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On contact with water dicalcium pyrophosphate will dissociate to calcium cations and phosphate anions. A determination of the hydrolysis of the calcium cation and the phosphate anion according to OECD guideline 111 was not conducted since both ions have no potential mechanism for further hydrolysis or degradation.

The hydrolysis of well soluble sodium tripolyphosphate was investigated in sterile aqueous buffers at pH 3, 4, 5 and 7, and at temperatures between 40 and 70 °C, by Zidner, Hertz and Oswald (1984). The experimental data were in good agreement with the following mechanism and gave a pseudo first-order reaction law.

P3O105- + H2O → PO43- + P2O74- + 2 H

P2O74- + H2O →2 O43- + 2H+

In sterile water the predicted half-life of triphosphate at pH 7-8 and at 20 °C is in the order of years.

The kinetics of hydrolysis of triphosphate and pyrophosphate were also studied in sterile lake water and sterile algal culture media and in non-sterile media at 25 °C by Clesceri and Lee (1965a, 1965b),and compared to published results obtained in distilled water. The results showed that triphosphate and pyrophosphate were hydrolysed in orthophosphate in a period of several days. Addition of glucose increased the rate of hydrolysis, indicating that microbial activity was one of the primary mechanisms of hydrolysis.

The hydrolytic half-life anticipated for the anions of specified phosphates, pyrophosphates and triphosphates has been addressed by read across from a single example for each chemical class, where applicable. The ionic substances were assumed to undergo dissociation in aqueous solution and the resulting cation to have negligible influence on the hydrolysis rate of the anion within the buffer solutions used as instructed by Method 111 of the OECD Guidelines (Harlan, 2011).

The available data demonstrate that triphosphates and triphosphates are hydrolytically stable under environmental conditions with a half-life > 1 year.

Chemical Class

Substance Used for Experimental Determination

Anticipated Half-Life at 25°C


Phosphates Orthophosphates

Not applicable, no possible mechanism for hydrolysis


Pyrophosphates Diphosphates

Tetrapotassium Pyrophosphate

CAS 7320-34-5

pH4 > 1 year pH 7 > 1 year

Triphosphates Tripolyphosphates

Pentapotassium Triphosphate

CAS 13845-36-8

pH 9

> 1 year


pH 7

14.5 days > 1 year

pH 9

> 1 year



Clesceri N.L. and Lee G.F. (1965a) Hydrolysis of Condensed Phosphates – II : Sterile Environment, Int. J. Air Wat. Poll. 9, 743-751.

Clesceri N.L. and Lee G.F. (1965b) Hydrolysis of Condensed Phosphates – I : Non-Sterile

Zinder B., Hertz J. and H. R. Oswald (1984) Kinetic Studies on the Hydrolysis of Sodium Tripolyphosphate in Sterile Solution, Water Res. 18 (5), 509-512.