Trisodium trimetaphosphate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Testing was conducted between 07 October 2009 and 19 January 2010.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

Date of GLP inspection: 2009-09-15 Date of Signature on GLP certificate: 2009-11-26

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 20 g/l in the three buffer solutions.

The test solutions were split into individual vessels for each data point.

The solutions were shielded from light whilst maintained at the test temperature.

Preliminary test/Tier 1

Sample solutions at pH 4, 7 and 9 were maintained at 50.0 ± 0.5°C for a period of 120 hours.

Tier 2

Results from the Preliminary test/Tier 1 showed it was not necessary to undertake any further testing.

Analysis of sample solutions

Sample solutions were taken from the waterbath at various times and the pH of each solution recorded.

The concentration of the sample solution was determined by ion chromatography (IC).

Samples

An aliquot of each sample solution was analysed without further treatment.

Sample blanks

pH 4 buffer solution.
pH 7 buffer solution.
pH 9 buffer solution.

Standards

Duplicate standard solutions of trisodium trimetaphosphate (Aldrich, lot number: 058K1129, purity*: 96 %) (* Value quoted by supplier) were prepared in reverse osmosis water at a nominal concentration of 20 mg/l.

Standard blank

Reverse osmosis water.

Buffers:

Specification of buffer solutions

pH4
Citric acid 3 mmol.dm-3
Sodium chloride 2 mmol.dm-3
Sodium hydroxide 3 mmol.dm-3

pH7
Citric acid 3 mmol.dm-3
Sodium chloride 2 mmol.dm-3
Sodium hydroxide as required, to adjust the buffer solution pH to approximately 7.0

pH9
Disodium tetraborate 0.5 mmol.dm-3
Sodium chloride 1 mmol.dm-3

The buffer solutions were filtered through a 0.2 µm membrane filter to ensure they were sterile before commencement of the test. Also these solutions were subjected to ultrasonication and degassing with nitrogen to minimise dissolved oxygen content.

Details on test conditions:

Refer to details on sampling and analytical methods.

Duration:

120 h

pH:

4

Initial conc. measured:

0.02 g/L

Duration:

120 h

pH:

7

Initial conc. measured:

0.02 g/L

Duration:

120 h

pH:

9

Initial conc. measured:

0.02 g/L

Number of replicates:

An aliquot of each sample solution was analysed without further treatment.

Positive controls:

no

Negative controls:

no

Preliminary study:

Preliminary test/Tier 1
The mean peak areas relating to the standard and sample solutions are shown in Attachment 2

Test performance:

Validation
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 65 mg/l. This was satisfactory with a correlation coefficient of 1.000 being obtained.
Discussion
No significant peaks were observed at the approximate retention time of the test material on analysis of any matrix blank solutions.
As the test material was determined to be hydrolytically stable under acidic conditions, no additional testing was performed at pH 1.2, 37.0 ± 0.5°C.

Transformation products:

no

Details on hydrolysis and appearance of transformation product(s):

Less than 10% hydrolysis after 5 days at 50°C at pH 4, 7 and 9.

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

pH:

9

Temp.:

25 °C

DT50:

> 1 yr

Details on results:

At pH4, 7 and 9 there was less than 10% hydrolysis after 5 days at 50°C, equivalent to a half-life greater than 1 year at 25°C.

Preliminary test/Tier 1

The mean peak areas relating to the standard and sample solutions are shown in the following table:

Solution	Mean peak area
Standard 20.5 mg/l	2.556
Standard 22.0 mg/l	2.685
Initial Sample A, pH 4	2.551
Initial Sample B, pH 4	2.575
Initial Sample A, pH 7	2.587
Initial Sample B, pH 7	2.593
Initial Sample A, pH 9	2.581
Initial Sample B, pH 9	2.572
Standard 20.5 mg/l	2.468
Standard 22.0 mg/l	2.624
24 Hour Sample A, pH 4	2.553
24 Hour Sample B, pH 4	2.513
24 Hour Sample A, pH 7	2.565
24 Hour Sample B, pH 7	2.562
24 Hour Sample A, pH 9	2.516
24 Hour Sample B, pH 9	2.518
Standard 20.5 mg/l	2.482
Standard 20.1 mg/l	2.325
120 Hour Sample A, pH 4	2.349
120 Hour Sample B, pH 4	2.348
120 Hour Sample A, pH 7	2.574
120 Hour Sample B, pH 7	2.563
120 Hour Sample A, pH 9	2.430
120 Hour Sample B, pH 9	2.465

 

The test material concentrations at the given time points are shown in the following tables:

pH 4 at 50.0 ± 0.5ºC

Time (Hours)	Concentration (g/l)		Log10[concentration (g/l)]		% of mean initial concentration
	A	B	A	B	A	B
0	1.98 x 10^-2	2.00 x 10^-2	-1.70	-1.70	-	-
24	2.05 x 10^-2	2.01 x 10^-2	-1.69	-1.70	103	101
120	1.91 x 10^-2	1.91 x 10^-2	-1.72	-1.72	95.6	95.6

Result:           Less than 10% hydrolysis after 5 days at 50°C, equivalent to a half-life greater than 1 year at 25°C.

pH 7 at 50.0 ± 0.5ºC

Time (Hours)	Concentration (g/l)		Log10[concentration (g/l)]		% of mean initial concentration
	A	B	A	B	A	B
0	2.01 x 10^-2	2.02 x 10^-2	-1.70	-1.70	-	-
24	2.05 x 10^-2	2.05 x 10^-2	-1.69	-1.69	102	102
120	2.09 x 10^-2	2.08 x 10^-2	-1.68	-1.68	104	103

Result:           Less than 10% hydrolysis after 5 days at 50°C, equivalent to a half-life greater than 1 year at 25°C.

pH 9 at 50.0 ± 0.5ºC

Time (Hours)	Concentration (g/l)		Log10[concentration (g/l)]		% of mean initial concentration
	A	B	A	B	A	B
0	2.01 x 10^-2	2.00 x 10^-2	-1.70	-1.70	-	-
24	2.01 x 10^-2	2.02 x 10^-2	-1.70	-1.70	101	101
120	1.97 x 10^-2	2.00 x 10^-2	-1.71	-1.70	98.4	99.8

Result:           Less than 10% hydrolysis after 5 days at 50°C, equivalent to a half-life greater than 1 year at 25°C.

Validity criteria fulfilled:

yes

Remarks:

The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 65 mg/l. This was satisfactory with a correlation coefficient of 1.000 being obtained.

Conclusions:

The estimated half-life at 25°C of the test material at pH 4, 7 and 9 is greater than 1 year. This study is considerd to be acceptable and satisfies the guideline requirement as a key study for this endpoint in accordance with Regulation (EC) No. 1907/2006 (REACH).

Executive summary:

Method

The determination was carried out using Method C7 of Commission Directive 92/69/EEC (which constitutes Annex V of Council Directive 67/548/EEC), Method 111 of the OECD Guidelines for Testing of Chemicals, 13 April 2004.

Conclusion

The estimated half-life at 25°C of the test material are shown in the following table:

pH	Estimated half-life at 25°C
4	>1 year
7	>1 year
9	>1 year

Description of key information

A number of studies exist to assess the hydrolysis of trisodium trimetaphosphate under both laboratory and natural conditions.
The key study for the endpoint ‘hydrolysis as a function of pH’ (Walker J, 2010 ) has been selected on the basis that the study is conducted to the recommended OECD guideline and under the conditions of GLP and therefore meets the regulatory requirements for this endpoint. However the data does not necessarily reflect a ‘real world’ situation as phosphates and essential cations such as Na+ are rapidly assimilated by microorganisms in soil and waters.  

Key value for chemical safety assessment

Half-life for hydrolysis:

1 yr

at the temperature of:

25 °C

Additional information

The key study, conducted in fresh water, shows that trisodium trimetaphosphate was hydrolytically stable over the course of the study. However this data should be viewed in parallel with the supporting data provided as this information gives a more accurate picture of the behaviour and stability of the substance in natural waters and therefore is more relevant for the purposes of exposure estimations and risk assessment. Trisodium trimetaphosphate will not persist in natural waters as the trimetaphosphate will be degraded.

Hydrolysis occurs at a rate much slower than that of linear condensed phosphates due trimetaphosphate's ring structure, which requires opening prior to hydrolysis.

This process may be catalysed by enzymes (trimetaphosphatases) following the reaction scheme:

trimetaphosphate + H2O ↔ triphosphate. (tripolyphosphate is thenrapidly hydrolysed to orthophosphate).

Alternatively, catalysis via Ca2 +/Mg2+ ions may also occur.

The ultimate degradation product of trimetaphosphate is orthophosphate.