sodium tripolyphosphate, polygon, STPP
|Molar mass||367.864 g/mol|
|Melting point||622 °C (1,152 °F; 895 K)|
|14.5 g/100 mL (25 °C)|
|EU Index||Not listed|
Except where noted otherwise, data is given for materials in their standard state (at 25 °C (77 °F), 100 kPa)
|what is: / ?)(|
Sodium triphosphate (STP, sometimes STPP or sodium tripolyphosphate or TPP,) is an inorganic compound with formula Na5P3O10. It is the sodium salt of the polyphosphate penta-anion, which is the conjugate base of triphosphoric acid. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with eutrophication are attributed to its widespread use.
Preparation and properties
- 2 Na2HPO4 + NaH2PO4 → Na5P3O10 + 2 H2O
In this way, approximately 2 million tons are produced annually.
STPP is a colourless salt, which exists both in anhydrous form and as the hexahydrate. The anion can be described as the pentanionic chain [O3POP(O)2OPO3]5−. Many related di-, tri-, and polyphosphates are known including the cyclic triphosphate P3O93−. It binds strongly to metal cations as both a bidentate and tridentate chelating agent.
The majority of STPP is consumed as a component of commercial detergents. It serves as a "builder," industrial jargon for a water softener. In hard water (water that contains high concentrations of Mg2+ and Ca2+), detergents are deactivated. Being a highly charged chelating agent, TPP5− binds to dications tightly and prevents them from interfering with the sulfonate detergent.
STPP is a preservative for seafood, meats, poultry, and animal feeds. It is common in food production as E number E451. In foods, STPP is used as an emulsifier and to retain moisture. Many governments regulate the quantities allowed in foods, as it can substantially increase the sale weight of seafood in particular. The United States Food and Drug Administration lists STPP as "generally recognized as safe.".
Other uses (hundreds of thousands of tons/year) include ceramics (increase viscosity of the glazes up to a certain limit), leather tanning (as masking agent and synthetic tanning agent - SYNTAN), anticaking, setting retarders, flame retardants, paper, anticorrosion pigments, textiles, rubber manufacture, fermentation, antifreeze." TPP is used as a polyanion crosslinker in polysaccharide based drug delivery.
Polyphosphates are hydrolyzed into simpler phosphates, which in moderate amounts are nutritious. For example, ATP, a related derivative of triphosphate, is essential for life. Thus, the toxicity of polyphosphates is low, as the lowest LD50 after oral administration is >1,000 mg/kg body weight. [clarification needed] Similarly, no mutagenic or carcinogenic effects nor reproductive effects have been noted. Salts of polyphosphate anions are moderately irritating to skin and mucous membrane because they are mildly alkaline.
In 2000, the worldwide consumption of STPP was estimated to be approximately 2,000,000 tonnes. Because it is very water-soluble, it is not significantly transferred to sewage sludge, and therefore to soil by sludge spreading. No environmental risk related to STPP use in detergents is indicated in soil or air. As an ingredient of household cleaning products, STPP present in domestic waste waters is mainly discharged to the aquatic compartment, directly, via waste water treatment plants, via septic tanks, infiltration or other autonomous waste water systems.
As STPP is an inorganic substance, biodegradation studies are not applicable. However, STPP can be hydrolysed, finally to orthophosphate, which can be assimilated by algae and/or by micro-organisms. STPP thus ends up being assimilated into the natural phosphorus cycle. Reliable published studies confirm biochemical understanding, showing that STPP is progressively hydrolysed by biochemical activity in contact with waste waters (in sewerage pipes and within sewage works) and also in the natural aquatic environment. This information enabled the calculation of “worst case” PEC (Predicted Environmental Concentrations) using the EUSES model and the HERA detergent scenario. A default regional release of 10% was applied instead of the 7% regional release indicated in the HERA detergent scenario. Reliable acute aquatic ecotoxicity studies are available which show that STPP is not toxic to aquatic organisms: all EC/LC50 are above 100 mg/l (Daphnia, fish, algae). Because of this, and because of the only temporary presence of STPP in the aquatic environment (due to hydrolysis), no studies have been carried out to date concerning the chronic effects of STPP on these aquatic organisms. Predicted no-effect concentrations (PNECs) were therefore calculated for the aquatic environment and sediments on the basis of the acute aquatic ecotoxicity results.
Effects of wastewater containing phosphorus
Detergents containing phosphorus contribute together with other sources of phosphorus to the eutrophication of many fresh waters. Eutrophication is an increase in chemical nutrients—typically compounds containing nitrogen or phosphorus—in an ecosystem. It may occur on land or in water. The term is however often used to mean the resultant increase in the ecosystem's primary productivity (excessive plant growth and decay), and further effects including lack of oxygen and severe reductions in water quality, fish, and other animal populations.
Phosphorus can theoretically generate its weight 500 times in algae (Wetzel 1983). Whereas the primary production in marine waters is mainly nitrogen limited, freshwaters are considered to be phosphorus limited. A large part of the sewage effluents in many countries is released untreated into freshwater recipients, and here the use of phosphorus as complexing agents is still an environmental concern.
- Complexing agents, Environmental and Health Assessment of Substances in Household Detergents and Cosmetic Detergent Products, Danish Environmental Protection Agency, Accessed 2008-07-15
- Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0080379419.
- Corbridge, D. E. C. (1960). "The crystal structure of sodium triphosphate, Na5P3O10, phase I". Acta Crystallographica 13: 263. doi:10.1107/S0365110X60000583.
- Davies, D. R.; Corbridge, D. E. C. (1958). "The crystal structure of sodium triphosphate, Na5P3O10, phase II". Acta Crystallographica 11: 315. doi:10.1107/S0365110X58000876.
- Klaus Schrödter, Gerhard Bettermann, Thomas Staffel, Friedrich Wahl, Thomas Klein, Thomas Hofmann "Phosphoric Acid and Phosphates" in Ullmann’s Encyclopedia of Industrial Chemistry 2008, Wiley-VCH, Weinheim. doi:10.1002/14356007.a19_465.pub3
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