2 6 0
0 16 I 26 I 94 6 55 29 9 0 57
ND ND ND ND 2 27
AMAD (pm)
4 96 6 29 7 07 II 8 35 7 0 96
0 IO 0 33 0 56 2 10 736 0 60
0 22 0 50 1 40 4 07 164 0 60
0 19 0 66 1 14 3 55 138 0 60
>70 70-33 3 3-2 0 2&l I 1 I> AMAD (pm)
2 25 2 18 1 94 2 48 829 1 15
0 24 0 62 I 41 3 17 107 0 7s
ND ND ND ND 1 II
0 13 0 19 051 I 05 2 95 0 80
017 037 0 96 2 09 6 18 0 75
ND ND 031 0 65 I 62
>70 7LL-33 3 3-2 0 2&l 1 1 I> AMAD (pm)
0 59 0 64 0 44 051 2 23 0 95
0 13 0 26 0 80 I 77 4 55 0 85
ND ND ND ND 0 61
ND 0 10 0 21 0 57 1 29
ND 011 034 107 255
ND ND ND ND ND
>70 70-33 3 3-2 0 2cLll
I I> IO
May
16 May
16 May 23 May
ND, Not determmed AMAD, actwty median aerodynamic
AR, 43,s-G
(Bq m -’ x IO’)
“’ Ru
I I>
10 May
1111 0 60 0 75 0 90 1 63 4 92 0 94
>70 70-33 3 3-2 0 2&l I AMAD (pm)
6 May
653
diameter
06 17 40 19 78 80
09 28 83 36 70 80
654
N MATSUOKA et al
6 E
80
-
ii
70
-
0L
60 50 40
--. -
5
30
-
;
20
-
G
10
-
:
131,
‘03Ftu
'3'CS ‘32Te ‘%a AMAD 7
diameter
Parttcle Fig 3 Cumulative
particle-size-dlstrlbutlons
of radlonuchdes 1986. at Fukuoka
However, each year m May, the so-called YellowSand season brings a great deal of coarse sand, carried by air mass from the Aslan Continent At this time, MMD of airborne aerosols shifts to a larger size, therefore It would be reasonable to conclude to the larger that the gaseous 13’1 was attached particles and shifted the AMAD of particulate “’ I to a larger size Actually, the MMDs of airborne aerosols ranged from 2 9 to 6 6 pm during the present observation The data on radloactlvlty m seaweeds at Shlkanoshlma and Kadokawa Bay are listed m Tables 3 and 4. Among these seaweeds, Gelldium amansri belongs to red algae, and others belong to
Table 3 Concentrahons
, pm
m axborne
dust collected
from 6 to 10 May
brown algae. If we compare the actlvltles at the two collectlon sites, the seaweeds at Kadokawa Bay showed higher concentrations of “I I than those at Shlkanoshlma. This 1s probably a result of the dlfferent geographical sltuatlons of the sampling sites: the site at Shlkanoshima faced the open sea, while that at Kadokawa Bay faced the enclosed sea with an area of about 8 8 km’ The Isuzu River, with a drainage area of 208 km?, flows mto Kadokawa Bay, and a great deal of preclpltatlon (187 mm) occurred from 3 to 6 May 1986, m this dlstnct. Thus a large amount of river water, which originated from the rainwater, flowed mto Kadokawa bay The chlormlty of the sea water m the bay was actually low, between 7 8 and
of “‘I III seaweeds at Shlkanoshmm
after the Chernobyl
accident
L” 1986 Species of sample
Date sample collected I2 I7 17 17
May May May Mav
1986 1986 1986 1986
“‘I concentratmn Treatment 114+7 625f27 283k25 112+18
I’
(Bq kg-’
Treatment IlO& 626+29 200*25 6 83 +
23
I 68
wet wt)’ Treatment
3&
89lk72 141*15 8 21* I 68 3 93 * I 34
’ Error shows a countrng error ‘Treatment I seaweeds were washed wth fresh sea water followed by drymg at 110X? for bh “Treatment 2 seaweeds were washed first wth fresh sea water and second wth tap water, followed by drymg at 110°C for 6 h 4Treatment 3 after washmg wth fresh sea water and tap water, seaweeds were bolled for 30 mm m tap water followed by drymg at 110°C for 6 h
Chernobyl-derived Table
4 Concentratmns
radionuchdes at Kyushu Is
of “‘I and
‘O”Ru m seaweeds
at Kadokawa
655 Bay after the
Chernobyl accident III 1986 Concentration Nuchde “1I
I May
-2 -2
lo3Ru ’ Error shows a countmg 2Not collected
23 May
277Oi30 339+9
‘OjRU 131I
(Bq kg-’ wet wt)’ 30 May
6 June
392& I1 341+37
11055 204k26
74lf78 198k46
112*5 531+37
151 *I 491+36
648_+56 303+41
error
of individuals of G. amanszr made it possible to evaluate half-lives of radionuclides quantitatively. As shown m Fig. 4, G amansu seemed to have only one component on elimmation of 13’I, but two components of lo3Ru. The effective half-life (Tr) of 13’I m G. amansii was estimated to be 5.5 d, and those of lo3Ru were estimated to be less than 4 8 d for the first (rapid) loss component and 17.9 d for the second (slow) loss component The biological half-life (TB) of a radionuchde can be obtained by the followmg equation:
13.2%, on 7 May. The concentrations of radionuchdes m sea water should have been Increased, because of the inflow of a considerable amount of ramwater with high concentrations of radtonuchdes. Consequently the high radionuclide concentrattons m seaweeds were attributed to those m sea water at Kadokawa Bay. The G amanslr at Kadokawa Bay on 7 May contained 132Te (156Bq kg-’ wet wt), ‘06Ru (87 8 Bq kg-’ wet wt), ‘34Cs (15 4 Bq kg-’ wet wt) and “‘Cs (26 1 Bq kg-’ wet wt) as well as 1311and lo3Ru. The changes m I31I and lo3Ru concentrations m seaweeds at Kadokawa Bay are shown m Fig 4 An evaluation of the half-lives of radionuchdes was difficult for Sargassum jiilvellum because of the bulky size of mdividuals The variation of activity among mdividuals would be directly reflected in the results shown m Fig. 4. On the other hand, the very tmy size
l/T, = l/TR + l/T, where Ta is the radiological half-hfe. The biological half-life of 13’1 m G. amansu was calculated to be 17.4d Bnks (1975) reported the behavior of 13’1 m brown algae, Focus serratus, grown m a marme environment contaminated with
L _
+
Gelldlum Sargassum
amans fulvellum
0
‘3’1
, . ‘03R”
0
13’1
,
10
30
1 June
DATE
Changes
-
I
20
May
4
lo3RU +
1
10
Fig
n
,
1966
of 13’1 and ‘03Ru concentrations In seaweeds at Kadokawa Bay after accident. TE 1s the effective half-life Error bar shows a counting error
the Chernobyl
656
N
MATSUOKAet al
tally used 13’1 and observed an effective half-life of 8 d, which is comparable to the radtological half-life of 8.04 d. That study suggested that the biological half-life of 13’1 was fairly long in brown algae The present mvestigation indicated that the btological half-life of 13’1 m red algae, G amansrz, m contrast, was relatively short The biological half-lives of lo3Ru were calculated to be less than 5 5 d for the first (rapid) loss component and 32.9 d for the second (slow) loss component Taking mto account the fact that Ru extsts m various chemical forms m the marme environment (Hethermgton and Harvey, 1978) tt would not be tmprobable that lo3Ru had two components on ehmmation from G amansrl. Nakamura et al (1976) calculated the TB of lo6Ru m green algae, Ulna pertusu, to be 24 d on the basts of an experimental transfer of radionuchdes from sea water mto seaweed In then calculation, only one component was assumed on ehmmation of lo6Ru. On brown algae, Fucus ueslculo sus, however, Martin and Heaton (1989) reported longer biological half-hves, 70 and 85 d, for lo3Ru and lo6Ru, respecttvely, through field experiments after the Chernobyl accident Hence, brown algae may have a stronger affinity for radioactive Ru than red and green algae We estimated the concentratton factors of 13’I and lo3Ru for G umun~lr at Kadokawa Bay mdirectly under several assumptions. The first assumption 1s that the concentrattons of 13’I and lo3Ru m rainwater were the same m the area around Kadokawa Bay and Fukuoka (Table 1) m early May 1986 This would be reasonable because the distance between Fukuoka and Kadokawa Bay is quite close The second assumption 1s that sea water m Kadokawa Bay was diluted directly by the rainwater supplied through the Isuzu River, and that “I I and lo3Ru were transferred mto the bay without being adsorbed by surface sot1 This would also be reasonable, because the drainage area of the river 1s small and the rainfall that occurred m the drainage area from 3 to 6 May 1986, 187 mm, was fairly large The third assumptton is that the radtonuchdes m the river water mixed rapidly with the sea water, and concentration equthbrium of a radtonuchde was rapidly established within the bay Under these assumptions, the concentrations of “‘I and lo3Ru m sea water at Kadokawa Bay on 7 May 1986, were estimated using the chlormmes observed and the mean value for general sea water About 44% of the sea water was calculated to be exchanged with the rainwater at Kadokawa Bay on 7 May, based on the dtfference between the usual chlornuty of about 190/Wand the mean value of chlornnty of 10 6%0 on that day The radionuchde concentrattons m the sea water were estimated to be 0 89 and 0 07 Bq L-’ for “‘1 and lo3Ru, respectively, at Kadokawa Bay on 7 May 1986, using the ram data m Table 1 Consequently, concentration factors for 13’I and lo’Ru on red algae, G. umansll, were estimated to be 3 x lo3 and 5 x 103, respectively. IAEA recommended the
values of 1 x IO’ and 2 x lo3 as the concentration factors for radtoactive I and Ru mto macro-algae, respectively (IAEA, 1985) Our results seemed to be slightly larger than these recommended values. However, our results are within the range of the concentration factors prevtously reported on red algae. The concentration factors summarized by Coughtrey et al ranged from 7 x 10-r to 1.8 x lo4 for 13’1 on red algae, and 1 5 x lo3 was given as the representative value (Coughtrey et al, 1983a) In the case of radioactive Ru on red algae, the concentration factors summarized by Coughtrey et al. ranged from 6 x 10’ to 4 6 x lo3 (Coughtrey et al., 1983b) G. umunszr showed relatively large concentration factors for “’ I and lo3Ru. so tt must be an effective bto-indicator for momtormg of radioacttve pollution m the marme environment In Japan, seaweeds are consumed as daily foods Among the present seaweeds, G. umuns~z (red algae), Hzzrkla fisrformls (brown algae) and Unduria pmnatrfidu (brown algae) are common foodstuffs. Before they are eaten, however, these are usually washed and boiled So it is very important to know how much of the radionuchdes 1s removed through washing and botlmg The extents to which “‘I was removed from various seaweeds through washing and bothng are shown m Table 3. In the cases of H. fuslformts, Surgussum thunbergu and U pmnutzfidu, considerable amounts of 13’I were removed through the boiling process In the case of G amunsri, however, only about 20% of “‘I was removed through the same treatment In Table 3, the column for treatment 3 probably corresponds to the strongly tissue-bound component of “‘I The difference between treatments 2 and 1 probably represents the water-extractable component, and that between treatments 3 and 2 may be the weakly tissue-bound component. On the assumption that ‘I’ I concentration m a seaweed becomes maximum Just after its inJection mto the environment and then decreases according to the effective half-life (T,), the committed effective dose equivalent (H) from 13’1 through mgestton of the seaweed 1s calculated by the followmg equation H = I R C,,E
{FZoexp(-O
693 t/T,)dt
where I is the dally mgestion (kg wet wt d-‘) of the seaweed, R IS the residual factor of 13’I after cooking, r IS the time elapsed from the mJection of I31I mto the environment, Co is the concentratton of 13’I m the seaweed at the time of t = 0 and E 1s the committed effective dose equivalent per unit intake of 13’I. The committed effective dose equivalent due to intake of “I I was calculated assuming that each person ingests 0 01 kg wet wt of G amunsri daily In this calculation 0 8 and 2770 Bq kg-’ wet wt were used as R and Co, respectively The committed effective dose equivalent per unit intake of 13’1 (E) is 14 x lo-’ mSv Bq-’ (Kawai et al, 1987) About 2 5 x 10m3mSv was obtained for G amunsu from the Kadokawa Bay area after the Chernobyl accident This level is not
Chernobyl-der’ved
so high, but if the concentration level of 13’I m the seaweed was two orders of magnitude higher than this level, the committed effective dose equivalent would become close to 1 mSv, which ICRP recommended as the annual dose-equivalent limit for the general public. The present estimation mdicates the fundamental sigmficance of seaweeds as the momtormg material of environmental radioact’vities in Japan, because Japanese people customarily consume fairly high amounts of seaweeds as daily foods compared with other nations
Conclusions Rad’onuchde concentrat’ons m airborne dust, ramwater and seaweeds were measured at Kyushu Island after the Chernobyl accident. The rad’oact’ve an mass probably arrived at Fukuoka, 8000 km away from Chernobyl, w’thm 7 days or at least 10 days after the accident At Fukuoka, “‘I, ‘03Ru, ‘06Ru, 99~~ 132~~ , 14’ Ce, I40 Ba and I40La ‘34Cs, ‘36Cs 137~ were detecied m inborne dust part’cles The rad’oactivity level m airborne dust at Fukuoka was two orders of magnitude lower than m Western Europe, and one order of magmtude lower than m the central part of Japan The d’stribution of 13’1 m a’rborne dust shifted to a larger s’ze compared w’th other radionuchdes, suggesting that gaseous 13’I was adsorbed to larger particles during the transport of a radioactive an mass. Relatively h’gh radioact’vit’es were detected m seaweeds depending on the geograph’cal s’tuat’on, and a sigmficant impact of radioactive pollut’on was observed m seaweeds. The biolog’cal half-life for 13’I m G amanszl (red algae) was estimated to be 17 4 d G. arnan~h showed two components on ehmmat’on of lo3Ru, and one component for 13’I For lo3Ru m G amanszl, the first (rapid) loss component had a b’ological half-life of less than 5 5 d and the second (slow) loss component had a half-life of 32 9 d The concentrat’on factors m G amun.r~ were estimated to be 3 x IO3 and 5 x lo3 for “‘I and ‘03Ru, respectively, md’catmg that G. urnun~h ‘s the effective b’o-md’cator for these nuchdes m the marme environment Considerable amounts of 13’I m brown algae (H fisrformls, S thunbergrz and U pmnurlfidu) were removed by cookmg, but were scarecely removed ‘n red algae, G umun~rz Assuming dally consumpt’on of log of G amunsu, the committed effective dose equivalent by the intake of 13’I through th’s seaweed was estimated to give 2 5 x 10m3mSv for people around the Kadokawa Bay area after the Chernobyl acc’dent. Acknowledgement-We of Kyushu Umverslty manuscript
651
rad’onuclides at Kyushu Is
wish to thank Dr N Momoshlma for his advice and comments on the
References Aoyama M , H’rose K , Suzuki Y., moue H and Sug’mura Y (1986) H’gh level rad’oact’ve nucl’des m Japan ‘n May Nature 321, 819 Aoyama M., Hlrose K and Suglmura Y (1991) The temporal variation of stratospheric fallout derived from the Chernobyl accident J Emu-on Rudloact 13, 103 ApSlmon H M , Wilson J J N , Gmrgms S and Stott P A (1987) Assessment of the Chernobyl release m the lmmedlate aftermath of the accident Nuclear Energy 26, 295 Barks J L (1975) Medlcal radlonuchdes m marme envlronment Nature 255, 621 Chung C and Lo J G (1986)Radioactive Iodine- 13 I over Taiwan after the Chernobyl accident J Radzonal Nucl Chem , L&f 105, 325 Costa C and Kuroda P K (1989) Flsslon products m air over the United States after the 1986 Chernobyl event. Radtochlm Acta 47, 199 Coughtrey P J , Jackson D and Thorne M C (1983a) Iodine m aquatic ecosystems In Radlonuchde Dlstrlbutlon and Transport m Terrestrral and Aquatlc Ecosystems 3, p 358 A A Balkema, Rotterdam Coughtrey P J, Jackson D and Thorne M C (1983b) Ruthenium m aquatic ecosystems In Radronuclrde Dlstrrbutron and Transport m Terrestrral and Aquatlc Ecosystems I, p 304 A A Balkema, Rotterdam Hethermgton J A and Harvey B R (1978) Uptake of radloactlvlty by marme sediments and lmphcatlon for momtormg metal pollutant Marrne Pollut Bull 9, 102. Hlguchl H , Fukatsu H , Hashlmoto T, Nonaka N, Yoshlmlzu K ,Omme M , Takano N and Abe T (1988) Radloactlvlty m surface air and preclpltatlon m Japan after the Chernobyl accident J Enolron Radzoact 6, 13 1 Hoffmann P , PIIZ N , Lleser K H , Ilmstadter V and Grlesbach M (1987) Radlonuchdes from the Chernobyl accident m the environment of Chattla, region of the FRG Radlochlm Acta 41, 173 IAEA (1985) Concentration factors for biologIca material In Sediment Kds and Concenrratron Factors for Radionuclrdes m the Marme Envrronment, p 24 Internatlonal Atomic Energy Agency, Vienna ICRP (1966) Deposition and retention models for internal doslmetry of the human respiratory tract He&h Phys 12, 173 Jost D T , Gaggeler H W , Baltensperger U , Zmder B and Hailer P (1986) Chernobyl fallout in size fractionated aerosol Nature 255, 621 Juzdan Z R , Helfer I K , Miller K. M., Rlvera W and Sanderson C G (1986) Deposltlon of radlonuchdes m the northern hemisphere followmg the Chernobyl accident CJSDOE Rep, EML-460, p 105 Kawal K , Tachlbana H , Hattorl T and Suga S (1987) Table of Committed effective dose equivalents according to the ICRP Pubhcatlon 30 JAERI-M 87-172 Martin C J and Heaton B (1989) The impact of Chernobyl on the marme environment m Northern Scotland J Envrron Radloacr 9, 209 Nakamura R ,Suzuki Y and Ueda T (1976) Dlstrlbutlon of radlonuchdes among green algae (Ulva pertusa), sea water and marme sediment Natronal Institute of Radiological Science (Japan) Rep 5 (NIRS-R-5), p 20 Noguchl H and Murata M (1988) Physlcochemlcal speclatlon of airborne 13’I m Japan from Chernobyl J Envrron. Radroact 7, 65 Thomas A J and Martin J M (1986) First assessment of Chernobyl radioactIve plume over Paris Nature 321,817 UNSCEAR (1988) Exposure from the Chernobyl accident In Sources, Effects and Risks of Ionrzrng Radratron, p 309 United Nations, New York
1992 Copynght
0883-2889/92 S5 00 + 0 00 0 1992 Pergamon Press plc
Study on the Environmental Behavior of Chernobyl-derived Radionuclides in Kyushu Island, Japan N. MATSUOKAl*,
M. OKAMURA’,
E. HIRAI’
and Y. TAKASHIMA’
’ Kyushu Environmental Evaluation Assoclatlon, I-10-1, Matsukadal, Hlgashl-ku, Fukuoka 813, Japan and 2Department of Chemistry, Faculty of Science, Kyushu Umverslty 33, Hakozakl, Hlgashl-ku, Fukuoka 812, Japan (Recetved 15 July 1991, m revlsedform 20 August 1991)
The envlronmental behavior of Chernobyl-derived radlonuchdes m Kyushu Island was mvestlgated for one month after the accident The radloactlvlty level m alrborne dusts was two orders of magnitude lower than that observed m Western Europe The dlstributlon of 13’I m axborne dusts slufted to a larger particle Size compared with other radlonuchdes The radlonuchde concentration m seaweeds varied dependmg on the geographical situation where the samphng was done The blologlcal half-lives m red algae were calculated to be 17 4d and 32 9 d for “‘I and ““Ru , respectively The concentration factors m red algae were estimated to be 3 x 10” and 5 x 10” for ‘7’1 and ‘03Ru, respectively The cookmg effect of 13’1 m seaweeds and the committed effective dose eqmvalent through ingestion of seaweed were also evaluated
Introduction The Chernobyl accident on 26 April 1986, caused serious environmental contammatlon with radlonuchdes m the Northern Hemisphere (Juzdan et al., 1986). In Western Europe, the concentration of 13’Cs m surface air after the accident had increased to two orders of magmtude higher than that m 1963, Just after the moratormm on atmospheric nuclear exploslon tests, and the “‘Cs deposlted by the accident was estimated to be equivalent to the annual deposltlon of 13’Cs m 1963 (Thomas and Martin, 1986). In Japan, 8000 km away from Chernobyl, various radlonuchdes began to be detected m surface an samples within a week after the accident (Aoyama et al., 1986) and the monthly deposltlon of 13’Cs m May 1986 was about the same level as that m 1963 (Aoyama et al, 1991), and furthermore the total deposltlon of 13’Cs by the accident was estimated to be 10 times larger than that from the 26th Chmese nuclear explosion test m October 1980 (Hlguchl et al, 1988) Many sclentlsts have investigated the worldwide impact of environmental contammatlon by the accident, and a great deal of information has been obtained on the behavior of radlonuchdes m the environment. However, few mvestlgatlons have focused on the marme environment, especially marme products. Marme products such as seaweeds are dally foods m Japan,
*Author
for correspondence 651
so research on the contammatlon level of seaweeds 1s very important for evaluating the radiation to which the Japanese population was exposed. Kyushu Island, located in the southern part of Japan, received less radloactlve fallout from the accident than the northern part of Japan (Hlguchl et al, 1988) However, significant amounts of radlonuchdes were observed m Kyushu Island, and continuous measurements were conducted for over a month after the accident m our laboratory. In this paper, we describe the results for seaweeds, airborne dust and ram samples
Experimental To measure radlonuchdes m airborne dust, air was passed through a glass fiber filter (TOY0 GBlOOR, with warranted collection efficiency for particles with a diameter of 0.3 pm of 99 99%) at a flow-rate of 1 m3 mln-’ by a high-volume air sampler (Shlbata HVC-1000) The samphng of airborne dust was carried out on a daily basis (24 h) at a height of 1 m above ground-level from 7 May to 6 June 1986, at Fukuoka. Collection of airborne dust was carried out several times by a high-volume air sampler equipped with a five-stage Andersen cascade lmpactor to evaluate distribution of radlonuclides by particle size. The filter sample was cut mto pieces and compressed mto a disk with a diameter of 48 mm and a thickness of 5 mm, and then subJected to gamma-ray spectroscopy
N
652
MATSIJOKA et al
with a high-resolution pure germanmm detector The measurement time was from 2 to 3 h The detector was calibrated usmg an “*Eu standard solution and a potassium chloride powder, for relative and geometrical effictenctes, respectively The gamma-ray spectrum was analyzed by a computer, and the determmation limit was set at the confidence level of 95% Rainwater was collected at the ttme of each rainfall using a 0 5 m* receptor Iodine- 13 1 was enrtched by the AgI coprectpttation method usmg a 1 L portion of rainwater collected The AgI prectpttate was dried and the acttvity was measured by gamma-ray spectroscopy The restdual portton of the rainwater was reduced to a volume of 100 mL by a rotary evaporator and subjected to gamma-ray measurement Seaweeds were collected m May and June 1986 at two different sues, Shikanoshima, 10 km northwest and Kadokawa Bay, 180 km southeast of Fukuoka (Fig 1). The seaweed samples were pretreated m three different ways In the first case, the seaweed was washed only wtth fresh sea water. In the second case, after being washed with fresh sea water, tt was washed again with tap water In the third case, after bemg washed wtth fresh sea water and tap water, it was boiled m tap water for 30 mm A seaweed sample treated m each way was dried at 110°C for 6 h and ground to powder. Acttvity was measured m the same way as for airborne dust
Results and Discussion The variations of radtonuchde concentrations m airborne dust at Fukuoka after the accident are shown m Ftg 2 In European countries, the effect of
Be-7 T
I-131 __i__
Te-132 a
Ru-103 -*_
Ru-106 _. .
1
Rainfall -
Japan .&
Kyushu Island
I
A
I
0
130-E
Fig
100 km
1 Sampling locations 0, Airborne dust and ram, 0, seaweeds
the accident began to be detected at the end of April (ApSimon er al, 1987). In Astan countries and North America, however, the effect began to appear only after 3 May (Aoyama et al, 1986, Chung and Lo, 1986, Costa and Kuroda, 1989) We started to collect airborne dust on 7 May, so the early effect of the Chernobyl accident m Kyushu was not clearly specified by the atrborne dust samples. However, fatrly htgh concentrations of 13’I and ““Ru were
G-134
Cs-136
Cs-137
MO-99
G-141
Ba-140
J :rl
(A)
1
50
7
12
17
22
27
1
6
June
May
Fig 2 Variations of radionuchde concentrations Fukuoka
(A) ‘Be, “‘I, 13*Te,‘03Ru
12
7 May
17
22
27
6
1
June
in airborne dust after the Chernobyl accident at and lo6Ru, (B) ‘34Cs, lz6Cs, “‘Cs, WMo, ““Ce and “‘Ba
Chernobyl-derived Table
I
Concentratmns
of “‘I and “‘Ru Fukuoka
m ram, May
Radloactwty (Bq L-‘) Period Id May 13-14 May 19-20 Mav 27-31 Ma;
radionuchdes at Kyushu Is
1986, at
DeposItIon m ram (Bq mm2)
Ramfall (mm)
‘,‘I
‘O3RU
104 60 5 45 0 29 5
2 02 0 95 1 47 0 50
0 0 0 0
17 34 13 86
131,
111I
210 54 5 66 2 14 8
177 20 6 59 2; 4
observed m the composite ram samples collected from 1 to 6 May at Fukuoka (Table 1). In this period major precipitations occurred on 1 May (35.5 mm), 3 May (15.5 mm) and 6 May (40 0 mm), so it could be considered that the radioactive air mass reached Fukuoka by 6 May and probably on 3 May as observed m other places m Japan. The concentration level of radioactivity m the airborne dust at Fukuoka was one order of magmtude lower than that at Fukui, Japan. The contamtnation level m Japan, however, was one or two orders of magnitude lower than m West Germany, which received a great deal of fallout (UNSCEAR, 1988) Fukui is located m the central part of Japan, 570 km northeast of Fukuoka, and faces the Japan Sea The level at Fukuoka was comparable to that at Tsukuba, which is also located m the central part of Japan, but faces the Pacific Ocean (Aoyama et al., 1986) We observed 34.8 Bq kg-’ wet wt of r3’I concentration m grass sampled at Fukuoka on 9 May 1986, which was one order of magnitude higher than that m Taiwan, located 1500 km southwest of Fukuoka (Chung and Lo, 1986). According to the above facts, it seemed that the mam stream of radioactive air mass from Table 2 Part&
Chernobyl passed over the central part of Japan, and mountains above 1500 m high prevented the passage of airborne dust from the Japan Sea side to the Pacific Ocean side (Higuchi et al., 1988) The major radionuchdes m the airborne dust samples were I” I and lo3Ru until the middle of May, but ro3Ru, lo6Ru, ‘34Cs and 13’Cs became significant m early June The level of radioactivity m the airborne dust was decreased after rainfall. Here it must be noticed that gaseous 13’I was not evaluated m our measurement As the existence of gaseous 13’I was revealed by other mvestigators (Hoffmann et al, 1987, Noguchi and Murata, 1988) it would be reasonable to postulate the existence of gaseous 13’1 as well as particulate 13’1 at Fukuoka The size distributions of radionuclides m the airborne dust samples are summarized m Table 2 For all radionuchdes, most of the radioactivtty was distributed m size fracttons smaller than 2.0 pm AMAD (actrvity median aerodynamic diameter) was obtamed from cumulative particle size distributions of radionuchdes, as shown m Fig 3 (ICRP, 1966). The AMADs for radioactive Cs, radioactive Ru and r3*Te were m the range between 0 57 and 0.85 pm, while those for “’ I were between 0 94 and 1.15 pm. The AMAD for 13’I was distmctly shifted to a larger size This would be explained by the mteraction of gaseous 13’I with airborne aerosols durmg transport from Chernobyl to Japan (Jost et al., 1986, Noguchi and Murata, 1988) The size distribution of particulate 13’1was considered to be influenced to a certain extent by gaseous 13’I attached to airborne aerosols at the sampling site In Japan, MMD (mass median diameter) of airborne aerosols is usually from 1 to 2 pm.
we dlstnbutlons of radlonuchdes m surface an at Fukuoka after the Chernobyl accident m 1986 Radloactwty
Penod 30 Apnl 6 May
Part& we (urn)
‘O6RU
“4CS
“‘CS
“2Te
0 10 0 30 0 72 2 34 681 0 80
ND ND ND ND 1 93
ND 0 IO 0 17 0 56 1 33
0 0 0 I 2 0
0 0 0 2 6 0
0 16 I 26 I 94 6 55 29 9 0 57
ND ND ND ND 2 27
AMAD (pm)
4 96 6 29 7 07 II 8 35 7 0 96
0 IO 0 33 0 56 2 10 736 0 60
0 22 0 50 1 40 4 07 164 0 60
0 19 0 66 1 14 3 55 138 0 60
>70 70-33 3 3-2 0 2&l I 1 I> AMAD (pm)
2 25 2 18 1 94 2 48 829 1 15
0 24 0 62 I 41 3 17 107 0 7s
ND ND ND ND 1 II
0 13 0 19 051 I 05 2 95 0 80
017 037 0 96 2 09 6 18 0 75
ND ND 031 0 65 I 62
>70 7LL-33 3 3-2 0 2&l 1 1 I> AMAD (pm)
0 59 0 64 0 44 051 2 23 0 95
0 13 0 26 0 80 I 77 4 55 0 85
ND ND ND ND 0 61
ND 0 10 0 21 0 57 1 29
ND 011 034 107 255
ND ND ND ND ND
>70 70-33 3 3-2 0 2cLll
I I> IO
May
16 May
16 May 23 May
ND, Not determmed AMAD, actwty median aerodynamic
AR, 43,s-G
(Bq m -’ x IO’)
“’ Ru
I I>
10 May
1111 0 60 0 75 0 90 1 63 4 92 0 94
>70 70-33 3 3-2 0 2&l I AMAD (pm)
6 May
653
diameter
06 17 40 19 78 80
09 28 83 36 70 80
654
N MATSUOKA et al
6 E
80
-
ii
70
-
0L
60 50 40
--. -
5
30
-
;
20
-
G
10
-
:
131,
‘03Ftu
'3'CS ‘32Te ‘%a AMAD 7
diameter
Parttcle Fig 3 Cumulative
particle-size-dlstrlbutlons
of radlonuchdes 1986. at Fukuoka
However, each year m May, the so-called YellowSand season brings a great deal of coarse sand, carried by air mass from the Aslan Continent At this time, MMD of airborne aerosols shifts to a larger size, therefore It would be reasonable to conclude to the larger that the gaseous 13’1 was attached particles and shifted the AMAD of particulate “’ I to a larger size Actually, the MMDs of airborne aerosols ranged from 2 9 to 6 6 pm during the present observation The data on radloactlvlty m seaweeds at Shlkanoshlma and Kadokawa Bay are listed m Tables 3 and 4. Among these seaweeds, Gelldium amansri belongs to red algae, and others belong to
Table 3 Concentrahons
, pm
m axborne
dust collected
from 6 to 10 May
brown algae. If we compare the actlvltles at the two collectlon sites, the seaweeds at Kadokawa Bay showed higher concentrations of “I I than those at Shlkanoshlma. This 1s probably a result of the dlfferent geographical sltuatlons of the sampling sites: the site at Shlkanoshima faced the open sea, while that at Kadokawa Bay faced the enclosed sea with an area of about 8 8 km’ The Isuzu River, with a drainage area of 208 km?, flows mto Kadokawa Bay, and a great deal of preclpltatlon (187 mm) occurred from 3 to 6 May 1986, m this dlstnct. Thus a large amount of river water, which originated from the rainwater, flowed mto Kadokawa bay The chlormlty of the sea water m the bay was actually low, between 7 8 and
of “‘I III seaweeds at Shlkanoshmm
after the Chernobyl
accident
L” 1986 Species of sample
Date sample collected I2 I7 17 17
May May May Mav
1986 1986 1986 1986
“‘I concentratmn Treatment 114+7 625f27 283k25 112+18
I’
(Bq kg-’
Treatment IlO& 626+29 200*25 6 83 +
23
I 68
wet wt)’ Treatment
3&
89lk72 141*15 8 21* I 68 3 93 * I 34
’ Error shows a countrng error ‘Treatment I seaweeds were washed wth fresh sea water followed by drymg at 110X? for bh “Treatment 2 seaweeds were washed first wth fresh sea water and second wth tap water, followed by drymg at 110°C for 6 h 4Treatment 3 after washmg wth fresh sea water and tap water, seaweeds were bolled for 30 mm m tap water followed by drymg at 110°C for 6 h
Chernobyl-derived Table
4 Concentratmns
radionuchdes at Kyushu Is
of “‘I and
‘O”Ru m seaweeds
at Kadokawa
655 Bay after the
Chernobyl accident III 1986 Concentration Nuchde “1I
I May
-2 -2
lo3Ru ’ Error shows a countmg 2Not collected
23 May
277Oi30 339+9
‘OjRU 131I
(Bq kg-’ wet wt)’ 30 May
6 June
392& I1 341+37
11055 204k26
74lf78 198k46
112*5 531+37
151 *I 491+36
648_+56 303+41
error
of individuals of G. amanszr made it possible to evaluate half-lives of radionuclides quantitatively. As shown m Fig. 4, G amansu seemed to have only one component on elimmation of 13’I, but two components of lo3Ru. The effective half-life (Tr) of 13’I m G. amansii was estimated to be 5.5 d, and those of lo3Ru were estimated to be less than 4 8 d for the first (rapid) loss component and 17.9 d for the second (slow) loss component The biological half-life (TB) of a radionuchde can be obtained by the followmg equation:
13.2%, on 7 May. The concentrations of radionuchdes m sea water should have been Increased, because of the inflow of a considerable amount of ramwater with high concentrations of radtonuchdes. Consequently the high radionuclide concentrattons m seaweeds were attributed to those m sea water at Kadokawa Bay. The G amanslr at Kadokawa Bay on 7 May contained 132Te (156Bq kg-’ wet wt), ‘06Ru (87 8 Bq kg-’ wet wt), ‘34Cs (15 4 Bq kg-’ wet wt) and “‘Cs (26 1 Bq kg-’ wet wt) as well as 1311and lo3Ru. The changes m I31I and lo3Ru concentrations m seaweeds at Kadokawa Bay are shown m Fig 4 An evaluation of the half-lives of radionuchdes was difficult for Sargassum jiilvellum because of the bulky size of mdividuals The variation of activity among mdividuals would be directly reflected in the results shown m Fig. 4. On the other hand, the very tmy size
l/T, = l/TR + l/T, where Ta is the radiological half-hfe. The biological half-life of 13’1 m G. amansu was calculated to be 17.4d Bnks (1975) reported the behavior of 13’1 m brown algae, Focus serratus, grown m a marme environment contaminated with
L _
+
Gelldlum Sargassum
amans fulvellum
0
‘3’1
, . ‘03R”
0
13’1
,
10
30
1 June
DATE
Changes
-
I
20
May
4
lo3RU +
1
10
Fig
n
,
1966
of 13’1 and ‘03Ru concentrations In seaweeds at Kadokawa Bay after accident. TE 1s the effective half-life Error bar shows a counting error
the Chernobyl
656
N
MATSUOKAet al
tally used 13’1 and observed an effective half-life of 8 d, which is comparable to the radtological half-life of 8.04 d. That study suggested that the biological half-life of 13’1 was fairly long in brown algae The present mvestigation indicated that the btological half-life of 13’1 m red algae, G amansrz, m contrast, was relatively short The biological half-lives of lo3Ru were calculated to be less than 5 5 d for the first (rapid) loss component and 32.9 d for the second (slow) loss component Taking mto account the fact that Ru extsts m various chemical forms m the marme environment (Hethermgton and Harvey, 1978) tt would not be tmprobable that lo3Ru had two components on ehmmation from G amansrl. Nakamura et al (1976) calculated the TB of lo6Ru m green algae, Ulna pertusu, to be 24 d on the basts of an experimental transfer of radionuchdes from sea water mto seaweed In then calculation, only one component was assumed on ehmmation of lo6Ru. On brown algae, Fucus ueslculo sus, however, Martin and Heaton (1989) reported longer biological half-hves, 70 and 85 d, for lo3Ru and lo6Ru, respecttvely, through field experiments after the Chernobyl accident Hence, brown algae may have a stronger affinity for radioactive Ru than red and green algae We estimated the concentratton factors of 13’I and lo3Ru for G umun~lr at Kadokawa Bay mdirectly under several assumptions. The first assumption 1s that the concentrattons of 13’I and lo3Ru m rainwater were the same m the area around Kadokawa Bay and Fukuoka (Table 1) m early May 1986 This would be reasonable because the distance between Fukuoka and Kadokawa Bay is quite close The second assumption 1s that sea water m Kadokawa Bay was diluted directly by the rainwater supplied through the Isuzu River, and that “I I and lo3Ru were transferred mto the bay without being adsorbed by surface sot1 This would also be reasonable, because the drainage area of the river 1s small and the rainfall that occurred m the drainage area from 3 to 6 May 1986, 187 mm, was fairly large The third assumptton is that the radtonuchdes m the river water mixed rapidly with the sea water, and concentration equthbrium of a radtonuchde was rapidly established within the bay Under these assumptions, the concentrations of “‘I and lo3Ru m sea water at Kadokawa Bay on 7 May 1986, were estimated using the chlormmes observed and the mean value for general sea water About 44% of the sea water was calculated to be exchanged with the rainwater at Kadokawa Bay on 7 May, based on the dtfference between the usual chlornuty of about 190/Wand the mean value of chlornnty of 10 6%0 on that day The radionuchde concentrattons m the sea water were estimated to be 0 89 and 0 07 Bq L-’ for “‘1 and lo3Ru, respectively, at Kadokawa Bay on 7 May 1986, using the ram data m Table 1 Consequently, concentration factors for 13’I and lo’Ru on red algae, G. umansll, were estimated to be 3 x lo3 and 5 x 103, respectively. IAEA recommended the
values of 1 x IO’ and 2 x lo3 as the concentration factors for radtoactive I and Ru mto macro-algae, respectively (IAEA, 1985) Our results seemed to be slightly larger than these recommended values. However, our results are within the range of the concentration factors prevtously reported on red algae. The concentration factors summarized by Coughtrey et al ranged from 7 x 10-r to 1.8 x lo4 for 13’1 on red algae, and 1 5 x lo3 was given as the representative value (Coughtrey et al, 1983a) In the case of radioactive Ru on red algae, the concentration factors summarized by Coughtrey et al. ranged from 6 x 10’ to 4 6 x lo3 (Coughtrey et al., 1983b) G. umunszr showed relatively large concentration factors for “’ I and lo3Ru. so tt must be an effective bto-indicator for momtormg of radioacttve pollution m the marme environment In Japan, seaweeds are consumed as daily foods Among the present seaweeds, G. umuns~z (red algae), Hzzrkla fisrformls (brown algae) and Unduria pmnatrfidu (brown algae) are common foodstuffs. Before they are eaten, however, these are usually washed and boiled So it is very important to know how much of the radionuchdes 1s removed through washing and botlmg The extents to which “‘I was removed from various seaweeds through washing and bothng are shown m Table 3. In the cases of H. fuslformts, Surgussum thunbergu and U pmnutzfidu, considerable amounts of 13’I were removed through the boiling process In the case of G amunsri, however, only about 20% of “‘I was removed through the same treatment In Table 3, the column for treatment 3 probably corresponds to the strongly tissue-bound component of “‘I The difference between treatments 2 and 1 probably represents the water-extractable component, and that between treatments 3 and 2 may be the weakly tissue-bound component. On the assumption that ‘I’ I concentration m a seaweed becomes maximum Just after its inJection mto the environment and then decreases according to the effective half-life (T,), the committed effective dose equivalent (H) from 13’1 through mgestton of the seaweed 1s calculated by the followmg equation H = I R C,,E
{FZoexp(-O
693 t/T,)dt
where I is the dally mgestion (kg wet wt d-‘) of the seaweed, R IS the residual factor of 13’I after cooking, r IS the time elapsed from the mJection of I31I mto the environment, Co is the concentratton of 13’I m the seaweed at the time of t = 0 and E 1s the committed effective dose equivalent per unit intake of 13’I. The committed effective dose equivalent due to intake of “I I was calculated assuming that each person ingests 0 01 kg wet wt of G amunsri daily In this calculation 0 8 and 2770 Bq kg-’ wet wt were used as R and Co, respectively The committed effective dose equivalent per unit intake of 13’1 (E) is 14 x lo-’ mSv Bq-’ (Kawai et al, 1987) About 2 5 x 10m3mSv was obtained for G amunsu from the Kadokawa Bay area after the Chernobyl accident This level is not
Chernobyl-der’ved
so high, but if the concentration level of 13’I m the seaweed was two orders of magnitude higher than this level, the committed effective dose equivalent would become close to 1 mSv, which ICRP recommended as the annual dose-equivalent limit for the general public. The present estimation mdicates the fundamental sigmficance of seaweeds as the momtormg material of environmental radioact’vities in Japan, because Japanese people customarily consume fairly high amounts of seaweeds as daily foods compared with other nations
Conclusions Rad’onuchde concentrat’ons m airborne dust, ramwater and seaweeds were measured at Kyushu Island after the Chernobyl accident. The rad’oact’ve an mass probably arrived at Fukuoka, 8000 km away from Chernobyl, w’thm 7 days or at least 10 days after the accident At Fukuoka, “‘I, ‘03Ru, ‘06Ru, 99~~ 132~~ , 14’ Ce, I40 Ba and I40La ‘34Cs, ‘36Cs 137~ were detecied m inborne dust part’cles The rad’oactivity level m airborne dust at Fukuoka was two orders of magnitude lower than m Western Europe, and one order of magmtude lower than m the central part of Japan The d’stribution of 13’1 m a’rborne dust shifted to a larger s’ze compared w’th other radionuchdes, suggesting that gaseous 13’I was adsorbed to larger particles during the transport of a radioactive an mass. Relatively h’gh radioact’vit’es were detected m seaweeds depending on the geograph’cal s’tuat’on, and a sigmficant impact of radioactive pollut’on was observed m seaweeds. The biolog’cal half-life for 13’I m G amanszl (red algae) was estimated to be 17 4 d G. arnan~h showed two components on ehmmat’on of lo3Ru, and one component for 13’I For lo3Ru m G amanszl, the first (rapid) loss component had a b’ological half-life of less than 5 5 d and the second (slow) loss component had a half-life of 32 9 d The concentrat’on factors m G amun.r~ were estimated to be 3 x IO3 and 5 x lo3 for “‘I and ‘03Ru, respectively, md’catmg that G. urnun~h ‘s the effective b’o-md’cator for these nuchdes m the marme environment Considerable amounts of 13’I m brown algae (H fisrformls, S thunbergrz and U pmnurlfidu) were removed by cookmg, but were scarecely removed ‘n red algae, G umun~rz Assuming dally consumpt’on of log of G amunsu, the committed effective dose equivalent by the intake of 13’I through th’s seaweed was estimated to give 2 5 x 10m3mSv for people around the Kadokawa Bay area after the Chernobyl acc’dent. Acknowledgement-We of Kyushu Umverslty manuscript
651
rad’onuclides at Kyushu Is
wish to thank Dr N Momoshlma for his advice and comments on the
References Aoyama M , H’rose K , Suzuki Y., moue H and Sug’mura Y (1986) H’gh level rad’oact’ve nucl’des m Japan ‘n May Nature 321, 819 Aoyama M., Hlrose K and Suglmura Y (1991) The temporal variation of stratospheric fallout derived from the Chernobyl accident J Emu-on Rudloact 13, 103 ApSlmon H M , Wilson J J N , Gmrgms S and Stott P A (1987) Assessment of the Chernobyl release m the lmmedlate aftermath of the accident Nuclear Energy 26, 295 Barks J L (1975) Medlcal radlonuchdes m marme envlronment Nature 255, 621 Chung C and Lo J G (1986)Radioactive Iodine- 13 I over Taiwan after the Chernobyl accident J Radzonal Nucl Chem , L&f 105, 325 Costa C and Kuroda P K (1989) Flsslon products m air over the United States after the 1986 Chernobyl event. Radtochlm Acta 47, 199 Coughtrey P J , Jackson D and Thorne M C (1983a) Iodine m aquatic ecosystems In Radlonuchde Dlstrlbutlon and Transport m Terrestrral and Aquatlc Ecosystems 3, p 358 A A Balkema, Rotterdam Coughtrey P J, Jackson D and Thorne M C (1983b) Ruthenium m aquatic ecosystems In Radronuclrde Dlstrrbutron and Transport m Terrestrral and Aquatlc Ecosystems I, p 304 A A Balkema, Rotterdam Hethermgton J A and Harvey B R (1978) Uptake of radloactlvlty by marme sediments and lmphcatlon for momtormg metal pollutant Marrne Pollut Bull 9, 102. Hlguchl H , Fukatsu H , Hashlmoto T, Nonaka N, Yoshlmlzu K ,Omme M , Takano N and Abe T (1988) Radloactlvlty m surface air and preclpltatlon m Japan after the Chernobyl accident J Enolron Radzoact 6, 13 1 Hoffmann P , PIIZ N , Lleser K H , Ilmstadter V and Grlesbach M (1987) Radlonuchdes from the Chernobyl accident m the environment of Chattla, region of the FRG Radlochlm Acta 41, 173 IAEA (1985) Concentration factors for biologIca material In Sediment Kds and Concenrratron Factors for Radionuclrdes m the Marme Envrronment, p 24 Internatlonal Atomic Energy Agency, Vienna ICRP (1966) Deposition and retention models for internal doslmetry of the human respiratory tract He&h Phys 12, 173 Jost D T , Gaggeler H W , Baltensperger U , Zmder B and Hailer P (1986) Chernobyl fallout in size fractionated aerosol Nature 255, 621 Juzdan Z R , Helfer I K , Miller K. M., Rlvera W and Sanderson C G (1986) Deposltlon of radlonuchdes m the northern hemisphere followmg the Chernobyl accident CJSDOE Rep, EML-460, p 105 Kawal K , Tachlbana H , Hattorl T and Suga S (1987) Table of Committed effective dose equivalents according to the ICRP Pubhcatlon 30 JAERI-M 87-172 Martin C J and Heaton B (1989) The impact of Chernobyl on the marme environment m Northern Scotland J Envrron Radloacr 9, 209 Nakamura R ,Suzuki Y and Ueda T (1976) Dlstrlbutlon of radlonuchdes among green algae (Ulva pertusa), sea water and marme sediment Natronal Institute of Radiological Science (Japan) Rep 5 (NIRS-R-5), p 20 Noguchl H and Murata M (1988) Physlcochemlcal speclatlon of airborne 13’I m Japan from Chernobyl J Envrron. Radroact 7, 65 Thomas A J and Martin J M (1986) First assessment of Chernobyl radioactIve plume over Paris Nature 321,817 UNSCEAR (1988) Exposure from the Chernobyl accident In Sources, Effects and Risks of Ionrzrng Radratron, p 309 United Nations, New York
