福岡県における海洋環境放射能調査 (1971年度～1992年度)

抄録

Samples of sea water and sea sediments collected during a period of fiscal year 1971-1992 and those of marine products during fiscal year 1975-1992 from the territorial waters of Fukuoka prefecture were analyzed and the results are summarized.
As for the concentration of radioactive substances in sea water, the measurements fell in a range from 1.70 to 7.31mBq/l for ⁹⁰Sr and from 2.80 to 6.29mBq/l for ¹³⁷Cs. Their values in 1992 came down to one third and one half of their maximum values, respectively. The ¹³⁷Cs concentration in sea sediments was found in a range from 1.70 to 9.62Bq/kg dried soil. The distribution coefficient of sea sediments vs sea water was as large as 887 on average.
The ¹³⁷Cs concentration in sea bream was found in a range from 0.180 to 0.311Bq/kg wet, representing a higher level than those of other foods such as cereal crops, vegetables and milk.
At the time of nuclear explosion tests in China in 1976 and 1980 as well as the accident at the Chernobyl nuclear power plant in 1986, the concentration of ¹³⁷Cs increased in sea water and sea sediments, while no apparent change was detected in sea bream.
As a result of the present survey, it was concluded that the measurements of ⁹⁰Sr and ¹³⁷Cs concentration in marine samples have shown no significant difference between the values for Fukuoka prefecture and the national mean values. Furthermore, Fukuoka's level has always stayed at or below what has been representative in the national coastal waters of the Sea of Japan.