The mushroom cloud from the “Ivy Mike” nuclear test over Enewetak Atoll in the Marshall Islands on November 1, 1952.
Image: Photo/Los Alamos National Laborator

An analysis of soil samples, ocean sediment, and fruits from the Marshall Islands—the site of nearly 70 nuclear weapons tests during the 1940s and 1950s—has revealed alarmingly high levels of radiation, with some regions at levels exceeding areas affected by the Fukushima and Chernobyl disasters.

From 1946 to 1958, the United States conducted 67 nuclear tests in the Marshall Islands, a series of atolls located north of the equator between Hawaii and Australia. Twenty-three of these tests were conducted at Bikini Atoll and 44 near Enewetak Atoll, but fallout spread throughout the entire Marshall Islands, exposing the indigenous people there to dangerous levels of radiation.

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Much of the Marshall Islands remains uninhabitable as a consequence of these nuclear tests, and it’s not immediately clear when Marshallese residents will be able to return to their ancestral homes. Three new studies published today in Proceedings of the National Academy of Sciences suggests their long-awaited return won’t happen anytime soon. A research team led by Emlyn Hughes and Malvin Ruderman from the Center for Nuclear Studies at Columbia University has detected unsafe levels of radiation in the soil, ocean sediment, and fruits in these contaminated areas.

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Three years ago, the same team discovered alarming levels of gamma radiation in the Marshall Islands, and at levels that exceeded scientists’ expectations. The three new PNAS studies add to this prior work, which is being done to determine which, if any, of the Marshall Islands are safe for resettlement, and the specific risks that would be faced by returning indigenous peoples.

For the first study, the researchers measured background gamma radiation in soil samples taken from four atolls in 2017 and 2018: Bikini, Enewetak, Rongelap, and Utirik. Gamma radiation on Bikini and Naen islands were well beyond the maximum exposure limit as stipulated in agreements between the United States and the Republic of the Marshall Islands. On Bikini, the levels were as high as 648 millirems per year, and on Naen they were as high as 460 millirems per year. Safe exposure to radiation is 100 millirems per year, according to the U.S.-Republic of the Marshall Islands agreement.

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A hydrogen bomb detonated above Bikini Atoll on May 21, 1956.
Image: Associated Press

These levels are “significantly higher” than “areas affected by the Chernobyl and Fukushima accidents,” wrote the study authors. The “radiation levels on Bikini Island, which served as the primary island for habitation on the atoll, before and in the aftermath of the testing, are too high for relocation to Bikini,” according to the new research. Some of the outer islands “may not [be] suitable for habitation on their own, but... islanders may visit in search of food, especially in times of harvest.”

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For the second paper, the researchers explored the Castle Bravo crater—the site of the most powerful nuclear test ever conducted by the United States, which happened on March 1, 1954. This 15-megaton explosion vaporized the land beneath it, forming a crater 1.5 kilometers (0.9 miles) wide and 75 meters (246 feet) deep on Bikini Atoll. The ensuing fallout was comprised of pulverized coral, water, and radioactive particles. Traces of the radioactive debris were detected as far as Japan, India, Australia, Europe, and even the United States.

The Castle Bravo explosion also produced radioactive material that settled into the ocean sediment. From the research vessel Indies Surveyor, the researchers collected nearly 130 core samples from the Castle Bravo crater from 2017 to 2018. Analysis showed that, six decades later, the radiation levels are still “orders of magnitude” above normal levels within the top inch of sediment across the entire crater. The researchers conclude thusly:

In summary, there is still residual contamination of radionuclides throughout the Bravo bomb crater, from center to rim. We find that the radionuclide distribution is fairly uniform across the crater with some tapering off toward the crater rim....Although the lagoon is gradually filling in over time, contamination levels from residual long-lived radioactive isotopes, such as plutonium and americium, will likely last for centuries. The nuclear weapon tests caused a dramatic change in sediment composition. Additional studies to determine what the impact on life is in the lagoon craters, especially at the deeper depths, would be valuable.

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The third paper is an analysis of fruits found in the Marshall Islands, namely coconuts and pandanus fruits. Cesium-137 features a half-life of around 30 years, and it’s easily absorbed by plants, presenting a potential health hazard. Sadly, 11 islands were found to have coconuts and pandanus fruits with radioactivity exceeding limits established by several countries and international organizations, including International Physicians for the Prevention of Nuclear War (IPPNW). Once again, some of the levels exceeded values found near Fukushima and Chernobyl.

“Based upon our results, we conclude that to ensure safe relocation to Bikini and Rongelap Atolls, further environmental remediation... appears to be necessary to avoid potentially harmful exposure to radiation,” wrote the authors in the study.

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All-in-all, some very discouraging results, as much of the Marshall Islands remain unsafe for resettlement. It’s not immediately clear when these islands will be free of radiation, or if people will ever return to Bikini Atoll. Sadly, climate change is making a bad situation worse, as rising sea levels could render many of the safe Marshall Islands uninhabitable.

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