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Environmental fate & pathways

Hydrolysis

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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:
EU Method C.7 (Degradation: Abiotic Degradation: Hydrolysis as a Function of pH)
Deviations:
no
GLP compliance:
yes (incl. certificate)
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.