Strontium : nm Strontium (Sr) is a chemical element with atomic number 38. It is an alkaline earth, soft, malleable, gray-yellow in color.
On contact with air, strontium forms a protective oxide film. It ignites and burns easily in air and reacts with water.
Strontium was isolated by Sir Humphry Davy (England) in 1808 after its oxide was identified in ore from a mine in Scotland near Strontian, strontianite SrCO3 in 1790 by Thomas Charles Hope. This was based on the work of William Cruickshank and Adair Crawford, the first to mention the existence of an unknown element in strontianite.
Strontium is found in minerals such as celestite SrSO4 and strontianite SrCO3.
The level of strontium present in the earth's crust is low (0,034%).
Certain compounds (soluble) are present in seawater and certain springs (mineral waters).
Radioactive strontium (90Sr) and radioactive cesium (137 Cs) have contaminated the biosphere following nuclear tests in the air, and following the Chernobyl disaster and then Fukushima. Part of this strontium has been reconcentrated by the food chain, via certain fungi in particular. The leaching of strontium and/or its bioconcentration in the food web means that water and air pollution has rapidly decreased, according to UNSCAR (In 2009, drinking and irrigation water no longer exceeded 1 becquerel of cesium and strontium per litre).
Strontium and the body: Strontium is absorbed by the digestive tract by the same mechanisms as calcium, but the absorption of calcium is preferential. the non-eliminated part of strontium ingested or inhaled or having contaminated a human organism is 99% concentrated in the bone system and connective tissue.
Use of strontium: Strontium is found in:
– red dye: nitrate or chlorate in fireworks and distress flares to give a red tint. Strontium azoate is a component of red bengal lights.
– varnishes and glazes for ceramics where it serves as a flux.
– certain pigments which are strontium salts.
– the glasses of the color cathode-ray tube slab (SrCO3 carbonate) to slow down the X-rays produced. In Western Europe, barium carbonate is preferred, which is less expensive.
– the extraction of sugar from beet molasses (strontium oxide, strontian SrO).
– car electric window motors (strontium hexaferrite).
The measurement of the isotopic ratios of strontium and rubidium in certain rocks allows their absolute dating.
Strontium could also become a "dopant" for new catalysts (perovskite oxides) currently being tested to reduce the cost of catalytic converters, by limiting the use of platinum, which is rare and expensive.
The strontium level of seawater is much higher than that of human serum (ratio of 650 to 1). Fresh water contains much less strontium than sea water, but still more than serum (about 5 times more). This is why strontium is a proposed indicator for dating a drowning (especially at sea). Strontium levels in drowned serum and in water samples can be measured by atomic absorption spectrometry.
Health: The strontium 90 isotope is one of the most dangerous fission products (atomic explosions, nuclear reactor). Indeed, the experiments of Sydney Ringer showed, more than a hundred years ago, that strontium replaced calcium in the bones. In addition, its half-life is long: almost 29 years.
The effects of strontium on bone:
– taken as a replacement for calcium or in greater quantities than this, it causes bone disorders reminiscent of those of rickets and hypocalcaemia.
– taken at the same time as calcium, it promotes bone formation. It has been authorized and widely used in women in the treatment of osteoporosis in the form of strontium ranelate (antiosteoporotic), not without the risk of undesirable side effects.
Except at very low doses, non-radioactive strontium is toxic to animals and humans with symptoms varying according to species, age, dose, and possibly possible synergies with other products or depending on the isotope considered. In humans, even at low doses, strontium chromate causes lung cancer when inhaled.
When strontium in the form of carbonate (SrCO3) is ingested through the digestive tract, it can cause cramps, painful contraction of various muscles and a purgative effect.
As for strontium nitrate (SrNO3), if it is inhaled, it can cause several problems of different types (cardiac, pulmonary, hepatic and renal).
Radioactive strontium also causes anemia and oxygen deficiency, and at higher doses, cancers, by affecting the DNA of cells that are directly exposed to it.
Consuming high concentrations of strontium is generally not known to be hazardous to health. Only one case of strontium allergy. In children, excessive consumption of strontium can pose a risk because it can cause problems with bone growth.
Strontium ranelate: strontium has a high affinity for bone. Radioactive strontium is used in the treatment of bone metastases. The radioactive isotope administered is Sr89, the half-life of which is 50 days. It accumulates in bone metastases which are thus preferentially irradiated. Its main indication is the palliative treatment of pain due to bone metastases from prostate cancer. To promote the uptake and fixation of radioactive strontium, it is important to stop all calcium supplementation for at least two weeks before its administration.
Toxicity and ecotoxicity of strontium: In nature, strontium is often naturally present in the ground and sometimes even in the air, in the form of aerosols, or adsorbed on other particles. Coal or incinerator ashes are a source likely to locally pollute drinking water. Several of its soluble compounds are easily found in water and therefore in sediments and in certain plants and animals, including freshwater (zebra mussel for example, which detoxifies by fixing it in the shell) which can bioconcentrate. The test of marine protozoa of the class Acantharia also consists of strontium sulphate.
It would be the most present in certain foods (seeds, leafy vegetables and dairy products). In animals, the part that is not eliminated in the mucus, urine or excrement is fixed preferentially in the bones. Cattle, game, fish or shellfish may contain it.
In the past, strontium has been trapped underground, in oil and coal in particular. The combustion of these fossil products releases strontium in the form of dust or particles into the air.
Strontium oxidizes rapidly in air, it reacts violently with water to produce strontium hydroxide, corrosive, and hydrogen.