Sodium tripolyphosphate
Encyclopedia
Sodium triphosphate 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.
, Na2HPO4, and monosodium phosphate
, NaH2PO4, under carefully controlled conditions.
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]].
s. 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.
for seafood, meats, poultry, and animal feed
s. It is common in food production as E number
E451. 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. The United States Food and Drug Administration
lists STPP as "generally recognized as safe
.".
, 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. 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.
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.
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.
Inorganic compound
Inorganic compounds have traditionally been considered to be of inanimate, non-biological origin. In contrast, organic compounds have an explicit biological origin. However, over the past century, the classification of inorganic vs organic compounds has become less important to scientists,...
with formula Na5P3O10. It is the sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...
salt of the polyphosphate
Polyphosphate
Triphosphates are salts or esters of polymeric oxyanions formed from tetrahedral PO4 structural units linked together by sharing oxygen atoms. When two corners are shared the polyphosphate may have a linear chain structure or a cyclic ring structure. In biology the polyphosphate esters AMP, ADP...
penta-anion, which is the conjugate base of triphosphoric acid
Triphosphoric acid
Triphosphoric acid, also tripolyphosphoric acid, with formula H5P3O10, is a condensed form of phosphoric acid.In polyphosphoric acids, it is the next after pyrophosphoric acid, H4P2O7, also called diphosphoric acid....
. It is produced on a large scale as a component of many domestic and industrial products, especially detergents. Environmental problems associated with eutrophication
Eutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
are attributed to its widespread use.
Preparation and properties
Sodium tripolyphosphate is produced by heating a stoichiometric mixture of disodium phosphateDisodium phosphate
Disodium hydrogen phosphate is a sodium salt of phosphoric acid. It is a white powder that is highly hygroscopic and water soluble. It is therefore used commercially as an anti-caking additive in powdered products. It is also known as disodium hydrogen orthophosphate, sodium hydrogen phosphate...
, Na2HPO4, and monosodium phosphate
Monosodium phosphate
Monosodium phosphate , also known as anhydrous monobasic sodium phosphate is a chemical compound of sodium with a phosphate counterion. It is used as a laxative and, in combination with other sodium phosphates, as a pH buffer....
, NaH2PO4, under carefully controlled conditions.
- 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
Anhydrous
As a general term, a substance is said to be anhydrous if it contains no water. The way of achieving the anhydrous form differs from one substance to another...
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]].
In detergents
The majority of STPP is consumed as a component of commercial detergentDetergent
A detergent is a surfactant or a mixture of surfactants with "cleaning properties in dilute solutions." In common usage, "detergent" refers to alkylbenzenesulfonates, a family of compounds that are similar to soap but are less affected by hard water...
s. 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.
Food applications
STPP is a preservativePreservative
A preservative is a naturally occurring or synthetically produced substance that is added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes....
for seafood, meats, poultry, and animal feed
Compound feed
Compound feeds are feedstuffs that are blended from various raw materials and additives. These blends are formulated according to the specific requirements of the target animal...
s. It is common in food production as E number
E number
E numbers are number codes for food additives that have been assessed for use within the European Union . They are commonly found on food labels throughout the European Union. Safety assessment and approval are the responsibility of the European Food Safety Authority...
E451. 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. The United States Food and Drug Administration
Food and Drug Administration
The Food and Drug Administration is an agency of the United States Department of Health and Human Services, one of the United States federal executive departments...
lists STPP as "generally recognized as safe
Generally recognized as safe
Generally recognized as safe is an American Food and Drug Administration designation that a chemical or substance added to food is considered safe by experts, and so is exempted from the usual Federal Food, Drug, and Cosmetic Act food additive tolerance requirements.-History:On January 1, 1958,...
.".
Other uses
Other uses (hundreds of thousands of tons/year) include "ceramics, leather tanning (as masking Agent and Synthetic Tanning Agent-SYNTAN), anticaking, setting retarders, flame retardants, paper, anticorrosion pigments, textiles, rubber manufacture, fermentation, antifreeze."Health effects
Polyphosphates are hydrolyzed into simpler phosphates, which in moderate amounts are nutritious. For example, ATPAdenosine triphosphate
Adenosine-5'-triphosphate is a multifunctional nucleoside triphosphate used in cells as a coenzyme. It is often called the "molecular unit of currency" of intracellular energy transfer. ATP transports chemical energy within cells for metabolism...
, 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. 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.
Environmental effects
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
Biodegradation
Biodegradation or biotic degradation or biotic decomposition is the chemical dissolution of materials by bacteria or other biological means...
studies are not applicable. However, STPP can be hydrolysed, finally to orthophosphate, which can be assimilated by algae
Algae
Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...
and/or by micro-organisms. STPP thus ends up being assimilated into the natural phosphorus cycle
Phosphorus cycle
The phosphorus cycle is the biogeochemical cycle that describes the movement of phosphorus through the lithosphere, hydrosphere, and biosphere. Unlike many other biogeochemical cycles, the atmosphere does not play a significant role in the movement of phosphorus, because phosphorus and...
. 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
Aquatic ecosystem
An aquatic ecosystem is an ecosystem in a body of water. Communities of organisms that are dependent on each other and on their environment live in aquatic ecosystems. The two main types of aquatic ecosystems are marine ecosystems and freshwater ecosystems....
. This information enabled the calculation of “worst case” PEC (Predicted Environmental Concentrations) using the EUSES model and the HERA
Hera
Hera was the wife and one of three sisters of Zeus in the Olympian pantheon of Greek mythology and religion. Her chief function was as the goddess of women and marriage. Her counterpart in the religion of ancient Rome was Juno. The cow and the peacock were sacred to her...
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
Toxicity
Toxicity is the degree to which a substance can damage a living or non-living organisms. Toxicity can refer to the effect on a whole organism, such as an animal, bacterium, or plant, as well as the effect on a substructure of the organism, such as a cell or an organ , such as the liver...
studies are available which show that STPP is not toxic to aquatic organisms: all EC/LC50 are above 100 mg/l (Daphnia
Daphnia
Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...
, 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 eutrophicationEutrophication
Eutrophication or more precisely hypertrophication, is the movement of a body of water′s trophic status in the direction of increasing plant biomass, by the addition of artificial or natural substances, such as nitrates and phosphates, through fertilizers or sewage, to an aquatic system...
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.