Sodium tripolyphosphate

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ImageFile=sodium tripolyphosphate.pngImageSize=200px
IUPACName=sodium triphosphate
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Section1= Chembox Identifiers
CASNo= 7758-29-4
PubChem=517047
SMILES= [O-] P(=O)( [O-] )OP(=O)( [O-] )OP(=O)( [O-] ) [O-] . [Na+] . [Na+] . [Na+] . [Na+] . [Na+]
Section2= Chembox Properties
Formula=Na₅O₁₀P₃
MolarMass=367.86 g/mol
Appearance=
Density=
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Section3= Chembox Hazards
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Sodium tripolyphosphate (STPP, sometimes STP or sodium triphosphate or TPP), with formula Na₅P₃O₁₀, is a polyphosphate of sodium. It is the sodium salt of triphosphoric acid.

Preparation

Industrially sodium tripolyphosphate is prepared by heating a stoichiometric mixture of disodium phosphate, Na₂HPO₄ and monosodium phosphate, NaH₂PO₄ in carefully controlled conditions. [Greenwood&Earnshaw] :2Na₂HPO₄ + NaH₂PO₄ → Na₅P₃O₁₀ + 2H₂O

Uses

It is used in various applications such as a preservative for seafood, meats, poultry and pet foods. It is also used in toothpaste and as a builder in soaps and detergents, improving their cleansing ability. The United States Food and Drug Administration lists STPP as "generally recognized as safe", along with salt, vinegar, and baking powder.

STPP is a solid inorganic compound used in a large variety of household cleaning products, mainly as a builder, but also in human foodstuffs, animal feeds, industrial cleaning processes and ceramics manufacture. STPP is widely used in regular and compact laundry detergents and automatic dishwashing detergents (in powder, liquid, gel and/or tablet form), toilet cleaners, surface cleaners, and coffee urn cleaners [Urnex brand coffee cleaner lists this as an ingredient. http://www.urnex.com/urninfo.htm] . It also provides a number of chemical functions including: sequestration of "water hardness", enabling surfactants to function effectively; pH buffering; dirt emulsification and prevention of deposition; hydrolysis of grease; and dissolving-dispersing dirt particles.

Food Applications

In foods, STPP is used to retain moisture. Many governments regulate the quantities allowed in foods, as it can substantially increase the sale weight of seafood in particular.

Many people find STPP to add an unpleasant taste to food, particularly delicate seafood. The taste tends to be slightly sharp and soapy and is particularly detectable in mild-tasting foods. The increased water holding properties can also lead to a more diluted flavor in the food.

Health effects

Toxicokinetics and acute toxicity

Polyphosphates are hydrolyzed into smaller units (orthophosphates) in the gut before absorption, which may induce a metabolic acidosis. The acute toxicity of polyphosphonates is low as the lowest LD50 after oral administration is > 1,000 mg/kg body weight. [http://www2.mst.dk/udgiv/publications/2001/87-7944-596-9/html/kap07_eng.htm#7.1.1 Complexing agents] , [http://www2.mst.dk/udgiv/publications/2001/87-7944-596-9/html/default_eng.htm Environmental and Health Assessment of Substances in Household Detergents and Cosmetic Detergent Products] , [http://www.mst.dk/English/ Danish Environmental Protection Agency] , Accessed 2008-07-15]

kin and eye irritation

Polyphosphates are moderately irritating to skin and mucous membrane because of their alkalinity.

Mutagenicity and carcinogenecity

No mutagenic potential was observed when TTP was tested in a Salmonella/microsome assay (Ames test) and in a chromosomal aberration assay in vitro using a Chinese hamster fibroblast cell line (Ishidate et al. 1984). Tetrasodium pyrophosphate was not mutagenic in an in vitro assay using S. cerevisiae strains and S. typhimurium strains with and without the addition of mammalian metabolic activation preparations (IPCS 1982).

Reproductive toxicity

Sodium tripolyphosphate showed no maternal toxicity or teratogenic effects at dose levels up to 238 mg/kg body weight in mice and 40 mg/kg in rats (IPCS 1982). Reproduction studies in three generations of rats on diets with 0.5% TTP were performed. TTP had no effects on fertility or litter size, or on growth or survival on offspring (Hodge 1964). Tetrasodium diphosphate showed no maternal toxicity or teratogenic effects at dose levels up to 130 mg/kg body weight in mice and 238 mg/kg in rats (IPCS 1982).

Environmental Effects

In 2000, the total consumption of STPP in these applications was estimated to be approximately 300,000 tonnes in Western Europe and is estimated to represent 90-95% of STPP use in Europe. Due to its physico-chemical properties, STPP is not distributed or transported to the atmosphere, and thus is not expected to end up in soil via atmospheric deposition. 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 theonly 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. PNEC (Predicted No Effect Concentrations) 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.

References