Willow, Salix alba, ext.

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2019-01-16 to 2019-03-01

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

adopted July 1995

Deviations:

no

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

European Commission Regulation (EC) No. 440/2008 and No. 260/2014

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Type of method:

flask method

Key result

Water solubility:

50 mg/L

Conc. based on:

test mat. (total fraction)

Remarks:

no precipitate observed

Loading of aqueous phase:

50 mg/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

>= 7.1 - <= 7.2

Water solubility:

441 mg/L

Conc. based on:

test mat. (dissolved fraction)

Remarks:

at the end of the incubation phase precipitate was observed

Loading of aqueous phase:

500 mg/L

Incubation duration:

>= 24 - <= 72 h

Temp.:

20 °C

pH:

>= 7.1 - <= 7.2

Water solubility:

ca. 1 g/L

Conc. based on:

test mat. (total fraction)

Remarks:

neither precipitate nor suspended particles observed

Loading of aqueous phase:

0.99 g/L

Incubation duration:

0.5 h

Temp.:

23 °C

pH:

10.3

Remarks on result:

other: water solubility based on nominal loading and complete dissolution;

Remarks:

formation of supsended particles after adjustment of pH with HCl to pH 7.0.

Results from preliminary testing

Initial dispersion of the test item at high concentration in water resulted in alkaline pH >10. Therefore, preliminary testing was performed a) at neutral pH (ca. 7.0) relevant for ecotoxicity testing as well as environmentally relevant; and b) in demineralized water without pH adaption to check for pH dependence of solubility in water.

The first series of preliminary testing was performed at pH 7.0 (buffered solution). In a stepwise procedure, increasing volumes of buffer solution were added at room temperature to a defined amount of the test item. After each addition of an amount of buffer solution the mixture was treated with ultrasound for 15 minutes and visually checked for any undissolved particles (with the help of a torch light). Six nominal concentrations between 956 g/L and 0.956 g/L were obtained this way. Uniformly, at all concentration levels no complete dissolution was obtained but a precipitate was observed at any case.

In a further series of preliminary testing at pH 7, specified amounts of the test item and 50 ml, 100 ml and 500 ml of pH 7 buffered solution, respectively, were stirred at room temperature (approx. 23 °C) for at least 24 hours and the five concentration levels obtained (634, 210, 83, 23.7, and 9 mg/L) visually checked for any undissolved particles (with the help of a torch light). Uniformly, yellow solutions without precipitate were obtained, but suspended particles were observed throughout these samples.

A final series of preliminary testing was performed in demineralized water without pH adaption to check for pH dependence of solubility in water.

ln a stepwise procedure, increasing volumes of demineralized water were added at room temperature (approx. 23 °C) to defined amounts of the test item and stirred (see table below for details). Stirring times were based on observation of dissolution: stirring was discontinued if no relevant changes could be observed anymore. The sample contaíning 152.5 mg in a total volume of 20 mL was stirred overnight (18 h) to ascertain if suspended particles would not dissolve after a prolonged stirring time, which obviously was not the case. After the stirring time the mixtures were visually checked for any undissolved particles (with the help of a torch light).

Results of the preliminary test, demineralized water:

Amount of test item / mg	Added volume of demineralized water / mL	Total volume of demineralized water / mL	Stirring time / h	Final nominal concentration [g/L]	Appearance of mixture
10.1	10	10	1	1.01	yellow solution with few suspended particles, no precipitate
152.5	10	10	0.5	15.25	yellow solution with suspended particles, no precipitate
	10	20	18	7.62	yellow solution with suspended particles, no precipitate
	10	30	1	5.08	yellow solution with suspended particles, no precipitate, pH = 10.5^1)
9.9	10	10	0.5	0.99	light yellow solution, dissolved, pH = 10.3^2)

¹⁾Adjustment of the pH value to 7.2 using HCl led to a yellow solution with suspended particles, no precipitate. Overnight little precipitate was formed.

²⁾Adjustment of the pH value to 7.0 using HCl led to a yellow solution with suspended particles, no precipitate.

The solubility of the test item in demineralized water without adaption of pH was higher than the solubility determined at pH 7. Dissolved test item shifted the pH value of the mixture into the alkaline range. This obviously increased the solubility of the test item. Neutralisation afterwards of the samples of nominal 5.08 mg/L (suspended particles, no precipitate) and 0.99 mg/L (dissolved, neither suspended particles, nor precipitate) to pH 7 using HCl led to formation of suspended particles and later on (overnight) of little precipitate only at the higher concentration of 5.08 mg/L. Accordingly, solubility of the test item obviously is dependent on pH, with higher solubility at alkaline pH compared to the neutral range.

In order to have stable conditions for the water solubility study the main test was performed at pH 7. The test item is an UVCB. Therefore, the main test for the water solubility was performed according to the flask method with two loading rates as recommended in ECHA guidance document on Information Requirements and Chemical Safety Assessment, chapter R.7a. As loading rates approx. 50 mg/L and approx. 500 mg/L were chosen.

Results from final testing (flask method)

The flask method was performed with two loading rates (approx. 50 mg/L and approx 500 mg/L) at pH 7. The data for the evaluation are given per concentration in the tables below.

After the equilibration time only a slight turbidity was observed in the flasks of the experiments with a loading rate of 50 mg/L. ln the experiments with a loading rate of 500 mg/L precipitate was observed.

Water solubility experiments of the test item, loading rate 50 mg/L:

Experiment	24 h experiment	72 h experiment^1)	72 h experiment	Blank experiment (72 h)
Amount of test item / mg	5.0	5.0	5.1	-
Amount of buffer solution / ml	100	100	100	100
Stirring time at 30 °C / h	24	72	72	72
pH at ambient temperature	7.2	7.2	7.1	7.1
Dilution factor	5	5	5	5
Measured carbon concentration / mg/L	5.37 / 5.40	3.68 / 3.74	5.02 / 5.05	- / -^2)
Mean carbon concentration / mg/L	5.39	3.71	5.04	-
Water solubility / mgcarbon/L	26.9	18.6	25.2	-
Conversion factor	2.55	2.55	2.55	-
Water solubility / mg/L	68.5	47.2	64.1	-

¹⁾The measured value of the 48 h was an outlier. For this reason an additional experiment was analyzed. This experiment had a stirring time at 30 °C of 72 h and a prolonged stirring time at 20 °C of 96 h. In order to exclude further irregularities due to the inhomogeneity of the test item (UVCB) a prolonged stirring time was chosen for this additional experiment.

²⁾Below the limit of quantification

Water solubility experiments of the test item, loading rate 500 mg/L (for blank value, see table above):

Experiment	24 h experiment	48 h experiment	72 h experiment
Amount of test item / mg	53.7	54.8	51.1
Amount of buffer solution / ml	100	100	100
Stirring time at 30 °C / h	24	48	72
pH at ambient temperature	7.2	7.2	7.2
Dilution factor	50	50	50
Measured carbon concentration / mg/L	3.60 / 3.64	3.52 / 3.49	3.28 / 3.24
Mean carbon concentration / mg/L	3.62	3.50	3.26
Water solubility / mgcarbon/L	181	175	163
Conversion factor	2.55	2.55	2.55
Water solubility / mg/L	461	446	415

The water solubility was calculated from the measured and unrounded concentration values and not from the rounded values given in the tables above. The measured carbon content was converted into the

water solubility of the test item with an organic carbon content of the test item of 39.29 % (information from the sponsor).

The measured water solubility at nominally 50 mg/L was slightly above the loading rate. This deviation was within the accuracy of the overall method. Possible sources for this deviation are e.g. weighing errors, dilution errors and the accuracy of the analytícal method. After the stirring time only a slight turbidity was observed. For this reason it can be assumed that the test item was almost completely dissolved at this loading rate and the loading rate was taken as final result.

Accordingly, at a loading rate of 50 mg/L the water solubility of the test item at 20 °C was determined to be 50 mg/L.

At a loading rate of 500 mg/L the water solubility of the test item at 20 °C was determined to be 441 mg/L.

Conclusions:

Water solubility (OECD 105) for the test item (UVCB) was determined according to the flask method at pH 7:
50 mg/L at a nominal loading rate of 50 mg/L;
441 mg/L at a nominal loading rate of 500 mg/L (precipitate observed).
Solubility at pH 10.3 (demineralized water; no pH adaption; nominal concentration; neither precipitate nor suspended particles) ca. 1.0 g/L at room temperature (23 °C).

Executive summary:

The water solubility of the test item (UVCB) was determined compliant with GLP in a valid study performed according to OECD 105 and EU method A.6.

The water solubility cs of the test item at a temperature of 20 °C and at pH 7 was determined according to the flask method with two different loading rates. lt was found to be:

Loading rate / mg/L	Water solubility / mg/L
50	50
500	441

For UVCBs, water solubility is dependent on the loading rate, with preferential dissolution of the more soluble compound fraction and increasing formation of precipitate (fraction of the more poorly water soluble components) with increasing nominal concentration.

Preliminary experiments using demineralized water without adaption of pH indicate a water solubility (nominal concentration; neither precipitate nor suspended particles) of approx. 1.0 g/L at pH 10.3. Neutralization with HCl to pH 7 led to formation of suspended particles.

As such, solubility in water seems to be dependent on pH, with higher solubility at alkaline pH.

Description of key information

Water solubility (OECD 105) for the test item (UVCB) was determined according to the flask method at pH 7:

50 mg/L (20 °C) at a nominal loading rate of 50 mg/L;

441 mg/L (20 °C) at a nominal loading rate of 500 mg/L (precipitate observed).

Solubility at pH 10.3 (demineralized water; no pH adaption; nominal concentration; neither precipitate nor suspended particles) ca. 1.0 g/L at room temperature (23 °C).

Key value for chemical safety assessment

Water solubility:

50 mg/L

at the temperature of:

20 °C

Additional information

The water solubility of the test item (UVCB) was determined compliant with GLP in a valid study performed according to OECD 105 and EU method A.6.

The water solubility cs of the test item at a temperature of 20 °C and at pH 7 was determined according to the flask method with two different loading rates. lt was found to be:

Loading rate / mg/L	Water solubility / mg/L
50	50
500	441

Preliminary experiments using demineralized water without adaption of pH indicate a water solubility (nominal concentration; neither precipitate nor suspended particles) of approx. 1.0 g/L at pH 10.3. Neutralization with HCl to pH 7 led to formation of suspended particles.

As such, solubility in water seems to be dependent on pH, with higher solubility at alkaline pH.

For UVCBs, water solubility is dependent on the loading rate, with preferential dissolution of the more soluble compound fraction and increasing formation of precipitate (fraction of the more poorly water soluble components) with increasing nominal concentration. Further, solubility was identified to be dependent on pH: in deionized water, alkaline pH is induced by the test item and solubility is considerably increased compared to pH 7. As a key value for chemical safety assessment, the value of 50 mg/L associated with full solubility (no precipitate, measured concentration equal to nominal concentration) at pH 7 (representative for prevailing environmental conditions as well as ecotoxicity testing) is given.