Reaction mass of ditungsten carbide and tungsten carbide

Water solubility

Link to relevant study record(s)

Reference

Endpoint:

transformation / dissolution of metals and inorganic metal compounds

Type of information:

read-across based on grouping of substances (category approach)

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)

Justification for type of information:

1. HYPOTHESIS FOR THE CATEGORY APPROACH: The hypothesis is that properties are likely to be similar or follow a similar pattern because of the presence of a common metal ion, in this case tungstate.
2. SOURCE AND TARGET CHEMICAL(S) (INCLUDING INFORMATION ON PURITY AND IMPURITIES):
Source: Tungsten Carbide
Target: Fused tungsten carbide
3. CATEGORY APPROACH JUSTIFICATION: See Annex 3 in CSR
4. DATA MATRIX: See Annex 3 in CSR

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

Principles of method if other than guideline:

Standardized 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:

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

Mean dissolved conc.:

536 µg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

708 µg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

21°C

Key result

Type of test:

screening transformation/dissolution test - sparingly soluble metal compounds

Mean dissolved conc.:

1 037 µg/L

Element analysed:

Dissolved 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.:

1 358 µg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

24 h

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

119 µg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

156 µg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

10 mg/L

Incubation duration:

7 d

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

877 µg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

1 168 µg/L

Element analysed:

Tungsatete anion

Loading of aqueous phase:

100 mg/L

Incubation duration:

7 d

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

23 µg/L

Element analysed:

Dissolved tungsten

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

21°C

Key result

Type of test:

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

Mean dissolved conc.:

31 µg/L

Element analysed:

Tungstate anion

Loading of aqueous phase:

1 mg/L

Incubation duration:

28 d

Test conditions:

21°C

Details on results:

The results for the most soluble sample of tungsten carbide tested are presented above. Only the most relevant data for classifictaion and risk assessment are presented in the sections above, but all resilts are presented in this text box.

Results for Sample #1
Definitive seven-and 28-day tests at pH 6:
The T/D reaction kinetic data for the 1 mg/L loadings of the tungsten carbide-1 powder, reveal that the tungsten carbide 1 released net average 672 hr W and WO4-- concentrations of 19 ug/L and 29 ug/L, respectively, corresponding to about 2% dissolution of the W in the compound. The concentrations elevated slightly above preferable levels in the blank test do not affect the conclusion that the tungsten carbide-1 was but slightly reactive. The T/D data also suggest nearly linear reaction rates.
For the 10 and 100 mg/L loadings, the T/D reaction kinetic data for W and WO4-- and the net average concentrations, reveal initial rapid increases over the first 24 hr, followed by reduced rates of reaction over the next 144 hr, with perhaps a tendency towards limiting values sometime after 168 hr. The T/D are consistent with the low reactivity observed with the 1 mg/L loadings. For instance, the 98 ug/L (and 126 ug/L concentrations of W and WO4--, respectively, at 168 hr and with the 10 mg/L loadings correspond to about 1% dissolution of the W in the tungsten carbide-1. For the 100 mg/L loadings, the 797 ug/L and 1,055 ug/L levels of W and WO4--, respectively, indicate about 0.85% dissolution of the tungsten carbide-1. The 0.778 and 0.756 values of y at 168 hr for the 10 and 100 mg/L loadings suggest that such W as dissolved did so as WO4--.

Results for Sample #2
Definitive seven-and 28-day tests at pH 6:
As relatively unreactive as was the tungsten carbide-1, the tungsten carbide-2 powder was less so. For instance, from the T/D reaction kinetic data, the maximum net average 1 mg/L loading concentrations of W and WO4-- at 672 hr were 7.7 ug/L and 7.8 ug/L, respectively. The relatively high values of y in the range 0.758-1.811 may be related to the low net ug/L concentrations of both W and WO4--. The reaction rates were nearly linear.

Similarly, the 10 mg/L loadings yielded 168-hr concentrations of W and WO4-- of 14 ug/L and 18 ug/L, respectively, while the corresponding concentrations for the 100 mg/L loadings were 138 ug/L and 170 ug/L, respectively. From the 100 mg/L T/D data, about 0.15% of the W in the tungsten carbide-2 dissolved. The plots of the 1 mg/L loading T/D data suggest that the rates of increase in W and WO4-- concentrations are more or less linear, while those for the 10 and 100 mg/L loadings fit classic exponential formation behaviour.
The values of y in the range 0.789-0.815 for both the 10 and 100 mg/L loadings are somewhat closer to the molecular weight ratio of 0.742 than for the 1 mg/L loadings.

Results for Sample #3
Definitive seven-and 28-day tests at pH 6:
Among the three tungsten carbide powders, the tungsten carbide-3 was the most reactive. As with the tungsten carbides 1- and -2, the 1 mg/L loadings exhibited nearly linear reaction rates after an initial rapid increase in concentrations, and attained maximum W and WO4-- concentrations of 23 ug/L and 31 ug/L, respectively, at 672 hr. The average value of y was 0.755, suggesting that most of the W was present as WO4--.
The maximum concentrations of W and WO4-- concentrations were 119 ug/L and 156 ug/L, respectively, for the 10 mg/L loadings, and 877 ug/L and 1,168 ug/L, respectively, for the 100 mg/L loadings, all occurring at seven days and, in common with the other two tungsten carbides, both loadings presenting classic exponential formation behaviour. The seven-day T/D data for the 100 mg/L loadings represent about 0.95% dissolution of the W in the tungsten carbide-3 powder.
The values of y in the range 0.735-0.761 are essentially as expected for all W to exist as WO4--.

24-hr scoping tests at pH 8.5
To examine the effect of pH on their T/D characteristics, 100 mg/L loadings of all of the tungsten carbides were subjected to 24-hr scoping tests at pH 8.5. The resulting T/D data for tungsten carbide-1, -2 and 3, reveal that the increased pH more or less doubles the 24-hr concentrations compared to the values at pH 6. As an example, for the tungsten carbide-1, the net 24-hr concentrations of W were 846 ug/L and 484 ug/L at pH 8.5 and 6, respectively, and for the tungsten carbide-3, they were 1,037 ug/L and 536 ug/L at pH 8.5 and 6, respectively.

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.

Correlation of seven-day WO4-- concentrations to surface area loading:

The seven-day concentrations of WO4-- as a function of surface area loading for all three separately-produced tungsten carbide powders at pH 6 were well-fit to the following regression equation:

log (WO₄^2-, ug/L) = -2.2388 + log 1.0287 log (A, mm²/L) (n = 27; r² = 0.987)

in which A is the surface area loading of tungsten carbide, as determined from their BET-measured surface areas, to the pH 6 medium.

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. However, only 24 data at 100 mg/L loading was available for pH 8.5, being 1.04 mg/L of soluble tungsten. The remaning data were from testing at pH 6. The soluble tungsten values at 1, 10, and 100 mg/L loadings at pH 6 0.0097, 0.12, and 0.88 mg/L at 7 days, respectively. The 28 day soluble tungsten value for 1 mg/L loading at pH 6 was 0.0.023 mg/L. The values of y in the range of 0.726-0.763 indicated that most of the W was dissolved as the WO4-- anion.

Executive summary:

Due to the similar chemical constituency and structure between the source substance (tungsten carbide) and the target substance (fused tungsten carbide), the physico-chemical properties would be expected to be the same or sufficiently similar such that application of read-across is appropriate for this endpoint. For more details, refer to the attached read-across approach document.

Description of key information

The water solubility of fused tungsten carbide was most adequately assessed by the transformation/dissolution studies on the read-across source substance, tungsten carbide. At a 100 mg WC/L loading was available for pH 8.5, being 1.04 mg/L of soluble tungsten.

Key value for chemical safety assessment

Water solubility:

1.04 mg/L

at the temperature of:

21 °C

Additional information

The water solubility of fused carbide was most adequately assessed by the transformation/dissolution studies on tungsten carbide. Due to the similar chemical constituency and structure between the source substance (tungsten carbide) and the target substance (fused tungsten carbide), the physico-chemical properties would be expected to be the same or sufficiently similar such that application of this read-across is appropriate for this endpoint. For more details, refer to the attached read-across approach document.