Earlier this month, UN Secretary-General Antonio Guterres cited concerns that a decades-old nuclear “kind of coffin” could be leaking radioactive fallout into the Pacific Ocean but was still heavily ignored by the rest of the world.

Between 1946 and 1958, the US government tested 67 nuclear weapons in the Marshall Islands, including the 1954 Bravo hydrogen bomb measuring 1,000 times bigger than the atomic bomb on Hiroshima – the biggest and most powerful nuclear weapon ever detonated by the US. Testing occurred on the surface of atoll lagoons, many of the islands, and underwater, resulting in it what is known as a “close in” fallout. This contaminated sediment from local islands that eventually flow into the North Pacific Ocean.

In the late 1970s, the US government gathered radioactive soil from contaminated nearby islands and buried some 84,000 cubic meters (almost 3 million cubic feet) in a bomb-created crater on the Enewetak Atoll. Officials covered the fallout with a 45-centimeter-thick (18-inch) concrete dome that has become known as Cactus Dome, or Runit Dome – but it was only meant to be a temporary solution. The bottom of the pit is not lined, and as exposure has caused cracks to form in the dome, officials are concerned that it may be leaching radioactive material into the ocean, a threat only expected to worsen with rising sea levels and increased frequency of tropical storms heightened by climate change.

"[The dome] is stuffed with radioactive contaminants that include plutonium-239, one of the most toxic substances known to man," Marshal Islands Senator Jack Ading told the Agence France-Presse. “The coffin is leaking its poison into the surrounding environment. And to make matters even worse, we're told not to worry about this leakage because the radioactivity outside of the dome is at least as bad as the radioactivity inside of it."

After the US military withdrew from the region in 1986, it paid a a “full settlement of all claims, past, present and future” relating to the nuclear test program. However, many argue that these retributions made weren’t enough.

“I’ve just been with the president of the Marshall Islands [Hilda Heine], who is very worried because there is a risk of leaking of radioactive materials that are contained in a kind of coffin in the area,” Guterres said in Fiji, Agence France-Presse reported.

A 2013 US inspection found that radioactive fallout in lagoon sediment is already so high that even a “catastrophic failure” would not result in an increase in radiation exposure to the some 800 residents. The findings did confirm a “rapid tidal response” to rising groundwater beneath the structure. Under a more “plausible release scenario”, the potential for contaminated groundwater to flow from the dome to the marine environment exists. Furthermore, it is unclear what the total inventory and isotopic mix of fallout contained in and around the waste pile is.

A 2018 study that calculated radioactivity fluxes in lagoon waters found that Bikini and Enewetak Atolls are still a long-term source of Plutonium and Cesium to the North Pacific. Additionally, higher levels of radioactive fallout in seawater and sediments are found here than in the rest of the world’s oceans. In particular, Runit contributes to about half of the Plutonium in the Enewetak lagoon water column. However, researchers concluded that groundwater from below the dome is not a significant source. The government adds that the groundwater flowing out into the ocean reef will be “very rapidly diluted” and would result in little or no measurable increase in radiation to marine or human populations. 

 [H/T: AFP]