Potassium phosphinate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study (OECD)

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Deviations:

no

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)

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

Before and after incubation at 50 °C, 50 µL aliquots of the test solutions at each pH value were analyzed after 1:100 dilution with water by IC separation of the injected sample solution.

Buffers:

- Composition of buffer:
The buffer solutions, pH 4.0, 7.0 and 9.0, were prepared as recommended by the OECD guideline 111. The authors do not precise the buffer system, but according to the main substance used in the buffer solution cited by the authors we can conclude they used the buffer mixtures of Clark and Lubs (Annex 3 of the OECD guideline).

- Details of composition (according to guideline):
Buffer pH 4.0: 0.40 ml. 0.1 N NaOH +50 ml. biphthalate to 100 ml
Buffer pH 7.0: 29.63 ml. 0.1 N NaOH + 50 ml. phosphate to 100 ml
Buufer pH 9.0: 21.30 ml. 0.1 N NaOH + 50 ml. boric acid to 100 ml

Details on test conditions:

The test item was dissolved in an aqueous solution at a specific pH value (pH 4.0, pH 7.0 and pH 9.0).
Test item at pH 4.0: 581.34 mg of Sodium Hypophosphite (Solid) were dissolved in 100 mL of buffer solution (pH 4.0) to prepare a test solution of 5.8134 mg/mL Sodium Hypophosphite (Solid).
Test item at pH 7.0: 590.52 mg of Sodium Hypophosphite (Solid) were dissolved in 100 mL of buffer solution (pH 7.0) to prepare a test solution of 5.9052 mg/mL Sodium Hypophosphite (Solid).
Test item at pH 9.0: 548.49 mg of Sodium Hypophosphite (Solid) were dissolved in 100 mL of buffer solution (pH 9.0) to prepare a test solution of 5.4849 mg/mL Sodium Hypophosphite (Solid).
After preparation the solution was incubated in the dark and at a specific temperature in a water bath thermostated at the specific temperature with a maximum deviation of ± 0.5 °C. The concentration of the test item was determined as a function of time, using a suitable analytical method. Major hydrolysis products representing more than 10 % of the applied dose should be identified.
Preliminary test : performed at 50 °C ± 0.5 °C at each of pH 4.0, pH 7.0 and pH 9.0. Aliquots of each test solution were analyzed before incubation, after 2.4 hours and after 120 hours.
As no degradation was observed, sterility tests were not considered as needed.

TEST SYSTEM
- Type, material and volume of test flasks: 50 mL Erlenmeyer flasks. All glassware and flasks rinsed with sterile buffer and stopperedwith inert material
- Sterilisation method: buffered solutions and milliQ water autoclaved for 25 min before first use
- Lighting: test solution protected from direct light
- Measures to exclude oxygen: nitrogen bubbling for 10 min before preparation of solution + seal flasks

TEST MEDIUM
- Volume used/treatment : 50 mL
- Kind and purity of water: milliQ water
- Preparation of test medium: 581.34 mg of Sodium Hypophosphite (Solid) were dissolved in 100 mL of buffer solution (pH 4.0)
- Renewal of test solution:
- Identity and concentration of co-solvent:

Duration:

120 h

pH:

4

Temp.:

50 °C

Duration:

120 h

pH:

7

Temp.:

50 °C

Duration:

120 h

pH:

9

Temp.:

50 °C

Number of replicates:

2

Preliminary study:

Less than 10% of hydrolysis was observed at every pH tested.
As no degradation was observed, sterility tests were not considered as needed.
A main study was not required, as the test item was found to be stable according to the criteria given in the guideline.

Transformation products:

not specified

% Recovery:

95.8 - 96.1

pH:

4

Temp.:

50 °C

Duration:

120 h

% Recovery:

99.8 - 100.9

pH:

7

Temp.:

50 °C

Duration:

120 h

% Recovery:

98.2 - 99.8

pH:

9

Temp.:

50 °C

Duration:

120 h

pH:

4

Temp.:

25 °C

DT50:

> 1 yr

Type:

not specified

Remarks on result:

other: <10% hydrolysis after 5 days at 50°C

pH:

7

Temp.:

25 °C

DT50:

> 1 yr

Type:

not specified

Remarks on result:

other: <10% hydrolysis after 5 days at 50°C

pH:

9

Temp.:

25 °C

DT50:

> 1 yr

Type:

not specified

Remarks on result:

other: <10% hydrolysis after 5 days at 50°C

Table1       Results of the Preliminary Test of Sodium Hypophosphite (Solid)

	Initial concentration measured	Concentration measured after 2.4 hours incubation	Concentration measured after 5 days incubation	Hydrolysis reaction after 5 days incubation	Recovery
	[mg/mL]	[mg/mL]	[mg/mL]	[%]	[%]
pH 4.0	5.588	5.627	5.218	7	96.1
	5.570	5.773	5.114	8	95.8
pH 7.0	5.892	5.590	6.144	-4	99.8
	5.961	5.515	6.425	-8	100.9
pH 9.0	5.472	5.396	5.396	1	99.8
	5.385	5.489	5.380	0	98.2

 

Validity criteria fulfilled:

yes

Conclusions:

In the test conditions, the tests at pH 4.0, pH 7.0 and pH 9.0 showed no significant degradation of Sodium Hypophosphite (Solid) at 50 °C. The hydrolysis of Sodium Hypophosphite (Solid) was less than 10% after 5 days.
Therefore, the estimated half-life time is higher than one year under representative environmental conditions (25 °C). Therefore, Sodium Hypophosphite (Solid) is considered to be hydrolytically stable, and no further testing was necessary.

Executive summary:

Hydrolysis as function of pH of Sodium Hypophosphite (solid) as been determined according to OECD guideline 111 under GLP procedure.

Preliminary study was conducted in duplicate at pH 4.0, 7.0 and 9.0 at a temperature of 50°C. Concentration in the test substance was measured by ion chromatography before the test after 2.4 hours and 120h (5 days) of incubation under no direct light and avoiding oxygen.

In the test conditions, the tests at pH 4.0, pH 7.0 and pH 9.0 showed no significant degradation of Sodium Hypophosphite (Solid) at 50 °C. The hydrolysis of Sodium Hypophosphite (Solid) was less than 10% after 5 days.

As no degradation was observed, sterility tests were not considered as needed.

Therefore, the estimated half-life time is higher than one year under representative environmental conditions (25 °C). Therefore, Sodium Hypophosphite (Solid) is considered to be hydrolytically stable, and no further testing was necessary.

This study is considered as reliable without restriction.

Description of key information

Hydrolysis of sodium phosphinate at
pH 4, 50°C, 120h: < 10% (OECD guideline 111)
pH 7, 50°C, 120h: < 10% (OECD guideline 111)
pH 9, 50°C, 120h: < 10% (OECD guideline 111)
Therefore, the estimated half-life time is higher than one year under representative environmental conditions (25 °C) and sodium phosphinate is considered to be hydrolytically stable. By read-across, potassium phosphinate is expected to be hydrolytically stable as well.

Additional information

The study of Habeck (2009) was chosen as key study since it is reliable without restriction (Klimisch 1; GLP guideline study). Hydrolysis as function of pH of sodium phosphinate was determined according to OECD guideline 111 under GLP procedure. A preliminary study at pH 4.0, 7.0 and 9.0 and at a temperature of 50°C measured the concentration of the test substance before the test and after 2.4 hours and 120 hours (5 days) of incubation under no direct light and avoiding oxygen. Under these conditions no significant degradation of sodium phosphinate was observed at 50 °C for all tested pH-values. After 5 days the hydrolysis of sodium phosphinate was less than 10%.

The estimated half-life time is higher than one year under representative environmental conditions. Therefore, sodium phosphinate is considered to be hydrolytically stable.