US honey still contains traces of the radioactive fallout of nuclear bomb testing in the '50s and '60s, study finds

• Honey from much of the eastern US shows traces of a cesium-137, a radioactive element.
• A study traced this back to nuclear testing that took place decades ago.
• There is no risk to human health, but the honey can help locate "hot spots" of soil contamination.

Some US honey still carries traces of cesium-137 from atom-bomb testing during the Cold War, according to a new study.

The levels of contamination in the honey are not high enough to be harmful to humans. But the research provides more information on the long-lasting effects of nuclear fallout on the environment.

The radioactive traces in honey were found by chance.

The lead author of the study, the geologist Jim Kaste of the College of William & Mary in Williamsburg, Virginia, sent his students on a spring-break assignment to measure radiation in food like nuts and fruit, Science Alert reported.

Much of it had faint traces of cesium-137, a radioactive element that is created by the nuclear reaction of uranium and plutonium that powers atomic weapons.

But Kaste said in a blog post that when he tested a jar of honey from a North Carolina farmers' market, "my detector was bonkers."

To make honey, bees concentrate nectar from flowers into a liquid five times as concentrated. This has the effect of also concentrating any contaminants picked up by the plants.

For that reason it can be used to identify "hot spots" of pollutants.

In a study published in the journal Nature Communication on March 29, Kaste and colleagues mapped radioactivity levels for honey in the eastern US.

Of the 122 honey samples tested, 68 showed detectable traces of the radioactive cesium, Science Alert reported.

They found that the honey in that area had on average about 0.03 becquerels per kilogram more than six decades after the bulk of nuclear bomb testing.

This surprised the scientists, as the half-life of cesium-137 is 30 years, meaning that after so long most of the radioactivity ought to have dissipated.

The scientists found negligible levels of cesium-137 in four samples of honey from the central US and one from Cuba.

The study noted previous research indicating that weather patterns had caused the east coast of the US to receive an unusually high amount of fallout from nuclear weapon tests around the world - much more fallout than could be traced, for example, back to high-profile nuclear disasters at the Chernobyl and Fukushima power plants.

From 1951 to 1980, the equivalent of 440 megatons of explosive yield were blasted aboveground, most of it launched by the Soviet Union and the US. China, France, and the UK also ran tests.

More than 500 nuclear devices were exploded at 13 testing sites.

Seventy-five percent of the explosive force from those bombs came from tests before 1963 at just two testing sites: the Marshall Islands in the Pacific Ocean and Novaya Zemlya in northern Russia.

Though it isn't clear which of the explosions contaminated the honey, the cesium-137 production from these bombs was "more than 400 times" as high as the production in New Mexico and Nevada, Kaste said in the blog post.

"What that did was put a blanket of these isotopes into the environment during a very narrow time window," Kaste said in a blog post.

The radioactive elements, or radionuclides, fell down on the soil. By the early 1960s, almost everywhere on the planet had been exposed to the radioactive contaminants.

Because the contamination of the soil was ubiquitous, scientists use these radionuclides to date samples of soil to the 1960s. Traces of fallout radionuclides are in glaciers all around the world and in deep-sea trenches.

Scientists are concerned about the effect of the longer-lived radioactive elements, like cesium, on the environment. This has been poorly studied so far, the scientists said in the study.