Status of a national monitoring program for environmental radioactivity and investigation of artificial radionuclide concentrations (Cs-134, Cs-137 and I-131) in rivers and lakes

A survey of the artificial radionuclides in rivers and lakes was conducted to investigate their levels in surface water. Water samples were collected at 60 points and analyzed by gamma-ray spectrometry with a measurement time of 10,000 seconds for Cs-134, Cs-137, and I-131. The obained values were lower than MDA for all points, except one point for I-131 that was 0.533 +/- 0.058 Bq/L. I-131 is known as a radioactive material that occurs frequently in sewage treatment plants. Because it is often used for medical treatments and subject to spreading into the environment due to the excretion from the patients. For the point where I-131 was detected, we conducted additional investigation on the upstream river point and the effluent points of nearby sewage treatment plant to find the source of I-131. I-131 was not detected at the upstream points of one of the upstream sewage treatment plants but found at the downstream points with the level being 0.257 +/- 0.034 to 0.799 +/- 0.051 Bq/L, proving the sewage treatment plant was the (131)Isource.