Fukushima’s Radioactive Ocean Plume Heading Towards You

Radiation Plume Across Pacific Ocean


Show here is a map of the Japanese nuclear power plants. Image courtesy of the USA Government.

How much Cesium 137 will reach the Pacific coast of the United States from the Fukushima accident? It’s a complex subject. How the isotope moves through the ocean, and how much gets to the United States, depends not only on the transport mechanism of the Kuroshio-extension currents from Japan but the food chain of marine life. So let’s start with the projections suggested by Deep Sea Research as well as several other studies referenced below.

    • Cs-137 has a half-life of 30.1 years – that means it can travel a very long way before decay.
    • According to simulations,  the Kuroshio Current and Extension, a very active current, strongly dilutes the Cs-137 plume.
    • Projections show that greater than 10 Bq/m3 will reach the U.S. Coast and Hawaiian Islands by early 2014.
    • Projections expect Cs-137 levels between 2014 and 2020 to be 10-30 Bq/m3.
    • The California coast should see slightly lower levels between 2016 and 2025 due to subsurface pathways.
    • Projections show the concentration of the diluted radioactive material well below the WHO’s safety levels.
    • The majority of the North Pacific Gyre, a region of ocean that circulates slowly clockwise, has trapped debris and continues to dilute the radiation.
    • About 25% will eventually travel to the Indian Ocean and the South Pacific over two to three decades.

Fukushima Radiation Plume: How Dangerous Is It?

Comparing radioactive measurements in Becquerels/m3 with the projections of the radiation level from Cs-137 to hit the Pacific coastal areas from the U.S. through Canada clearly shows these levels considerably below human health safety levels of concern – both projected from the Environmental Protection Agency and the World Health Organization. The Fukushima radiation plume looks scary, but the material’s half-life, sedimentation, mixing, and the movement of radioactive material via ocean currents should dilute the impact of the Cs-137 coming from the nuclear disaster in Japan on the United States West Coast for now, and for the generations to come.


Hsu, Jeremy. Fukushima’s Radioactive Ocean Plume to reach US Waters by 2014(2013). Live Science, Accessed November 17, 2013.

Anscombe, Nadya. Fukushima radiation could reach US coast in five years. (2012). Environment Research. Accessed November 17, 2013.

Nuclear Energy Institute. Public Health: Protecting Our Communities, Measuring Radiation. Accessed November 17, 2013.

EPA. EPA Facts about Cesium-137. Accessed November 17, 2013.

Rossi,Vincent, Sebille, Eric, Gupta, Alexander, Garcon, Veronique, England, Matthew. Deep Sea Research Part 1: Oceanographic Research Papers, Multi-decadal projections of surface and interior pathways of the Fukushima Cesium-137 radioactive plume. (2013). Science Direct. Accessed November 17, 2013.

Global Research. Fukushima Radiation Levels Will concentrate in Pickets at Specific US and Canada West Coast Locations. (2013). Accessed November 17, 2013.

© Copyright 2013 Judy Haar, All rights Reserved. Written For: Decoded Science
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  2. Arthur Cook says

    All this data relates to the initial discharge. The latest discharge from a ditch is over 30,000Bqs. So, what happens to the numbers from this? And if they mess up removing the rods?

  3. greenthinker2012 says

    I prefer neutral language be used in science articles.
    Compare this early sentence in the article…
    “Fukushima released huge amounts of radionuclides into the Earth’s atmosphere and the Pacific ocean.”

    with the reality being that the amount is measured in Kilograms.
    Even if we measure the amount using Becquerels, it is dwarfed by the amounts of natural radionuclides present on the planet.

  4. ChrisLHPhys14 says

    Judy Haar,

    Thank you for an informative article. This adds to the radioecological understanding of the aftermath of Fukushima. What I would like to comment on is the following paragraph: “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.” I think you meant to put in the second parenthesis, (Becquerel, Gray, and Sievert), since a Gray=100 rad, and a Sv=100 rem. Thank you.

  5. Dillon says

    Here’s a couple thoughts.

    1. Is it safe to drink water with a diluted toxic substance in it? Sure over time in low quantities it’s probably harmless. But these fish LIVE in the water, they breath the water. Over their lives they will accumulate these elements in their bodies.

    2. It will take 30 years for these elements to decay, Have scientist thought about the hydrosphere and how water gets DEPOSITED into systems like aquifers and so on. Certainly where one radioactive isotope goes, another will follow. Where one radioactive isotope gets deposited, another will follow.

    • Scott Haas says

      One small correction. Thirty years is the half life. It takes 10 half-lives for the material to essentially disappear to undetectable levels. In short…300 years for Cesium.

      Some fish bio-accumulate Cesium, swim upstream, die and deposit their Cesium into the fresh waters or potentially into an animal who then deposits the Cesium onto land. We are stuck with the Cesium for a long time and it will spread very long distances.

  6. Rebecca says

    With all the graphs and defined scientific terms, it’s disturbing that all these “positive” articles about Fukushima end with sentences like it “should dilute”, that things “should” be okay, indicating no scientist will say that it actually will be. And to quote the EPA who raised the acceptable levels of radiation right after the meltdown, and who work for the government who was put into office with funds provided by the Nuclear Industry, it reminds me of the nuclear bomb tests that went on in this country for so long contaminating so many people. If the Nuclear Industry wants to gain our trust, they obviously need to put all their resources towards cleaning up the radiation that’s pouring into our atmosphere from this nuclear plant before asking to build more plants.

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