Sodium thiosulphate

Hydrolysis

Link to relevant study record(s)

Reference

Endpoint:

hydrolysis

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2010-10-26 to 2010-11-03

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

other: GLP guideline study relibale without restrictions

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

OECD Guideline 111 (Hydrolysis as a Function of pH)

Version / remarks:

2004

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2010-10-20

Specific details on test material used for the study:

Details on properties of test surrogate or analogue material (migrated information):
not applicable

Radiolabelling:

no

Analytical monitoring:

yes

Details on sampling:

- Sampling intervals for the parent/transformation products: samples were taken at test start (0 hours) and test end (120 hours). All samples were analysed immediately (max. 30 min for preparation and start of analysis) via HPLC DAD.
- Sample storage conditions before analysis: the samples of pH 4 were diluted with HPLC-water (dilution factor 1:15) and subsequently analysed. The samples of pH 7 and 9 were diluted with HPLC-water (dilution factor 1:15) and 2µL o-phosphoric acid were aadded. Afterwards the samples were analysed.
- Other observation, if any (e.g.: precipitation, color change etc.): The temperature was checked automatically once per hour.

Buffers:

Sterile buffer solutions at pH 4, 7 and 9
- pH: 4
45 mL of 0.1 mol/L NaOH were mixed with 250 mL 0.1 mol/L KH2-citrate and diluted to 500 mL with double distilled water
- pH 7
148.15 mL of 0.1 mol/L NaOH were mixed with 250 mL 0.1 mol/L KH2PO4, diluted to 500 mL with double distilled water
- pH 9
106.5 mL of 0.1 mol/L NaOH were mixed with 250 mL 0.1 mol/L H3BO3 in 0.1 mol/L KCL, diluted to 500 mL with double distilled water
Buffers were prepared from chemicals with p.a. or better quality, purged with nitrogen for 5 minutes and the pH was checked to a precision of at least 0.1 at test temperature. After wrds the buffer solution pH 4 was sterilised by filtration through 0.20 µm.

Details on test conditions:

TEST SYSTEM
- Type, material and volume of test flasks, other equipment used: amber HPLC vials (sterile): 4 mL
- Sterilisation method: the test solutions were sterilised by filtration through 0.20 µm sterile membrane filters into the test containers.
- Measures taken to avoid photolytic effects: photolytic effects were avoided by using amber vials.
- Measures to exclude oxygen: Buffers were purged with nitrogen for 5 minutes
- Is there any indication of the test material adsorbing to the walls of the test apparatus? not stated

TEST METHOD
- Test concentration: 150 mg/L buffer solution
- Test volume: 4 mL
- Application: the test item was applied once at test start by direct weighing. After the vials were sealed they were transferred into the thermostat. The time between test item application and transfer to laboratory incubator/analysis did not exceed 30 minutes.
- Incubation: 120 hours
- Temperature: 50 ± 0.5 °C

Duration:

120 h

pH:

4

Initial conc. measured:

150 mg/L

Duration:

120 h

pH:

7

Initial conc. measured:

150 mg/L

Duration:

120 h

pH:

9

Initial conc. measured:

150 mg/L

Number of replicates:

Duplicates

Positive controls:

no

Negative controls:

no

Statistical methods:

No evaluation was nevessary, because the test was completed after the preliminary test.

Preliminary study:

The test item was found to be stable in the preliminary test at pH 4, 7 and 9 at 50°C (please refer to "Any other information on results incl. tables" below). Reaction rate constant and half lives could not be calculated due to the fact that the test item undergoes no hydrolsysis. With regard to the guidelines a half life of > 1 year could be assumed.

Transformation products:

no

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

The test item undergoes no hydrolysis.

DT50:

> 1 yr

Remarks on result:

other:

Remarks:

The test item undergoes no hydrolysis.

Details on results:

TEST CONDITIONS
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: No
- Anomalies or problems encountered (if yes): The temperature of the water bath as in good agreement with the nominal range throughout the test. The mean temperature was 49.9 ± 0.2 °C with a minimum of 49.2 °C and a maximum of 50.0°C during the study.
Due to a low water level caused by evaporation, the thermometer was not completely immersed into the water for a period of 9 hours. Therefore the temperature measured was lower than the actual temperature. After refilling of the water bath, the temperature measured was inside addressed range. The test temperature could be assumed to be inside the addressed temperature range of 50 ± 0.5 °C for the whole study duration.

Table 1: Hydrolysis results for soidum thiosulphate anhydrous at pH 4 and 50°C

Hydrolysis Time [hours]	Replicate	Concentration [mg/L]	Mean	Degradation [%]
0	1	150	150	-
	2	149
120	1	152	147	2.0
	2	142

Table 2: Hydrolysis results for soidum thiosulphate anhydrous at pH 7 and 50°C

Hydrolysis Time [hours]	Replicate	Concentration [mg/L]	Mean	Degradation [%]
0	1	140	142	-
	2	144
120	1	146	144	0.0
	2	142

Table 3:

Hydrolysis results for soidum thiosulphate anhydrous at pH 7 and 50°C

Hydrolysis Time [hours]	Replicate	Concentration [mg/L]	Mean	Degradation [%]
0	1	140	141	-
	2	141
120	1	143	144	0.0
	2	145

Validity criteria fulfilled:

yes

Conclusions:

The test item was found to be stable in the preliminary test at pH 4, 7 and 9 at 50°C (please refer to "Any other information on results incl. tables" below). Reaction rate constant and half lives could not be calculated due to the fact that the test item undergoes no hydrolsysis. With regard to the guidelines a half life of > 1 year could be assumed.

Executive summary:

Method validation was performed in accordance SANCO/3029/99 rev. 4 (2000) with guideline conform accuracy, precision and specificity. For more details on HPLC-DAD method validation please refer to section 8 "Analytical method" (s_Lange_2011).

Description of key information

Hydrolysis is not possible as sodium thiosulfate dissociates rapidly into thiosulfate anions and sodium cations and is transformed e.g. by oxidation, reduction, speciation, precipitation in environmental solutions. Data available according to a OECD 111 (Hydrolysis as a function of pH) conform study show no indication of hydrolysis for the test substance in aqueous media (Lange, 2011). Under the conditions of the study, sodium thiosulfate was shown to be stable and did not undergo hydrolysis at pH 4, 7 and 9 with an estimated half-life of >1 year at room temperature.