Sodium metaphosphate

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 02 October 2009 and 24 December 2009.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (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:

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.

Preparation of samples
Sample solutions were prepared in stoppered glass flasks at a nominal concentration of 100 mg/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.

Analysis of sample solutions
Sample solutions were taken from the water bath at various times and the pH of each solution recorded.
The sample solutions were analysed 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 test material were prepared in reverse osmosis water at a nominal concentration of 100 mg/l.
Mixed Reference Standard
Duplicate standards solutions of potassium dihydrogen phosphate, sodium pyrophosphate decahydrate, sodium tripolyphosphate, trisodium trimetaphosphate were prepared in reverse osmosis water at nominal concentrations of 30 mg/l as the respective anion.
Standard blank
Reverse osmosis water

Buffers:

Pleast see Attachment 2 for Table of Buffer Specification

Estimation method (if used):

Not used.

Details on test conditions:

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

Duration:

120 h

pH:

4

Initial conc. measured:

100 mg/L

Duration:

120

pH:

7

Initial conc. measured:

100 mg/L

Duration:

120

pH:

9

Initial conc. measured:

100 mg/L

Number of replicates:

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

Positive controls:

no

Negative controls:

no

Statistical methods:

Not specified.

Preliminary study:

The mean peak areas relating to the standard and sample solutions are shown in table 8.2 (please see Attachment 4).

The test material concentrations at the given time points are shown in tables 8.3 to 8.8 (please see Attachment 5).
The test material concentration for Peak 6 in terms of common logarithm of the concentration and percentage of initial concentration is shown in tables 8.9 to 8.11 (please see Attachment 6).

For Graphs of log10 Concentration (g/l) versus Time (Hours) please see Attachment 3.

Test performance:

Validation
The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 0 to 200 mg/l. For the components present in the test material at levels greater than 1 % (i.e. Peaks 1 and 3 to 9), this was satisfactory with correlation coefficients (R) of greater than 0.995 being obtained. For the remainder of the components present in the test material, the correlation coefficients (R) for Peaks 2, 10 and 11 were in the range 0.976 to 0.986 and were considered to be satisfactory for the low levels present. There were insufficient data points to adequately assess the linearity of Peak 12 due to the low levels present in the test material.
Standards prepared in reverse osmosis water were used in the analysis since it was shown that there was no significant difference in response or chromatographic profile from those standards prepared in the respective buffer solutions.
No significant peaks were observed at the approximate retention time of the test material on analysis of any matrix blank solutions.

Transformation products:

yes

No.:

#1

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

The test material was demonstrated to undergo hydrolysis, evident by the formation of orthophosphate, and also by assessment of individual components. However, it was not possible to obtain a definitive result for hydrolytic stability since the test material is a complex mixture of phosphates and the concentration of any individual component monitored may be influenced by the hydrolysis of larger complex phosphates.

pH:

4

Temp.:

50 °C

DT50:

28.1 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other:

Remarks:

See table 'Overall remarks' below for full discussion

pH:

7

Temp.:

50 °C

DT50:

48.6 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other:

Remarks:

See table 'Overall remarks' below for full discussion

pH:

9

Temp.:

50 °C

DT50:

39.5 h

Type:

(pseudo-)first order (= half-life)

Remarks on result:

other:

Remarks:

See table 'Overall remarks' below for full discussion

Other kinetic parameters:

None.

Details on results:

The test material was demonstrated to undergo hydrolysis, evident by the formation of orthophosphate, and also by assessment of individual components. However, it was not possible to obtain a definitive result for hydrolytic stability since the test material is a complex mixture of phosphates and the concentration of any individual component monitored may be influenced by the hydrolysis of larger complex phosphates.

Due to the high volume of tables and figures please see Attachments 4 to 6

Validity criteria fulfilled:

yes

Conclusions:

The test material was demonstrated to undergo hydrolysis, evident by the formation of orthophosphate, and also by assessment of individual components. However, it was not possible to obtain a definitive result for hydrolytic stability since the test material is a complex mixture of phosphates and the concentration of any individual component monitored may be influenced by the hydrolysis of larger complex phosphates.

This study is conducted according to an appropriate guideline and under the conditions of GLP and therefore the study is considered to be acceptable and to adequately satisfy both the guideline requirement and the regulatory requirement as a key study for this endpoint.

Executive summary:

Method

The determination was carried out using Method C7 Abiotic Degradation, Hydrolysis as a Function of pH of Commission Regulation (EC) No 440/2008 of 30 May 2008.

Conclusion

The test material was demonstrated to undergo hydrolysis, evident by the formation of orthophosphate, and also by assessment of individual components. However, it was not possible to obtain a definitive result for hydrolytic stability since the test material is a complex mixture of phosphates and the concentration of any individual component monitored may be influenced by the hydrolysis of larger complex phosphates.

Description of key information

The key study for the endpoint 'hydrolysis as a function of pH' (Butler RE, 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 must be viewed in conjunction with the data generated in natural waters as phosphates and essential cations such as Na+ are rapidly assimilated by microorganisms in water. 
The key study reports that the test material is a complex mixture of different types of phosphate and as such no meaningful data could be produced. For this reason, although the test material was observed to be hydrolytically unstable, no further testing (Tier 2) was performed.
It was demonstrated that the more complex phosphates (indicated by exhibiting longer retention times) present in the test material hydrolysed to simpler phosphate species such as orthophosphate, pyrophosphate and tripolyphosphate, all of which were observed to increase significantly during the test. Several components of the test material increased in magnitude during the course of the test. This is consistent with the process of the phosphate species in the test material hydrolysing to other species already present in solution.
The amount of orthophosphate present in the test material was initially negligible and not reported as a test material component. During the study the amount of orthophosphate in the sample solutions increased significantly. Orthophosphate is therefore considered to be the ultimate hydrolysis product.
This theory is supported by the additional supporting literature. 

Additional information

Sodium metaphosphate is not considered to be hydrolytically stable, however as the substance, in aqueous solutions, is a complex mixture of phosphate species a half-life was not determined. The ultimate degradation products of sodium metaphosphate are sodium and orthophosphate ions. However sodium metaphosphate was also observed to hydrolyse to other phosphate species such as pyrophosphate, trimetaphosphate and tripolyphosphate. All of these species have also been shown to hydrolyse to orthophosphate.