In the Pacific Ocean sits an island nation with higher radiation levels than Chernobyl.

On sight, the Marshall Islands in the Pacific are just how you’d imagine any other tropical destination: Coral reefs and crystal clear blue lagoons, white sandy beaches leading to the warm Pacific waters, lush green vegetation and locals who enjoy typically ‘off-the-grid’ living.

What’s not visible to the naked eye is that the Marshall Islands, located halfway between Australia and Hawaii, is also home to radiation levels that in some parts measure higher than Chernobyl and Fukushima.

After World War II, many inhabitants of the island nation were relocated by the United States. Their land became the site of 67 nuclear tests by the US from 1946 to 1958, including testing of both the first and the largest hydrogen bombs.

The real story behind HBO’s Chernobyl. Post continues after podcast.

The US entombed nuclear waste under a concrete dome on the island of Runit, in the Enewetak Atoll, but the US Department of Energy believe it is leaching highly toxic waste into the ocean and the impact of the contamination is now becoming clearer.

Research from Columbia University published this week showed radiation levels are far higher than previously thought – in fact, on Bikini Atoll researchers found concentrations of particular radioactive material “were up to 15-1000 times higher than in samples from areas affected by the Chernobyl and Fukushima disasters”.

Bikini and Enewetak atolls were used as “ground zero” for the tests, and according to researchers “caused unprecedented environmental contamination and, for the indigenous peoples of the islands, long-term adverse health effects”.

The researchers detected unsafe levels of radiation in the soil, ocean sediment and fruits in these contaminated areas.

Safe exposure to radiation is 100 millirems per year, according to the U.S.-Republic of the Marshall Islands agreement, but levels on Bikini were as high as 648 millirems per year.

This level is "significantly higher" than "areas affected by the Chernobyl and Fukushima accidents," wrote the researchers.

Coconuts and fruit on 11 islands were found to have radioactivity exceeding limits established by the International Physicians for the Prevention of Nuclear War (IPPNW) as safe - and again, some of these levels exceeded what was found at the nuclear disaster sites in Ukraine and Japan.

Though banished from the island by the United States, some of the indigenous population returned and now more than 600 people call Enewetak home. The Marshall Islands has a population of approximately 53,000.

Increased exposure to radiation can have devastating effects on humans, but official death tolls are difficult to determine as it is often impossible to know if a person's sickness - such as cancer - is due to radiation or if they would have become sick anyway.

In 2005, the World Health Organisation estimated the number of deaths potentially resulting from the Chernobyl accident in Ukraine could reach up to 4000 people.

A journalist named Kate Willsher, however, who visited Chernobyl during the late 1980s estimated a much larger number.

Willsher said doctors saw a spike in cancers and leukaemias, with many babies born with rare deformities. Many children, she recalls, had "unexplained sickness" and quietly died in the years after. Willsher says there was no data kept for these victims, and therefore decades later, it is difficult to prove anything.

The non-government organisation the Chernobyl Union of Ukraine, estimated the death toll to be 734,000, with most due to related cancers.

Radiation scientists Ian Fairlie and David Summer estimated the final death count resulting from the explosion would likely fall between 30,000 and 60,000 people.