The health ministry has instructed water purification plants nationwide to temporarily stop taking in rainwater to prevent tap water being contaminated from radiation leaking from the crippled Fukushima No. 1 nuclear plant, ministry officials said Sunday.
While calling on the plants to keep tap water supplies stable, the Health, Labor and Welfare Ministry also proposed covering the water pools at the plants with tarps to keep rainwater out or using powdered activated carbon to help get rid of radioactive materials. The instruction came after abnormal radiation levels were found in tap water at multiple purification plants in Fukushima, Tokyo and other prefectures.
Radioactive materials sent into the atmosphere by the crisis-hit power plant apparently fell to Earth with the rain. When the rain stops, radiation levels in water tend to fall over time.
The Tokyo Metropolitan Government said its test showed radioactive iodine was undetectable Sunday in water at the Kanamachi purification plant in Katsushika Ward, Tokyo, where water with radiation considered unsafe for infants was found March 22.
The undetectable level means the reading of radioactive iodine per kilogram of water sampled was 20 becquerels or less.
At the Kanamachi plant, the level of radioactive iodine has been falling since March 22, when it was 210 becquerels, exceeding the legal limit of 100 becquerels set for infants but below the 300-becquerel limit for adults.
Radioactive iodine also went undetected at the Ozaku purification plant in Hamura in the suburbs of Tokyo the same day, while 27 becquerels was logged at the Asaka plant in Asaka, Saitama Prefecture, north of Tokyo.
Another government survey over the weekend showed that radiation levels in Yamagata Prefecture had returned to normal.
The maximum radiation level in Yamagata was 0.074 microsievert from 5 p.m. Saturday to 9 a.m. Sunday, down from 0.089 observed between Friday and Saturday. A human is exposed to radiation of 50 microsieverts in one chest X-ray.
The maximum radiation level detected in Tokyo, Tochigi and Ibaraki prefectures also continued to fall.
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