Traces of radioactive fallout from nuclear tests in the 1950s and 1960s can still be found in American honey, new research reveals.
The radioactive isotope identified, cesium-137, falls below levels considered to be harmful – but the amounts measured nonetheless emphasize the lingering persistence of environmental contaminants in the nuclear age, even a half-century after international bomb tests ended.
One of those isotopes was cesium-137, a byproduct of nuclear fission involving the reaction of uranium and plutonium, which can often be found in trace amounts in food sources due to such nuclear contamination of the environment.
Some of these traces are much fainter than others, Kaste found out – but only by chance, as it happened, after assigning his students a Spring Break assignment in 2017.
To demonstrate to his class how radioactive contaminants from mid-20th century nuclear testing still persisted in the environment today, Kaste asked his students to bring back locally sourced foods from wherever they spent the holidays.
As expected, various samples of fruits, nuts, and other foods revealed very faint traces of cesium-137 when measured with a gamma detector, but even Kaste wasn’t prepared for what happened when he ran the same test with a jar of honey from a North Carolina farmer’s market.
Of the 122 honey samples tested, 68 showed detectable traces of the radioactive isotope – a legacy of atmospheric nuclear tests conducted by the US, the USSR, and other nations during the Cold War era.
The majority of detonations occurred above the Marshall Islands in the Pacific Ocean and Novaya Zemlya, an Arctic archipelago in northern Russia, with other tests being conducted in New Mexico and Nevada.
According to the researchers, the cumulative effect of over 500 of these test detonations released more ionizing radiation to the atmosphere than any other event in human history – not that all the blasts were equal in scope.
“We know that the cesium-137 production from the Pacific and Russian sites was more than 400 times the production of the New Mexico and Nevada explosions,” Kaste says.
Not just rainfall
While the pollution may be globally ubiquitous, honey’s high levels of cesium-137 compared to other food sources show that the fallout appears to concentrate in unexpected ways – but we can now explain that mystery too.
Rainfall might be the predominant force taking cesium-137 out of the atmosphere and depositing in on Earth’s surface, but the honey samples registering the highest amounts of the radioactive isotope weren’t produced in regions of the US that receive the most precipitation.
“What we see today is a small fraction of the radiation that was present during the 1960s and 1970s,” Kaste says.
“And we can’t say for sure if cesium-137 has anything to do with bee colony collapse or the decline of population.”