Strontium, a chemical element, has the symbol Sr and atomic number 38. It belongs to the alkaline earth metals, a group found in Group 2 of the periodic table. Its atomic structure and placement define its chemical properties.
Characteristics and Presence
Strontium is a soft, silvery-white metal that quickly develops a yellowish tint upon air exposure due to oxide formation. It is highly reactive, interacting readily with air and water. Due to this reactivity, strontium is never found freely in nature, existing only in compounds with other elements.
Strontium is the 15th most abundant element in Earth’s crust, with an average concentration estimated at 360 parts per million. It primarily occurs in two minerals: celestine (strontium sulfate) and strontianite (strontium carbonate). Strontium is also present in seawater at concentrations of 7 to 8 milligrams per liter.
Its Role in Living Organisms
Strontium is a trace element in biological systems. Its presence in living organisms is due to its chemical resemblance to calcium. This similarity allows strontium to substitute for calcium in certain biological processes.
In mammals, strontium can be absorbed and incorporated into the structure of bones and teeth. It can influence bone formation and reduce bone resorption rates, though its biological necessity for humans is still under investigation. Stable forms of strontium are not considered toxic to humans at environmental exposure levels.
Diverse Uses
Strontium compounds are known for producing a bright red or crimson color when burned. They are a common ingredient in fireworks and signal flares. Strontium is also used in manufacturing hard ferrite magnets.
Historically, strontium played a role in specialized glass for cathode ray tube (CRT) displays, helping block X-ray emissions. Although CRTs are largely replaced by newer display technologies, this was once a major use. Strontium also finds application in refining zinc, where it helps remove lead impurities.
Health Implications and Therapeutic Uses
Stable strontium is not harmful to humans at environmental levels. However, high levels, especially with diets low in calcium and protein, can cause bone development problems in children. The chemical form of strontium can influence how it is absorbed by the body.
Radioactive isotopes of strontium, such as Strontium-90, are by-products generated in nuclear reactors and through nuclear weapons testing. Due to its chemical similarity to calcium, Strontium-90 can be absorbed and deposited in bone tissue. Once in the bones, it emits beta radiation, which can damage bone marrow and surrounding soft tissues, potentially leading to reduced blood cell counts and an increased risk of cancer. This risk is particularly concerning for children, who may retain radioactive strontium in their bones for longer periods.
Despite risks from radioactive forms, stable strontium compounds have therapeutic applications. Strontium ranelate has been used in Europe and Australia to treat osteoporosis. It promotes new bone formation by increasing osteoblast activity and reduces bone breakdown by inhibiting osteoclast differentiation. This dual action improves bone density and decreases fracture incidence.
Additionally, radioactive Strontium-89 alleviates bone pain in patients with metastatic prostate cancer. Strontium chloride is also an ingredient in toothpastes for sensitive teeth.