Strontium (Sr) is an element which in the event of a nuclear accident is the one that is most released into the atmosphere. The chemical behaviour of strontium is similar to that of calcium and can accumulate in the soil, in plants and in animals (in bones, especially). It is an element with two main radioisotopes (90Sr and 89Sr) which have an effective biological life that is relatively high for human beings, and due to its fixation in the bones, ends up giving a dose of radiation over many years.