Aluminium metaphosphate

Hydrolysis

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Summary report with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Principles of method if other than guideline:

Summary report for three chemical classes about biotic degradation, hydrolysis as a function of pH for phosphates, pyrophosphates and triphosphates.

GLP compliance:

no

Analytical monitoring:

yes

Transformation products:

not measured

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

Chemical Class	Substance Used for Experimental Determination	Anticipated Half-Life at 25°C	References
Phosphates Orthophosphates	Not applicable, no possible mechanism for hydrolysis	pH 4 > 1 year pH 7 > 1 year pH 9 > 1 year	N/A
Pyrophosphates Diphosphates	Tetrapotassium Pyrophosphate CAS No. 7320-34-5	pH 4 > 1 year pH 7 > 1 year pH 9 > 1 year	1
Triphosphates Tripolyphosphates	Pentapotassium Triphosphate CAS No. 13845-36-8	pH 4 = 14.5 days pH 7 > 1 year pH 9 > 1 year	2

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 DECD Guidelines for Testing of Chemicals, 13 April

2004.

Such a phenomenon may be replicated at environmentally relevant concentrations and on dissolution into complex environmental matrices. Although the cation composition of the final matrix may retain some minor influence on the hydrolytic rate, such a relationship is considered beyond the scope of the standard test method and would not have been addressed or identified by testing in accordance with OECD Method 111. The reported data was generated using buffer solutions with sodium salt

compositions.

References:

1. Tetrapotassium pyrophosphate: Determination of water solubility and abiotic

degradation, hydrolysis as a function of pH. Harlan Laboratories Ltd, Shardlow, UK, final

report for project number292010047.

2. Pentapotassium triphosphate: Determination of water solubility and abiotic

degradation, hydrolysis as a function of pH. Harlan Laboratories Ltd, Shardlow, UK, final

report for project number292010053.

3. Watanabe, Matsuura and Yamada (1981) The Mechanism of the Hydrolysis of

Polyphosphates. V. The Effect of Cations on the Hydrolysis of Pyro- and Triphophates.

Bull. Chem. Soc. Jpn,54, 738-741.

4. Watanabe (1982) The Mechanism of the Hydrolysis of Polyphosphates. V. The Effect

of Cations on the Hydrolysis of cyclo-Tri- and cyclo-Tetraphosphate.Bull. Chem. Soc.

Jpn,55,3766-3769.

Reference 2

Endpoint:

hydrolysis

Type of information:

migrated information: read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

The change of water activity due to the variation of the aluminium content of alkaline aluminate solutions was determined.

GLP compliance:

no

Analytical monitoring:

yes

Details on sampling:

Sodium aluminate solutions with concentrations of 4.5, 5.8, 7.2 and 9 mole/dm³ were prepared

Transformation products:

not measured

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

The water activity increased with increasing aluminium concentration. The increase was attributed to the coordination of hydroxide ion to aluminium and/or dimerization connected with the dehydration of the monomeric species.

 On the basis of the GIBBS-DUHEM equation the water activity data gave an indication of the concentration ranges in which the sodium aluminate solution exists mainly as I) NaOH + monomeric Al(OH)4-and II) NaOH + dimeric Al2O(OH)62-ions.

In systems of the same total alkali concentration an increase of the aluminium content leads to a general increase in the water activity of the solution.The water activity at low aluminium concentrations showed a smaller, almost linear, increase. In case smaller mole ratios (greater aluminium concentrations) a greater increase of water activity occurred leading to a steeper straight line. The change in water activity can be described - depending on the total electrolyte concentration - by assuming the presence of Al(OH)4- and NaOH in the solution of smaller aluminium concentrations (1 -4 M/dm3) and NaOH and dimer Al2O(OH)62- complex aluminate ions in systems of higher aluminium concentrations (2 -7 M/dm3) under alkaline conditions.

Reference 3

Endpoint:

hydrolysis

Type of information:

migrated information: read-across based on grouping of substances (category approach)

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Principles of method if other than guideline:

The effect of pH on aluminium chloride hydrolysis was determined.

GLP compliance:

no

Details on sampling:

A test substance concentration of 1.5E-4 mol/L was prepared. The pH of the solution was adjusted to 4.0, 4.8, 5.0, 5.2, 5.8, and 6.4 respectively

Buffers:

- pH: 4.01 and 7.00
- Type of buffer: Tetramethylammmonium hydroxide pentahydrate and HCL solution

Transformation products:

not measured

Remarks on result:

not measured/tested

Remarks on result:

not measured/tested

When AlCl3 was diluted to a concentration of 1.5*E-4 mol/L hydrolysis occurred immediately At pH 4 mono- and dimeric aluminium species were detected as main products. With increasing pH the hydrolysis and polymerisation increased. Monomeric and dimeric aluminium species hydrolysed and polymerised into small polymeric aluminium species at pH 4.8. At pH 5 the small polymeric aluminium species polymerised into median polymeric species. At pH 5.8 metastable median and large polymers decomposed into small aluminium species and disaggregated into dimeric species. At pH 6.4 the majority of aluminium species formed Al(OH)3 amorphous flocks.

Additional information

According to the column II of Annex VIII, an experimental study on hydrolysis as a function of pH is not required for aluminium metaphosphate (CAS 13776-88-0) as the substance is poorly soluble.

Basically aluminium metaphosphate is subject to hydrolysis when the substance is released to water. During hydrolysis, triphosphate decomposes into orthophosphate ion and pyrophosphate ion in a parallel step. The pyrophosphate ion undergoes further hydrolysis and is converted into orthophosphate ions. Thus the hydrolysis reaction leads directly to the formation of orthophosphate.

The kinetic of hydrolysis of cyclic sodium trimetaphosphate (P3O92-) was investigated at acidic and alkaline solution, and at temperatures between 50 and 70 °C, by Healy & Kilpatrick (1955). The hydrolysis was rapid in acid solution, less rapid in alkaline solution, but negligible at pH9. The kinetic data showed that although H3P3O9 has been classified as a strong tribasic acid, it is necessary to take into account that the reaction solution reactivity increases with increase in (positive) charge of species involved and hydrolysis will speed up in present of metal ions, such Ca. Mg, Ba and Al. The experimental data were in good agreement with the following mechanism and gave a pseudo first-order reaction law and the hydrolysis may be written as:

P3O92- + H2O → P3O105- → PO43- + P2O74- + 2H

P2O74- + H2O →2 O43- + 2H+

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	N/A
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
		pH4 - pH 7:  14.5 days > 1 year
		pH 9:  > 1 year

The presence of multivalent metal ions, such as aluminium ion, catalyses hydrolysis reactions and increases hydrolysis rate, as hydrolysis of aluminium itself forms insoluble hydrolytic precipitantes, such as aluminium hydroxide or oxide. Orthophosphate can be incorporated into either biological solids (e.g. microorganisms) or chemical precipitates and removed from water,

The hydrolysis of aluminium strongly depends on pH and on the aluminium concentration. The pH dependency of aluminium hydrolysis was investigated by Zhao et al. (2009). The hydrolysis of aluminium chloride was tested at pH values ranging from 4 to 6.4. When AlCl3 was diluted to a concentration of 1.5*E-4 mol/L hydrolysis occurred immediately. At pH 4 mono- and dimeric aluminium species were detected as main products. With increasing pH the hydrolysis and polymerisation increased. Monomeric and dimeric aluminium species hydrolysed and polymerised into small polymeric aluminium species at pH 4.8. At pH 5 the small polymeric aluminium species polymerised into median polymeric species. At pH 5.8 metastable median and large polymers decomposed into small aluminium species and disaggregated into dimeric species. At pH 6.4 the majority of aluminium species formed Al(OH)3 amorphous flocks. Szabo et al. (1978) determined the change of water activity due to the variation of the aluminium content of alkaline aluminate solutions. In systems of the same total alkali concentration an increase of the aluminium content leads to a general increase in the water activity of the solution. The water activity at low aluminium concentrations showed a smaller, almost linear, increase. In case smaller mole ratios (greater aluminium concentrations) a greater increase of water activity was determined leading to a steeper straight line.

References:

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

Healy R.M., Kilpatrick M.L., (1955) A Kinetic Study of the Hydrolysis of Trimetaphosphates, J. Am. Chem. Soc., 1955, 77 (20), pp 5258–5264