Octanoic acid, 2-phenoxyethyl ester

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 December 2008 to 17 February 2009

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Due to the experimental difficulties for low solubility measurements, the final result is an estimation. For more information see "Any other information on results incl. tables".

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

GLP compliance:

yes (incl. QA statement)

Remarks:

Food and Consumer Product Safety Authority, Den Haag, Netherlands

Type of method:

flask method

Key result

Water solubility:

< 1 mg/L

Temp.:

19.8 °C

pH:

6.7

Preliminary test

The content of test substance dissolved in the water sample was 1.8 mg/L. This result was obtained after applying an alternative sample treatment, i.e. phase separation by standing instead of centrifugation. The latter was found to be not a suitable technique to remove excess test substance from the water solution; whilst test substance was detected at low concentration after the second centrifugation step there was no test substance detected after the third centrifugation step. This is an indication for adsorption of the test substance to the walls of the centrifugation tube, which is expected based on the chemical structure of the test substance.

 

Main study

The results for the samples taken at 24, 48 and 72 hours are given in the following tables.

 

Main study - water solubility of the test substance: phase separation after standing

Stirring time	Analysed concentration	Mean	MD	pH
[hours]	[mg/L]	[mg/L]	[%]
24	1.38	2.38 (1)	117 (1)	6.7
	1.19
	1.23
48	1.83	2.94 (2)	84.7 (2)	6.7
	2.30
	2.51
72	3.17			6.7
	3.28
	4.52

(1) Mean of all analysed concentrations after 24, 48 and 72 hours of stirring

(2) Mean of all analysed concentrations after 48 and 72 hours of stirring

 

Main study - water solubility of the test substance: centrifugation

Stirring time	Centrifugation steps	Analysed concentration	Mean	MD	pH
[hours]		[mg/L]	[mg/L]	[%]
24	1	0.225	0.26 (1)	30.8 (1)	6.7
	2	0.0749
48	1	0.307	0.28 (2)	21.9 (2)	6.7
	2	0.0924
72	1	0.246			6.7
	2	0.120

(1) Mean of the analysed concentrations after 24, 48 and 72 hours of stirring and 1x centrifugation.

(2) Mean of the analysed concentrations after 48 and 72 hours of stirring and 1x centrifugation.

 

After the respective stirring times, the test substance appeared to be uniformly spread over the test solution as small (floating) droplets with little tendency to move towards the surface upon standing. Care was taken to collect samples a distance away from clearly visible droplets, but the spread in the results indicates that this approach was not successful. Also, a tendency to increasing values was observed, suggesting that the water solubility improved with time. However, it might also be possible that longer stirring caused a finer distribution of the droplets in the solution, resulting in an overestimation of the dissolved amount of test substance.

Since the maximum difference (MD) of the mean concentrations determined in the 24, 48 and 72 hour test samples as well as the 48 and 72 hour samples was > 15%, the sample treatment using phase separation after standing is not considered suitable to remove excess test substance from the solution.

No test substance was detected in the pre-treated samples from the blank water mixture.

 

Centrifugation did result in much lower values for the water solubility of the test substance as the phase separation treatment, however, after one centrifugation step there was greater consistency in the data from the sampling moments indicating that the water solubility does not increase with time. A following centrifugation step resulted in a drastic decrease in test substance concentration in the water sample indicating that test substance adsorbs to the walls of centrifugation vessels. Therefore, this technique is considered not suitable to remove excess test substance from the solution.

Since the test substance is a liquid, filtration is not an option to separate excess test substance from the aqueous test solution.

 

A theoretical estimation of the water solubility of test item by calculation (WSKOWWIN, v1.41, U.S. Environmental Protection Agency, 2000) resulted in a value of 0.95 mg/L.

 

In conclusion, centrifugation and phase separation after standing proved to be no suitable sample treatment methods to remove excess test sample from the aqueous test solutions. However, both techniques resulted in a water solubility value in the low mg/L concentration range which was expected based on the chemical structure of the test substance. An estimation of the water solubility of the test substance by calculation resulted in a value of 0.95 mg/L. Based on all these findings it was concluded that the water solubility of the test substance is < 1 mg/L.

 

Conclusion

The flask method was chosen for the determination of the water solubility of the test item. The water solubility of the test substance at 19.8°C ± 0.6°C was estimated to be < 1 mg/L. The pH of the aqueous sample after 72 hours stirring was 6.7.

Description of key information

< 1 mg/L at 19.8 ± 0.6 °C and pH 6.7 (OECD Guideline 105, flask method)

Additional information

Due to the experimental difficulties for low solubility measurements, several adaptation of the flask method were tested but did not result as suitable for the determination of the water solubility of the test substance. The results were however in a low mg/L concentration range, which was expected based on the chemical structure of the test substance.

An estimation of the water solubility was performed by means of a QSAR model (WSKOWWIN, v1.41, U.S. Environmental Protection Agency, 2000) resulting in a value of 0.95 mg/L.

Based on all these findings it was concluded that the water solubility of the test substance is < 1 mg/L.