Sodium tripolyphosphate

Sodium tripolyphosphate (STPP, sometimes STP or sodium triphosphate), 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.
 * 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. Unfortunately, for consumers an excessive amount of STPP in food can cause an increase in price, for products sold by weight contain more water than products without STPP.

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. 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.

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 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. PNEC (Predicted No Effect Concentrations) were therefore calculated for the aquatic environment and sediments on the basis of the acute aquatic ecotoxicity results.