Relation between tritium concentration and chemical composition in rain at Fukuoka

Journal of Radioanalytical and Nuclear Chemistry, Vol. 239, No. 3 (1999) 517-522

Relation between tritium concentration and chemical composition in rain at Fukuoka

Y. Hayashi, N. Momoshima,* Y. Maeda, H. Kakiuchi

Department of Chemistry, Faculty of Science, Kyushu University, Hakozaki, Higashi-ku, Fukuoka 812-81, Japan

(Received April 8, 1998)

Tritium concentrations in rain collected at Fukuoka, Japan from 1982 have been measured. From May 1996 tritium concentrations and chemical species have been analyzed for each rain to examine their relationship. Recent rain was concluded not to be affected by tritium from atmospheric nuclear tests. Tritium concentrations showed a seasonal pattern, high during winter and spring and low during summer and fall and had positive correlations with non-sea-salt SO42-, indicating a long distance transport of acidic materials as well as tritium from continental China.

Introduction

Japan is situated at the east of continental China and thus air pollutants from the continent come flying over the Sea of Japan. However, the distinction of air pollutants between a long distance transport and local emission fractions is a difficult problem. Analysis of chemical composition of rain and estimation of the fraction due to a long distance transport have been carried out. Some chemical species such as SO42- are considered to be transported from China. 1,2 Isotopic composition will give a more useful information about the origin of pollutants. For example, the 34S/325 ratio is known to differ between coal and oil. 3

Tritium (3H) is an isotope of hydrogen and decays to 3He with a half-life of 12.34 y.4 Restricted circulation of surface water in the continental area where evaporation and precipitation are repeated, results in a longer residence time of tritium compared to the oceanic area where dilution by seawater is large. Japan is surrounded by the ocean and belongs to the oceanic climate, so low tritium concentrations have been observed compared to those in continental area. However, tritium level in recent rain has been reported to be affected by meteorological conditions. 5 When low pressure or front exists in the south of Fukuoka, rain with higher tritium was observed at high frequency. Air mass transported a long distance from continental China is considered to be related to high tritium level at Fukuoka.

To evaluate the influence of a long distance transport of air pollutants on rain at Fukuoka, we collected each rain from May 1996 and analyzed major cation and anion as well as tritium concentrations.

Experimental

Rain samples have been collected at Fukuoka, Japan (Fig. 1) from 1982. Composite rain samples during the

period of the first and the latter halves of each month, were prepared for tritium analysis. In order to examine relationship between chemical species and tritium beginning May 1996, cation and anion as well as tritium concentrations have been analyzed for each rain. The composite rain samples were collected with a rain gauge (area: 0.031 m 2) and each rain with a polypropylene box (area: 0.30 m2). The rain collectors were placed at a roof of a building at Kyushu University.

Tritium concentrations were measured by liquid scintillation counting (LSC). 50 ml of the composite rain sample was mixed with 50 ml of scintillation cocktail (PACKARD, PICO-FLUOR LLT) in a 100 ml Teflon vial and measured for 1000 min with a low back-ground liquid-scintillation counter (ALOKA, LSC-LB2).

1 I ! L . . : - , , a ~

.... 50 N ........................ ~ ............................. ~ ..................... ~"~~" ...............................

i ~ .,

i: T 3 f ' ~ J ~ Japan i ................ i}

: u k : ................................ i ................................................. i .........................

/ / I ~ the Paclfic Ocean

15"E 125"E 135~ 145~

Fig. 1. Sampling location

* E-mail: momoscc @mbox.nc.kyushu-u.ac.jp

0236-5731/99/USD 17. O0 �9 1999 Akad~miai Kiadd, Budapest All rights reserved

Elsevier Science B. V., Amsterdam Akad~miai Kiad6, Budapest

Y. HAYASHI et al.: RELATION BETWEEN TRITIUM CONCENTRATION AND CHEMICAL COMPOSITION

Counting efficiency was determined by the external standard channel ratio (ESCR) of the sample. The relation between ESCR and counting efficiency was determined in advance using standard samples with known tritium concentrations. The background was determined with samples which were prepared using tritium-free deep well water. On the other hand, each rain sample was electrolyzed before tritium measurement. 6 About 11 times enrichment of tritium was attained by volume reduction from an initial 200ml to a final volume of about 15 ml. After distillation of the enriched sample, a 10 ml portion was mixed with 10 ml of the scintillation cocktail in a 20 ml Teflon vial and measured by LSC. Counting efficiency and background was determined in the same manner as for the composite sample.

Hydrogen ion concentration was measured with a pH meter (HORIBA, F-13). Cation concentrations, Ca 2+, Mg 2§ K § and Na +, were determined by atomic absorption spectrometry (SHIMADZU, AA-625-11) and anion concentrations, CI-, N O 3- and SO42-, by ion chromatography (SHIMADZU, PIA-1000).

Result and discussion

Cation and anion in rain

As shown in Fig. 1, Fukuoka is located east of continental China, and we have often observed materials

such as radioactive fallout 7 and loess 8 transported from the continent through atmosphere by westerlies. Fukuoka faces the 'Sea of Japan and the sampling site at Kyushu University is only 1 km away from the coast. This situation allows a large influence of sea-salt on the present rain samples a s compared to those collected far away from sea. A relation between Na + and C1- concentrations is shown in Fig. 2, indicating a straight line being consistent with the chemical composition of seawater. This suggests that most of the Na + and C1- are derived from sea-salt. The averages of Na + and C1- are 1.98 mg/1 and 3.51 mg/1, respectively, being 1.2 times higher than those observed in rain collected at Dazaifu, Fukuoka 14 km away from the coast. 9 A similar relation is observed between Mg 2+ and CI-, thus Mg 2§ is also derived mainly from sea-salt. Na +, Mg 2§ and C1- concentrations in the present sample are 1.6-2.0 times higher than their averages of rain at 14 cities mostly facing the Pacific Ocean side over Japan. 1~ The data of extremely high Na + and C1- concentrations in Fig. 2 were ones for the rain samples collected in winter (11/26/1996-12/2/1996 and 1/7/1997-1/9/1997) and there was a strong wind blowing from the coast to the sampling site during the rain. Average concentrations of Na § Mg 2+ and C1- from October to March were 4.2, 2.7 and 3.9 times higher than those from April to September, respectively. High cation concentrations in rain during the winter season are common at coastal regions facing the Sea of Japan. 11,12

Z

o Na+l �9 C a 2 + L 20 I i I i ~

�9 Z ............... i ................. i ................. i .................. ::.- ................. r .............

1 5 o J i i i , g I'

, o ............ I .................. [... ............. ! ...............

. . . . . . . . . . .

0 ~- - -" t "~ i i i i 0 10 20 30

C1. mg/1

4

3

2 ~

0

L)

Fig. 2. Relation ofNa § and Ca 2+ concentrations to CI- concentration in each rain from May 1996 to December 1997. Solid and open circles denote Na + and Ca 2+ concentrations, respectively. Upper straight line denotes ratio of Na + to CI- concentrations in seawater and lower Ca 2+ to C1-

518


Table 1. Correlation coefficients of tritium and chemical species in rain

Species H + Na § Mg 2+ Ca 2+ CI- NO3- SO42- nssSO42- nssCa 2+

Na + 0.59** Mg 2+ 0.56** 0.98** Ca 2§ 0.24 0.47** 0.55** CI- 0.57** 1.00"* 0.97** NO 3- 0.39* 0.18 0.27 5042- 0.46** 0.62** 0.68** nssSO42- 0.31" 0.32* 0.40** nssCa 2§ 0.12 0.31" 0.40** Tritium 0.33* -0.0l 0.03

0.46** 0.58** 0.19 0.69** 0.62** 0.64** 0.63** 0.32* 0.69** 0.94** 0.98** 0.30* 0.59** 0.63** 0.26 0.00 0.38* 0.45**

0.62** 0.55** 0.29

Level of significance*: 5%, **: 1%.

%

!

r,#3 r#] o'J

20

15

10

5

0

i......'.. ............. i ............... ................

5 7 9 11 1 3 5 7 1996 1997

o n s s C a 2 + ~ �9 n s s S 0 4 2 - [

: , i 0 i

' i 0 ' . . . . . . . . . . . . . . . . . . . . . . . . . . ,:, ........................... . ....................................................... ~ ..........................

io i i O i 0

0 ..................... 4 ............................ .L ........................... ,.- ....................................................... i -" i 0 -:. t i ~ I

i;" ;';1 9 11

4

3 e~0

2 +~

0

2 2+ Fig. 3. Variations of nssSO 4 - (solid circle) and nssCa (open circle) concentrations in each rain from May 1996 to December 1997

The relation between Ca 2+ and CI- is shown in Fig. 2 and the Ca 2+ concentrations are significantly higher than the sea-salt line, indicating the influence of other source besides sea-salt. There is a good correlation between Ca 2+ and SO42-, r=069 , P<0.01, as listed in Table 1 and charge balance calculation suggests that most o f the Ca 2+ is neutralized by 5042-. To eliminate the sea-salt fraction on Ca 2+ and SO42-, non-sea-salt Ca 2+ and non- sea-salt SO42- (nssCa 2+ and nssSO42- ) are calculated according to the following equation assuming that all of the Na + and C1- are supplied by sea-salt.

nssX:Xobs.[l_(.__ _ x ] .i"Na+] ] L t Na+ )sea t,'--X"-Jobs_l

where Xobs is the observed concentration of Ca 2+ or SO42-. (X/Na+)sea is the ratio of Ca 2+ or 5042- to Na § concentrations in seawater, i.e., 0.0379 or 0.251, and

(Na+/X)obs is the ratio of Na + to Ca 2+ or SO42- observed in rain. The nssCa 2+ concentrations ranged from

0.27 mg/1 to 3.21 mg/1, and the nssSO42- from 0.87 mg/1 to 11.85 rag/1. Both Ca 2+ and 5042- are suspected to be derived not from sea salt but another source, because the averages of nssCa2+/Ca 2+ and nssSO42-/SO42- are 0.94 and 0.88.

nssS0 42- and nssCa 2+ concentrations in rain

As shown in Fig. 3, a pronounced seasonal variation is detected for the nssSO42-. The nssSO42- concentrations are evidently high during winter and low during summer. This seasonal pattern is similar to that observed in other coastal regions facing the Sea of Japan. 11,12 The average concentration, 3.72 mg/1, is higher than the average of Japan, 2.14mg/1.13 The increase in nssSO42- during the winter is probably attributed to a seasonal wind from the northwest that causes a long distance transport from the continent. Local industry and automobiles are emitting anthropogenic sulfur-dioxide and this could be an additional source for nssSO42- in the present sample.

519


Atmospheric sulfur-dioxide concentration increased in 1960s has decreased in Fukuoka by the regulation of sulfur-dioxide emission in 1969, and its annual average after 1988 is about 0.004 ppm which has satisfied the environmental quality standard of Japan (0.04 ppm). Contribution of sulfur f r o m local industry and automobiles to the present rain is uncertain. The measurement of stable isotope ratio of sulfur which is peculiar to the origin of sulfur would probably throw light on this problem.

The nssCa 2+ concentrations have a seasonal pattern similar to nssSO42- concentration that is high during winter and low during summer as shown in Fig. 3. An increase in nssCa 2+ during the spring was often observed in other coastal regions facing the Sea of Japan and attributed to loess transported from the continent. 14,15 The present rain samples have no increase in nssCa 2+ during the spring. This would be attributed to different sampling methods. The increase in nssCa 2+ was observed for total (wet and dry) deposition samples, while the present sample is wet deposition only. The average concentration of nssCa 2+, 1.02 rag/l, is two times higher than the average of other coastal regions facing the Sea of Japan) 1

Tr i t i um c o n c e n t r a t i o n in ra in

Annual averages of tritium concentrations in rain are shown in Fig. 4, together with data for 1982 to 1992

previously reported. 16 The tritium concentrations at Fukuoka decreased from 1982 to 1988 with an apparent half-life of 8.4 years and after 1989 a clear decrease has not been observed. The present data for 1993 to 1997 follows the previous observation that the tritium concentrations are fairly constant. Recent rain is confirmed to be not containing tritium from atmospheric nuclear tests judging from the fact that the annual averages are very close to the rain collected in Kobe before initiation of atmospheric nuclear tests (0.78 Bq/l). 17 Tritium concentrations in each rain are shown in Fig. 5. There seem to be rains with high tritium concentration in the winter and spring. The average of each quarter season is calculated and is statistically analyzed by the analysis of variance (ANOVA). As shown in Fig. 6. the averages are 1.01+0.25 Bq/1 in spring (March to May), 0.62+0.38 Bq/l in summer (June to August), 0.66+0.32 Bq/1 in fall (September to November) and 1.10+0.61 Bq/l in winter (December to February), showing high averages of tritium concentrations in winter and spring. Analysis of variance shows statistical difference on the season at the 0.05 probability level and the multiple comparison using Scheffe's method indicates the winter has difference in average of tritium concentrations from the summer and fall (Fig. 6).

.5 i �9 �9 �9 | �9 m �9 �9 | �9 ,

- 2 0 t7' "

=- o

4 ,b

r

1.5

1.0

0.5

0.G 1980

.................. .... " ...................... ~ t I !1. iill t ~ ........................................ i!ii~ i~i if" ....................................... !iiili ii I tiili iii I~" ................... iiii i t , | | | | | i I | | | | | |

1985 1990 1995 Year

Fig. 4. Annual averages of tritium concentrations in rain for 1982 to 1997. Vertical bars denote standard deviations

520

Y . H A Y A S H I e t al.: R E L A T I O N B E T W E E N T R I T I U M C O N C E N T R A T I O N A N D C H E M I C A L C O M P O S I T I O N

2 . 5

2.0

1.5 '4 ~1.0

0.5 c.)

0 . 0

| n | i �9 i

! : -"

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i

........................... ; i : i i ............................ T ..........................

�9 I ~ . '" ~. .............................................. -: ................. ./R..~. ......................................................

..... , ............... . ~ ................. ~,..L ........................... : ............ ~ ' ~ " ~ " t .......... " ......

i i i i m i i m i i n i

5 7 9 11 1 3 5 7 9 11 1996 1997

Fig. 5. A variation of tritium concentrations in each rain from May 1996 to December 1997. Vertical bars denote counting errors

1.8

~ 1.5

~ 1.2 @

0.9

~ 0 . 6

~ 0.3 O r ~

g o

> <

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . o . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . ,,~

1 �9 _...a......_l

Mar . -May Jun . -Aug. Sep.-Nov. Dec . -Feb .

Month

Fig. 6. Averages of tritium concentrations in each season, March to May, June to August, September to November and December to February. Means marked by the same letter are significantly different (p<0.01). Vertical bars denote standard deviations

MATSUOKA et al. 5 have reported that tritium concentration is high when low pressure or front exists in the south of Kyushu area or anticyclone covers continental China and is low when low pressure or front exists in the north of Kyushu area or typhoons exist in

Kyushu area. Our data is in an agreement with Matsuoka's observation because low tritium

concentrations in the summer and fall often occurred in relation to typhoons while high tritium concentrations in

winter and spring were related to low pressure or front condition in the south of Kyushu area. This suggests that meteorological conditions are the primary factor causing the seasonal variation of tritium concentration.

521


Relation between tritium concentration and chemical composition in rain

The correlation coefficients between concentration of tritium and chemical species measured in the present study are listed in Table 1. High positive correlations between Na + and CI- (r= 1:00, p<0.01) and between Mg 2§ and C1- (r=0.97, p<0.01) prove their sea-salt origin. Both nssSO42- and NO 3- have high correlation with nssCa 2+ among cations. This suggests that Ca 2+ is a major counter ion for anthropogenic SO42- and NO3-.

The tritium concentration shows a high positive correlation with nssSO42- (r=0.55, p<0.01) as well as SO42- (r=0.45, p<0.01), but no correlation with Na +, Mg 2+, Ca 2+ and C1-. This suggests that tritium and nssSO42- are of the same origin and the fact that rain derived from continental China has a high tritium concentration makes us to speculate that nssSO42- is also derived from continental China.

Conclusions

Relations of Na + and Mg 2+ to C1- in each rain were consistent with those of the chemical compositions of seawater, indicating that Na +, Mg 2+ and C1- were derived from seawater. Most of the 5042- and Ca 2+ are derived from another source, not seawater, because of high nssSO42-/SO42-, 0.88, and high nssCa2+/Ca 2+, 0.94. The nssSO42- and nssCa 2+ showed a clear seasonal pattern being high during the winter and low during the summer. Both nssSO42- and NO 3- had high correlations with nssCa 2+, suggesting that nssCa 2§ is a major counter ion for anthropogenic nssSO42- and NO3-.

Annual averages of tritium concentrations in rain after 1989 were very close to the data of pre-nuclear

tests. The tritium concentration in each rain showed a seasonal variation, high during the winter and spring and low during the summer and fall. This is attributed to the seasonal changes in meteorological conditions. Tritium would be transported together with nssSO42- from continental China because the tritium shows a positive correlation with nssSO42-.

References

1. H. UEDA, Kagaku, 59 (1989) 610. 2. H. SATAKE, T. YAMANE, Geochem. J., 26 (1992) 299. 3. H. R. KROUSE, V. A. GRINENKO, Stable Isotopes, Natural and

Anthropogenic Sulphur in the Environment, Scope 43, John Wiley and Sons, New York, 1991.

4. S. OKADA, N. MOMOSHIMA, Health Phys., 65 (1993) 595. 5. N. MATSUOKA, E. HIRAI, H. TAGOMORI, N. MOMOSHIMA

Y. TAKASHIMA, Sci. Total Environ., 145 (1994) 197. 6. T. KAJI, Y. TAKASttIMA, Radioisotopes, 39 (1990) 106. 7. N. MOMOSHIMA, Y. TAKASHIMA, J. Radioanal. Chem.,

76 (1983) 7. 8. R. A. DUCE, C. K. UNNI, B. J. RAY, J. M. PROSPERO

J. T. MERRILL, Science, 209 0980) 1522. 9. O. OISHI, A. UTSUNOMIYA, Ann. Rep. Fukuoka Inst. Health

Environ. Sci., 21 (1994) 56. 10. H. HARA, E. I1"o, T. KATOU, Y. KITAMURA, T. KOMEIJI,

M. OOHARA, T. OKrrA, K. SEKIGUCHI, K. TAGUCHI, M. TAMAKI, Y. YAMANAKA, K. YOSItIMURA, Bull. Chem. Soc. Japan., 63 (1990) 2691.

11. S. TORIYAMA, H. SHIMADA, H. ARAKAWA, T. TAKATA, Y. TOHEZOU, Nippon Kagaku Kaishi, 5 (1991 ) 682.

12. H. TSURUTA, Kagaku, 59 (1989) 305. 13. M. TAMAKI, T. KATOU, K. SEKIGUCHI, M. KITAMURA,

K. TAGUCHI, M. OOHARA, A. MORI, S. WAKAMATSU, K. MURANO, T. OKITA, Y. YAMANAKA, H. HARA, Nippon Kagaku Kaishi, 5 (1991) 667.

14. M. ICHIKUNI, J. Geophys. Res., 83 (1978) 6249. 15. S. TSUNOGAI, T. SHINAGAWA, T. KURATA, Geochem. J.,

19 (1985) 77. 16. N. MOMOSHIMA, Y. TAKASHIMA, Mem. Fac. Sci., Kyushu Univ.,

Ser. C, 18 (1991) 21. 17. H. V. BUTTLAR, W. F. L1BBY, J. Inorg. NucL Chem., 1 (1955) 75.

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Relation between tritium concentration and chemical composition in rain at Fukuoka