Radioactive Fallout From Nuclear Bombs Detected in US Honey

A study published in Nature Communications has found that fallout from nuclear bomb tests that occurred in the 1950s and 1960s can be detected in honey.

The research was a collaboration between scientists at the Appalachian Laboratory at the University of Maryland Center for Environmental Science and the College of William & Mary in Williamsburg. Andrew Elmore, professor of landscape ecology at the Appalachian lab told Technology Networks that the level of radioactivity is not harmful to humans. However, it is possible that it might be dangerous to bee colonies that are exposed to a large amount of the contaminated honey in their hive.

Nuclear bombs and bees

The twentieth century saw several countries, including the United States, Novaya Zemlya (formerly the Union of Soviet Socialist Republics, or USSR) and others test and detonate nuclear weapons. Many of these detonations occurred in a specific set of locations in the Northern Hemisphere, however their power meant that radioactive fission products were ejected high into the atmosphere and subsequently distributed around the world. One such product was ¹³⁷Cs radiocesium,  an active form of the element cesium. Nuclear disasters, such as Chernobyl, also produced radiocesium but such events were localized.

Cesium possesses similar chemical properties to potassium, such as ionic charge and radius, and so radiocesium can be mistakenly absorbed by plants via certain potassium-specific membrane transporters. "This is more likely when potassium is less available in the soil. The presence of cesium is therefore a potential indicator of potassium limitation in plants," Elmore explains.

He continues, "Since radiocesium was created as a by-product of atomic weapons testing that occurred over a relatively short period of time, it is an interesting tracer of multiple earth system processes. We can date soils, for example, by evaluating the concentration and location of radiocesium in soil profiles. Refining these methods requires understanding how it interacts with plants."

In the 1950s-1980s the absorption of radiocesium by plants was noted and several US government surveillance programs were launched. However, the authors of the new study write that "there is no published research documenting the presence or absence of ¹³⁷Cs in eastern U.S. plants or in the U.S. food supply since 1988."

In this new body of work, Dr Jim Kaste, a geologist at the College of William & Mary, decided that, alongside his students, he would measure the levels of radiocesium in as many food products as he could. They identified that honey had the highest levels of any of the food products tested, and so the scientists placed their focus for further research on honey. 

The scientists obtained 122 honey samples from a range of US producers from various locations. "We packed it into a standard geometry (a cup with a lid, similar in size to something you might buy honey in) and put it in a lead box," Elmore describes. The purpose of the lead box was to block radiation from the earth and the sky and enabled the team to only measure radiation that had been emitted from the honey. "We used a gamma ray detector to count the number of decays per second due to ¹³⁷Cs in the Honey. The longer we counted, the greater the precision of the measurement," Elmore adds.

Radiocesium was detected in 68 of the honey samples. Despite the fact that there were no atmospheric nuclear weapon tests in the eastern part of the US, it was present at levels over 0.03 becquerels per kilogram in honey from this region. In contrast, of the 40 honey samples that were obtained from US states north of Virginia, 12 were found to have detectable levels of radiocesium. "It was interesting that some of the areas that received the largest amount of bomb fallout where areas where there was little to no radiocesium in honey," Elmore recalls. Honey samples obtained from Florida had levels of radiocesium measured at 19.1 becquerels per kilogram. "The most striking pattern was the high 137Cs found in low Potassium soils common to Florida and rest of the south eastern coastal plain region of the USA," Elmore adds.

Nonetheless, the levels detected were far below the 1200 becquerels per kilogram cut-off point determined by the US Food and Drug Administration. However, it's unclear exactly how the presence of this radioactive element might have impacted bee populations over the course of the last 50 years. "There are many threats to bees," says Elmore. "It is hard to know how this honey pollution combines with other, more acute threats. Radiation from ¹³⁷Cs could certainly have a negative impact on bee health in certain situations, however." He identified the question of bee health as a potentially impactful avenue for next research steps: "Could the processes leading to increased concentration of ¹³⁷Cs in honey be used to understand how pesticides and other pollutants get into honey?"

Radioactivity: A tool for measuring change?

There are a range of different directions that this research could take. Elmore is personally interested to know what radiocesium in honey and other plants could teach us about potassium limitation over time. "As plants are provided greater access to carbon due to rising atmospheric CO₂, I think it is interesting to consider how this might decrease the availability of Potassium and other nutrients," he says.

The research may be useful to guide new work on the biogeochemical fate of other fission-products in the environment. "This can be done to understand exposure risks, but just as interesting is using contaminants to date soils and water," Elmore comments. He emphasizes that the world is changing, and radiocesium is one of the tools we can use to track and understand the importance of different drivers of change.

Andrew Elmore was speaking to Molly Campbell, Science Writer for Technology Networks. 

Reference: Kaste JM, Volante P, Elmore AJ. Bomb ¹³⁷Cs in modern honey reveals a regional soil control on pollutant cycling by plants. Nat Comms. 2021;12(1):1937. doi: 10.1038/s41467-021-22081-8.