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Warning For Parents and Caretakers About Radioactive Iodine Detected in Tokyo Drinking Water Supply

March 24, 2011

The Tokyo metropolitan government on Wednesday, March 23, 2011, cautioned residents that infants should drink only bottled water because radioactive iodine exceeding the limit for that age group was detected in water at a purification plant.

The U.S. Embassy in Japan suggests U.S. citizens who live in Tokyo follow these recommendations. In addition, women who are pregnant or nursing should also follow these recommendations and drink bottled water. This guidance is consistent with the guidance that the United States Government would provide to Americans in the United States under similar circumstances.

U.S. citizens in metropolitan Tokyo can take the following steps to safeguard the health of infants (aged 0-3 years):

  • If giving water to infants, use only bottled water.
  • Use only bottled water to mix formula, cereal or other infant foods.

Health experts say that changing the water source for infants from tap water to bottled water should be adequate protection from exposure to radioactive iodine. No additional medication, such as potassium iodide (KI), is necessary at this time. Taking KI when it is not needed can harm a person's health.

At this time, no changes in drinking water are recommended for adults because the limit for adults is higher than the amount detected in the water purification plant. Embassy staff is consulting with health experts and radiation experts to continuously monitor these new developments. If more information becomes available, we will share it with you on the Embassy Web site.

Q & A:

  1. What are we advising U.S. citizens? Why?
    Due to an elevated level of Iodine-131 found at a local Tokyo water purification plant, we are advising American citizens in Tokyo that infants (aged 0-3), as well as women who are pregnant or nursing, should drink only bottled water.

  2. What is the Japanese standard being used?
    The Japanese standard for Iodine-131 in drinking water is 100 becquerels per liter if the water is to be consumed by an infant (0-12 months) and 300 becquerels per liter if the water is to be consumed by an adult. The current reported contamination of 210 becquerels per liter is therefore about twice the permitted level for infants and about two thirds of the permitted level for adults, under Japanese regulations.

  3. What is the U.S. standard?
    The U.S. Environmental Protection Agency’s published standard for Iodine-131 contamination in drinking water is 3 picocuries per liter, which is equal to about 0.1 becquerels per liter. However, the assumptions underlying the EPA standard for continuous exposure do not apply to the current situation in Japan, which is a temporary exposure resulting from an accidental release. In addition, the science of radiation protection has advanced considerably since the EPA standard was published in 1974. If one uses the latest science and makes the adjustments in the calculations underlying the EPA standard in order to make it applicable to the temporary exposure occurring in Japan, one obtains a figure practically identical to the standard that the Japanese authorities are applying.

  4. What is the risk of the current Iodine-131 levels to adults drinking the water?
    Short-term exposures at the levels that have been reported do not present significantly increased risks beyond the sensitive populations already identified.