(CNN)Radiation levels across parts of the Marshall Islands in the Pacific Ocean, where the United States tested nuclear bombs during the Cold War, are higher than areas contaminated by the Chernobyl and Fukushima nuclear disasters, new research suggests.
Parts of the Marshall Islands are more radioactive than Chernobyl and Fukushima, study finds
From 1946 to 1958, the US government conducted 67 nuclear tests on several small islands -- called atolls -- in the Marshall Islands.
The US government relocated entire populations and exposed others to cancer and disease-causing radiation.
More than 60 years later, researchers at Columbia University say radiation on four of these atolls remains alarmingly high -- in some areas ten to 1,000 times higher than radioactive areas near the Chernobyl powerplant, which exploded in 1986, and Fukushima, where an earthquake and tsunami caused a nuclear disaster in 2011.
Analyzing soil samples, researchers found concentrations of americium-241, cesium-137, plutonium-238, and plutonium-239,240 on 11 islands across the four northern atolls.
The population of the Marshall Islands is relatively small, with just over 75,000 people living on the chains as of July 2018. It is a combination of islands and atolls, which are usually circular islands ringing a wide lagoon or coral reef.
Some of the atolls and islands have just a few hundred people on them. Enewtak Atoll was home to just 664 people in the 2011 census.
Enewtak was one of two atolls, along with Bikini, which were described by researchers as "ground zero" for the nuclear tests.
While a fraction of the 1,054 total nuclear tests carried out by the US from 1946 to 1992 took place on the Marshall Islands, the coral atolls withstood more than half the total energy yielded from all US nuclear tests during that time, the researchers said.
Bikini was the site of the US's largest hydrogen bomb test known as Castle Bravo in 1954 -- the blast was 1,000 times as powerful as those dropped on Japan during World War II.
Bikini Island was found to have the highest levels of radiation of areas studied, with the report's authors recommending that Bikini remains uninhabited, owing to its high levels of radiation.