Reaction mass of ditungsten carbide and tungsten carbide

Ecotoxicological Summary

Hazard for aquatic organisms

Freshwater

Hazard assessment conclusion:

no hazard identified

Marine water

Hazard assessment conclusion:

no hazard identified

STP

Hazard assessment conclusion:

no hazard identified

Sediment (freshwater)

Hazard assessment conclusion:

insufficient hazard data available (further information necessary)

Sediment (marine water)

Hazard assessment conclusion:

insufficient hazard data available (further information necessary)

Hazard for air

Air

Hazard assessment conclusion:

no hazard identified

Hazard for terrestrial organisms

Soil

Hazard assessment conclusion:

no hazard identified

Hazard for predators

Secondary poisoning

Hazard assessment conclusion:

no potential for bioaccumulation

Additional information

All PNECs presented herein are expressed in terms of the concentration of tungsten ion, as toxicity is expected to occur from the metal ion. The dissolution of tungsten from tungsten carbide (read-across source substance) of 1% obtained from transformation/dissolution studies was used to estimate the equivalent tungsten concentration contributed from sodium tungstate and to determine if a PNEC needs to be estimated. A PNEC was developed when the tungsten equivalent dose was lower than the recommended limit dose (on a tungsten basis) of the respective ecotoxicity study. 

Conclusion on classification

Inorganic metals and metal compound are classified by comparing T/D data generated using the standard protocol (UN GHS, 2007 Annex 10) with toxicity data for the most soluble metal substance as described in the CLP technical guidance (section IV. 5 Application of classification criteria to metals and metal compound) (EU, 2008). In the case of fused tungsten carbide, T/D data for tungsten carbide are compared to the aquatic toxicity reference values derived from read-across to sodium tungstate.

The T/D data are ideally obtained at the pH at which the highest dissolution is expected, within the range defined by the test protocol (pH 5.5-8.5). Inorganic tungsten substances have a higher T/D rate at pH 8.5 than pH 6. Tungsten carbide was tested at pH 6 and pH 8.5 for 24 h, but only pH 6 for the full test T/D test (7 and 28-d testing) (CANMET-MMSL, 2010). The mean amount of W measured (three WC trials were done for 7 and 28-d tests) after 7 and 28 d when WC was tested was 6.33 and 16.7 µg W/L, respectively. In order to conservatively estimate the 7- and 28-d WC dissolution at pH 8.5, a factor of 10 was applied to the pH 6 concentration values to obtain values of 63.3 and 770 µg W/L. This factor is based on the difference between pH 6 and 8.5 results in the 24-h, 7-d, and 28-d tests for tungsten metal powder, which has a similar solubility as tungsten carbide and was tested at both pHs for all tests (CANMET-MMSL, 2010). For tungsten metal, the concentration of dissolved W at pH 8.5 was a maximum of 5.5 times higher than the concentration of dissolved W at pH 6, which supports the use of a factor of 10 for extrapolation from pH 6 to pH 8.5 dissolution for tungsten carbide.

Therefore, the 7- and 28-d T/D values (pH 6.0) with the applied factor of 10 (63.3 and 167 µg/L, respectively) were compared to the corresponding aquatic toxicity reference values derived from sodium tungstate testing of P. subcapitata (the most sensitive aquatic species), (31,000 μg W/L for acute toxicity (based on the ErC50) and 3380 μg W/L for chronic toxicity (based on the ErC10). The results of this comparison demonstrate that the acute and chronic reference toxicity values (based on sodium tungstate data) are orders of magnitude greater than the T/D values determined for tungsten carbide; therefore, fused tungsten carbide does not classify for aquatic toxicity endpoints. This difference reflects the high water solubility of sodium tungstate.