Tungsten trioxide

Water solubility

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Well-documented study that uses scientifically acceptable methodology.

Principles of method if other than guideline:

A dissolution study was performed on the test substance by mixing solutions of the test substance at a range of pHs and measuring pH and dissolved tungsten (via ICP-OES) in each solution after 4 and 7 days.

GLP compliance:

not specified

Type of method:

flask method

Water solubility:

0.3 - 20 mg/L

Temp.:

20 °C

pH:

3.53 - 11.1

Details on results:

- Dissolved tungsten concentrations for tungsten trioxide were similar after 4 and 7 days, confirming the results found in the preliminary studies (ie dissolution equilibrium was achieved after 48 h) The concentration of total dissolved tungsten increased from 0.3 to 2.0 mg/L with increasing initial pH up to a value of 10.0. Increases above a pH of 10.0 lead to up to approximately 20.0 mg/L total dissolved tungsten.
- The concentration increases from 0.3 to 2.0 mg/L with increasing initial pH up to a value of 10.0, and increases above pH 10.0 to a value around 20.0 mg/L.
- The most noticeable conclusion is the large reduction in pH associated with the dissolution of the oxides at pH 5 and above. This pH reduction is in the order of 4.0 pH units for the more alkaline pHs tested.

Conclusions:

For initial pH smaller than 10.0, dissolved tungsten concentration remained fairly constant, increasing from 0.3 to 2.0 mg/L with increasing pH. At pH values greater than 10.0, the dissolved tungsten concentration increased to approximately 20.0 mg/L for the test substance with increasing values of initial pH.

Reference 2

Endpoint:

water solubility

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

data from handbook or collection of data

Remarks:

Data from peer-reviewed handbook or collection of data.

Reason / purpose for cross-reference:

reference to same study

Principles of method if other than guideline:

Data in this peer-reviewed publication were taken from many sources, including both compilations and primary literature. Where conflicts were found, the value deemed most reliable was chosen for inclusion in the handbook. Reference sources were not provided for this parameter, nor was the experimental method.

GLP compliance:

not specified

Details on results:

insoluble in water

Reference 3

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Remarks:

Well documented, scientifically sound study that determined the dissolution of the test substance according to the UN Guidance on transformation/dissolution (T/D) of metals and metal compounds (UN GHS Annex 10).

Qualifier:

according to guideline

Guideline:

other: UN Guidance on transformation/dissolution (T/D) of metals and metal compounds (UN GHS Annex 10)

Principles of method if other than guideline:

Standardised amounts of powdered solids are added to specified simulated aquatic media and amounts of the relevant soluble metal ion are measured after defined timepoints.

GLP compliance:

not specified

Type of method:

other: Guidance on transformation/dissolution (T/D) of metals and metal compounds (UN GHS Annex 10)

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

18.154 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

20.225 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

0.607 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

0.814 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

6.03 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

8.156 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

62.47 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

83.516 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

0.627 mg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH=8.5, 20-23 °C

Key result

Type of test:

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

Mean dissolved conc.:

0.831 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

pH=8.5, 20-23 °C

Details on results:

Screening tests at pH 8.5:
The screening test data for the test substance revealed that the measured concentrations of total dissolved W and WO4-- speciation at 24 hr were 18.154 mg/L (σ% = 3) and 19.884 mg/L (σ% = 2), respectively, representing 23% and 19% dissolution of the 100 mg/L loadings of the test substance. For these data, the ratio y = [W]/[WO42-] was 0.898, and was higher than the value of 0.742 calculated from the molecular weights.

Definitive 28- and seven- day tests at pH 8.5, respectively:
The net average concentrations of both total dissolved W and the WO4-- species attained maximum values of 0.607 mg/L (σ% = 7) and 0.814 mg/L (σ% = 7), respectively, at 168 hr (7 days), thereafter increasing slightly to 627 ug/L (σ% = 7) and 831 ug/L (σ% = 8), at 672 hr (28 days). Over the 672 hr, the average value of y was 0.752, which compares favorably with the calculated value of 0.742, and is reflected in the quite good agreement between the values of W and WO4-- calculated from the corresponding measured concentrations over the 672 hr. Values of y close to 0.742 mean that all the W existed in solution as the WO4-- anion.
Both the 10 and 100 mg/L loadings initially exhibit near-linear increases in net W and WO4-- concentrations, followed by reduced rates of concentration change with the suggestion of an approach to limiting values by the end of 168 hr. For the 10 mg/L loadings, the 168 hr values of W and WO4-- were 6.03 mg/L (σ% = 1) and 8.156 mg/L (σ% = 2), respectively, with an attendant y value of 0.739. For the 100 mg/L loadings, W and WO4-- were 62.4 mg/L (σ% = 5) and 83.5 mg/L (σ% = 4), respectively, at 168 hr and y was 0.747. There was good agreement between the calculated and measured concentrations of W and WO4--. The W and WO4-- concentrations for the 100 mg/L loadings represent about 79% and 78% dissolution of the test substance.

The average temperature among all seven- and 28-day tests varied in the range 21.0-21.6 °C, with 19.9 °C as the single value below 20.0 °C, which was not expected to affect the reaction kinetics. With the maximum temperature of 22.0 °C, essentially all temperatures fell within the 20-23 °C proposed for the T/DP. The average D.O. readings met or exceeded the >70% saturation criterion.

All target 8.5 pH levels in the W-series for the test substance lay in the range 8.3-8.7, which is the variability proposed from the T/DP. Similarly, all but 21 of the 480 target 6 pHs were less than the proposed upper limit of 6.25, and it was not expected that these variations would have had a significant effect on the T/D kinetics of the tested substances. The pH levels less than the lower limit of 5.85, since the variability appears to have been random, are not expected to have affected the substances’ reaction kinetics.

Conclusions:

Interpretation of results (migrated information): slightly soluble (0.1-100 mg/L)
The test substance was found to be more soluble at a pH of 8.5 than 6. The respective W and WO4-- concentrations of about 62 and 84 mg/L for the 7 day, 100 mg/L loadings at pH 8.5 corresponding to about 79% dissolution. The seven-day value of 0.747, which indicated that all W dissolved as the WO4-- anion.

Description of key information

The test substance was found to be more soluble at a pH of 8.5 than 6. The respective W and WO₄^2- concentrations of about 62 and 84 mg/L for the 7 day, 100 mg/L loadings at pH 8.5 corresponding to about 79% dissolution. The seven-day y value of 0.747, which indicated that all W dissolved as the WO₄^2- anion.

Key value for chemical safety assessment

Water solubility:

84 mg/L

at the temperature of:

21 °C