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Water solubility

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Reference
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
The study was conducted between 01 November 2017 and 26 May 2018.
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 105 (Water Solubility)
Deviations:
yes
Remarks:
The study plan specified that during the water solubility test, “vessels will be incubated for 24 hours, 48 hours and 72 hours, respectively”; however actual times were 24, 49 and 72¾ hours.
GLP compliance:
yes
Type of method:
flask method
Specific details on test material used for the study:
Identification: PG-RAW-0004
Appearance/physical state: clear, colorless liquid
Storage conditions: approximately 4 °C, in the dark
Remarks on result:
not determinable
Details on results:
Preliminary Test
The initial preliminary test prepared at a nominal initial loading rate of 10 g/L resulted in a visibly saturated solution, with a pH value of 6.0. Analysis however indicated either selective solubility/extraction of limited test item components only, or hydrolysis/transformation in solution, with only two test item components detected on GC analysis. Based on this fact, and as additional peaks not seen in the test item were observed in the sample solution, quantification of this solution against standard solutions prepared from the parent test item was considered neither feasible nor appropriate.
Preliminary testing therefore continued with an evaluation of the effect of loading rate. On visual evaluation, complete dissolution was achieved at an initial nominal loading rate of 0.2 g/L, however the nominal 1.0 and 5.0 g/L samples were both still visually saturated. The pH of the three sample solutions was 4.5, 6.3 and 6.9 respectively. Analysis again resulted in only detection of the two test item components seen in the initial preliminary test, as well as additional peaks not initially present in the test item, and confirmed that either hydrolysis or transformation in solution was the origin of this phenomenon. Quantification of these solutions against standard solutions prepared from the parent test item was again considered neither feasible nor appropriate, but did indicate complete dissolution at a nominal concentration of 0.2 g/L, albeit the solubilized products were not representative of the parent test item composition.
The definitive test was therefore initiated to evaluate the behaviour of the test item over the standardized time periods specified in the regulatory method and was adapted to also contain an evaluation of the effect of loading rate.

Main Test

Observations on completion of the 20 °C re-equilibration period and the sample solution pH values are shown in the following table:

Sample Number

Nominal Saturation Loading Rate (g/L)

Saturation Period at 30 °C (hours)

Observations

Solution pH

1

0.10

24

No excess, undissolved test item present.

6.8

2

1.00

24

No excess, undissolved test item present.

6.4

3

10.0

24

Excess, undissolved test item present, as a clear, colorless liquid.

4.2

4

1.0

49

No excess, undissolved test item present.

5.7

5

1.0

72¾ 

No excess, undissolved test item present.

5.7

 

Analysis again resulted in only detection of the two components seen in the preliminary testing, once more confirming either significant hydrolysis or transformation of the test item in solution. Quantification of these solutions against standard solutions prepared from the parent test item was considered neither valid nor feasible. Testing did however indicate complete dissolution of the test item at a nominal concentration of 1.0 g/L under the standardized conditions of the regulatory water solubility methods; albeit the solubilized products were not representative of the parent test item composition.

 Validation

The linearity of the detector response with respect to concentration was assessed over the nominal concentration range of 10 to 500 mg/L. The results were satisfactory with a first order correlation coefficient (r) of 0.9993 being obtained.

Conclusions:
No quantification of the water solubility of the test item was possible due to significant transformation and/or hydrolysis of the test item during the evaluation. Although no excess, undissolved test item was observed for samples saturated at a nominal concentration of 1.0 g/L and lower, on analysis, very significant changes to the chemical composition of the test item were identified, such that the dissolved content of the aqueous solutions was no longer representative of the initial test item.

Executive summary:

No quantification of the water solubility of the test item was possible due to significant transformation and/or hydrolysis of the test item during the evaluation. Testing used a flask method, designed to be compatible with Method 105 of the OECD Guidelines for Testing of Chemicals, 27 July 1995. Although no excess, undissolved test item was observed for samples saturated at a nominal concentration of 1.0 g/L and lower, on analysis, very significant changes to the chemical composition of the test item were identified, such that the dissolved content of the aqueous solutions was not representative of the initial test item. Quantification of these sample solutions against standard solutions prepared from the parent test item was therefore considered to be neither feasible nor appropriate.

Description of key information

No quantification of the water solubility of the test item was possible due to significant transformation and/or hydrolysis of the test item during the evaluation. Testing used a flask method, designed to be compatible with Method 105 of the OECD Guidelines for Testing of Chemicals, 27 July 1995. Although no excess, undissolved test item was observed for samples saturated at a nominal concentration of 1.0 g/L and lower, on analysis, very significant changes to the chemical composition of the test item were identified, such that the dissolved content of the aqueous solutions was not representative of the initial test item. Quantification of these sample solutions against standard solutions prepared from the parent test item was therefore considered to be neither feasible nor appropriate.

Key value for chemical safety assessment

Additional information