In a paper published in the peer-reviewed scientific journal Nature Communications, researchers found that these tests affected honey from the eastern region of the United States. Though the region is far away from former nuclear test sites, it has still received a disproportionately high amount of fallout. This is due to a combination of westerlies – prevailing winds that blow from west to east between 30 and 60 degrees of latitude – and precipitation.
Fallout produced in events that occurred decades prior can be found in a range of foodstuffs
The caesium-137 then makes its way into honey by entering the region’s soil. There, it is absorbed by plants, including ones that flower. Bees then collect nectar from these flowers, and in turning it into honey, reduce its water content by fivefold. Fallout produced in events that occurred decades prior – so-called ‘legacy contaminants’ – can be found in a range of foodstuffs. However, this detail in the process of nectar conversion ensures that caesium-137 is particularly concentrated in honey.
Also key to the paper’s findings is the potassium content of soil. Potassium inhibits vegetation’s uptake of caesium-137, with the isotope only being absorbed when there are insufficient amounts of potassium. Vegetation converts potassium into energy, though caesium-137 has similar enough ionic properties that it can be used as a substitute, albeit an imperfect one.
The concentrations of caesium-137 are below 50-100 becquerels per kilogram, meaning the honey is still considered safe for consumption
As such, honey produced in north-east America tends to contain less radioactive material than honey produced in south-east America. South-eastern soil is old, weathered and leached, meaning it has lost water-soluble nutrients due to precipitation. As such, it suffers from a deficiency in a range of nutrients, including potassium. Farming decisions, though, such as the use of certain potassium-rich fertiliser, can lead to exceptions. Meanwhile, recent bedrock exposure in the Appalachian Mountains and glaciation ensure that north-eastern soil is relatively rich in potassium.
The researchers who authored the paper note that the concentrations of caesium-137 are below 50-100 becquerels per kilogram, a widely used threshold for concern. As such, the honey is still considered safe for consumption.
However, the researchers also note that the level of residual radiation is higher than what might be expected. This is because almost two half-lives have elapsed since the majority of the caesium-137 that was made in bomb testing was produced.