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Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

From 19 December 2018 to 22 February 2019

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study

Reason / purpose for cross-reference:

reference to same study

Qualifier:

according to guideline

Guideline:

other: OECD Guideline 115: Surface Tension of Aqueous Solutions

Version / remarks:

27 July 1995

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EU Method A5: Surface tension

Version / remarks:

30 May 2008

Deviations:

no

Principles of method if other than guideline:

Below the CMC, a surfactant is considered to be thermodynamically soluble in the water; whereas above the CMC, the solubility of a surfactant in water has been exceeded and the excess surfactant aggregates to form micelles. These micelles have significantly less effect on the surface tension of a solution and are considered not to be in solution. Thus, the water solubility of a surfactant may be expressed in terms of the CMC.

GLP compliance:

no

Remarks:

The study was conducted in a facility which operates in accordance with Good Laboratory Practice principles; however no claim of GLP compliance was intended nor is made for this study

Type of method:

other: by determining the surface tension of a range of aqueous sample solutions of differing concentration

Key result

Water solubility:

ca. 2 270 mg/L

Conc. based on:

test mat.

Incubation duration:

ca. 18.25 h

Temp.:

20 °C

pH:

ca. 6.3

Remarks on result:

other: Water solubility determined as CMC

Details on results:

Please see below table.

Results

The readings and temperatures for the sample solutions are shown in the following table:

Table1: Surface tension values

Concentration (mg/L)	Reading (mN/m)	Temperature (°C)
3.037 x10^3	36.0	20.0
	31.5	20.0
	31.5	20.0
	31.0	20.0
1.012 x 10^3	37.0	20.2
	33.0	20.2
	32.5	20.2
	32.5	20.2
303.7	46.5	20.2
	44.0	20.2
	44.0	20.2
	43.5	20.2
101.2	53.5	20.2
	50.5	20.2
	50.5	20.2
	50.0	20.2
30.37	59.0	20.4
	57.0	20.4
	57.0	20.4
	57.0	20.4
10.12	65.5	20.4
	64.5	20.4
	64.5	20.4
	64.0	20.4
3.037	70.0	20.4
	69.0	20.4
	69.0	20.4
	68.5	20.4
1.012	70.5	20.4
	70.5	20.4
	70.5	20.4
0.3037	72.5	20.4
	72.5	20.4
	72.5	20.4
0.1012	72.5	20.4
	72.5	20.4
	72.5	20.4

Mean surface tension values were based on the last three readings for a particular concentration which were considered to be constant.

The concentration (mg/L), log₁₀ [concentration (mg/L)] and mean surface tension values for the sample solutions are shown in the following table:

 

Table 2: The concentration (mg/L), log₁₀ [concentration (mg/L)] and mean surface tension values

Concentration (mg/L)	Log10Concentration	Mean Surface Tension (mN/m)	Solution pH
3.037 x 10^3	3.482	31.3	6.3
1.012 x 10^3	3.005	32.7	6.4
303.7	2.482	43.8	6.2
101.2	2.005	50.3	6.6
30.37	1.482	57.0	n/a
10.12	1.005	64.3	5.9
3.037	0.482	68.8	6.1
1.012	0.005	70.5	6.0
0.3037	-0.518	72.5	6.1
0.1012	0.995	72.5	6.1

The plot of log₁₀ [concentration (mg/L)] versus surface tension (mN/m) was drafted. For graph, kindly refer the attached background material section.

Line 1 (red) was generated from linear regression of 4 sample solution concentrations for which the surface tension was shown to be concentration dependent and Line 2 (green) was generated from linear regression of 2 sample solution concentrations for which the surface tension was observed to be essentially independent of concentration. The intersection of these two lines gave the critical micelle concentration and was calculated by solving the two equations:

Line 1 equation:y = -13.759x + 77.843
Line 2 equation:y = -2.933x + 41.515

The sample solutions at 3.037, 1.012, 0.3037 and 0.1012 mg/L were not used in generating the two lines. At this concentration the surface tension was only slightly affected and was approaching that of purified water.

The CMC was determined to be 2.27 x 10³ mg/L.

Conclusions:

Under the study conditions, the water solubility of the test substance based on critical micelle concentration (CMC) was determined to be 2270 mg/L at 20.0 ± 0.5°C.

Executive summary:

A study was conducted to determined the water solubility of the test substance, based on critical micelle concentration (CMC), according to OECD Guideline 115 and EU Method A.5. Due to the surface activity of the test substance, the CMC value was considered as a water soluibility equivalent in accordance with the ECHA R.7a Guidance. Under study conditions, the CMC of the test substance was determined to be 2270 mg/L at 20 ± 0.5˚C (Envigo, 2019).

Description of key information

The water solubility of the test substance was determined based on the critical micelle concentration (a water solubility equivalent of surfactant), according to OECD Guideline 115 and EU Method A.5 (Envigo, 2019).

Key value for chemical safety assessment

Water solubility:

2 270 mg/L

at the temperature of:

20 °C

Additional information

(based on CMC)