In isolated regions across the US, the Pacific Ocean, and Russia, the ground was littered with destruction as the USA and USSR tested some of the first atomic bombs during the Cold War. Throughout the next few decades, both superpowers would test hundreds of devices that painted the skies with radiation. New research suggests you could be seeing relics of this atomic testing in a modern, everyday item – researchers have detected trace levels of the radioactive element cesium-137 in American honey, even all these years later. 

While it may sound alarming, the levels of cesium-137 are far below the amounts that can cause harm. Honey is still safe and delicious, but it does demonstrate the far-reaching and lasting impacts of the slew of nuclear bomb testing throughout the 20th century. 

It certainly hasn’t put off lead author Jim Kaste, whose research was published in Nature Communications.  

“I’m not trying to tell people they shouldn’t eat honey. I feed my kids honey,” Kaste, associate professor at William & Mary University, Virginia said in a statement. “I eat more honey now than I did when I started this project.” 

The research began as a freshman seminar in 2017. While teaching Geology 150: Radioactive Pollution, Kaste wanted to demonstrate to his students the impacts of H-bomb testing carried out in New Mexico, Nevada, and Utah in the US. As they went off on spring break, he asked them to bring back some locally sourced plant foods from wherever they went to test for cesium in the lab. 

Plenty of the products brought back showed minute detections of cesium, but honey from a farmers market in Raleigh, North Carolina was 100 times hotter than the rest.

“I couldn’t believe it, really,” Kaste said last year. “I measured it again because I thought something happened to the container or my detector was bonkers. I reproduced the measurement. And it was, again, 100 times hotter than any of these other foods.“

This led Kaste and colleagues to investigate how cesium-137 could travel such distances, from isolated atomic test sites to the shelves of America’s east coast. Taking honey jars from various regions in North America, they analyzed each sample for evidence of the radioactive isotope. In total, 122 honey samples were tested.  

Incredibly, 68 out of these were found to contain varying quantities of cesium-137. Florida, Georgia, and South Carolina took the top prizes as most often radioactive, whilst states north of Virginia had just 12 samples out of a total 40 containing cesium-137. So, how come bees are so good at picking up one of the most dangerous isotopes in history? 

Kaste presents an interesting hypothesis. Following atom bomb tests, radioactive fallout was cast high into the atmosphere, owing to the intense pressure gradients of the fission reactions. Much of this fell back down and remained in its birthplace, the test sites, while the remainder was carried east and returned to Earth via rainfall.  

As the cesium-137 lay on the ground, it would therefore make sense that the most "radioactive" honey would be found in places with more rainfall. However, Kaste and his team spotted an alternative correlation – it was not rainfall that correlated with cesium-137 content, but soil potassium levels. 

Potassium is an essential element for plant growth. If you have ever fertilized your backyard, part of that fertilizer is made of potassium, and it is found widely in soil. By coincidence, potassium atoms happen to look very similar to cesium-137 atoms, and plants think the same thing. When potassium supply is low, it is possible that the plants are lowering their standards and grabbing the next available element, which in this case, is a Cold War-era radioactive isotope. Bees then come along and feast on the nectar, which carries the cesium-137 into their hives and into the honey. 

Now, Kaste wants to use the work to highlight the long-term environmental impacts of pollutants. Cesium-137 has a 30-year half-life, so it will eventually fade from existence within the honey, but to find detectable levels now demonstrates this must have been far higher in the 1960s and '70s when the testing was carried out.