Applications

Strontium has uses similar to those of calcium and barium, but it is rarely employed because of its higher cost. Principal uses of strontium compounds are in pyrotechnics, for the brilliant reds in fireworks and warning flares and in greases. A little is used as a getter in vacuum tubes to remove the last traces of air. Most strontium is used as the carbonate in special glass for television screens and visual display units. Although strontium-90 is a dangerously radioactive isotope, it is a useful by-product of nuclear reactors from whose spent fuel is extracted. Its high-energy radiation can be used to generate an electric current, and for this reason it can be used in space vehicles, remote weather stations and navigation buoys.

Strontium in the environment

Strontium is commonly occurs in nature, forming about 0.034% of all igneous rock and in the form of the sulfate mineral celestite (SrSO₄) and the carbonate strontianite (SrCO₃). Celestite occurs frequently in sedimentary deposits of sufficient size, thus the development of mining facilities attractive. The main mining areas are UK, Mexico, Turkey and Spain. World production of strontium ores is about 140.000 tonnes per year from an unassessed total of reserves.  Foods containing strontium range from very low e.g. in corn (0.4 ppm and oranged (0.5 ppm) to high, e.g. in cabbage (45 ppm), onions (50 ppm) and lattuce (74 ppm).

Health effects of strontium

Strontium compounds that are water-insoluble can become water-soluble, as a result of chemical reactions. The water-soluble compounds are a greater threat to human health than the water-insoluble ones. Therefore, water-soluble forms of strontium have the opportunity to pollute drinking water. Fortunately the concentrations in drinking water are usually quite low.

People can be exposed to small levels of (radioactive) strontium by breathing air or dust, eating food, drinking water, or by contact with soil that contains strontium. We are most likely to come in contact with strontium by eating or drinking.  Strontium concentrations in food contribute to the strontium concentrations in the human body. Foodstuffs that contain significantly high concentrations of strontium are grains, leafy vegetables and dairy products.

For most people, strontium uptake will be moderate. The only strontium compound that is considered a danger to human health, even in small quantities, is strontium chromate. The toxic chromium that it contains mainly causes this. Strontium chromate is known to cause lung cancer, but the risks of exposure have been greatly reduced by safety procedures in companies, so that it is no longer an important health risk.
The uptake of high strontium concentrations is generally not known to be a great danger to human health. In one case someone experienced an allergic reaction to strontium, but there have been no similar cases since. For children exceeded strontium uptake may be a health risk, because it can cause problems with bone growth.  Strontium salts are not known to cause skin rashes or other skin problems of any kind.
When strontium uptake is extremely high, it can cause disruption of bone development. But this effect can only occur when strontium uptake is in the thousands of ppm range. Strontium levels in food and drinking water are not high enough to be able to cause these effects.

Effects of strontium on the Environment

Strontium in its elemental form occurs naturally in many compartments of the environment, including rocks, soil, water, and air. Strontium compounds can move through the environment fairly easily, because many of the compounds are water-soluble.
Strontium is always present in air as dust, up to a certain level. Strontium concentrations in air are increased by human activities, such as coal and oil combustion. Dust particles that contain strontium will settle to surface water, soils or plant surfaces at some point. When the particles do not settle they will fall back onto earth when rain or snow falls. All strontium will eventually end up in soils or bottoms of surface waters, where they mix with strontium that is already present.
Strontium can end up in water through soils and through weathering of rocks. Only a small part of the strontium in water comes from dust particles from the air. Most of the strontium in water is dissolved, but some of it is suspended, causing muddy water at some locations. Not much strontium ends up in drinking water.
When strontium concentrations in water exceed regular concentrations, this is usually caused by human activities, mainly by dumping waste directly in the water. Exceeded strontium concentrations can also be caused by settling of dust particles from air that have reacted with strontium particles from industrial processes.
Strontium concentrations in soil may also be increased by human activities, such as the disposal of coal ash and incinerator ash, and industrial wastes. Strontium in soil dissolves in water, so that it is likely to move deeper into the ground and enter the groundwater. A part of the strontium that is introduced by humans will not move into groundwater and can stay within the soil for decades.
Because of the nature of strontium, some of it can end up in fish, vegetables, livestock and other animals.
One of the isotopes of strontium is radioactive. This isotope is not likely to occur naturally in the environment. It ends up in the environment, though, as a result of human activities, such as nuclear bomb testing and radioactive storage leaking. The only way to decrease concentrations of this isotope is through radioactive decay to stable zirconium.
The concentrations of radioactive strontium in the environment are relatively low and the particles will always end up in soils or water-bottoms eventually, where they mix with other strontium particles. It is not likely to end up in drinking water.

Certain deep-sea creatures incorporate strontium into their shells as strontium sulphate, and stony corals require it, which is why it needs to be added in the water in aquaria.

Strontium and water: reaction mechanisms, environmental impact and health effects

Seawater contains 8 ppm strontium on average. River water generally contains about 50 ppb of strontium and in oyster tissue 10 ppm of strontium (dry mass) was found. When dissolved in water strontium mainly occurs as Sr²⁺ (aq). One other possible form is SrOH⁺ (aq).

In what way and in what form does strontium react with water?

Strontium reacts with water slowly, generally to strontium hydroxide and hydrogen gas. It reacts with water quicker than calcium, which is placed directly above strontium in the periodic chart, and slower than barium, placed directly below strontium.

The following reaction mechanism is applicable:

Sr (s) + 2H₂O (g) -> Sr(OH)₂ (aq) + H₂ (g)

Solubility of strontium and strontium compounds

Strontium is water insoluble, but it does react with water. Strontium compounds can be water soluble. Examples include strontium carbonate with a water solubility of 10 mg/L, and strontium chromate with a water solubility of 9 mg/L.

Why is strontium present in water?

The most significant strontium mineral is celestite (strontium sulphate; SrSO₄), followed by strontianite (strontium carbonate; SrCO₃). At least 140,000 ton is exploited annually. This may produce strontium metal, which is not applied widely, but it may extract residue air from vacuum tubes. As a carbonate strontium is mainly applies for TV-screen production. This is the main application of the element. It insulates X-rays that occur from electric radiation in the cathode ray tube. This is however required less and less because of the increasing popularity of the flat screen TV. Strontium is applied for alloy refinery, and strontium sulphate was applied as imitation diamond. Because of its red inflammation it is suitable for application in fireworks. Strontium ferrite is applied in permanent ceramic magnets that are highly coercive and can be applied in small engines because of its resistance to heat and corrosion.
Radioactive ⁸⁹Sris applied in nuclear physics and in nuclear medicine. ⁹⁰Sr is a product of nuclear explosions. It strongly contaminated earth in the 1950's and 1960's, because above-ground test explosions were carried out. It is also a by-product of nuclear reactors and the highly energetic radiation is applied in for example space vehicles.

What are the environmental effects of strontium in water?

Strontium is only a dietary requirement in a few exceptional cases. A number of deep sea organisms apply strontium sulphate in shells, and stone corals also have a requirement for the element. Plants contains between 3 and 400 ppm strontium (dry mass). Strontium is usually immobile in the environment, because of rapid precipitation as strontium carbonate, or because it is applied in shells. The highest strontium concentrations are found in deserts and forest soils.
Strontium naturally occurs as four separate stable isotopes, and nineteen instable isotopes. ⁹⁰Sr spread throughout the globe after nuclear test explosions in the 20^th century, was washed out of the atmosphere, and ended up in soils, crops, grazing cows and other animals, and eventually in humans. It was taken up in measurable amounts by virtually every land organism. The extremity of the carcinogenic and mutagenic mechanisms was not described adequately so far.

What are the health effects of strontium in water?

The human body contains approximately 4.6 ppm strontium. It has no specific function, but it is absorbed because of its similarity to calcium. Consequently, the larger part of absorbed strontium is inserted in bones.
Strontium is non-toxic and a daily intake of about 0.8-5 mg through food is harmless, when it only contains non-radioactive strontium. In the 20^th century this ended up in food and drinking water. Later, it was found mainly in infant's teeth.
The risk of radioactive strontium intake is mainly based on its carcinogenic and mutagenic mechanism, problems that occur in cell division, and possible increased infant mortality. ⁹⁰Sr decays to radioactive yttrium, which accumulates in hypophysis and ovaries, and subsequently disrupts infant hormonal development, and infant growth.