Flowering plants can transfer radiocesium from the soil to honey bees, which can then concentrate the contamination in honey.
Arx0nt / iStock
By Nikk Ogasa
Atomic bomb test failures in the 1950s and 1960s appear in American honey, according to a new study. While radioactivity levels aren’t dangerous, they may have been much higher in the 1970s and 1980s, researchers say.
“It’s really unbelievable,” said Daniel Richter, a soil scientist at Duke University who is not involved in the work. The study, he says, shows that the fallout “is still present and disguises itself as an important nutrient.”
In the aftermath of World War II, the United States, the former Soviet Union and other countries detonated hundreds of nuclear warheads in above-ground tests. The bombs threw radiocesium – a radioactive form of the element cesium – into the upper atmosphere, and winds spread it around the world before it fell from the sky in microscopic particles. However, the distribution was not uniform. For example, there was much more rainfall on the east coast of the US, thanks to regional wind and rain patterns.
Radiocesium is water soluble and plants can mistake it for potassium, an essential nutrient with similar chemical properties. To see if plants continue to absorb this nuclear contamination, James Kaste, a geologist at the College of William & Mary in Williamsburg, Virginia, gave his students an assignment: Bring back local foods from their spring break destinations to test for radiocesium.
A college student returned with honey from Raleigh, North Carolina. To Caste’s surprise, it contained cesium levels 100 times higher than the rest of the food collected. He wondered if bees from the eastern US that collected nectar from plants and turned them into honey were concentrating radiocesium from the bomb tests.
So Kaste and his colleagues – including one of his students – collected 122 samples of locally produced, raw honey from all over the eastern United States and tested them for radiocesium. They found it in 68 of the samples, at levels in excess of 0.03 becquerels per kilogram – about 870,000 radiocesium atoms per tablespoon. The highest levels of radioactivity occurred in a sample from Florida: 19.1 becquerels per kilogram.
The findings, reported last month in Nature Communications, reveal that thousands of miles from the nearest bomb site and more than 50 years after the bombs dropped, radioactive fallout still circulates through plants and animals.
Still, those numbers are nothing to worry about, says the U.S. Food and Drug Administration Science. The radiocesium levels reported in the new study fall “well below” 1,200 becquerels per kilogram – the limit for all food safety concerns, the agency says.
“I’m not worried at all,” adds Kaste. “I now eat more honey than before I started the project. And I have children, I give them honey. “
Radiocesium decays over time, so honey probably contained more of it in the past. To find out how much more, Caste’s team searched data from cesium tests in American milk – which was checked out of concerns about radiation contamination – and analyzed archived plant samples.
In both datasets, the researchers found that radiocesium levels had plummeted since the 1960s – a similar trend that likely occurred in honey. “The cesium content in honey was probably 10 times higher in the 1970s,” speculates Kaste. “Due to radioactive decay, what we measure today is just a hint of what came 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 wiped out by pesticides, but there are other lesser known toxic effects from humans, such as precipitation, that can affect their survival.”
After the Chernobyl nuclear disaster in 1986, scientists showed that nearby radiation levels could hinder the reproduction of bumblebee colonies. But those levels were 1,000 times higher than the modern levels reported here, notes Nick Beresford, a radioecologist at the UK Center for Ecology & Hydrology.
So even though the new study shouldn’t ring alarm bells about today’s honey, understanding how nuclear pollutants move is still vital to measuring the health of our ecosystems and our agriculture, says Thure Cerling, a geologist at the University of Utah. “We have to watch these things.”