Depending who you ask and what data you consult, the atomic bombs dropped by the United States on Hiroshima and Nagasaki killed somewhere between 90,000 and 140,000 people.
But the number of human victims is not the only way to measure the catastrophic effects of the greatest crime committed against humanity.
According to recent accounts, 70 years after the bombs fell over Japanese territory, the bottom of the sea, soils and plants on pacific islands have radiation levels higher than those of Fukushima or Chernobyl.
It had not been a year since the bombs on Hiroshima and Nagasaki ended World War II, when the US began its nuclear test program in the Marshall Islands, then under US administration.
Between 1946 and 1958, atomic weapons exploded in this archipelago in the middle of the Pacific.
Now, 70 years later, an exhaustive independent study reminds us that sea bottoms, soils and even the fruits of atolls such as Bikini or Enewetak accumulate radioactive particles well above the permitted levels and, locally, in concentrations higher than those measured in areas affected by Chernobyl or Fukushima disasters.
Until now there had been no independent investigations of radioactive contamination and its consequences, but when scientists conducted a series of scientific missions to the Marshall Islands between 2015 and 2018, they discovered the devastation.
Before this study was conducted, the only studies carried out on the effects of such a nuclear test had been made by governmental and military scientists, especially the Lawrence Livermore National Laboratory, so there was a lack of knowledge and confidence in previous data on the part of the population of the islands.
Scientists from Project K = 1 were able to analyze environmental gamma radiation levels in successive campaigns, whose first results were published in 2016, and more recently also the concentration of several radioactive elements, such as plutonium-238, americium-241 or cesium-137. in samples of soils and sea beds and fruits collected on all the atolls and islands where the bombs were detonated and where radioactive fallout was present.
The Marshall Islands are made up of thirty atolls and several other islands.
The nuclear tests of the USA were concentrated in two of them, those of Enewetak and Bikini, located to the north. Many of the explosions took place inside the lagoons but there were some on small islands that were vaporized.
Although the 67 bombs account for only 6% of all US nuclear tests, they released more than half of the megatons: 108.5 Mt of a total of 196 Mt. One megaton equals the energy released by one million tons of TNT .
The authors of the new study, also published in PNAS, measured gamma radiation in a dozen islands of four atolls, those already mentioned and those of Rongelap and Utirik.
These atolls and islands were contaminated with radioactive fallout even though they were as far up as 600 kilometers. They also took hundreds of soil samples to measure the concentration of five radioactive elements.
From the bottom of the Bikini lagoon, where the US military detonated Castle Bravo, its largest thermonuclear bomb, researchers took 129 sample cylinders from the sediment layer.
“Our study of the Castle Bravo crater is the first systematic investigation with a large enough number of samples to obtain a measurement of the extent of contamination by different radio isotopes,” said the current director of the K = 1 Project.
In this samples, there is scarcely a trace of plutonium-238 and cesium-137, but there is a high activity of three other elements, plutonium-239.240, americium-241 and bismuth-207, all of which are radioactive. The concentration multiplies by 10 or up to 100 that detected in other areas of the Marshall Islands.
As for environmental gamma radiation, the worst places are the Bikini Islands, and Naen, in Rongelap. In both cases dozens of measurements reach and exceed five millisieverts.
In comparison, the natural radiation a human being receives each year is around 2.4 mSv, according to a guide from the Nuclear Safety Council.
But the worst is on the ground. Although they only detected the presence of plutonium-238, they did find four other radioactive isotopes and very high concentrations.
The US established the maximum security limit for one of them, americio-241, at 1,110 beckerels per kilogram of matter. On the island of Naen, they reached 3,090 Bq / kg.
Other elements, such as cesium-137, in Bikini came to measure 7.140 Bq / kg. Although only found in very isolated places, they are numbers that exceed by far those recorded in areas near Chernobyl a decade after the explosion of reactor number 2 or those measured after the tsunami that dismantled the Fukushima power plant.
“For each radioisotope (Am-241, Cs-137, Pu-238, and Pu-239,240) we sought to compare the values we obtained with the available standards and / or concentrations that have been measured in other regions of the world affected by the radiation caused by humans,” explains Nikolic-Hughes.
“In particular, the comparison of the concentrations of Pu-239.240 with the values measured in the regions affected by the Fukushima and Chernobyl accidents indicates that they are significantly higher in some of the northern Marshall Islands,” he adds.
But the director of Project K = 1 clarifies that to be able to compare it would be necessary to have many more records of the different sources and radiation types of the areas to be compared.
In 2018, the research went further in the search for other sources of radiation risk: they stopped in the possibility that it would get into the body with contaminated food.
In these islands, the vegetable part of the local diet consists almost exclusively of coconuts and pandanos, a fruit reminiscent of pineapple. The members of Project K = 1 collected two hundred of both fruits from eleven of the islands punished by bombs or radioactive fallout.
Here they measured the presence only of cesium-137. “It is extremely soluble, it quickly combines with the surface layer of the soil and is captured by the roots of the plants,” recalls Rouco.
Following the Fukushima accident, the Japanese authorities set a maximum of 600 Bq / kg for cesium-137 in fruits. Some of the coconuts and pandanos harvested in Bikini exceeded 3,700 Bq / kg.