UPDATED 3/29/1 12:30 a.m.

The Environmental Protection Agency confirmed Monday that one of its monitors found trace amounts of the radioactive particle Iodine-131 in Honolulu’s air last week.

In an email to Civil Beat, EPA spokesman Dean Higuchi said the findings were “still thousands of times below levels of concern.” The radioactive isotope is consistent with particles being released by the damaged Japanese nuclear power plant.

The detailed analysis came after a RadNet air monitor in Honolulu picked up a “minuscule increase” in radiation on March 21. The charcoal sampling filter from the monitor was sent to the EPA’s national radiation lab in Alabama to find out which isotope was present.

UPDATE: Higuchi told Civil Beat there have been no other spikes in radiation for Honolulu since last week.

Iodine-131 has a half life of eight days. In other words, when the radioactive particles reach Hawaii after a week-long journey from Japan, half of them stabilize and are no longer harmful.

According to Higuchi, the analysis showed the following results for Oahu. The measurements used for Iodine-131 are picocuries per meter cubed:

  • March 20, 2011 – iodine-131: 0.759 pCi/m3
  • March 21, 2011 – iodine-131: 1.35 pCi/m3
  • March 23, 2011 – iodine-131: 0.182 pCi/m3

Honolulu’s radiation levels peaked March 21 and dropped two days later.

In very large doses, Iodine-131 can cause acute radiation syndrome, which can produce symptoms like nausea, vomiting, fatigue and certain forms of cancer. For a sense of how much Iodine-131 a person must be exposed to before it becomes unsafe, Higuchi offered the following comparisons1:

  • 37,000,000 pCi/m3 (if people would be exposed for one hour)
  • 1,500,000 pCi/m3 (if people would be exposed for 24 hours)
  • 385,000 pCi/m3 (if people would be exposed for 96 hours)

Using the peak number of Iodine-131 detected on March 21, Honolulu was more that 285,000 times below dangerous levels. (And even then, exposure would have to last for four days.)

However, Higuchi says the EPA would begin consulting state health officials if radiation levels reached even one percent of those mentioned above. State and federal officials have not indicated that there have been any spikes in radiation levels for Honolulu since last week. The EPA uses historical data to determine if there’s been a notable increase.


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  1. An earlier version of this story said EPA Spokesman Dean Higuchi said Honolulu residents need not evacuate or seek shelter. This was not what Higuchi said. He merely provided EPA conversions for shelter and evacuation related to radiation. The numbers indicate that Honolulu’s radiation readings are far below levels requiring either shelter or evacuation, per EPA guidelines.