Even One Becquerel Represents a Health Risk
Fact: One Becquerel (Bq) does not represent a measurable health risk. It equals one radioactive decay (or disintegration) per second of any radionuclide and is part of a natural process. The truth is that most things we eat and drink contain naturally-occurring radioactive elements, such as potassium and carbon. For example, 250 g of red meat and 250 g of bananas naturally contain 28 Bq and 33 Bq of potassium-40 isotope respectively.
What needs to be considered is the energy released during the disintegration. The higher the energy the greater the ionising effect and it is the total ionising effect that needs to be considered. Hence 1000 Becquerel from a radionuclide with a relatively low ionising effect is less dangerous than 10 Becquerel from a radionuclide with a relatively high ionising effect.
Furthermore, the type of disintegration needs to be considered. Does the isotope emit alpha (α) or beta (β) particles with or without an associated gamma (γ) ray with each disintegration? Each gamma ray may have the potential to pass though solid matter, i.e. flesh and bone, where it will cause ionisation of the atoms/molecules it passes them. Whereas an alpha particle can be stopped and absorbed by a sheet of paper, but will cause extensive damage (ionisation) at the impact site.