Octanoic acid, zinc salt, basic

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2012-03-23 to 2012-05-25

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Deviations:

yes

Remarks:

Two vessels were set up in a parallel design at 20 ± 1.0 °C, each solution was sampled several times over time instead of setting up multiple vessels and sampling solutions from a different vessel at each sampling date.

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

2008

Deviations:

yes

Remarks:

Two vessels were set up in a parallel design at 20 ± 1.0 °C, each solution was sampled several times over time instead of setting up multiple vessels and sampling solutions from a different vessel at each sampling date.

GLP compliance:

yes (incl. QA statement)

Remarks:

signed 2011-02-07

Type of method:

flask method

Water solubility:

320.6 other: mg/L dissolved octanoic acid, zinc salt basic

Temp.:

20 °C

pH:

>= 6 - <= 6.8

Remarks on result:

other: Estimated water solubility value calculated based on dissolved zinc and the zinc content of 22.6 %

Water solubility:

72.47 other: mg/L dissolved Zn

Temp.:

20 °C

pH:

>= 6 - <= 6.8

Details on results:

Under the conditions of this test (flask method; loadings of 2.0001 and 2.0000 mg/L in vessel A and B, respectively), a solubility equilibrium was reached during the 13 days of testing. The mean amount of dissolved Zn from day 2 until day 13 at 20.0 ± 1.0°C is 72.47 ± 3.32 mg/L (determined as dissolved Zn, separated by filtration from undissolved test item). This corresponds to a water solubility of dissolved octanoic acid, zinc salt basic of 320.6 ± 14.7 mg/L, calculated based on a zinc content of 22.6%. The pH measured in both test vessels remained relatively constant ranging from 6.0 – 6.6, except after 12 days in vessel B (pH of 6.8). In both method blanks the pH ranged from 5.9 to 6.6.

Observations

During the study, undissolved test material was observed in the medium, especially on the surface. Furthermore, test material was adsorbed to the flask wall. After filtration, the solution was clear. In order to verify this, turbidity was measured in filtered samples (see Table 3 and Table 4). The turbidity of blank and test solutions appears to be similar (see below).

Temperature

The study was performed in a thermostatically controlled temperature precise incubation cabinet (Binder, Tuttlingen, Germany). Besides the constant display of 20.0 °C, the temperature inside the cabinet was measured by a reference thermometer and remained at 20.0 °C (reading accuracy of 0.3 °C) at every sampling point.

Solution pH

The pH measured in both test vessels remained relatively constant from 6.0 – 6.6, except after 12 days in vessel B (pH of 6.8). In both method blanks, the pH ranged from 5.9 to 6.6.The temperature measurements of the pH meter varied marginally from those of the reference thermometer and were not always at 20.0 ± 1.0 °C. The pH meter was calibrated for pH measurements every working week and furthermore verified every working day; however, this calibration was not performed for the temperature measurement since a reference thermometer was used during the test. All measured pH values are listed in Table 1and Table 2.

Table 1: Solution pH of solutions containing the test item

test day [d]	sample vessel	temperature of pH measurement [°C]	pH	sample vessel	temperature of pH measurement [°C]	pH
2	A	22.2	6.3	B	22.1	6.4
3	A	20.7	6.5	B	21.5	6.5
4	A	21.0	6.4	B	21.8	6.5
12	A	20.6	6.6	B	21.5	6.8
13	A	20.9	6.4	B	21.7	6.6

Table 2: Solution pH of method blanks

test day [d]	blank vessel	temperature of pH measurement [°C]	pH	blank vessel	temperature of pH measurement [°C]	pH
2	1	22.1	6.3	2	21.8	6.3
3	1	21.1	6.2	2	20.3	6.1
4	1	20.5	5.9	2	20.7	5.9
12	1	20.0	6.6	2	20.4	5.9
13	1	20.5	6.3	2	20.8	6.4

Turbidity

The turbidity was measured after filtering to verify that only dissolved zinc concentrations would get measured. The turbidity was always <<1 NTU, indicating that there was not any undissolved material left and that micelles did not form after the filtration step. Turbidity data are compiled in Table 3 and Table 4

Table 3: Turbidity of samples 

test day [d]	turbidity of sample vessel A [NTU]	turbidity of sample vessel B [NTU]
2	0.05	0.09
3	0.10	0.08
4	0.04	0.11
12	0.06	0.02
13	0.10	0.04

Table 4: Turbidity of blanks

test day [d]	turbidity of blank vessel 1 [NTU]	turbidity of blank vessel 2 [NTU]
2	0.09	0.06
3	0.03	0.05
4	0.03	0.04
12	0.02	0.03
13	0.04	0.06

Dissolved zinc concentrations

Dissolved zinc concentrations in all method blanks sampled at each time point were below the limits of detection (LOQs ranging from25 to 37) of the respective measurement series. All test samples were diluted (dilution factor 100), so that the respective zinc concentrations would be in the calibrated range of the ICP-OES instrument. The variation of zinc concentrations between subsequent sampling points is listed in Table 5 (in percent). Constant zinc concentrations as defined by the study guideline OECD 105 and the Regulation 440/2008/EC A.6 were measured during the 13 days of testing.

Table 5: Measured Zn concentrations in test samples (internal calculations were performed with more digits, values were rounded)

test day [d]	Zn conc. of samples vessel A [mg/L]	mean Zn conc. ± SD vessel A [mg/L]	Zn conc. of samples vessel B [mg/L]	mean Zn conc. ± SD vessel B [mg/L]	mean Zn mean conc. ± SD [mg/L]	variation between samplings [%]
2	73.09	73.36 ± 0.38	71.14	71.47 ± 0.46	72.41 + 1.15	-
	73.63		71.79
3	77.86	77.11 ± 1.06	75.07	75.75 ± 0.95	76.43 + 1.14	5.5
	76.36		76.42
4	74.97	75.35 ± 0.54	75.46	75.05 ± 0.58	75.20 + 0.49	-1.6
	75.73		74.64
12	69.32	67.46 ± 2.64	70.40	69.87 ± 0.76	68.66 + 2.11	-8.7
	65.59		69.33
13	67.81	68.92 ± 1.57	70.70	70.34 ± 0.52	69.63 + 1.26	1.4
	70.03		69.97

Table 6: Measured zinc concentrations in method blanks

test day [d]	Zn conc. blank A [µg/L]	Zn conc. blank B [µg/L]	LOD [µg/L]	LOQ [µg/L]
2	< LOD	< LOD	27	91
	< LOD	< LOD
3	< LOD	< LOD	27	91
	< LOD	< LOD
4	< LOD	< LOD	25	82
	< LOD	< LOD
12	< LOD	< LOD	37	125
	< LOD	< LOD
13	< LOD	< LOD	37	125
	< LOD	< LOD

Conclusions:

Under the conditions of this test (flask method; loadings of 2.0001 and 2.0000 mg/L in vessel A and B, respectively), a solubility equilibrium was reached during the 13 days of testing. The mean amount of dissolved Zn from day 2 until day 13 at 20.0 ± 1.0°C is 72.47 ± 3.32 mg/L (determined as dissolved Zn, separated by filtration from undissolved test item). This corresponds to a water solubility of dissolved octanoic acid, zinc salt basic of 320.6 ± 14.7 mg/L, calculated based on a zinc content of 22.6%. The pH measured in both test vessels remained relatively constant ranging from 6.0 – 6.6, except after 12 days in vessel B (pH of 6.8). In both method blanks the pH ranged from 5.9 to 6.6.

Description of key information

Based on measured maximum zinc concentrations, the water solubility of Octanoic acid, zinc salt basic is 320.6 mg/L at pH 6 and at 20 °C.

Key value for chemical safety assessment

Water solubility:

320.6 mg/L

at the temperature of:

20 °C

Additional information

Under the conditions of this test (flask method; loadings of 2.0001 and 2.0000 mg/L in vessel A and B, respectively), a solubility equilibrium was reached during the 13 days of testing. The mean amount of dissolved Zn from day 2 until day 13 at 20.0 ± 1.0 °C is 72.47 ± 3.32 mg/L (determined as dissolved Zn, separated by filtration from undissolved test item). This corresponds to a water solubility of dissolved octanoic acid, zinc salt basic of 320.6 ± 14.7 mg/L, calculated based on a zinc content of 22.6 %. The pH measured in both test vessels remained relatively constant ranging from 6.0 – 6.6, except after 12 days in vessel B (pH of 6.8). In both method blanks the pH ranged from 5.9 to 6.6.