Tungsten oxide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

experimental study

Adequacy of study:

key study

Study period:

NA to: 2009-08-25

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).

Reason / purpose for cross-reference:

reference to same study

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.:

ca. 6.615 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

21°C; pH=8.5

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

ca. 9.118 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

0.145 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 188 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

1 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 3.774 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 4.984 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 48.644 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 65.081 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

ca. 0.201 mg/L

Element analysed:

Tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

21°C; pH=8.5

Key result

Type of test:

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

Mean dissolved conc.:

0.265 mg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

21°C; pH=8.5

Details on results:

24-hr screening tests at pH 8.5:
The T/D data for the 24-hr screening tests of the 100 mg/L loadings, reveal 24-hr W and WO4--concentrations of 6.615 mg/L and 9.118 mg/L, respectively, with an attendant y value of 0.725 that indicates most of the W in solution as the WO4-- anion. These concentrations represent about 8% dissolution of the W content of the tungsten oxide.

Definitive seven- and 28-day tests at pH 8.5
The T/D data for the 1 mg/L loadings exhibit exponential formation behaviour over the first 336 hr followed by approaches to limiting W and WO4-- concentrations of 0.201 mg/L and 0.265 mg/L, respectively, at 672 hr, which correspond to about 25% dissolution of the W in the tungsten oxide. As per the 672-hr value of 0.757 for y, essentially all of the W dissolved as WO4--.

For the 10 mg/L loadings, the concentrations of W and WO4-- increase over the seven days to values of 3.774 mg/L (σ% = 4) and 4.984 mg/L (σ% = 5), respectively. For the 100 mg/L loadings, 48.644 mg/L (σ% = 10) and 65. 081 mg/L (σ% = 8) for W and WO4-- were measured, respectively. These concentrations represented about 60% dissolution of the tungsten oxide W content. The average value of 0.781 for y suggests that the WO4-- anion accounted for most of the W in solution.

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.

Conclusions:

The respective W and WO4-- concentrations of about 49 and 65 mg/L for the 7 day, 100 mg/L loadings at pH 8.5 corresponding to about 60% dissolution. The seven-day y value of 0.781, which indicated that most 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 concentrations of about 49 and 65 mg/L for the 7-day, 100 mg/L loadings at pH 8.5 corresponding to about 60% dissolution. The seven-day y value of 0.781, which indicated that all W dissolved as the WO4-anion..

Key value for chemical safety assessment

Water solubility:

65 mg/L

at the temperature of:

21 °C