Radioactive Lagoons at Atomic Test Sites


Scientists found lingering radioactivity in the lagoons of remote Pacific atolls where the United States conducted nuclear weapons tests more than 50 years ago. (Woods Hole Oceanographic Institution)

The ocean isn’t the only place radiation is lingering—meet the scientists who pee plutonium.

Teachers, scroll down for a quick list of key resources in our Teachers Toolkit, including today’s simple MapMaker Interactive map.

An iconic mushroom cloud spreads from an impressive water column over the lagoon at Bikini Atoll in 1946. (This test was conducted underwater.) New analyses of the lagoon found levels of radioactive plutonium 100 times higher than the surrounding Pacific Ocean—but the levels still do not exceed U.S. and international water-quality standards.
Photograph courtesy U.S. Navy


Discussion Ideas


Zoom in on the Enewetak and Bikini Atolls with today’s MapMaker Interactive map.


  • How did scientists measure radioactivity at Enewetak and Bikini Atolls?
    • Scientists measured the presence of radionuclides of three elements: plutonium, cesium, and radium. They took samples from the ocean, lagoons, seafloor sediments, cisterns, wells, beaches, and other sites in and around the atolls.
      • Pu. Although tiny, tiny amounts of plutonium exist in nature, it is, by definition, a “rare earth element.” Most plutonium on Earth is radioactive fallout from nuclear testing. Learn more about plutonium radionuclides here.
        • The levels of plutonium are 100 times higher in lagoon waters when compared to the surrounding Pacific Ocean.
      • Cs. Cesium is not a rare earth element, but the isotope cesium-137 is the principal source of radioactivity associated with nuclear power plants. (Spent nuclear fuel rods and radioactive waste are contaminated with cs-137, for instance.) The radioactivity associated with both the Fukushima and Chernobyl nuclear disasters is cs-137, but it is not the principal contaminant in nuclear weapons fallout. (That would be plutonium.) Learn more about cs-137 here.
        • The levels of cesium are two times higher in lagoon waters when compared to the surrounding Pacific Ocean.
      • Ra. Radium is not emitted during nuclear testing, but is a naturally occurring radionuclide. It acts as a “tracer” that helps scientists determine how much and how fast groundwater flows from land into the ocean. Learn more about radioactive tracers here.


  • What is the source of most radioactivity in the Enewetak and Bikini lagoons?
    • Seafloor sediments contributed the most plutonium to the ocean. This wasn’t a complete surprise: “Until atmospheric testing was banned in 1963, more than 5 tons of plutonium were dispersed in the atmosphere in the form of small particles blown around the globe by the wind … Most of this plutonium dust fell into the oceans, and approximately 96% of that amount simply sank as sediment onto the ocean floors because plutonium is not readily soluble in seawater. The fact that plutonium dissolves very slowly in water also explains why the plutonium concentration in our oceans is low and will continue to be so.”


NGS Picture Id:436360
The Runit Dome, seen here in 1986, is not lined below sea level. But so far, it’s not leaking.
Photograph by James P. Blair, National Geographic
  • What surprised scientists about the radioactivity in the Enewetak and Bikini atolls?
    • In a modestly pleasant surprise, scientists discovered that radioactive groundwater was not leaking into the ocean in large amounts. (This is why that radium tracer was so important!) Scientists were concerned about the possibility of a leak because the bottom of Runit Dome, an enormous concrete lid that covers 111,000 cubic yards of radioactive soil and debris on Enewetak Atoll, is not lined below sea level.
      • “The foundations of these island atolls are ancient coral reefs that have the porosity of Swiss cheese, so groundwater and any mobilized radioactive elements can percolate through them quite easily,” said WHOI geochemist Matt Charette. Though that does not seem to be happening now, the scientists advise that the Runit Dome area should be continuously monitored as sea level rises and the dome deteriorates.



Woods Hole Oceanographic Institute: Radioactivity Lingers from 1946-1958 Nuclear Bomb Tests

Nat Geo: Radioactivity at Enewetak and Bikini Atolls

Nat Geo: The Scientists Who Pee Plutonium

Nat Geo: Bombs Away on YouTube

(extra credit!) Science of the Total Environment: Lingering radioactivity at the Bikini and Enewetak Atolls

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