Since the first atomic bomb detonation, the Trinity Test of 1945, hundreds of nuclear weapons have been detonated in above ground tests. The fallout from these explosions contain a radioactive isotope of the element cesium, called radiocesium or 137Cs.
Wind and rainfall caused much of this fallout to be dispersed far from the testing sites and deposited into the soil. Since it is highly soluble in water, it is absorbed by plants which mistake it for potassium. It ends up in plant nectar, which is then used by bees to make honey.
According to a study in March 2021, trace amounts of radiocaesium from nuclear fallout are still cycling through plants and animals to this day, even on the US East coast, thousands of miles from the nearest testing sites.
Though being slightly radioactive, this honey is still safe to eat. Radioactivity is measured in becquerels, (Bq), and the honey samples in the study ranged from 0.03–19.1 Bq/kg. The US Food & Drug Administration places the cutoff for any food safety concerns at 1,200 Bq/kg.
The half-life of radiocesium is 30 years, so honey produced in the 1970's was likely to have 10x more 137Cs.
a) Detectable (filled black circles) 137Cs in honey on a map with 20th century 137Cs deposition to soils determined at the county scale decay corrected to 2019.
b) Circles scaled logarithmically showing the relative magnitude of 137Cs in honey on a map in Bq/kg (becquerel=nuclear disintegration per second) with county mean soil K (potassium) concentrations determined from airborne radiometric surveys.