Scientists testing batches of American honey found fallout from nuclear tests conducted in the 1950s and 1960s, reports Nikk Ogasa for Science.
Researchers detected traces of the radioactive isotope cesium-137 in 68 of 122 samples of fresh honey produced by bees from across the eastern United States, they report in a paper published in March in the journal Nature Communications. The concentrations of cesium-137 found in some honeys were around 100 times higher than those seen in other foods.
The researchers stressed that the levels of this radioactive isotope detected in U.S. honey are well below what is considered a health risk. For reference, the most radioactive honey tested in the study came from Florida and contained 19.1 becquerels—a unit used to measure radioactivity—per kilogram (~2.2 pounds), according to Science. The cutoff for food safety is at 1,200 becquerels per kilogram.
“I’m not trying to tell people they shouldn’t eat honey. I feed my kids honey,” says James Kaste, a geochemist at William and Mary and the study’s lead author, in a statement. “I eat more honey now than I did when I started this project.”
However, the findings underscore the lasting legacy of the atomic bomb in the natural world. George Dvorsky of Gizmodo reports that in the mid-20th century five countries, especially the U.S. and former Soviet Union, detonated more than 500 nuclear weapons in the air, dispersing vast quantities of radioactive particles into the atmosphere. Most of these tests occurred in the Marshall Islands in the South Pacific and the Russian Arctic Archipelago Novaya Zemlya, but some also occurred on U.S. soil in New Mexico and Nevada.
Much of the nuclear fallout from these tests took the form of cesium-137, a byproduct of nuclear fission, and atmospheric winds carried these radioactive particles far and wide before they slowly fell to Earth. Because wind patterns aren’t evenly distributed, some parts of the world got an extra dose of radiation. In the U.S., prevailing winds and plentiful rainfall led to more cesium-137 reaching the ground in the eastern half of the country.
But the patterns of radioactivity the researchers observed in local honey added another layer to this story. The highest concentrations of cesium didn’t simply correlate to the areas with the highest rainfall. Soil chemistry—specifically the presence or absence of potassium—played a key role in which areas produced the most radioactive honey.
Potassium is a vital nutrient for plants, and potassium and cesium atoms happen to have a similar structure. This leads plants to sometimes mistakenly take up cesium when they’re short on potassium.
Sure enough, the researchers found that the highest concentrations of cesium-137 in honey occurred in locations with low-potassium soils. Once, the cesium gets into the plants, it gets incorporated into their nectar, which is then lapped up by hungry bees and turned into honey back at the hive.
Luckily for humans, the radioactive decay of cesium-137 has reduced the levels of the isotope in the environment since the weapons tests.
“What we see today is a small fraction of the radiation that was present during the 1960s and 1970s,” Kaste says in the statement.
But the study raises interesting questions about what impact the legacy of nuclear fallout may have had on insects. Kaste says the study doesn’t allow us to “say for sure if cesium-137 has anything to do with bee colony collapse or the decline of [the] population.”
But as Justin Richardson, a biogeochemist at the University of Massachusetts, tells Science, bees are “getting wiped out from pesticides, but there are other lesser known toxic impacts from humans, like fallout, that can affect their survival.”