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Water solubility

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Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2008-09-08 to 2008-09-16
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study - The stability of the test substance is missing.
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Version / remarks:
, 1995
Deviations:
no
GLP compliance:
no
Type of method:
flask method
Water solubility:
70.5 mg/L
Temp.:
20 °C
pH:
>= 6.01 - 6.73
Remarks on result:
other: based on a measured concentration of 6.64 x 10^-03 g Co/L
Water solubility:
479 mg/L
Temp.:
37 °C
pH:
>= 5.58 - <= 6.26
Remarks on result:
other: based on a measured concentration of 4.51 x 10^-02 g Co/L
Details on results:
The water solubility of Cobalt Stearate at 20 °C depending on the shaking time and was 7.05 x 10^-02 g/L based on a measured concentration of 6.64 x 10^-03 g Co/L after 120 hours. The measured results differ by 32.16%. The water solubility at 37 °C also depending on the shaking time and was 4.79 x 10^-01 g/L based on a measured concentration of 4.51 x 10^-02 g Co/L after 120 hours. The measured results differ by 25.99%. Therefore, the study is considered to be valid.

The latter was obtained by correlation of the peak area of the analytical standards with their corresponding concentration using the AAS software (Perkin-Elmer AAWinLab).

C = x - Blank

where

C = concentration of cobalt in the test item solution after saturation (μg/mL)

x = measured concentration of cobalt in the sample solution (μg/mL)

Blank = measured concentration of cobalt in the blank solution (μg/mL)

Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
During this study the water solubility at 20 °C and 37 °C were determined and found to be time depending. The highest water solubility was found after 120 hours shaking time to be at 20 °C 7.05 x 10^-02 g/L (based on a measured concentration of 6.64 x 10^-03 g Co/L) and at 37 °C 4.79 x 10^-01 g/L (based on a measured concentration of 4.51 x 10^-02 g Co/L) using the flask shaking method.
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Deviations:
yes
Remarks:
please refer to the field "Principle of method if other than guideline"
Qualifier:
according to guideline
Guideline:
EU Method A.6 (Water Solubility)
Deviations:
yes
Remarks:
please refer to the field "Principle of method if other than guideline"
Principles of method if other than guideline:
- Test was conducted under exclusion of carbon dioxide and oxygen, to avoid oxidative degradation of the organic anion.
- Two vessels were set up in a parallel design at 20 ± 1.0 °C, each vessel was sampled several times instead of sampling one vessel at every point in time, to reduce the weighing error.
GLP compliance:
yes (incl. QA statement)
Remarks:
2011-02-07
Type of method:
flask method
Water solubility:
>= 3 335 - <= 6 043 µg/L
Temp.:
20 °C
pH:
>= 6.2 - <= 6.6
Remarks on result:
other: dissolved cobalt stearate
Water solubility:
>= 321.6 - <= 582.6 µg/L
Temp.:
20 °C
pH:
>= 6.2 - <= 6.6
Remarks on result:
other: dissolved Co
Details on results:
Under the conditions of this test (under exclusion of CO2 and O2, under inert argon gas; flask method; loadings of 499 mg/L and 501 mg/L in vessel A and B, respectively), a solubility equilibrium was not reached. Not reaching solubility equilibrium may be explained by reactions of the test item during the test and/or a slow but consistent dissolution and/or transformation. The mean amount of dissolved Co from day 3 until day 42 at 20.0 ± 1.0°C is 452.1 ± 130.5 µg Co/L (determined as dissolved Co, separated by filtration from undissolved test item). This corresponds to dissolved cobalt stearate of 4.7 ± 1.4 mg/L.. At the beginning of the test the pH in the respective test vessel slightly decreased from 6.7 to 6.2 in vessel A and from 6.9 – 6.2 in vessel B. After the fourth sampling point the pH remained constant at 6.4 ± 0.2.

Method validation summary

Validation parameter

results

comment

selectivity

similar data with three different cobalt wavelengths for ICP-OES method

no matrix effects observed

linearity

applied calibration functions were linear

correlation coefficient at least 0.9996

limits of detection (LOD)

2.8 - 30 µg Co/L

limits of quantification (LOQ)

9.3 - 102 µg Co/L

method blanks

below LOD = < 2.8 - 30 µg Co/L;
except sample a, vessel 1, day 1 below LOQ (< 9.3 µg Co/L)

-

accuracy and precision

mean recovery for TMDA-70:
99.4 ± 2.1 % (n = 18)

corresponds to concentration range of samples (285 µg Co/L)

accuracy and precision

mean recovery for recalibration standards:
98.4 ± 0.8 % (n = 8)

corresponds to lower concentration range of samples (250 µg Co/L)

accuracy and precision

mean recovery for recalibration standards:
96.8 ± 2.5 % (n = 4)

corresponds to higher concentration range of samples (500 µg Co/L)

repeatability

recovery from fortification of samples: 99.3 -101 % (n = 3)

corresponds to lower concentration range of samples

reproducibility

mean recovery for CPI
(diluted to 500 µg Co/L):
99.6 ± 0.8 % (n = 6)

for concentration range of samples (500 µg Co/L)

reproducibility

mean recovery for CPI
(diluted to 250 µg Co/L):
95.2 ± 0.2 % (n =2)

for concentration range of samples (250 µg Co/L)

reproducibility

mean recovery for CPI
(diluted to 100 µg Co/L):
102 ± <1 % (n = 2)

for concentration range of samples (100 µg Co/L)

Measured cobalt concentrations in test samples

(internal calculations were performed with more digits, values were rounded)

stirring time [d]

Co conc. of samples
vessel A
[µg/L]

mean Co
conc. + SD
vessel A
[µg/L]

Co conc. of samples
vessel B
[µg/L]

mean Co
conc. + SD
vessel B
[µg/L]

mean Co
mean conc. + SD
[µg/L]

variation between samplings [%]

1

81.2

81.3 ± 0.2

122

122 ± <1

102 ± 23.3

 

81.4

122

2

366

376 ± 14

187

188 ± <1

282 ± 109

178

366

188

3

503

504 ± 1

226

226 ± 2

365 ± 161

29.6

505

226

13

538

540 ± 3

365

366 ± 1

453 ± 101

24.1

542

367

20

617

626 ± 12

434

435 ± 2

531 ± 110

17.1

634

437

28

477

478 ± <1

326

325 ± 1

401 ± 87.8

-24.3

478

325

35

584

578 ± 9

352

353 ± 1

465 ± 130

15.9

572

353

36

647

703 ± 79

397

398 ± 2

550 ± 182

18.3

759

399

42

482

481 ± 2

314

317 ± 4

399 ± 95.0

-27.5

480

319

43

811

816 ± 7

502

500 ± 3

658 ± 183

64.9

821

498

The shaking flask vessels were set up in duplicate. Samples were taken after 1 (24), 2 (48), 3 (72), 13 (312), 20 (480), 28 (672), 35 (840), 36 (864), 42 (1008) and 43 days (1032 hours). The pH was measured in the test vessels and Co concentrations as well as the turbidity were determined in samples after filtration. After adding the test substance At the beginning of the test the pH in the respective test vessel slightly decreased from 6.7 to 6.2 in vessel A and from 6.9 – 6.2 in vessel B. After the fourth sampling point the pH remained constant at 6.4 ± 0.2. The oxygen concentration inside the experimental setup remained around 0 %.

Co analysis was carried outviaICP-OES. The samples were measured in duplicate.Based on previous test results 500 mg of the test substance was added into 500 mL of argon saturated water under argon atmosphere (499 mg/500 mL and 501 mg/500 mL were weighed into vessel A and B, respectively). This applied loading corresponded to at least five times the quantity of the dissolved test item as determined in the previous test. Furthermore insoluble residues in the test vessels were observed throughout the test.

Constant Co concentrations according to the study guideline OECD 105 as well as the Regulation 440/2008/EC A.6 could not be measured during the test period of 42 days. From day 1 until 3 a distinct increase in cobalt concentrations was observed, followed by fluctuations in co-concentrations from day 3 to day 42. After day 43 a strong increase in the amount of solved cobalt was observed. Therefore, the mean concentration of day three until day 42 was calculated.

The mean dissolved Co concentrations between day 3 and day 42 are as follows:
Vessel A:558.4± 83.0 µg Co/L
Vessel B: 345.7 ± 64.2 µg Co/L

The calculated amount of cobalt stearate dissolved was calculated by:
 = mean of measured values * 100 % / 9.64 % [percentage of Co in test item]

 

mean calculated cobalt stearate dissolved day 3 – day 42:

Vessel A: 5.8 ± 0.9 mg/L
Vessel B: 3.6 ± 0.7 mg/L

 

The measured concentrations in vessel A and B diverged.The reason for the observed variations between vessel A and B might be the wider particle size distribution of the test item. Therefore, the particle size distribution of each loading replicate may differ resulting in differing overall surface areas. Furthermore, as the surface area is affecting solution of sparingly soluble metal compounds, these differences may be observed in tests of materials with wider particle size distributions.

Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
Under the conditions of this test a solubility equilibrium was not reached. Not reaching solubility equilibrium may be explained by reactions of the test item during the test and/or a slow but consistent dissolution and/or transformation. The mean amount of dissolved Co from day 3 until day 42 at 20.0 ± 1.0°C is 452.1 ± 130.5 µg Co/L (determined as dissolved Co, separated by filtration from undissolved test item). This corresponds to dissolved cobalt stearate of 4.7 ± 1.4 mg/L. At the beginning of the test the pH in the respective test vessel slightly decreased from 6.7 to 6.2 in vessel A and from 6.9 – 6.2 in vessel B. After the fourth sampling point the pH remained constant at 6.4 ± 0.2.
Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Qualifier:
according to guideline
Guideline:
other: OECD guideline for testing of chemicals - draft proposal - February 2001. Transformation dissolution of metals and metal compounds in aqueous media.
Qualifier:
according to guideline
Guideline:
other: The standard procedure for the transformation/dissolution of metals and sparingly soluble metal compounds, version February 2004.
GLP compliance:
no
Remarks:
The tests were following as close as possible the GLP guidelines proposed by OECD
Type of method:
flask method
Temp.:
21.5 °C
pH:
6.1
Remarks on result:
other: Cobalt stearate concentration at 0 hour sampling time at 1 mg/L loading was below detection limit. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
2 µg/L
Temp.:
21.6 °C
pH:
6.03
Remarks on result:
other: Cobalt stearate concentration at 24 hour sampling time at 1 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
2.7 µg/L
Temp.:
21.6 °C
pH:
6.11
Remarks on result:
other: Cobalt stearate concentration at 48 hour sampling time at 1 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
4.9 µg/L
Temp.:
21.6 °C
pH:
6.09
Remarks on result:
other: Cobalt stearate concentration at 96 hour sampling time at 1 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
6.2 µg/L
Temp.:
21.5 °C
pH:
6.08
Remarks on result:
other: Cobalt stearate concentration at 168 hour sampling time at 1 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
11.2 µg/L
Temp.:
22.1 °C
pH:
5.92
Remarks on result:
other: Cobalt stearate concentration at 672 hour sampling time at 1 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
0.5 µg/L
Temp.:
21.7 °C
pH:
6.09
Remarks on result:
other: Cobalt stearate concentration at 0 hour sampling time at 10 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
23.1 µg/L
Temp.:
21.2 °C
pH:
6.04
Remarks on result:
other: Cobalt stearate concentration at 24 hour sampling time at 10 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
30.3 µg/L
Temp.:
21.4 °C
pH:
5.99
Remarks on result:
other: Cobalt stearate concentration at 48 hour sampling time at 10 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
51.1 µg/L
Temp.:
20 °C
pH:
5.89
Remarks on result:
other: Cobalt stearate concentration at 168 hour sampling time at 10 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
1.4 µg/L
Temp.:
21.4 °C
pH:
6
Remarks on result:
other: Cobalt stearate concentration at 0 hour sampling time at 100 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Water solubility:
499.4 µg/L
Temp.:
21.2 °C
pH:
5.92
Remarks on result:
other: Cobalt stearate concentration at 168 hour sampling time at 100 mg/L loading. Sample analysis was conducted in triplicate per test vessel (3 test vessels per loading). Average value from the tests is given.
Conclusions:
Under the conditions of the transformation/dissolution test,
the dissolution of cobalt stearate is 11.2 µg/L at 1 mg/L loading for the 28-day endpoint.
The dissolution of cobalt stearate is 51.1 µg/L at 10 mg/L loading for the 7-day endpoint.
The dissolution of cobalt stearate is 499.4 µg/L at 100 mg/L loading for the 7-day endpoint.
Executive summary:

A seven day transformation/dissolution test according to the OECD guideline 29 and the GHS (Annex 10) protocol was run on cobalt stearate at a mass loading of 10 and 100 mg/L, at a pH of 6.0. Also a 28 day transformation/dissolution was run on cobalt stearate at a mass loading of 1 mg/L and at a pH of 6.0. Under the conditions of this test, the dissolution of cobalt stearate is 11.2 µg/L for the 28 -day endpoint (1 mg/L loading), 51.1 µg/L for the 7-day endpoint (10 mg/L loading) and 499.4 µg/L for the 7-day endpoint (100 mg/L loading).

Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2008-09-15 to 2008-10-07
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 105 (Water Solubility)
Deviations:
no
GLP compliance:
no
Type of method:
flask method
Water solubility:
92.6 mg/L
Temp.:
20 °C
Remarks on result:
other: pH not measured
Details on results:
The water solubility of the test item has been determined to be less than or equal to 9.26 x 10^-2g/L of solution at 20.0°C +/-0.5°C. However, from reviewing the trend of increasing saturation concentration with increased shaking time at 30°C, it can be anticipated that the final saturation plateau would most likely be greater than 100mg/L of solution at 20.0°C +/-0.5°C.
Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
The water solubility of the test item has been determined to be less than or equal to 9.26 x 10^-2g/L of solution at 20.0°C +/-0.5°C

Description of key information

Water solubility of cobalt stearate: 70.5 mg/L and 92.6 mg/L (at 20 °C under oxic atmosphere) and 4.7 mg/L (at 20 °C under inert gas atmosphere).

Key value for chemical safety assessment

Water solubility:
92.6 mg/L
at the temperature of:
20 °C

Additional information

The water solubility of cobalt stearate was measured in three different tests:

In Harbeck (2009) the water solubility at 20 °C and 37 °C was determined using the shaking flask method. The highest water solubility was found after 120 hours shaking time to be at 20 °C 7.05 x 10^-02 g/L (based on a measured concentration of 6.64 x 10^-03 g Co/L) and at 37 °C 4.79 x 10^-01 g/L (based on a measured concentration of 4.51 x 10^-02 g Co/L) using the flask shaking method.

In Walker and White (2008) the water solubility was determined to be less than or equal to 9.26 x 10^-2g/L of solution at 20.0 C +/-0.5 °C

To assess whether the oxic atmosphere interferes with the water solubility testing a third experiment was conducted under inert gas atmosphere. In Klawonn (2012) a solubility equilibrium was not reached, the cobalt concentration fluctuated from day 3 until day 42 around a constant value. Not reaching solubility equilibrium may be explained by reactions of the test item during the test and/or a slow but consistent dissolution and/or transformation. The mean amount of dissolved Co from day 3 until day 42 at 20.0 ± 1.0 °C is 452.1 ± 130.5 µg Co/L (determined as dissolved Co, separated by filtration from undissolved test item). This corresponds to dissolved cobalt stearate of 4689 ± 1354 µg/L. At the beginning of the test the pH in the respective test vessel slightly decreased from 6.7 to 6.2 in vessel A and from 6.9 – 6.2 in vessel B. After the fourth sampling point the pH remained constant at 6.4 ± 0.2.