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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:
2012-04-13 to 2012-09-13
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
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
GLP compliance:
yes (incl. certificate)
Type of method:
other: ICP-MS
Water solubility:
2.433 mg/L
Temp.:
21.5 °C
pH:
6
Remarks on result:
other: Screening test; loading 100 mg/L; sampling time 24 hours; dissolved Te
Water solubility:
30.6 mg/L
Temp.:
21.5 °C
pH:
8
Remarks on result:
other: Screening test; loading 100 mg/L; sampling time 24 hours; dissolved Te
Water solubility:
698.9 µg/L
Temp.:
21.5 °C
pH:
8
Remarks on result:
other: Main test: loading 1 mg/L; sampling time 7 days; dissolved Te
Water solubility:
6.254 mg/L
Temp.:
21.5 °C
pH:
8
Remarks on result:
other: Main test: loading 10 mg/L; sampling time 7 days; dissolved Te
Water solubility:
30.72 mg/L
Temp.:
21.5 °C
pH:
8
Remarks on result:
other: Main test: loading 100 mg/L; sampling time 7 days; dissolved Te
Details on results:
According to the guidance document “[…] the test can be stopped when three subsequent total dissolved metal concentration data points vary no
more than 15%” (3). Therefore, the equilibrium has already been reached after 336 h (14 d) for the loading of 1 mg/L. However, to verify this study,
samples were also taken and investigated after 21 d and 28 d.
Under the described conditions of this full test with tellurium dioxide at pH 8, dissolved tellurium concentrations were at a loading of 1 mg/L after 14 days 683.9 ± 19.7 μg/L.
At a loading of 10 mg/L dissolved tellurium concentrations after 7 days were at 6.254 ± 0.070 mg/L at pH 8 and the equilibrium has been reached
after 168 h (7 d). The observed variations within and between the test flasks are in compliance with the guidance document (< 20 %).
At a loading of 100 mg/L dissolved tellurium concentrations after 7 days were at 30.72 ± 3.74 mg/L at pH 8. Although, the observed variations
within and between the test flasks are in compliance with the guidance document (< 20 %), tellurium concentrations in vessel 2 are slightly lower
compared to vessel 1 and 3. One reason for this might be a 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 transformation and dissolution of sparingly soluble metals, differences in dissolved tellurium in the test flasks may be observed.

Screening test:

Measured dissolved Te concentrations for the loading of 100 mg/L:

Sample

pH

Mean Te concentration

mg/L±SD

24 h

8

30.60 ± 2.41

24 h

6

2.433 ± 0.214

 

Main Test:

Measured dissolved Te concentrations for the loading of 1 mg/L:

Sample time

pH

mean Te conc.

all vessels ± SD

[μg/L]

between vessel

variation [%]

variations of mean Te conc. between sampling intervals [%]

2 h

8

276.6 ± 35.8

12.9

-

6 h

8

433.9 ± 42.4

9.8

56.9

24 h

8

643.2 ± 51.3

8.0

48.2

96 h (4d)

8

698.2 ± 36.3

5.2

8.6

168 h (7d)

8

698.9 ± 24.5

3.5

0.1

336 h (14d)

8

683.9 ± 19.7

2.9

-2.1

504 h (21d)

8

675.2 ± 16.2

2.4

-1.3

672 h (28d)

8

613.5 ± 17.8

2.9

-9.1

 

 

Measured dissolved Te concentrations for the loading of 10 mg/L

Sample time

pH

mean Te conc.

all vessels ± SD

[μg/L]

between vessel

variation [%]

variations of mean Te conc. between sampling intervals [%]

2 h

8

2.624 ± 0.082

3.1

-

6 h

8

3.913 ± 0.033

0.8

49.1

24 h

8

5.644 ± 0.042

0.7

44.3

96 h (4d)

8

6.084 ± 0.215

3.5

7.8

168 h (7d)

8

6.254 ± 0.070

1.1

2.8

 

 

Measured dissolved Te concentrations for the loading of 100 mg/L

Sample time

pH

mean Te conc.

all vessels ± SD

[μg/L]

between vessel

variation [%]

variations of mean Te conc. between sampling intervals [%]

2 h

8

11.68 ± 0.95

8.1

-

6 h

8

15.86 ± 1.45

9.1

35.8

24 h

8

23.10 ± 2.22

9.6

45.6

96 h (4d)

8

31.28 ± 3.03

9.7

35.4

168 h (7d)

8

30.72 ± 3.74

12.2

-1.8

 

Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
For the transformation/dissolution test of tellurium dioxide a target pH of 8 was determined in a screening test at 21.5 °C. After 7 days Te concentrations were 698.9 µg/L, 6.254 mg/L and 30.72 mg/L at loadings of 1mg/L, 10 mg/L and 100 mg/L, respectively.
Executive summary:

A study was conducted to determine the transformation/dissolution of tellurium dioxide according to OECD guidance document 29 (2001). The test objective was to study the transformation & dissolution of the test item over 7 days with loadings of 1 mg/L, 10 mg/L and 100 mg/L.

The test with a loading of 1 mg/L was prolonged to 28 days.

Dissolved tellurium concentrations were determined by ICP-OES.

The OECD guidance document 29 requests the performance of the test at a pH which maximizes the dissolution. Therefore, prior to the full test a screening over 24 h (agitation at 100 rpm, 21.5 ± 1.5 °C, loadings of 100 mg/L) was conducted in test media at pH 6 and pH 8 in triplicate vessels and duplicate samples per vessel.

 

After 24 h the dissolved Te concentrations were 2.433 ± 0.214 mg/L and 30.60 ± 2.41 mg/L for pH 6 and 8, respectively.

Based on these results the full test was performed in test media at a target pH of 8.

 

Solutions in the full test were sampled after 2h, 6h, 24h, 96h (4d), 168h (7d). For the test up to 28 days samples were additionally taken after 336h (14d), 504h (21d) and 672h (28d).

Solution pHs, oxygen concentrations and total dissolved tellurium concentrations were measured. The test was performed in triplicates (three replicates per pH treatment, sampled twice at each sampling point).

 

Final results:

Under the described conditions of this full test with tellurium dioxide at pH 8, the equilibrium has already been reached after 14 d. Dissolved tellurium concentrations at a loading of 1 mg/L after 14 days were 683.9 ± 19.7μg/L.

 

At a loading of 10 mg/L dissolved tellurium concentrations after 7 days were at 6.254 ± 0.070 mg/L at pH 8 and the equilibrium has been reached after 168 h (7 d).

At a loading of 100 mg/L dissolved tellurium concentrations after 7 days were at 30.72 ± 3.74 mg/L at pH 8.

 

The observed variations within and between the test flasks are in compliance with the guidance document (< 20 %). The particle size distribution of each loading replicate may differ resulting in differing overall surface areas. Furthermore, as the surface area is affecting transformation and dissolution of sparingly soluble metals, differences in dissolved tellurium in the test flasks may be observed.

Endpoint:
water solubility
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2012-03-22 to 2012-04-05
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 105 (Water Solubility)
Qualifier:
according to
Guideline:
EU Method A.6 (Water Solubility)
GLP compliance:
no
Type of method:
flask method
Water solubility:
2.5 mg/L
Temp.:
23 °C
pH:
6.4
Details on results:
The average value of Tellurium concentration (determined in this study using ICP-MS method) was used to calculate the corresponding concentration of Tellurium dioxide.

Summary of the main tests

Main test

Concentration tellurium dioxide (g/L)

 

I (24 hours)

2.5 x 10 E-3

 

II (48 hours)

2.3 x  10 E-3

 

III 96 hours)

2.5 x 10 E-3

 

IV (168 hours)

2.6 x 10 E-3

 

Mean value

2.5 x 10 E-3

 

Standard deviation

0.0004

 

 

Conclusions:
Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
In a study conducted according to OECD guideline 105 and EU method A6 the water solubility of tellurium dixoide was determined to be 2.5 mg/L at 23 °C using a modified flask method.
Executive summary:

In a study conducted according to OECD guideline 105 and EU method A6 the water solubility of tellurium dixoide was determined using a modified flask method. The study was performed under argon.

For analytical determination the concentrations of Tellurium in the water extracts of the test item were measured by means of ICP-MS.

The mean solubility of tellurium dioxide was determined to be 2.5 mg/L at 23 °C.

Description of key information

Data are available from a transformation dissolution test, conducted according to OECD guideline 29, and a water solubility study according to OECD guideline 105.  Both study data are reliable without restrictions. 

Key value for chemical safety assessment

Water solubility:
30.72 mg/L
at the temperature of:
21.5 °C

Additional information

In a study conducted according to OECD guideline 105 and EU method A6 the water solubility of tellurium dioxide was determined to be 2.5 mg/L at 23 °C using a modified flask method.

Transformation/dissolution study of tellurium dioxide according to OECD guidance document 29 (2001). The test objective was to study the transformation & dissolution of the test item over 7 days with loadings of 1 mg/L, 10 mg/L and 100 mg/L.

The test with a loading of 1 mg/L was prolonged to 28 days.

Dissolved tellurium concentrations were determined by ICP-OES.

The OECD guidance document 29 requests the performance of the test at a pH which maximizes the dissolution. Therefore, prior to the full test a

Screening test (21.5 ± 1.5 °C, loading of 100 mg/L): 

After 24 h the dissolved Te concentrations were 2.433 ± 0.214 mg/L and 30.60 ± 2.41 mg/L for pH 6 and 8, respectively.

Main Test

Final results:

Under the described conditions of this full test with tellurium dioxide at pH 8, the equilibrium has already been reached after 14 d. Dissolved tellurium concentrations at a loading of 1 mg/L after 14 days were 683.9 ± 19.7μg/L.

According to the guidance document “[…] the test can be stopped when three subsequent total dissolved metal concentration data points vary no more than 15%” (3). Therefore, the equilibrium has already been reached after 336 h (14 d) for the loading of 1 mg/L (see Figure 1 and Table 20). However, to verify this study, samples were also taken and investigated after 21 d and 28 d. Under the described conditions of this full test with tellurium dioxide at pH 8, dissolved tellurium concentrations were at a loading of 1 mg/L after 14 days 683.9 ± 19.7 μg/L.

The 14-day value was reported, as equilibrium was reached and the measured concentration at 28 days was 613.5 µg/L.

At a loading of 10 mg/L dissolved tellurium concentrations after 7 days were at 6.254 ± 0.070 mg/L at pH 8 and the equilibrium has been reached after 168 h (7 d).

At a loading of 100 mg/L dissolved tellurium concentrations after 7 days were at 30.72 ± 3.74 mg/L at pH 8.

 

The value of  30.72 mg/L is chosen for chemical safety assessment, as a worst case assumption.