Flowering plants can transfer radiocesium from soils to bees, which can then concentrate the contaminant in honey.
Arx0nt / iStock
De Nikk Ogasa
According to a new study, the results of nuclear bomb tests in the 1950s and 1960s appeared in US honey. Although levels of radioactivity are not dangerous, they may have been much higher in the 1970s and 1980s, the researchers say.
“It’s really incredible,” says Daniel Richter, a soil scientist at Duke University who is not involved in the work. The study, he says, shows that the consequences “are still there and disguised as a major nutrient.”
Following World War II, the United States, the former Soviet Union, and other countries detonated hundreds of nuclear warheads in surface tests. The bombs evacuated radiocesium – a radioactive form of the element cesium – into the upper atmosphere, and winds scattered it around the world before falling from the sky into microscopic particles. However, the spread was not uniform. For example, much more rainfall dusts the east coast of the United States due to regional patterns of wind and precipitation.
Radiocesium is soluble in water, and plants can confuse it with potassium, a vital nutrient that shares similar chemical properties. To see if the plants continue to absorb this nuclear contaminant, James Kaste, a geologist at William & Mary College in Williamsburg, Virginia, gave his students a task: Bring local food from their spring destinations to test for radiocesium.
A student returned with honey from Raleigh, North Carolina. To Kaste’s surprise, it contained cesium levels 100 times higher than the rest of the food collected. He wondered if bees in the eastern United States that collect plant nectar and turn it into honey concentrate radiocesium in bomb tests.
So Kaste and his colleagues – including one of his students – collected 122 samples of locally produced raw honey from the eastern United States and tested them for radiocesium. They detected it in 68 samples, at levels above 0.03 becquerels per kilogram – about 870,000 radiocesium atoms per spoon. The highest levels of radioactivity occurred in a Florida sample – 19.1 becquerels per kilogram.
The findings, reported last month in Communications about nature, reveals that thousands of kilometers from the nearest bomb site and more than 50 years after the bombs fell, radioactive rainfall is still cycling among plants and animals.
However, these figures are not a cause for concern, says the US Food and Drug Administration Science. Radiocesium levels reported in the new study fall “well below” 1,200 becquerels per kilogram – the limit for any food safety issue, the agency says.
“I’m not worried at all,” Kaste added. “Now I eat more honey than I did before I started the project. And I have children, I feed them honey. ”
The radiocesium decomposes over time, so the honey of the past probably contained more of it. To find out how much, Kaste’s team analyzed records of cesium testing in US milk – which was monitored for concern about radiation contamination – and analyzed archived plant samples.
In both data sets, the researchers found that radiocesium levels had dropped sharply since the 1960s – a similar trend that probably occurred in honey. “Cesium levels in honey were probably 10 times higher in the 1970s,” Kaste speculates. “Because of the radioactive degradation, what we measure today is just a smell of what was there before.”
The findings raise questions about how cesium has affected bees over the past half century, says Justin Richardson, a biogeochemist at the University of Massachusetts, Amherst. “They are eliminated by pesticides, but there are other lesser-known toxic effects in humans, such as falls, which can affect their survival.”
After the 1986 Chernobyl nuclear disaster, scientists have shown that nearby radiation levels could prevent bee colonies from reproducing. But these levels were 1,000 times higher than the modern levels reported here, notes Nick Beresford, a radioecologist at the Center for Ecology and Hydrology in the UK.
So while the new study shouldn’t raise any alarms about today’s honey, understanding how nuclear contaminants move is still vital to measuring the health of our ecosystems and agriculture, says Thure Cerling, a geologist at the University of Utah. “We have to be careful about these things.”