抄録
The concentrations of medically used radionuclides in activated sludge samples were measured for 10 waste water treatment plants (WWTP) in Tokyo from October 1983 to March 1994. The nuclides 99mTc, 67Ga, 111In 123I 131I and 201Tl, among others, could be detected, but these concentration levels were lower than the legal concentration limits in Japan. The excess activated sludge is usually incinerated at WWTP; then the resulting ash is transported for reclamation in Tokyo Bay. Internal and/or external exposure doses were evaluated for the following cases: (1) The dose of the public attributed to radioactive iodine and 201Tl, which were released from the incinerator by burning sludge; (2) The dose of the workers during the process of transport and reclamation of the ash. As a result, the effective doses were sufficiently lower than the dose limit 1mSv/y. The decay of the radionuclides were calculated over a period of curing of the landfill. It was found that the radionuclides had decayed out to approximately one nuclide. The effective dose of the public can therefore be ignored. Moreover, it was clarified that the effective dose of the public resulting from 99Tc is negligibly low in value at the present time.
