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Temporal variations and behaviour of 90Sr and 137Cs in precipitation, river water and seawater in Japan
397
Temporal variations and behaviour of 90Sr and 137 Cs in precipitation, river water and seawater in Japan Yoshihiro Ikeuchi* Japan Chemical Analysis Center, Chiba 263-0002, Japan Abstract The 90 Sr and 137 Cs concentrations in precipitation (wet and dry deposition), in soil, river water, coastal surface seawater and seabed sediment were determined during 1963–1999 at 10–47 sites in Japan. The 90 Sr and 137 Cs concentrations in precipitation decreased during this time by more than 3 orders of magnitude, showing 4 peaks after the large-scale Chinese atmospheric nuclear weapons tests, and one sharp peak of 137 Cs due to the Chernobyl accident in 1986. The temporal variations in soil (0–20 cm depth), river water, seawater and seabed sediment had decreased gradually. Specific features were an increase of 137 Cs/90 Sr ratio in soil with time, higher 90 Sr than 137 Cs concentrations observed in river water, a lower 137 Cs/90 Sr ratio in seawater than in precipitation, and higher 137 Cs than 90 Sr concentrations in seabed sediment. The 90 Sr and 137 Cs cumulative depositions by precipitation were calculated from 1963 to 1999, having maximum values of 2,600 MBq/km2 and 3,700 MBq/km2 in 1965, respectively. 27% of 137 Cs and 51% of 90 Sr were removed from soil (0–20 cm depth) during 1980–1999. However, when comparing cumulative depositions by precipitation and concentrations in coastal surface seawater, the removal rate of 137 Cs was during 1980–1999 about 1.2 times higher than for 90 Sr, documenting that more 137 Cs was removed to seabed sediment, and more 90 Sr came to coastal waters via rivers. Keywords: Environmental radioactivity, Radionuclides, 90 Sr, 137 Cs, Temporal variation, Precipitation, Soil, Seawater, Sediment, Japan coast
1. Introduction Large amounts of 90 Sr and 137 Cs have been deposited globally due to fallout from atmospheric nuclear weapons tests conducted by USA, USSR, UK, France and China during 1945–1980, with maximum annual deposition in 1963. A smaller amount of 137 Cs was deposited over Japan after the Chernobyl accident which occurred in 1986. Therefore, large amounts of 90 Sr and 137 Cs were introduced into soil, river water and seawater via precipitation (dry and wet deposition). It has been therefore important to investigate the behaviour and fate of these * Address: Japan Chemical Analysis Center, 295-3, San-no-cho, Inage, Chiba 263-0002, Japan; phone: (+81) 43 424 8661; fax: (+81) 43 423 5326; e-mail: [email protected]
RADIOACTIVITY IN THE ENVIRONMENT VOLUME 8 ISSN 1569-4860/DOI 10.1016/S1569-4860(05)08032-0
© 2006 Elsevier Ltd. All rights reserved.
398
Y. Ikeuchi
radionuclides in order to assess the degree of contamination of the terrestrial and marine environments. Environmental samples were collected annually by the Japanese prefectural institutes from 1963–1999. Subsequent analyses of 90 Sr and 137 Cs were performed by governmental institutes, mainly by the Japan Chemical Analysis Center (JCAC). The resulting data has since been archived at the Ministry of Education, Culture, Sports, Science and Technology (MEXT); formerly the Science and Technology Agency (STA) of Japan. In this paper, temporal variations of 90 Sr and 137 Cs concentrations in precipitation, soil, river water, coastal surface seawater and seabed sediment during 1963–1999 are described. The behaviour of 90 Sr and 137 Cs in these environmental systems are discussed as well, specifically their transport between different compartments, e.g. between precipitation and soil, precipitation and seawater, soil and river water, river water and seawater, and finally between seawater and seabed sediment.
2. Sampling and analytical procedures Precipitation samples were collected during 1963–1999 once per month at 22–47 sites, soil samples were collected once per year at 30–47 sites, river water samples were collected twice per year at 29–47 sites, seawater and seabed sediment samples were collected once per year at 10–13 sites (9 sites on the Pacific side, 4 sites on the sea of Japan side). The sampling sites of seawater and seabed sediment were the same. 90 Sr and 137 Cs, collected from 0.5 m2 surface areas of monthly precipitation, 100 g of soil, 100 l of river water, 40 l of seawater and 100 g of seabed sediment were determined mainly in the Japan Chemical Analysis Center. 90 Sr was separated as carbonate, oxalate and nitrate. Ba and Ra impurities were removed as chromates. After scavenging of 90 Y, SrCO3 was recovered and weighed to obtain the chemical yield. After 2 weeks, 90 Y separated from the 90 Sr was analysed using a low background gas flow counter. 137 Cs in the supernatant solution at carbonate precipitation phase was separated as Cs3 PO4 · 12MoO3 , and 87 Rb impurity was removed by the cation exchange method. Cs2 PtCl6 was precipitated and weighed to obtain chemical yield. 137 Cs was analysed using a low background gas flow counter. The detection limits for both 90 Sr and 137 Cs (3σ criterion in counting statistics) were ∼0.2 mBq/l for river water, ∼0.5 mBq/l for seawater and ∼0.4 Bq/kg for seabed sediment.
3. Results and discussion The results are presented as the average values (arithmetic means) in order to investigate the behaviour and fate of 137 Cs and 90 Sr over the territory of Japan. The observed 90 Sr and 137 Cs concentrations in the environment were different due to sampling at different latitudes, or sampling either on the side of the Japan Sea, or on the Pacific side. The concentrations of 90 Sr and 137 Cs in precipitation decreased by more than 3 orders of magnitude, showing 4 peaks after the large-scale Chinese atmospheric nuclear weapons tests, and one sharp peak of 137 Cs
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
399
due to the Chernobyl accident in 1986 (Fig. 1). On the other hand, the concentrations in soil (0–20 cm depth), river water, seawater and seabed sediment had decreased gradually, showing 137 Cs levels of 2.0–4.5, 0.03–0.57, 0.98–2.0 and 9.2–33 times higher than 90 Sr levels, respectively (Figs. 2–5). The interesting features that can be observed from the presented data sets (Figs. 2–5) include: • • • •
the increase of 137 Cs/90 Sr ratio in soil with time (from 2.0 to 4.5); higher 90 Sr than 137 Cs concentrations in river water; lower 137 Cs/90 Sr ratios in seawater than in precipitation; higher 137 Cs than 90 Sr concentrations in seabed sediment.
Fig. 1. Average 90 Sr and 137 Cs depositions by precipitation at 22–47 sampling sites.
Fig. 2. Average 90 Sr and 137 Cs depositions in soil (0–20 cm depth) at 30–47 sampling sites.
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Fig. 3. Average 90 Sr and 137 Cs concentrations in river water at 29–47 sampling sites.
Fig. 4. Average 90 Sr and 137 Cs concentrations in seawater at 10–13 sampling sites.
Fig. 5. Average 90 Sr and 137 Cs massive activities in seabed sediment at 10–13 sampling sites.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
401
The 90 Sr and 137 Cs cumulative depositions by precipitation in 1962 (Figs. 6 and 7) were calculated from the data for the Northern Hemisphere (UNSCEAR, 1982), which were updated using more recent data published by Monetti (1996) comparing the analysed data in 1963 (Fig. 1). The 90 Sr and 137 Cs cumulative depositions by precipitation during 1963–1999 (Figs. 6 and 7) were calculated from analysed data (Fig. 1) considering decay corrections for 90 Sr and 137 Cs. It was found that maximum 90 Sr and 137 Cs cumulative depositions by precipitation were in 1965: 2,600 MBq/km2 for 90 Sr and 3,700 MBq/km2 for 137 Cs. List et al. (1965) reported for the maximum 90 Sr cumulative deposition in 1963 and early 1964 on soil at 30–45◦ N values between 1,000 and 1,600 MBq/km2 . About 2,200 MBq/km2 of 90 Sr was deposited on Japanese soil in 1965–1967 according to results published by Meyer et al. (1968), in a reasonable agreement with our value.
Fig. 6. 137 Cs cumulative deposition for precipitation and soil.
Fig. 7. 90 Sr cumulative deposition for precipitation and soil.
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Y. Ikeuchi
The 137 Cs/90 Sr activity ratio for the maximum cumulative deposition is 1.4 ± 0.1, a value close to 1.6, derived in the UNSCEAR (1982) Report. The cumulative deposition of 137 Cs by precipitation in 1972 and 1975 was almost the same as the observed deposition in soil (Fig. 6). On the contrary, for 90 Sr the observed cumulative deposition in soil was only 0.6 times of the cumulative deposition by precipitation (Fig. 7). Comparing the 137 Cs/90 Sr ratios in soil (0–20 cm depth) with 137 Cs/90 Sr ratios in cumulative deposition, we see that the ratios increased from 1.2 in 1962 to 2.4 in 1999 (Fig. 8). This indicates that 90 Sr has been removed from soil (0–20 cm depth) much faster than 137 Cs. Comparing cumulative depositions by precipitation and in soil after the Chinese atmospheric nuclear weapons tests, we find that in average 27% of 137 Cs and 51% of 90 Sr has been removed from soil during 1980–1999 (Figs. 9 and 10). This documents that the removal rate of 90 Sr from soil was about twice than that for 137 Cs.
Fig. 8. Average 137 Cs/90 Sr ratios in precipitation and soil.
Fig. 9. 137 Cs correlation – soil vs. precipitation.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
403
Fig. 10. 90 Sr correlation – soil vs. precipitation.
Fig. 11. 137 Cs correlation – seawater vs. precipitation.
A comparison of cumulative 90 Sr and 137 Cs deposition by precipitation and corresponding concentrations in seawater is more difficult, because we are dealing with different units (actually, water column and sediment inventories should be used in such comparison). Knowing the ratio of 90 Sr (and 137 Cs) in precipitation and seawater, and comparing 1/100 of cumulative deposition by precipitation and concentration of seawater (for convenience), we find that during 1980–1999, after the Chinese atmospheric nuclear weapons tests, around 55% of 137 Cs and 47% of 90 Sr have been removed from surface seawater (Figs. 11 and 12). The removal rate of 137 Cs was thus 1.2 times higher than that of 90 Sr. This ratio indicates that more 137 Cs than 90 Sr has been removed from seawater to seabed sediment (as expected, because Cs is more particle reactive and its Kd – distribution coefficient is higher than for Sr). This ratio, however, could also be influenced by the fact that more 90 Sr than 137 Cs has been transported by rivers to coastal waters.
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Fig. 12. 90 Sr correlation – seawater vs. precipitation.
4. Conclusions Several conclusions can be made from the present study: • Maximum cumulative deposition by precipitation in Japan in 1965 was 3,700 MBq/km2 and 2,600 MBq/km2 for 137 Cs and 90 Sr, respectively. • Comparing cumulative depositions for precipitation and soil during 1980–1999, 27% of 137 Cs and 51% of 90 Sr were removed from soil after the Chinese atmospheric nuclear weapons tests. The removal rate of 90 Sr was found to be about twice than that of 137 Cs. • Comparing cumulative depositions for precipitation and coastal surface seawater during 1980–1999, the removal rate of 137 Cs was found to be about 1.2 times than that of 90 Sr, probably due to the fact that more 137 Cs was removed to seabed sediment.
Acknowledgements The author wishes to thank the staff of prefectural institutes who collected environmental samples, as well as the colleagues of the JCAC who assisted in the analysis of samples. He would also like to express his gratitude to Prof. H. Hirao (Japan Chemical Analysis Center), and Prof. P.P. Povinec (International Atomic Energy Agency–Marine Environment Laboratory) for support and suggestions. The described research work was funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT, former the Science and Technology Agency (STA)) of Japan.
References List, R.J., Machta, L., Alexander, L.T., Allen, J.S., Meyer, M.W., Valasis, V.T., Hardy Jr., E.P. (1965). Strontium-90 on the Earth’s surface. In: Klement Jr., A.W. (Ed.), Radioactive Fallout from Nuclear Weapons Tests. AEC Symposium Series, No. 5 CONF-765. AEC, Washington, DC, pp. 359–368.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
405
Meyer, M.W., Allen, J.S., Alexander, L.T., Hardy, E. (1968). Strontium-90 on the Earth’s Surface. Summary and Interpretation of a World-Wide Soil Sampling Program: 1961–1967 Results. USAEC Report TID-24341. Health and Safety Laboratory. Monetti, A. (1996). Worldwide Deposition of Strontium-90 through 1990. USDOE Report EML-579. EML, New York, 56 pp. UNSCEAR (1982). Ionizing radiation: Sources and biological effects. United Nations Scientific Committee on the Effects of Atomic Radiation. Report to the General Assembly, United Nations, New York.
Further reading IAEA (1986). Summary report on the post-accident review meeting on the Chernobyl accident. Safety Series No. 75INSAG-1. IAEA, Vienna, pp. 33–34. Norris, R.S., Burrows, A.S., Fieldhouse, R.W. (1994). British, French and Chinese Nuclear Weapons. Nuclear Weapons Databook, vol. V. Natural Resources Defense Council (NRDC), Washington, DC.
Temporal variations and behaviour of 90Sr and 137 Cs in precipitation, river water and seawater in Japan Yoshihiro Ikeuchi* Japan Chemical Analysis Center, Chiba 263-0002, Japan Abstract The 90 Sr and 137 Cs concentrations in precipitation (wet and dry deposition), in soil, river water, coastal surface seawater and seabed sediment were determined during 1963–1999 at 10–47 sites in Japan. The 90 Sr and 137 Cs concentrations in precipitation decreased during this time by more than 3 orders of magnitude, showing 4 peaks after the large-scale Chinese atmospheric nuclear weapons tests, and one sharp peak of 137 Cs due to the Chernobyl accident in 1986. The temporal variations in soil (0–20 cm depth), river water, seawater and seabed sediment had decreased gradually. Specific features were an increase of 137 Cs/90 Sr ratio in soil with time, higher 90 Sr than 137 Cs concentrations observed in river water, a lower 137 Cs/90 Sr ratio in seawater than in precipitation, and higher 137 Cs than 90 Sr concentrations in seabed sediment. The 90 Sr and 137 Cs cumulative depositions by precipitation were calculated from 1963 to 1999, having maximum values of 2,600 MBq/km2 and 3,700 MBq/km2 in 1965, respectively. 27% of 137 Cs and 51% of 90 Sr were removed from soil (0–20 cm depth) during 1980–1999. However, when comparing cumulative depositions by precipitation and concentrations in coastal surface seawater, the removal rate of 137 Cs was during 1980–1999 about 1.2 times higher than for 90 Sr, documenting that more 137 Cs was removed to seabed sediment, and more 90 Sr came to coastal waters via rivers. Keywords: Environmental radioactivity, Radionuclides, 90 Sr, 137 Cs, Temporal variation, Precipitation, Soil, Seawater, Sediment, Japan coast
1. Introduction Large amounts of 90 Sr and 137 Cs have been deposited globally due to fallout from atmospheric nuclear weapons tests conducted by USA, USSR, UK, France and China during 1945–1980, with maximum annual deposition in 1963. A smaller amount of 137 Cs was deposited over Japan after the Chernobyl accident which occurred in 1986. Therefore, large amounts of 90 Sr and 137 Cs were introduced into soil, river water and seawater via precipitation (dry and wet deposition). It has been therefore important to investigate the behaviour and fate of these * Address: Japan Chemical Analysis Center, 295-3, San-no-cho, Inage, Chiba 263-0002, Japan; phone: (+81) 43 424 8661; fax: (+81) 43 423 5326; e-mail: [email protected]
RADIOACTIVITY IN THE ENVIRONMENT VOLUME 8 ISSN 1569-4860/DOI 10.1016/S1569-4860(05)08032-0
© 2006 Elsevier Ltd. All rights reserved.
398
Y. Ikeuchi
radionuclides in order to assess the degree of contamination of the terrestrial and marine environments. Environmental samples were collected annually by the Japanese prefectural institutes from 1963–1999. Subsequent analyses of 90 Sr and 137 Cs were performed by governmental institutes, mainly by the Japan Chemical Analysis Center (JCAC). The resulting data has since been archived at the Ministry of Education, Culture, Sports, Science and Technology (MEXT); formerly the Science and Technology Agency (STA) of Japan. In this paper, temporal variations of 90 Sr and 137 Cs concentrations in precipitation, soil, river water, coastal surface seawater and seabed sediment during 1963–1999 are described. The behaviour of 90 Sr and 137 Cs in these environmental systems are discussed as well, specifically their transport between different compartments, e.g. between precipitation and soil, precipitation and seawater, soil and river water, river water and seawater, and finally between seawater and seabed sediment.
2. Sampling and analytical procedures Precipitation samples were collected during 1963–1999 once per month at 22–47 sites, soil samples were collected once per year at 30–47 sites, river water samples were collected twice per year at 29–47 sites, seawater and seabed sediment samples were collected once per year at 10–13 sites (9 sites on the Pacific side, 4 sites on the sea of Japan side). The sampling sites of seawater and seabed sediment were the same. 90 Sr and 137 Cs, collected from 0.5 m2 surface areas of monthly precipitation, 100 g of soil, 100 l of river water, 40 l of seawater and 100 g of seabed sediment were determined mainly in the Japan Chemical Analysis Center. 90 Sr was separated as carbonate, oxalate and nitrate. Ba and Ra impurities were removed as chromates. After scavenging of 90 Y, SrCO3 was recovered and weighed to obtain the chemical yield. After 2 weeks, 90 Y separated from the 90 Sr was analysed using a low background gas flow counter. 137 Cs in the supernatant solution at carbonate precipitation phase was separated as Cs3 PO4 · 12MoO3 , and 87 Rb impurity was removed by the cation exchange method. Cs2 PtCl6 was precipitated and weighed to obtain chemical yield. 137 Cs was analysed using a low background gas flow counter. The detection limits for both 90 Sr and 137 Cs (3σ criterion in counting statistics) were ∼0.2 mBq/l for river water, ∼0.5 mBq/l for seawater and ∼0.4 Bq/kg for seabed sediment.
3. Results and discussion The results are presented as the average values (arithmetic means) in order to investigate the behaviour and fate of 137 Cs and 90 Sr over the territory of Japan. The observed 90 Sr and 137 Cs concentrations in the environment were different due to sampling at different latitudes, or sampling either on the side of the Japan Sea, or on the Pacific side. The concentrations of 90 Sr and 137 Cs in precipitation decreased by more than 3 orders of magnitude, showing 4 peaks after the large-scale Chinese atmospheric nuclear weapons tests, and one sharp peak of 137 Cs
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
399
due to the Chernobyl accident in 1986 (Fig. 1). On the other hand, the concentrations in soil (0–20 cm depth), river water, seawater and seabed sediment had decreased gradually, showing 137 Cs levels of 2.0–4.5, 0.03–0.57, 0.98–2.0 and 9.2–33 times higher than 90 Sr levels, respectively (Figs. 2–5). The interesting features that can be observed from the presented data sets (Figs. 2–5) include: • • • •
the increase of 137 Cs/90 Sr ratio in soil with time (from 2.0 to 4.5); higher 90 Sr than 137 Cs concentrations in river water; lower 137 Cs/90 Sr ratios in seawater than in precipitation; higher 137 Cs than 90 Sr concentrations in seabed sediment.
Fig. 1. Average 90 Sr and 137 Cs depositions by precipitation at 22–47 sampling sites.
Fig. 2. Average 90 Sr and 137 Cs depositions in soil (0–20 cm depth) at 30–47 sampling sites.
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Y. Ikeuchi
Fig. 3. Average 90 Sr and 137 Cs concentrations in river water at 29–47 sampling sites.
Fig. 4. Average 90 Sr and 137 Cs concentrations in seawater at 10–13 sampling sites.
Fig. 5. Average 90 Sr and 137 Cs massive activities in seabed sediment at 10–13 sampling sites.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
401
The 90 Sr and 137 Cs cumulative depositions by precipitation in 1962 (Figs. 6 and 7) were calculated from the data for the Northern Hemisphere (UNSCEAR, 1982), which were updated using more recent data published by Monetti (1996) comparing the analysed data in 1963 (Fig. 1). The 90 Sr and 137 Cs cumulative depositions by precipitation during 1963–1999 (Figs. 6 and 7) were calculated from analysed data (Fig. 1) considering decay corrections for 90 Sr and 137 Cs. It was found that maximum 90 Sr and 137 Cs cumulative depositions by precipitation were in 1965: 2,600 MBq/km2 for 90 Sr and 3,700 MBq/km2 for 137 Cs. List et al. (1965) reported for the maximum 90 Sr cumulative deposition in 1963 and early 1964 on soil at 30–45◦ N values between 1,000 and 1,600 MBq/km2 . About 2,200 MBq/km2 of 90 Sr was deposited on Japanese soil in 1965–1967 according to results published by Meyer et al. (1968), in a reasonable agreement with our value.
Fig. 6. 137 Cs cumulative deposition for precipitation and soil.
Fig. 7. 90 Sr cumulative deposition for precipitation and soil.
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Y. Ikeuchi
The 137 Cs/90 Sr activity ratio for the maximum cumulative deposition is 1.4 ± 0.1, a value close to 1.6, derived in the UNSCEAR (1982) Report. The cumulative deposition of 137 Cs by precipitation in 1972 and 1975 was almost the same as the observed deposition in soil (Fig. 6). On the contrary, for 90 Sr the observed cumulative deposition in soil was only 0.6 times of the cumulative deposition by precipitation (Fig. 7). Comparing the 137 Cs/90 Sr ratios in soil (0–20 cm depth) with 137 Cs/90 Sr ratios in cumulative deposition, we see that the ratios increased from 1.2 in 1962 to 2.4 in 1999 (Fig. 8). This indicates that 90 Sr has been removed from soil (0–20 cm depth) much faster than 137 Cs. Comparing cumulative depositions by precipitation and in soil after the Chinese atmospheric nuclear weapons tests, we find that in average 27% of 137 Cs and 51% of 90 Sr has been removed from soil during 1980–1999 (Figs. 9 and 10). This documents that the removal rate of 90 Sr from soil was about twice than that for 137 Cs.
Fig. 8. Average 137 Cs/90 Sr ratios in precipitation and soil.
Fig. 9. 137 Cs correlation – soil vs. precipitation.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
403
Fig. 10. 90 Sr correlation – soil vs. precipitation.
Fig. 11. 137 Cs correlation – seawater vs. precipitation.
A comparison of cumulative 90 Sr and 137 Cs deposition by precipitation and corresponding concentrations in seawater is more difficult, because we are dealing with different units (actually, water column and sediment inventories should be used in such comparison). Knowing the ratio of 90 Sr (and 137 Cs) in precipitation and seawater, and comparing 1/100 of cumulative deposition by precipitation and concentration of seawater (for convenience), we find that during 1980–1999, after the Chinese atmospheric nuclear weapons tests, around 55% of 137 Cs and 47% of 90 Sr have been removed from surface seawater (Figs. 11 and 12). The removal rate of 137 Cs was thus 1.2 times higher than that of 90 Sr. This ratio indicates that more 137 Cs than 90 Sr has been removed from seawater to seabed sediment (as expected, because Cs is more particle reactive and its Kd – distribution coefficient is higher than for Sr). This ratio, however, could also be influenced by the fact that more 90 Sr than 137 Cs has been transported by rivers to coastal waters.
404
Y. Ikeuchi
Fig. 12. 90 Sr correlation – seawater vs. precipitation.
4. Conclusions Several conclusions can be made from the present study: • Maximum cumulative deposition by precipitation in Japan in 1965 was 3,700 MBq/km2 and 2,600 MBq/km2 for 137 Cs and 90 Sr, respectively. • Comparing cumulative depositions for precipitation and soil during 1980–1999, 27% of 137 Cs and 51% of 90 Sr were removed from soil after the Chinese atmospheric nuclear weapons tests. The removal rate of 90 Sr was found to be about twice than that of 137 Cs. • Comparing cumulative depositions for precipitation and coastal surface seawater during 1980–1999, the removal rate of 137 Cs was found to be about 1.2 times than that of 90 Sr, probably due to the fact that more 137 Cs was removed to seabed sediment.
Acknowledgements The author wishes to thank the staff of prefectural institutes who collected environmental samples, as well as the colleagues of the JCAC who assisted in the analysis of samples. He would also like to express his gratitude to Prof. H. Hirao (Japan Chemical Analysis Center), and Prof. P.P. Povinec (International Atomic Energy Agency–Marine Environment Laboratory) for support and suggestions. The described research work was funded by the Ministry of Education, Culture, Sports, Science and Technology (MEXT, former the Science and Technology Agency (STA)) of Japan.
References List, R.J., Machta, L., Alexander, L.T., Allen, J.S., Meyer, M.W., Valasis, V.T., Hardy Jr., E.P. (1965). Strontium-90 on the Earth’s surface. In: Klement Jr., A.W. (Ed.), Radioactive Fallout from Nuclear Weapons Tests. AEC Symposium Series, No. 5 CONF-765. AEC, Washington, DC, pp. 359–368.
90 Sr and 137 Cs in precipitation, river water and seawater in Japan
405
Meyer, M.W., Allen, J.S., Alexander, L.T., Hardy, E. (1968). Strontium-90 on the Earth’s Surface. Summary and Interpretation of a World-Wide Soil Sampling Program: 1961–1967 Results. USAEC Report TID-24341. Health and Safety Laboratory. Monetti, A. (1996). Worldwide Deposition of Strontium-90 through 1990. USDOE Report EML-579. EML, New York, 56 pp. UNSCEAR (1982). Ionizing radiation: Sources and biological effects. United Nations Scientific Committee on the Effects of Atomic Radiation. Report to the General Assembly, United Nations, New York.
Further reading IAEA (1986). Summary report on the post-accident review meeting on the Chernobyl accident. Safety Series No. 75INSAG-1. IAEA, Vienna, pp. 33–34. Norris, R.S., Burrows, A.S., Fieldhouse, R.W. (1994). British, French and Chinese Nuclear Weapons. Nuclear Weapons Databook, vol. V. Natural Resources Defense Council (NRDC), Washington, DC.