For example, the nuclear fallout contains consistent quantities of the radionuclide strontium 90. Since the radioactive strontium simulates the same properties of calcium, it penetrates the alimentary chain by way of vegetables, meat and milk and it is then erroneously assimilated by the organism as material necessary to the formation of the bones. Hence it irradiates the spine's marrow and the blood's cells causing cellular mutations and cancers. Other radionuclide accumulate within specific body organs and behave in a similar way irradiating the adjacent tissues thus giving rise to illnesses and alterations.
Following the nuclear accident at Chernobyl, which from data released from the Lawrence Livermore Laboratory in California has resulted as having let loose 50% more of radioactive cesium (the most electropositive and alkaline metal, a radionuclide with an half-life of 100 years) more that the total quantity released from all the nuclear explosions which have taken place in the world to the present date, thus contaminating the air, the soils and the waters more that the totality of the aforesaid explosion, we have seen how in the European countries over which the radioactive cloud passed , sales of milk, fruit and vegetables had been prohibited, in particular those greens with a wide leaf whereon the fallout may deposit itself in a larger amount. These measures were made necessary for the presence, beyond the limits of the danger threshold, of the radionuclide iodine 131 which, if assimilated in the organism will deposit itself more easily in the thyroid hence resulting particularly dangerous to children between two and ten years of age to whom the thyroid gland is a determinant organ for normal growth and development and its radioactive contamination may deplete it efficacy resulting in physical malformations or cretinism. The damage to the thyroid can be so extended as to require its excision. It is useful to notice that also the environment around us emits weak radiation. Some of these radiations arrive to the earth from outer space, others from the earth's mantle and the remaining ones are the residual of nuclear tests, besides radiations due to traces of radioactive elements ( potassium 40 and radium 226) present in our organism.
However, the threshold of danger insofar as nuclear radiation is concerned, a social factor determined in a large measure from the dependence state/people than a real choice of the danger-limits of irradiation from radioactive substances and hence it is not the same in all countries and, even if there is a marked discordance in scientific circles concerning the threshold safety limits to be adopted in this respect, it is certain that even a slight accumulation of radioactivity will have negative consequences on the human organism and the effects are not easily foreseeable since each organism's response is different toward nuclear radiation.
The damages caused by radioactivity to the body's organisms due to ingestion or inhalation, hence absorbed and accumulated into the body, depend on several factors:

• The chemical nature of the radionuclide.
• The type of radiation emitted.
• The radionuclide's half-life, i.e., the time necessary for the radioactive particle to lose half of its radioactivity.
• The time necessary to the organism to expel half of the radionuclide within itself, called "biological half-life".
• The amount and placement within the body of the radioactive substances.
• The health conditions of the person affected.