Fukushima’s Radioactive Ocean Plume Heading Towards You


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Fukushima radiation spreads further than most would like to think – but is it dangerous to you? Image by Decoded Science.

On March 11, 2011, a huge earthquake and subsequent tsunami hit the east coast of the northeast Island of Honshu, Japan. We have all heard the results; major radioactivity emissions occurred involving a particularly bad actor, Cs-137.

So what’s new? Dispersion across the Pacific ocean. At the time of the accident and after, Fukushima released huge amounts of radionuclides into the Earth’s atmosphere and the Pacific ocean.

As the currents carry this radioactive material across the Pacific to the shores of United States, there have been many opinions on its direct impact to life on the coastal communities and the fishing industry.

To understand what’s really going on, we must delve into how we measure radiation, safe limits of radiation, and how much Cs-137 will hit the U.S. when it finally gets here. Let’s start with measuring radiation.

How To Measure Radiation

To understand how much Cs – 137, which has a half-life of 30 years, is going to hit the Pacific Coast of the United States, you must understand the meaning of the measurements.

Radioactivity, simply put, is the amount of ionizing radiation a material releases, or the amount of radiation a material gives off. It’s the amount a radioactive material decays, by emitting gamma, alpha, beta, x-rays or neutrons.

  • The units of measure for radioactivity are Curie (Ci) or Becquerel (Bq).
  • One Curie is 3.7×1010 Bq (37 billion Becquerels), and has a decay rate of one disintegration per second; a very large number.
  • Rad or Gray: For radiation a person absorbs,  the standard unit is Rad or Gray.
  • Rem or Sievert: For the biological risk of exposure, amount we absorb plus medical effects, the unit is Rem or Sievert.
  • Remember that a Curie or Becquerel will tell you the amount of energy release, while a Rem or Sievert will tell you how much is deposited in living tissue.

Which system you use to measure radiation depends on whether you are a U.S. agency (Curie, Rad and Rem) or international (Becquerel, Sievert and Gray). Japan and other countries use the term Becquerel.

High Exposure Produces Death or Radiation Sickness

What we know, regardless of what units we use, is how high the exposure needs to be to produce death or radiation sickness. The lower the dosage, however, the less certain the data. There is tremendous variation in ocean flow, weather and just plain background information, and few have correlated these differences with radiation affect on health.

Here is the Decay Scheme of Caesium-137. Image by Dirk Hünniger.

For example, 500 millisieverts (mSv)  or more can begin to cause symptoms of radiation poisoning. The average background dose (the amount we’re exposed to just from living here) in the U.S. is 2.6 mSv and the legal limit for annual exposure in Japan for emergency nuclear workers is 250 mSV.  A large dose at once is much worse than accumulated radiation over time.

Most sources use becquerels per cubic meter moving through the oceans and arriving at the Pacific coast.

The EPA-recommended level of Cesium-137 in drinking water to protect Human Health is 7400Bq/mtr3. 

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