Radiation levels across the Marshall Islands in the central Pacific Ocean, where the United States conducted more than 65 nuclear tests during the Cold War, are still alarmingly high — even higher than Fukushima and Chernobyl in some parts, a new study shows.

Researchers at Columbia University tested soil samples on four uninhabited isles and discovered that they contained concentrations of nuclear isotopes that are “significantly” higher than those found near the two disaster sites.

“All of these measurements are important due to the potential for repopulation of at least some of the atolls in the Marshall Islands,” explained David Krofcheck of the physics department at the University of Auckland in New Zealand.

“Such measurements of the effects of nuclear weapons testing in the Marshall Islands must continue on a regular basis into the indefinite future,” he told the Science Media Centre.

Two of the isles where the soil was analyzed — Bikini and Enewetak — were used as “ground-zero” for US nuclear tests between 1946 and 1958. The others, Rongelap and Utirik, were affected by radioactive fallout from the largest of the 67 tests conducted, known as the Bravo test.

Researchers at Columbia said they aimed to “present a picture of current radiological conditions” in the region “by examining external gamma radiation and soil radionuclide activity concentrations.”

Their findings, which were published Monday in the journal PNAS, showed that gamma radiation in some areas was “well above” the legal exposure limit established in agreements between the US and Republic of the Marshall Islands.

In Bikini, plutonium concentrations were “up to 15–1,000 times higher than in samples from areas affected by the Chernobyl and Fukushima disasters,” according to researchers.

The experts also conducted tests on fruits found in the Marshall Islands and discovered that levels of contamination on Bikini, Rongelap and the island of Naen were higher than safety levels established in Russia, Ukraine, Belarus and Japan. Some even exceeded the more lax US standards.

“Foods tested, coconuts and pandanus, show a variety of radioactivity levels with the lowest levels detected in fruits from atolls farthest away from the weapons test sites,” said Krofcheck. “Northern atolls where most weapons tests were performed showed the much higher radioactivity levels. Bikini Atoll had considerably larger levels, well above most international norms for food safety. Research needs to be done on local sea food.”

Despite the high levels, experts say that “exposure to radiation associated with environmental radioactivity at the reported levels is generally low or comparable to other sources of radiation, such as naturally occurring radon, cosmic radiation at higher altitudes and diagnostic medical exposures.”

“The National Radiation Laboratory, now within ESR [European Society of Radiology], has been continuously monitoring environmental radioactivity in New Zealand and the South Pacific region since 1960,” explained Cris Ardouin and Michael Lechermann, senior scientists at ESR’s National Radiation Laboratory.

“Levels of radioactive fallout have continued to decline as would be expected since the cessation of nuclear weapons testing in the region,” they told the Science Media Centre in a joint statement. “ESR also provide technical expertise and operational support in the verification of the Comprehensive Nuclear Test Ban Treaty (CTBT) that aims to abolish all types of nuclear weapons testing.”