Cesium tungsten oxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Qualifier:

according to guideline

Guideline:

EU Method A.6 (Water Solubility)

Version / remarks:

adopted in 2008

Qualifier:

according to guideline

Guideline:

OECD Guideline 105 (Water Solubility)

Version / remarks:

adopted in 1995

Type of method:

flask method

Water solubility:

<= 0.006 g/L

Conc. based on:

element

Remarks:

Based on analysed cesium concentration ≤ 9.77E-04 g/L

Temp.:

20 °C

pH:

>= 4.8 - <= 5.7

Water solubility:

<= 0.002 g/L

Conc. based on:

element

Remarks:

Based on analysed tungsten concentration ≤ 1.31E-03 g/L

Temp.:

20 °C

pH:

>= 4.8 - <= 5.7

Reference 2

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26-March-2021 - 16-August-2021

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

Remarks:

The study was conducted in line with the most up-to-date scientific methods, using the most up-to-date guidance from ECHA and the OECD on obtaining nanoform information on dissolution. Moreover, scientific advise was sought from major EU projects that are directly working on the current dissolution OECD test guideline.

Qualifier:

according to guideline

Guideline:

other: OECD Guidance Document 318 Testing of dissolution and dispersion stability of nanomaterials and the use of the data for further environmental testing and assessment strategies

Version / remarks:

2020

Deviations:

not applicable

Remarks:

Guidance document outlines general principles to be applied.

Qualifier:

according to guideline

Guideline:

OECD Series on Testing and Assessment No. 29 (23-Jul-2001): Guidance document on transformation/dissolution of metals and metal compounds in aqueous media

Version / remarks:

2001

Deviations:

not applicable

Remarks:

Guidance document outlines general principles to be applied.

GLP compliance:

no

Type of method:

other: centirfugal ultrafiltration - static method

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.4 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

0

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.47 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

1 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.47 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

2 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.49 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

4 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.48 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

8 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.5 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

24 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.51 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

48 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.52 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72 h

Test conditions:

pH 4, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0.45 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72 h

Test conditions:

pH 4, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.31 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

0 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.46 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

1 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.49 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

2 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.57 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

4 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.71 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

8 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.19 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

24 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.55 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

48 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.83 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72

Test conditions:

pH 7, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

1.73 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72 h

Test conditions:

pH 7, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.34 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

0 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.55 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

1 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.49 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

2 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.94 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

4 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.32 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

8 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.66 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

24 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.89 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

48 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.91 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.94 mg/L

Element analysed:

Cesium

Loading of aqueous phase:

3.2 mg/L

Incubation duration:

72 h

Test conditions:

pH 9, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

0 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

1 h

Test conditions:

pH 4, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

2 h

Test conditions:

pH 4, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

4 h

Test conditions:

pH 4, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

8 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4

Incubation duration:

24 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

48 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 4, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.12 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 4, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

0 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.17 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

1 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.37 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

2 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.78 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

4 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.61 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

8 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

4.85 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

24 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

6.5 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

48 h

Test conditions:

pH 7, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

8.2 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 7, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

7.78 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 7, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.12 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

0 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

0.92 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

1 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

1.78 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

2 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Mean dissolved conc.:

3.04 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

4 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

5.09 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

8 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

7.09 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

24 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

8.07 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

48 h

Test conditions:

pH 9, 22 °C

Key result

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

8.72 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 9, 22 °C

Type of test:

full transformation/dissolution test - metals and sparingly soluble metal compounds

Remarks:

full dissolution test for nanoforms

Mean dissolved conc.:

9.08 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

13.4 mg/L

Incubation duration:

72 h

Test conditions:

pH 9, 22 °C

Remarks on result:

other: Measurement used 5 kDa filters and was used to confirm suitable use of 10 kDa filters.

Details on results:

The results with the 5 kDa and 10 kDa filters were similar. In fact in some instances it was slightly higher, therefore, it is not expected particles were measured in the screening test or that filters were broken. The dissolution seen in the screening study was considered accurate and the 10 kDa filter appropriate for this test item. Considering the smallest particle seen during characterisation of this batch was > 2 nm and the 10 kDa filter would allow a particle size of this test item of ~1.3 nm, the appropriateness of the choice was expected but confirmed nonetheless. The measures represent dissolved ions only of each component (i.e. Cs and W).

For pH 4 only low concentrations of dissolved ions could be measured.

At pH 9 the max. observed dissolution rate was 5.24*10-5 mg m-2 s-1 for Cs and 2.47*10-4 mg m-2 s-1 for W.

At pH 7 the max. observed dissolution rate was 1.04*10-5 mg m-2 s-1 for Cs and 5.94*10-5 mg m-2 s-1 for W.

The dissolution was quick, followed by a slow phase likely due to test system saturation. For cesium, 50 to 72 % of the total observed dissolution was complete within 24 hours. For tungsten 65 to 75 % of the total observed dissolution was complete within 24 hours, a short time frame. 

The % dissolution of the cesium based on initial concentrations was 54 to 60 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

The % dissolution of total tungsten based on initial concentrations was 58 to 67 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

Table 4: Dissolution rate based on Cs:

	pH7 (mg L^-1 s^-1)	pH9 (mg L^-1 s^-1)
d(C1-C2)/d(t1-t2)	9.36E-06	5.04E-05
d(C1-C8)/d(t1-t8)	9.97E-06	3.06E-05
d(C4-C8)/d(t4-t8)	9.78E-06	2.65E-05

 

Table 5: Dissolution rate based on W:

	pH7 (mg L^-1 s^-1)	pH9 (mg L^-1 s^-1)
d(C1-C2)/d(t1-t2)	5.60E-05	2.38E-04
d(C1-C8)/d(t1-t8)	5.69E-05	1.65E-04
d(C4-C8)/d(t4-t8)	5.71E-05	1.43E-04

 

 

 

Table 6: Dissolution rate based on Cs normalized to the surface area (52.023 m²/g):

	pH7 (mg m^-2 s^-1)	pH9 (mg m^-2 s^-1)
d(C1-C2)/d(t1-t2)	9.74E-06	5.24E-05
d(C1-C8)/d(t1-t8)	1.04E-05	3.19E-05
d(C4-C8)/d(t4-t8)	1.02E-05	2.75E-05

 

 

Table 7: Dissolution rate based on W normalized to the surface area (52.023 m²/g):

	pH7 (mg m^-2 s^-1)		pH9 (mg m^-2 s^-1)
d(C1-C2)/d(t1-t2)	5.83E-05	2.47E-04
d(C1-C8)/d(t1-t8)	5.92E-05	1.72E-04
d(C4-C8)/d(t4-t8)	5.94E-05	1.48E-04

Dissolution rate figures are attached in the "Attached Background Material" section. 

Conclusions:

Based on the prelimenary testing results this nanoform is expected to dissolve rapidly in pH 7 and 9, but not at pH 4.

Executive summary:

The test item was analyzed for dissolution rate in simulated environmental medium according to OECD guidance documents 29 and 318. The simulated environmental media was prepared in ultrapure water containing 0.1 M NaHCO₃, at pH 4, 7 and 9. The study was conducted at a concentration of 20 mg/L of the test item (20 mg in 1 L medium).

The study was performed in 1-L glass bottles on an horizontal shaker at 150 rpm.

The concentration of dissolved test item was measured at 0 h, 1 h, 2 h, 4 h, 8 h, 24 h, 48 h and 72 h (after centrifugal ultrafiltration at 2000×g for 5 min). The whole setup was laid out in triplicates.

The concentration of the test item was analyzed using ICP-MS/ICP-OES.

The measured temperature in the flasks was 22±0.4°C.

The used MWCO 10 kDa membranes were perfectly suited for this test item.

At pH 9 a relatively high dissolution rate was observed for tungsten (W), and for pH 7 in the same order of magnitude. The dissolution rate based for measured cesium (Cs) was one order of magnitude smaller.

Furthermore, the total measured concentration of dissolved ions was for Cs approximately 2 mg/L (pH 7 and 9), while it was for W approximately 8 mg/L (pH 7 and 9).

For pH 4 only low concentrations of dissolved ions could be measured.

At pH 9 the max. observed dissolution rate was 5.24*10^-5 mg m^-2 s^-1 for Cs and 2.47*10^-4 mg m^-2 s^-1 for W.

At pH 7 the max. observed dissolution rate was 1.04*10^-5 mg m^-2 s^-1 for Cs and 5.94*10^-5 mg m^-2 s^-1 for W.

The dissolution was quick, followed by a slow phase likely due to test system saturation. For cesium, 50 to 72 % of the total observed dissolution was complete within 24 hours. For tungsten 65 to 75 % of the total observed dissolution was complete within 24 hours, a short time frame. 

The % dissolution of the cesium based on initial concentrations was 54 to 60 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

The % dissolution of total tungsten based on initial concnetrations was 58 to 67 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

Description of key information

Rosenfeldt 2021, screening and full dissolution test for nanoforms (OECD GD 29 and 318)

At pH 9 the max. observed dissolution rate was 5.24*10^-5 mg m^-2 s^-1 for Cs and 2.47*10^-4 mg m^-2 s^-1 for W.

At pH 7 the max. observed dissolution rate was 1.04*10^-5 mg m^-2 s^-1 for Cs and 5.94*10^-5 mg m^-2 s^-1 for W.

For cesium, 50 to 72 % of the total observed dissolution was complete within 24 hours. For tungsten 65 to 75 % of the total observed dissolution was complete within 24 hours, a short time frame. 

The % dissolution of the cesium based on initial concentrations was 54 to 60 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

The % dissolution of total tungsten based on initial concnetrations was 58 to 67 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

O'Connor 2017

The solubility of cesium and tungsten were ≤ 6.14E-03 g/L and ≤1.96E-03 g/L, respectively, OECD TG 105

Additional information

Rosenfeldt 2021

The test item was analyzed for dissolution rate in simulated environmental medium according to OECD guidance documents 29 and 318. The simulated environmental media was prepared in ultrapure water containing 0.1 M NaHCO₃, at pH 4, 7 and 9. The study was conducted at a concentration of 20 mg/L of the test item (20 mg in 1 L medium).

The study was performed in 1-L glass bottles on an horizontal shaker at 150 rpm.

The concentration of dissolved test item was measured at 0 h, 1 h, 2 h, 4 h, 8 h, 24 h, 48 h and 72 h (after centrifugal ultrafiltration at 2000×g for 5 min). The whole setup was laid out in triplicates.

The concentration of the test item was analyzed using ICP-MS/ICP-OES.

The measured temperature in the flasks was 22±0.4°C.

The used MWCO 10 kDa membranes were perfectly suited for this test item.

At pH 9 a relatively high dissolution rate was observed for tungsten (W), and for pH 7 in the same order of magnitude. The dissolution rate based for measured cesium (Cs) was one order of magnitude smaller.

Furthermore, the total measured concentration of dissolved ions was for Cs approximately 2 mg/L (pH 7 and 9), while it was for W approximately 8 mg/L (pH 7 and 9).

For pH 4 only low concentrations of dissolved ions could be measured.

At pH 9 the max. observed dissolution rate was 5.24*10^-5 mg m^-2 s^-1 for Cs and 2.47*10^-4 mg m^-2 s^-1 for W.

At pH 7 the max. observed dissolution rate was 1.04*10^-5 mg m^-2 s^-1 for Cs and 5.94*10^-5 mg m^-2 s^-1 for W.

The dissolution was quick, followed by a slow phase likely due to test system saturation. For cesium, 50 to 72 % of the total observed dissolution was complete within 24 hours. For tungsten 65 to 75 % of the total observed dissolution was complete within 24 hours, a short time frame. 

The % dissolution of the cesium based on initial concentrations was 54 to 60 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

The % dissolution of total tungsten based on initial concnetrations was 58 to 67 % in pH 7 to 9.  The rate of dissolution likely slowed down due to saturation of the test system. 

When considering testing of the nanoform or solute, it is important to consider what the organism is most likely to be exposed to.  This study shows that dissolution is quick (most dissolution occurs < 24 hours) and likely complete in the environment as saturation of the media would not occur.  Although pH 4 showed little to no dissolution, the pH of European waters is largely between 6.4 to 8.5.  The 5th percetnile is 6.69 and the 95th percentile is 8.36 (data from WaterBase https://eea.europa.eu).  The study showed the high and rapid dissolution rates at pH 7 and 9, indicating that the most appropriate test would be on the solute (i.e. Cs and W ions).  This is further confirmed in the aquatic toxicity studies. This is in line with OECD GD 317 (2020) and ECHA Guidance Document - Appendix R7-1 for nanomaterials applicable to Chapter R7b Endpoint specific guidance (v2.0, 2017, Section 1.2).