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Meteorological analysis of tritium concentrations in rain water collected in Fukuoka, Japan, from 1987–1991
the Science of the Total Environment i n ~ t ~ E n ~ n m e n t *rid n~ m l t ~ i p
ELSEVIER
w i ~ rain
The Science of the Total Environment 145 (1994) 197-205
Meteorological analysis of tritium concentrations in rain water collected in Fukuoka, Japan, from 1987-1991 N o b u a k i M a t s u o k a *a, Ei~i H i r a i a, H i s a y a T a g o m o r i a, Noriyuki Momoshima , Yoshimasa Takashima b
agyushu Environmental Evaluation Association, 1-10-1, Matsukadai, Higashi-ku, Fukuoka 813, Japan hDepartment of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki. Higashi-ku, Fukuoka 812, Japan
(Received 30 July 1992; accepted 19 January 1993)
Abstract Tritium concentrations in rain water collected in Fukuoka, Japan, from April 1987 to July 1991, were measured. The tritium concentration of each 'rain' showed a large variation from 0.06-3.39 Bq 1-~, with an average value of 0.62 Bq l-k Weather conditions significantly affected the tritium concentration in rain. Higher tritium concentrations were observed when air-mass moved dominantly from the Asian Continent to Fukuoka. The annual average concentrations were no longer decreased after 1987 in Fukuoka. Key words." Tritium; Rain water; Japan
1. Introduction The tritium concentration of 0.78 Bq 1-1 was observed in Kobe in 1953 as the only datum for Japanese rain water before the initiation of nuclear tests [1]. However, the concentration of tritium in rain increased abruptly during 1961 and 1963 due to atmospheric nuclear tests [2]. In that period, the tritium concentrations in rain water were reported to be from 12-180 Bq 1-l in Japan [3]. After 1963, the concentration in rain decreased gradually with the decrease of the number of nuclear tests. The * Corresponding author.
tritium in rain water in the 1960s and 1970s thus mainly originated from nuclear tests. The concentration was significantly affected by the frequency and size of the nuclear tests, and the variations of tritium concentrations were fairly large among rainfalls. On the other hand, after the 26th Chinese nuclear test, conducted on October 16, 1980, there was no more large scale atmospheric nuclear tests, hence the concentration of tritium in rain water has declined in the 1980s. In our previous papers [4,5], the half-life of decrease, of yearly averaged tritium concentrations in rain was estimated to be 8.4 years from 1981-1988 in Fukuoka, but there has been no distinct decrease since 1988. In those
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0048-9697(93)03645-1(
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N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
studies, the significance of meteorological factors was pointed out with respect to variation of tritium concentrations in rain after the 1980s. To evaluate a meteorological effect more clearly, the measurement of tritium concentration is necessary for each rain using extremely accurate techniques, such as low level counting combined with electrolytic enrichment of tritium in water. In the present investigation, we attempted to elucidate the effect of meteorological conditions on the tritium concentrations in rain.
2. Materials and methods Each rain water sample was collected using a receptor, with a diameter of 80 cm, at ground level in Fukuoka, Japan, from April 1987 to July 1991. The rain water collected was distilled using a distillation apparatus specially designed for tritium measurement. After distillation, the rain water was electrolytically enriched by a previously reported method [6,7]. The tritium retention and the volume reduction factors in enrichment were
Table 1 Tritium concentrations in individual rainfalls from April to December in 1987, in Fukuoka Date April
May
June
July
2 6 9 11 21 26 1 3 12 14 17 22 23 27 2 3 8 15 19 25 3 4 6 7 14 16 17 19 24 25 27
aRefer to text.
Weather type a
Pecipitation (mm)
Tritium (Bq l -I)
Date
S N F C N S S F N S S F F S N N F S F S F F N F T T N F N F P
9.0 5.0 17.0 5.0 17.5 10.5 8.0 14.0 5.5 40.0 16.0 40.0 3.0 7.0 51.5 0.5 114.5 44.0 58.0 10.0 37.0 66.5 8.5 24.5 47.0 23.0 7.5 196.5 3.5 20.0 8.0
1.13 0.78 0.84 0.97 0.58 1.27 1.03 0.72 0.63 1.17 1.21 0.75 0.71 0.84 0.63 0.37 0.59 0.73 0.58 1.08 0.80 0.60 0.71 0.72 0.49 0.26 0.85 0.57 0.36 0.57 0.53
Aug.
Sep.
Oct.
Nov. Dec.
2 9 10 13 20 22 24 25 26 31 7 13 24 I1 16 24 26 30 3 30 3 6 9 15
Weather type a
Precipitation (mm)
Tritium (Bq I -I)
F F F P P N F N N T N S S S T S S N N C C S S N
68.0 26.5 32.0 37.0 25.0 41.0 30.0 47.5 5.0 63.0 14.0 75.5 10.0 5.5 23.0 24.0 10.0 18.5 27.0 36.5 2.0 26.0 4.5 4.5
0.57 1.02 0.57 0.49 0.50 0.14 1.00 0.49 0.61 0.25 1.01 0.52 0.94 0.78 0.49 0.67 0.61 0.46 0.63 0.51 0.93 0.85 0.69 0.88
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
199
- 0.8 and 7.6, respectively. After enrichment, the water was distilled again. The distilled water was mixed with a liquid scintillation cocktail (NEN Research Products 'AQUASOL-2' or Packard 'PICO-FLUOR LLT') in a 100-ml teflon vial. The water/cocktail volume ratios were 4:6 and 5:5 in AQUASOL-2 and PICO-FLUOR LLT, respectively. The tritium concentration was measured by a low background liquid scintillation counter (ALOKA LB-1) for 1000 min after mixing the distilled water and the liquid scintillation cocktail. The counting efficiencies for tritium were 15-18
and 12-15%, in AQUASOL-2 and PICO-FLUOR LLT, respectively. The detection limit at a confidence level of 95°,/0 was 0.05-0.06 Bq 1-t for both cocktails. 3. Results and discussion
Tritium concentrations in individual rainfall samples and precipitation data are summarized in Tables 1-5. The annual average tritium concentrations, calculated from the measurements given in Tables 1-5, are shown in Fig. 1.
Table 2 Tritium concentrations in individual rainfalls in 1988, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
4 8 15 21 22 4 23 26 29 5 11 13 17 18 22 26 29 2 7 12 18 21 23 27 29 4 7 11 15 20 23
Weather type a
Precipitation (mm)
Tritium (Bq l -l)
Date
C F F F S C F S S C N P S S S S S S S N S S C S S F N S S S S
6.0 7.5 13.5 13.0 1.0 1.5 12.5 11.5 8.5 3.0 25.5 18.0 11.0 4.0 31.0 29.5 11.0 6.5 6.0 34.5 18.5 0.5 3.0 7.5 36.0 52.0 51.0 9.0 10.5 23.0 9.5
0.84 0.79 0.57 0.50 1.10 1.44 0.74 1.05 1.20 2.46 0.80 0.66 0.91 0.77 0.95 1.38 1.59 2.39 1.85 0.88 1.23 1.15 2.03 3.39 1.29 1.71 0.67 0.51 0.95 0.97 0.66
June
aRefer to text. bNot characterized.
July
Aug.
Sep.
Oct.
Nov. Dec.
3 10 12 24 29 11 16 17 21 26 28 4 12 16 17 18 22 24 27 5 12 19 26 28 6 24 26 19 29 5 17 24
Weather type a
Precipitation (mm)
Tritium (Bq 1-1)
T S S N F N F F F F F N.C. b T T T T N S N F F F T N.C. b T F N.C. b C N C C N
171.0 12.5 85.0 60.0 3.5 1.5 40.0 14.0 13.0 19.0 31.0 0.5 12.0 27.0 8.0 5.0 32.5 7.0 3.5 74.0 15.5 5.0 57.0 1.0 32.0 2.0 0.5 19.5 44.0 8.0 8.0 1.0
0.43 1.27 1.15 0.77 0.67 0.54 0.78 1.59 1.39 1.57 1.35 1.37 0.60 0.54 0.57 0.28 0.45 1.00 0.61 0.59 0.67 0.60 0.37 0.45 0.44 0.66 0.71 0.61 0.58 1.25 0.64 0.70
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N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
Table 3 Tritium concentrations in individual rainfalls in 1989, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
June
1 8 10 11 19 21 23 9 18 21 25 6 8 13 28 31 8 14 22 30 5 10 16 19 21 25 5 8 13 15 16 24 28 29
Weather type a
Precipitation (mm)
Tritium (Bq l -l)
Date
N N N.C. b N N F F S F C F C C F C S S S S S S F S S S S N N S F S T N S
15.5 7.0 0.5 20.0 18.5 16.0 34.0 43.0 65.5 8.0 31.0 55.5 13.0 28.0 9.5 11.0 3.0 5.0 0.5 10.0 17.5 3.0 29.0 30.5 6.0 18.5 3.5 28.0 7.5 25.0 51.0 24.0 1.5 4.0
0.59 0.50 0.41 0.54 0.28 0.46 0.66 0.58 0.54 0.97 0.59 0.91 1.22 0.81 1.13 1.41 1.39 0.81 0.98 0.94 0.97 1.11 0.81 0.36 1.01 2.09 0.53 0.37 0.74 0.37 0.84 0.21 0.59 1.16
July
Aug.
Sep.
Oct.
Nov.
Dec.
3 9 15 16 28 3 14 18 27 1 7 14 16 18 19 26 1 8 11 16 19 31 6 9 13 7 12 14 15 26 30
Weather type a
Precipitation (mm)
Tritium (Bq l -I)
S N P N.C. b T T F P T F F N F N T N.C. b N.C. b C S N N.C. b N N N N.C. b N C N N N S
18.5 39.0 5.5 0.5 22.0 5.5 10.0 9.0 4.0 138.5 21.0 100.0 47.5 50.0 98.5 6.5 0.5 1.5 10.5 6.0 1.5 8.5 16.0 24.0 9.5 6.0 0.5 3.0 7.0 31.0 10.5
1.06 0.50 0.40 1.03 0.27 0.48 0.93 0.59 0.33 0.60 1.05 0.39 0.40 0.38 0.39 0.64 0.38 0.63 0.42 0.62 0.48 0.70 0.21 0.49 0.40 0.91 0.95 0.67 0.72 0.75 0.60
aRefer to text. bNot characterized.
Previous measurements showed that the concentration level of tritium in rain water in Fukuoka had decreased with an apparent half-life of 8.4 years from 1981-1987, and that the level was relatively constant since 1988 [4,5]. This tendency was also confirmed by the present investigation, except for the slightly higher value observed in 1989. The overall average concentration was 0.62 Bq 1-l. In spite of the relatively constant average tritium concentrations for these 5 years, a signifi-
cant variation was observed for tritium concentrations in individual samples. During the present observation, the highest concentration of tritium was 3.39 Bq 1-l on April 27, 1988, and the lowest was 0.06 Bq 1-1 on July 9, 1990. A distinct correlation was not found between the quantity of precipitation on each occasion and the tritium concentration in the rain. Low tritium concentrations in rain are expected in Fukuoka, because only a small amount of tri-
Table 4 Tritium concentrations in individual rainfalls in 1990, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
9 16 19 24 29 1 11 14 15 19 24 26 1 4 8 14 24 29 4 7 13 17 22 7 14 18
Weather type a
Precipitation (nun)
Tritium (Bq l -I)
Date
S S S N.C. b N S N S S N F S S S C F N F S N N S S S F N
23.0 22.5 14.0 7.0 14.5 4.5 9.5 7.0 1.0 39.5 23.0 4.5 20.0 4.0 2.5 1.5 28.5 37.5 0.5 15.0 11.0 4.0 52.5 34.0 1.5 44.5
0.77 0.45 0.54 0.62 0.24 0.65 0.29 0.81 0.66 0.28 0.41 0.64 0.88 0.89 1.21 0.81 0.48 0.68 0.85 0.83 0.71 1.76 0.62 0.98 0.73 0.35
June
July
Sep.
Oct.
Nov.
Dec.
1 4 12 15 3 13 17 3 16 19 26 8 15 27 31 5 9 20 25 1 8 11 14 21 29
Weather type a
Precipitation (ram)
Tritium (Bq l -l)
N S P N N N N N F T S T F S S T N N N T C N.C. b N.C. b C C
45.0 13.5 1.5 120.0 173.5 20.0 6.5 14.5 41.5 69.5 8.0 55.5 12.5 5.0 0.5 5.5 37.0 15.5 3,0 6,0 14,5 3,5 2.0 5.5 1,0
0.38 0.65 0.22 0.14 0.06 0.28 0.48 0.16 0.57 0.54 0.66 0.69 0.64 1.02 0.73 0.37 0.33 0.35 0.57 0.29 1.23 0.56 0.68 0.89 0.64
Weather type a
Precipitation (mm)
Tritium (Bq l -I)
C S S S N F N F S N N N
10.0 28.0 15.5 63.0 47.0 18.5 231.0 20.0 24.5 79.5 115.0 86.5
0.81 1.05 1.11 1.22 0.37 0.49 0.33 0.32 1.03 0.19 0.38 0.35
aRefer to text. bNot characterized. Table 5 Tritium concentrations in individual rainfalls from January to July in 1991, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
1 7 17 25 28 10 15 25 1 4 11 16 22 30 7 10 15 19
Weather type a
Precipitation (mm)
Tritium (Bq 1-1)
Date
S N N S C F F N S S F S S S S F N.C. b F
28.0 2.0 2.5 9.0 4.5 33.5 33.5 14.0 28.0 15.0 52.0 8.0 51.0 7.5 48.0 22.5 1.5 34.0
0.58 0.45 0.49 0.25 1.09 0.37 0.33 0.83 1.05 0.53 0.47 1.17 0.68 0.78 0.70 0.33 0.63 0.58
May
aRefer to text. bNot characterized.
June
July
7 13 15 21 26 3 10 15 25 1 4 15
202
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
tritium concentrations. These concentrations were 3 - 5 times higher than the average concentration. Generally, high concentrations were observed in winter and spring, with relatively low concentrations in summer. This suggests that some meteorological factors affect the tritium concentrations in rain. To analyze the meteorological effects on tritium concentrations, we classified the meteorological conditions o f individual rainfalls into six weather types;
1.5 S ._1 ~" v t.0
1.0
"6
0.5
cO
(o 0.0
1A7
19188
19189
1990
1
1
Year Fig. 1. Annual averages of tritium concentrations in rain in Fukuoka. Weighted (13)and unweighted (O) by the quantity of precipitation in each rain event. Error bars show a S.D.
(a)
tium is released to the sea from Japanese nuclear facilities and it is diluted immediately by the oceanic waters with low tritium concentrations [8,91. However, we sometimes observed fairly high
(c)
a cyclone or a front exists in the north F u k u o k a (N type), a cyclone or a front exists in the south F u k u o k a (S type), a cyclone or a front exists near F u k u o k a type), an anticyclone from the Asian Continent the F u k u o k a area (C type),
(b)
(d)
of of (F in
%/
@
N-type
~
J
I
2000km
C-type
It/r.7 2000kin F-type
S-type
~
5
\
I
2000 km
P-type
I --
2000km
J
T-type
Fig. 2. Typical weather maps of individual meteorological conditions. Arrows indicate the main wind direction and solid circles indicate the location of Fuknoka. The letters L, H and T indicate a cyclone, an anticyclone and a typhoon, respectively, and numbers indicate center atmospheric pressures (mbar) (see text).
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
203
100 r
shown in Fig. 2. The weather types of individual rainfalls are also shown in Tables 1-5.
Av.=0.62 Bq L 1 n=264
O
e-
-1 O"
The frequency distributions of tritium concentrations are shown in Fig. 3 for the whole data set and in Fig. 4 for the individual weather types. The weather types of S and C shifted the frequency distributions to a higher side of the concentration than that from the whole data set. The weather types of N, P and T shifted to a lower side of the concentration. The weather type F had concentrations similar to that of the whole data set. In the weather types of S and C of higher tritium concentrations, the air mass moves dominantly from the Asian Continent to the direction of Fukuoka over the Japan Sea. In these weather types, the rain in Fukuoka would contain a fairly large amount of water vapor from the Asian Continent. In the weather types of N and P of lower tritium concentrations, the dominant direction of
50
ii
1.0
2.0
3.0
Bq L-1
Fig. 3. Frequency distribution of tritium concentrations in rain for the whole data set. The average concentration is weighted by the quantity of precipitation in each rain event.
(e) (f)
an anticyclone from the Pacific Ocean in the Fukuoka area (P type), and a typhoon near Fukuoka (T type). The typical weather maps of these conditions are
3ot, 201" "1 | IIII
III (ET
0
301
N-Type Av.=0.43 Bq L n=66
1.0
2.--'0
3.'~
1
S-Type I Av.=0.92Bq L-1 [ n=82
oLK
20 t
II
0
1.0
3.0
30
30
P-Type
C-Type
LL
Av.=0.91 Bq L -1 n=22
Av.=0.52 Bq L -1 n=7 10
10
•L•• 1.0
2.0
.1111 3.0
20[ [
F-Type
1.0
2.0
3.0
30[ 0
lo ~ l l l 0
I
I AV.=0.67 Bq L-1 I I n=54 I
1.0
2.0
3.0
T-Type
20
20
20
0
2.0
3o[ I
Av.=0.43 Bq L -1 n=20
1.0
2.0
3.0
Tritium Concentration(Bq L -1) Fig. 4. Frequency distributions of tritium concentrations in rain for the individual weather types. The average concentrations are weighted by the quantity of precipitation in each rain event (see text).
204
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
the air movement is from the Pacific Ocean or the East China Sea to Fukuoka. During the weather type T, a huge amount of oceanic vapor is brought to the Fukuoka area by a typhoon. Therefore it could be concluded that the rain water contains large amounts of water vapor from the oceans in the weather types of N, P and T. In the case of F
type, the water vapor from the continent and ocean would be mixed with rain, in different manners, depending on the complexity of air movement. The tritium concentrations in various environmental water samples, collected in the Asian Continent, the Japan Sea and the Pacific Ocean, are shown in Fig. 5. The tritium concentrations are
8.75 5.94
3.17 2.281I j
5.03c~O~/)
Irkutsk 1989 •
3.97! v s k ~
LakeBaikal 1989
3.04
1989
5.11 UranBator 1989 4.37
Beijing 1986 • ,
o, o
Fukuoka~
/ ~
~
o0
BqL1
0.44 o
[]
PacificOcean 1984
0
Place Year I
I
1000 km
Fig. 5. Tritiumconcentrationsin variousenvironmentalsamplesin the AsianContinent,the Japan Sea and the PacificOcean(values are in Bq l-I).
205
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
distinctly higher in rain at the Asian Continent than Japan, indicating the high tritium concentration o f water vapor at the continent. On the other hand, the tritium concentration o f water vapor from the ocean is considered to be low, because the tritium concentration o f surface seawater in the ocean is fairly low [8,9]. We could say that tritium levels are high in the continent and low in the ocean. The different tritium concentrations in rain water can be attributed to the mixing o f the two different sources, one is the surface water of the continent and the other is the surface seawater o f the ocean. This hypothesis could be further tested by measuring the ~D and ~180 o f rain waters. Consequently, in Japan, local meteorological conditions would have larger effects on the tritium concentration in rain than the so-called spring peak effect, which evidently elevated the tritium concentration in rain by descending and mixing of stratospheric bomb-tritium to the troposphere in the 1960s and 1970s [10].
4. Conclusions The tritium concentrations in rain water were measured in F u k u o k a from April 1987 to July 1991. The tritium concentration o f each rain varied rather widely, from 0.06-3.39 Bq 1-1, with the average value o f 0.62 Bq 1-l. The variation can be attributed to the difference o f meteorological conditions. High tritium concentrations appeared in rain when the continental water occupied a fairly high fraction in the rain water. Low tritium concentrations appeared when the rain water originated from the oceanic water. The annual averages o f tritium concentrations in rain
were fairly constant and no longer decreased in F u k u o k a since 1987. The present results may suggest that any other pollutants, such as nitrogen oxides and sulfur oxides, would come directly to Japan from the continent depending on the meteorological conditions.
5. References H.V. Buttlar and W.F. Libby, Natural distribution of cosmic-ray produced tritium, J. lnorg. Nucl. Chem., 1 (1955) 75-91. United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, Report to the Assembly (with annexes), United Nations, New York, 1977. T. Takahashi, M. Nishida, S. Ohno and T. Hamada, Tritium concentration in wine, rain and ground water, Radioisotopes, 18 (1969) 560-563. N. Momoshima and Y. Takashima, Variation of tritium concentration in rain at Fukuoka, Mem. Fac. Sci., Kyushu Univ., Ser. C, 18 (1991) 21-30. N. Momoshima, T. Okai, T. Kaji and Y. Takashima, Distribution and transformation of various chemical forms of tritium in the environment, Radiochim. Acta, 54 (1991) 129-132. E. Hirai, N. Matsuoka and Y. Takashima, Volume reduction and tritium retention factor in electrolytic enrichment of water, Radioisotopes, 39 (1990) 503-506. T. Kaji, N. Momoshima, Y. Nakamura and Y. Takashima, Low-level tritium measurements using electrolytic enrichment technique, Mem. Fac. Sci., Kyushu Univ., Ser. C, 14 (1984) 269-276. T. Kaji and Y. Takashima, Behaviour of tritium in the ocean, Radiochim. Acta, 54 (1991) 117-120. T. Kaji, N. Momoshima and Y. Takashima, Tritium concentrations of the deep sea-water in the Japan Sea and the Pacific Ocean, J. Radioanal. Nucl. Chem., Len., 127 (1988) 447-456. 10 H. Morishima, H. Kawai, T. Koga and T. Niwa, The trends of global tritium precipitations, J. Radiat. Res., 26 (1985) 283-312.
ELSEVIER
w i ~ rain
The Science of the Total Environment 145 (1994) 197-205
Meteorological analysis of tritium concentrations in rain water collected in Fukuoka, Japan, from 1987-1991 N o b u a k i M a t s u o k a *a, Ei~i H i r a i a, H i s a y a T a g o m o r i a, Noriyuki Momoshima , Yoshimasa Takashima b
agyushu Environmental Evaluation Association, 1-10-1, Matsukadai, Higashi-ku, Fukuoka 813, Japan hDepartment of Chemistry, Faculty of Science, Kyushu University 33, Hakozaki. Higashi-ku, Fukuoka 812, Japan
(Received 30 July 1992; accepted 19 January 1993)
Abstract Tritium concentrations in rain water collected in Fukuoka, Japan, from April 1987 to July 1991, were measured. The tritium concentration of each 'rain' showed a large variation from 0.06-3.39 Bq 1-~, with an average value of 0.62 Bq l-k Weather conditions significantly affected the tritium concentration in rain. Higher tritium concentrations were observed when air-mass moved dominantly from the Asian Continent to Fukuoka. The annual average concentrations were no longer decreased after 1987 in Fukuoka. Key words." Tritium; Rain water; Japan
1. Introduction The tritium concentration of 0.78 Bq 1-1 was observed in Kobe in 1953 as the only datum for Japanese rain water before the initiation of nuclear tests [1]. However, the concentration of tritium in rain increased abruptly during 1961 and 1963 due to atmospheric nuclear tests [2]. In that period, the tritium concentrations in rain water were reported to be from 12-180 Bq 1-l in Japan [3]. After 1963, the concentration in rain decreased gradually with the decrease of the number of nuclear tests. The * Corresponding author.
tritium in rain water in the 1960s and 1970s thus mainly originated from nuclear tests. The concentration was significantly affected by the frequency and size of the nuclear tests, and the variations of tritium concentrations were fairly large among rainfalls. On the other hand, after the 26th Chinese nuclear test, conducted on October 16, 1980, there was no more large scale atmospheric nuclear tests, hence the concentration of tritium in rain water has declined in the 1980s. In our previous papers [4,5], the half-life of decrease, of yearly averaged tritium concentrations in rain was estimated to be 8.4 years from 1981-1988 in Fukuoka, but there has been no distinct decrease since 1988. In those
0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0048-9697(93)03645-1(
198
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
studies, the significance of meteorological factors was pointed out with respect to variation of tritium concentrations in rain after the 1980s. To evaluate a meteorological effect more clearly, the measurement of tritium concentration is necessary for each rain using extremely accurate techniques, such as low level counting combined with electrolytic enrichment of tritium in water. In the present investigation, we attempted to elucidate the effect of meteorological conditions on the tritium concentrations in rain.
2. Materials and methods Each rain water sample was collected using a receptor, with a diameter of 80 cm, at ground level in Fukuoka, Japan, from April 1987 to July 1991. The rain water collected was distilled using a distillation apparatus specially designed for tritium measurement. After distillation, the rain water was electrolytically enriched by a previously reported method [6,7]. The tritium retention and the volume reduction factors in enrichment were
Table 1 Tritium concentrations in individual rainfalls from April to December in 1987, in Fukuoka Date April
May
June
July
2 6 9 11 21 26 1 3 12 14 17 22 23 27 2 3 8 15 19 25 3 4 6 7 14 16 17 19 24 25 27
aRefer to text.
Weather type a
Pecipitation (mm)
Tritium (Bq l -I)
Date
S N F C N S S F N S S F F S N N F S F S F F N F T T N F N F P
9.0 5.0 17.0 5.0 17.5 10.5 8.0 14.0 5.5 40.0 16.0 40.0 3.0 7.0 51.5 0.5 114.5 44.0 58.0 10.0 37.0 66.5 8.5 24.5 47.0 23.0 7.5 196.5 3.5 20.0 8.0
1.13 0.78 0.84 0.97 0.58 1.27 1.03 0.72 0.63 1.17 1.21 0.75 0.71 0.84 0.63 0.37 0.59 0.73 0.58 1.08 0.80 0.60 0.71 0.72 0.49 0.26 0.85 0.57 0.36 0.57 0.53
Aug.
Sep.
Oct.
Nov. Dec.
2 9 10 13 20 22 24 25 26 31 7 13 24 I1 16 24 26 30 3 30 3 6 9 15
Weather type a
Precipitation (mm)
Tritium (Bq I -I)
F F F P P N F N N T N S S S T S S N N C C S S N
68.0 26.5 32.0 37.0 25.0 41.0 30.0 47.5 5.0 63.0 14.0 75.5 10.0 5.5 23.0 24.0 10.0 18.5 27.0 36.5 2.0 26.0 4.5 4.5
0.57 1.02 0.57 0.49 0.50 0.14 1.00 0.49 0.61 0.25 1.01 0.52 0.94 0.78 0.49 0.67 0.61 0.46 0.63 0.51 0.93 0.85 0.69 0.88
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
199
- 0.8 and 7.6, respectively. After enrichment, the water was distilled again. The distilled water was mixed with a liquid scintillation cocktail (NEN Research Products 'AQUASOL-2' or Packard 'PICO-FLUOR LLT') in a 100-ml teflon vial. The water/cocktail volume ratios were 4:6 and 5:5 in AQUASOL-2 and PICO-FLUOR LLT, respectively. The tritium concentration was measured by a low background liquid scintillation counter (ALOKA LB-1) for 1000 min after mixing the distilled water and the liquid scintillation cocktail. The counting efficiencies for tritium were 15-18
and 12-15%, in AQUASOL-2 and PICO-FLUOR LLT, respectively. The detection limit at a confidence level of 95°,/0 was 0.05-0.06 Bq 1-t for both cocktails. 3. Results and discussion
Tritium concentrations in individual rainfall samples and precipitation data are summarized in Tables 1-5. The annual average tritium concentrations, calculated from the measurements given in Tables 1-5, are shown in Fig. 1.
Table 2 Tritium concentrations in individual rainfalls in 1988, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
4 8 15 21 22 4 23 26 29 5 11 13 17 18 22 26 29 2 7 12 18 21 23 27 29 4 7 11 15 20 23
Weather type a
Precipitation (mm)
Tritium (Bq l -l)
Date
C F F F S C F S S C N P S S S S S S S N S S C S S F N S S S S
6.0 7.5 13.5 13.0 1.0 1.5 12.5 11.5 8.5 3.0 25.5 18.0 11.0 4.0 31.0 29.5 11.0 6.5 6.0 34.5 18.5 0.5 3.0 7.5 36.0 52.0 51.0 9.0 10.5 23.0 9.5
0.84 0.79 0.57 0.50 1.10 1.44 0.74 1.05 1.20 2.46 0.80 0.66 0.91 0.77 0.95 1.38 1.59 2.39 1.85 0.88 1.23 1.15 2.03 3.39 1.29 1.71 0.67 0.51 0.95 0.97 0.66
June
aRefer to text. bNot characterized.
July
Aug.
Sep.
Oct.
Nov. Dec.
3 10 12 24 29 11 16 17 21 26 28 4 12 16 17 18 22 24 27 5 12 19 26 28 6 24 26 19 29 5 17 24
Weather type a
Precipitation (mm)
Tritium (Bq 1-1)
T S S N F N F F F F F N.C. b T T T T N S N F F F T N.C. b T F N.C. b C N C C N
171.0 12.5 85.0 60.0 3.5 1.5 40.0 14.0 13.0 19.0 31.0 0.5 12.0 27.0 8.0 5.0 32.5 7.0 3.5 74.0 15.5 5.0 57.0 1.0 32.0 2.0 0.5 19.5 44.0 8.0 8.0 1.0
0.43 1.27 1.15 0.77 0.67 0.54 0.78 1.59 1.39 1.57 1.35 1.37 0.60 0.54 0.57 0.28 0.45 1.00 0.61 0.59 0.67 0.60 0.37 0.45 0.44 0.66 0.71 0.61 0.58 1.25 0.64 0.70
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Table 3 Tritium concentrations in individual rainfalls in 1989, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
June
1 8 10 11 19 21 23 9 18 21 25 6 8 13 28 31 8 14 22 30 5 10 16 19 21 25 5 8 13 15 16 24 28 29
Weather type a
Precipitation (mm)
Tritium (Bq l -l)
Date
N N N.C. b N N F F S F C F C C F C S S S S S S F S S S S N N S F S T N S
15.5 7.0 0.5 20.0 18.5 16.0 34.0 43.0 65.5 8.0 31.0 55.5 13.0 28.0 9.5 11.0 3.0 5.0 0.5 10.0 17.5 3.0 29.0 30.5 6.0 18.5 3.5 28.0 7.5 25.0 51.0 24.0 1.5 4.0
0.59 0.50 0.41 0.54 0.28 0.46 0.66 0.58 0.54 0.97 0.59 0.91 1.22 0.81 1.13 1.41 1.39 0.81 0.98 0.94 0.97 1.11 0.81 0.36 1.01 2.09 0.53 0.37 0.74 0.37 0.84 0.21 0.59 1.16
July
Aug.
Sep.
Oct.
Nov.
Dec.
3 9 15 16 28 3 14 18 27 1 7 14 16 18 19 26 1 8 11 16 19 31 6 9 13 7 12 14 15 26 30
Weather type a
Precipitation (mm)
Tritium (Bq l -I)
S N P N.C. b T T F P T F F N F N T N.C. b N.C. b C S N N.C. b N N N N.C. b N C N N N S
18.5 39.0 5.5 0.5 22.0 5.5 10.0 9.0 4.0 138.5 21.0 100.0 47.5 50.0 98.5 6.5 0.5 1.5 10.5 6.0 1.5 8.5 16.0 24.0 9.5 6.0 0.5 3.0 7.0 31.0 10.5
1.06 0.50 0.40 1.03 0.27 0.48 0.93 0.59 0.33 0.60 1.05 0.39 0.40 0.38 0.39 0.64 0.38 0.63 0.42 0.62 0.48 0.70 0.21 0.49 0.40 0.91 0.95 0.67 0.72 0.75 0.60
aRefer to text. bNot characterized.
Previous measurements showed that the concentration level of tritium in rain water in Fukuoka had decreased with an apparent half-life of 8.4 years from 1981-1987, and that the level was relatively constant since 1988 [4,5]. This tendency was also confirmed by the present investigation, except for the slightly higher value observed in 1989. The overall average concentration was 0.62 Bq 1-l. In spite of the relatively constant average tritium concentrations for these 5 years, a signifi-
cant variation was observed for tritium concentrations in individual samples. During the present observation, the highest concentration of tritium was 3.39 Bq 1-l on April 27, 1988, and the lowest was 0.06 Bq 1-1 on July 9, 1990. A distinct correlation was not found between the quantity of precipitation on each occasion and the tritium concentration in the rain. Low tritium concentrations in rain are expected in Fukuoka, because only a small amount of tri-
Table 4 Tritium concentrations in individual rainfalls in 1990, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
May
9 16 19 24 29 1 11 14 15 19 24 26 1 4 8 14 24 29 4 7 13 17 22 7 14 18
Weather type a
Precipitation (nun)
Tritium (Bq l -I)
Date
S S S N.C. b N S N S S N F S S S C F N F S N N S S S F N
23.0 22.5 14.0 7.0 14.5 4.5 9.5 7.0 1.0 39.5 23.0 4.5 20.0 4.0 2.5 1.5 28.5 37.5 0.5 15.0 11.0 4.0 52.5 34.0 1.5 44.5
0.77 0.45 0.54 0.62 0.24 0.65 0.29 0.81 0.66 0.28 0.41 0.64 0.88 0.89 1.21 0.81 0.48 0.68 0.85 0.83 0.71 1.76 0.62 0.98 0.73 0.35
June
July
Sep.
Oct.
Nov.
Dec.
1 4 12 15 3 13 17 3 16 19 26 8 15 27 31 5 9 20 25 1 8 11 14 21 29
Weather type a
Precipitation (ram)
Tritium (Bq l -l)
N S P N N N N N F T S T F S S T N N N T C N.C. b N.C. b C C
45.0 13.5 1.5 120.0 173.5 20.0 6.5 14.5 41.5 69.5 8.0 55.5 12.5 5.0 0.5 5.5 37.0 15.5 3,0 6,0 14,5 3,5 2.0 5.5 1,0
0.38 0.65 0.22 0.14 0.06 0.28 0.48 0.16 0.57 0.54 0.66 0.69 0.64 1.02 0.73 0.37 0.33 0.35 0.57 0.29 1.23 0.56 0.68 0.89 0.64
Weather type a
Precipitation (mm)
Tritium (Bq l -I)
C S S S N F N F S N N N
10.0 28.0 15.5 63.0 47.0 18.5 231.0 20.0 24.5 79.5 115.0 86.5
0.81 1.05 1.11 1.22 0.37 0.49 0.33 0.32 1.03 0.19 0.38 0.35
aRefer to text. bNot characterized. Table 5 Tritium concentrations in individual rainfalls from January to July in 1991, in Fukuoka Date Jan.
Feb.
Mar.
Apr.
1 7 17 25 28 10 15 25 1 4 11 16 22 30 7 10 15 19
Weather type a
Precipitation (mm)
Tritium (Bq 1-1)
Date
S N N S C F F N S S F S S S S F N.C. b F
28.0 2.0 2.5 9.0 4.5 33.5 33.5 14.0 28.0 15.0 52.0 8.0 51.0 7.5 48.0 22.5 1.5 34.0
0.58 0.45 0.49 0.25 1.09 0.37 0.33 0.83 1.05 0.53 0.47 1.17 0.68 0.78 0.70 0.33 0.63 0.58
May
aRefer to text. bNot characterized.
June
July
7 13 15 21 26 3 10 15 25 1 4 15
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N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
tritium concentrations. These concentrations were 3 - 5 times higher than the average concentration. Generally, high concentrations were observed in winter and spring, with relatively low concentrations in summer. This suggests that some meteorological factors affect the tritium concentrations in rain. To analyze the meteorological effects on tritium concentrations, we classified the meteorological conditions o f individual rainfalls into six weather types;
1.5 S ._1 ~" v t.0
1.0
"6
0.5
cO
(o 0.0
1A7
19188
19189
1990
1
1
Year Fig. 1. Annual averages of tritium concentrations in rain in Fukuoka. Weighted (13)and unweighted (O) by the quantity of precipitation in each rain event. Error bars show a S.D.
(a)
tium is released to the sea from Japanese nuclear facilities and it is diluted immediately by the oceanic waters with low tritium concentrations [8,91. However, we sometimes observed fairly high
(c)
a cyclone or a front exists in the north F u k u o k a (N type), a cyclone or a front exists in the south F u k u o k a (S type), a cyclone or a front exists near F u k u o k a type), an anticyclone from the Asian Continent the F u k u o k a area (C type),
(b)
(d)
of of (F in
%/
@
N-type
~
J
I
2000km
C-type
It/r.7 2000kin F-type
S-type
~
5
\
I
2000 km
P-type
I --
2000km
J
T-type
Fig. 2. Typical weather maps of individual meteorological conditions. Arrows indicate the main wind direction and solid circles indicate the location of Fuknoka. The letters L, H and T indicate a cyclone, an anticyclone and a typhoon, respectively, and numbers indicate center atmospheric pressures (mbar) (see text).
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
203
100 r
shown in Fig. 2. The weather types of individual rainfalls are also shown in Tables 1-5.
Av.=0.62 Bq L 1 n=264
O
e-
-1 O"
The frequency distributions of tritium concentrations are shown in Fig. 3 for the whole data set and in Fig. 4 for the individual weather types. The weather types of S and C shifted the frequency distributions to a higher side of the concentration than that from the whole data set. The weather types of N, P and T shifted to a lower side of the concentration. The weather type F had concentrations similar to that of the whole data set. In the weather types of S and C of higher tritium concentrations, the air mass moves dominantly from the Asian Continent to the direction of Fukuoka over the Japan Sea. In these weather types, the rain in Fukuoka would contain a fairly large amount of water vapor from the Asian Continent. In the weather types of N and P of lower tritium concentrations, the dominant direction of
50
ii
1.0
2.0
3.0
Bq L-1
Fig. 3. Frequency distribution of tritium concentrations in rain for the whole data set. The average concentration is weighted by the quantity of precipitation in each rain event.
(e) (f)
an anticyclone from the Pacific Ocean in the Fukuoka area (P type), and a typhoon near Fukuoka (T type). The typical weather maps of these conditions are
3ot, 201" "1 | IIII
III (ET
0
301
N-Type Av.=0.43 Bq L n=66
1.0
2.--'0
3.'~
1
S-Type I Av.=0.92Bq L-1 [ n=82
oLK
20 t
II
0
1.0
3.0
30
30
P-Type
C-Type
LL
Av.=0.91 Bq L -1 n=22
Av.=0.52 Bq L -1 n=7 10
10
•L•• 1.0
2.0
.1111 3.0
20[ [
F-Type
1.0
2.0
3.0
30[ 0
lo ~ l l l 0
I
I AV.=0.67 Bq L-1 I I n=54 I
1.0
2.0
3.0
T-Type
20
20
20
0
2.0
3o[ I
Av.=0.43 Bq L -1 n=20
1.0
2.0
3.0
Tritium Concentration(Bq L -1) Fig. 4. Frequency distributions of tritium concentrations in rain for the individual weather types. The average concentrations are weighted by the quantity of precipitation in each rain event (see text).
204
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
the air movement is from the Pacific Ocean or the East China Sea to Fukuoka. During the weather type T, a huge amount of oceanic vapor is brought to the Fukuoka area by a typhoon. Therefore it could be concluded that the rain water contains large amounts of water vapor from the oceans in the weather types of N, P and T. In the case of F
type, the water vapor from the continent and ocean would be mixed with rain, in different manners, depending on the complexity of air movement. The tritium concentrations in various environmental water samples, collected in the Asian Continent, the Japan Sea and the Pacific Ocean, are shown in Fig. 5. The tritium concentrations are
8.75 5.94
3.17 2.281I j
5.03c~O~/)
Irkutsk 1989 •
3.97! v s k ~
LakeBaikal 1989
3.04
1989
5.11 UranBator 1989 4.37
Beijing 1986 • ,
o, o
Fukuoka~
/ ~
~
o0
BqL1
0.44 o
[]
PacificOcean 1984
0
Place Year I
I
1000 km
Fig. 5. Tritiumconcentrationsin variousenvironmentalsamplesin the AsianContinent,the Japan Sea and the PacificOcean(values are in Bq l-I).
205
N. Matsuoka et al. / Sci. Total Environ. 145 (1994) 197-205
distinctly higher in rain at the Asian Continent than Japan, indicating the high tritium concentration o f water vapor at the continent. On the other hand, the tritium concentration o f water vapor from the ocean is considered to be low, because the tritium concentration o f surface seawater in the ocean is fairly low [8,9]. We could say that tritium levels are high in the continent and low in the ocean. The different tritium concentrations in rain water can be attributed to the mixing o f the two different sources, one is the surface water of the continent and the other is the surface seawater o f the ocean. This hypothesis could be further tested by measuring the ~D and ~180 o f rain waters. Consequently, in Japan, local meteorological conditions would have larger effects on the tritium concentration in rain than the so-called spring peak effect, which evidently elevated the tritium concentration in rain by descending and mixing of stratospheric bomb-tritium to the troposphere in the 1960s and 1970s [10].
4. Conclusions The tritium concentrations in rain water were measured in F u k u o k a from April 1987 to July 1991. The tritium concentration o f each rain varied rather widely, from 0.06-3.39 Bq 1-1, with the average value o f 0.62 Bq 1-l. The variation can be attributed to the difference o f meteorological conditions. High tritium concentrations appeared in rain when the continental water occupied a fairly high fraction in the rain water. Low tritium concentrations appeared when the rain water originated from the oceanic water. The annual averages o f tritium concentrations in rain
were fairly constant and no longer decreased in F u k u o k a since 1987. The present results may suggest that any other pollutants, such as nitrogen oxides and sulfur oxides, would come directly to Japan from the continent depending on the meteorological conditions.
5. References H.V. Buttlar and W.F. Libby, Natural distribution of cosmic-ray produced tritium, J. lnorg. Nucl. Chem., 1 (1955) 75-91. United Nations Scientific Committee on the Effects of Atomic Radiation, Sources and Effects of Ionizing Radiation, Report to the Assembly (with annexes), United Nations, New York, 1977. T. Takahashi, M. Nishida, S. Ohno and T. Hamada, Tritium concentration in wine, rain and ground water, Radioisotopes, 18 (1969) 560-563. N. Momoshima and Y. Takashima, Variation of tritium concentration in rain at Fukuoka, Mem. Fac. Sci., Kyushu Univ., Ser. C, 18 (1991) 21-30. N. Momoshima, T. Okai, T. Kaji and Y. Takashima, Distribution and transformation of various chemical forms of tritium in the environment, Radiochim. Acta, 54 (1991) 129-132. E. Hirai, N. Matsuoka and Y. Takashima, Volume reduction and tritium retention factor in electrolytic enrichment of water, Radioisotopes, 39 (1990) 503-506. T. Kaji, N. Momoshima, Y. Nakamura and Y. Takashima, Low-level tritium measurements using electrolytic enrichment technique, Mem. Fac. Sci., Kyushu Univ., Ser. C, 14 (1984) 269-276. T. Kaji and Y. Takashima, Behaviour of tritium in the ocean, Radiochim. Acta, 54 (1991) 117-120. T. Kaji, N. Momoshima and Y. Takashima, Tritium concentrations of the deep sea-water in the Japan Sea and the Pacific Ocean, J. Radioanal. Nucl. Chem., Len., 127 (1988) 447-456. 10 H. Morishima, H. Kawai, T. Koga and T. Niwa, The trends of global tritium precipitations, J. Radiat. Res., 26 (1985) 283-312.