1992 Volume 41 Issue 9 Pages 444-450
Tritium concentrations of environmental waters in Aichi Prefecture were determined from 1973 to 1989. They are rain water, river waters and sea waters.
In 1970's, tritium concentrations of environmental waters were more than the natural levels under the influence of the atmospheric nuclear tests. However, atmospheric nuclear tests have not been carried out after Oct. 1980 and the tritium concentrations are going to return to the natural levels. Annual means of tritium concentration in 1989 were as follows: 0.67 Bq/l for rain water, 1.1 Bq/l for Kiso river and Shonai river, 0.85 Bq/l for Yahagi river, 0.70 Bq/l for Toyo river, and 0.41 Bq/l for surface sea water. Also, tritium concentration of sea bottom water was 0.50±0.28 Bq/l and rather constant yearly.
Among environmental waters, only rain water was previously having seasonal variation of tritium concentration and it was showing“spring peak”when the troposphere and the stratosphere were mixed actively. At present, tritium concentration of rain water has a little seasonal variation, and is slightly lower in summer under the influence of the atmosphere coming over from the ocean.
With regard to the direct influence of rain water to river waters, it was found by means of time series analysis that Kiso river was the least affected of river waters and Yahagi river was the most. The apparent residence time, in which rain water stayed in the underground before it flowed out as river water, was presumed to be 4.9 years for Kiso river, 3.6 years for Yahagi river, 2.0 years for Toyo river, respectively.
