Long-term decline of 137Cs concentration in honey in the second decade after the Chernobyl accident

In the years 2001–2004 the 137Cs activity was investigated in a total of 336 samples of different varieties of honey harvested in the Liguria Region of Northern Italy. Our purpose was to define (a) residual radioactive contamination following the Chernobyl accident and 137Cs long-term decline, (b) correlation between 137Cs activity and different honey varieties, and (c) correlation between 137Cs activity and the prevailing geomorphological configuration in the collection areas. The mean 137Cs specific activity was 4.33 ± 5.04 S.D. Bq/kg. Chestnut honey showed higher levels of radioactive contamination, which were ascribed to the extensive, superficial and deep, root apparatus of the tree. Honey samples from acidic argillite soils, which withhold radionuclides after deposition and slowly release them to plants, also showed higher 137Cs activity. Long-term decline was calculated at 456 days, a value lower than those published from different food sources in the years following the accident. The rate of long-term decline decreases with time.