Strontium plays a similar role to that of calcium in the human metabolism, so it is not toxicant. However, the natural isotopes Sr-89 and Sr-90 are extremely dangerous once ingested, because they take the place of calcium in the bone structure. They are a source of internal radiation and could damage the bony medulla and the blood cells formation, leading to cancer. The bromide and the chloride are used in Medicine to control certain nervous disturbances. Other compounds of this element are used in treating rheumatism.