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Titanium carbide was not tested for acute and chronic aquatic toxicity. Instead, read-across to titanium dioxide, titanium metal, titanium trichloride, and titanium tetrachloride was employed for these endpoints.

For titanium substances, the read-across strategy is predicated on the assumed presence and bioavailability of a common metal anion in environmental media after exposure to titanium compounds. This is a reasonable assumption for the majority of inorganic compounds.

For environmental endpoints, it is the relative mobility and the resulting bioavailability in various environmental compartments that determines the potential toxicity to ecological receptors. In the absence of data for titanium carbide, the most straightforward and conservative approach to hazard evaluation by read-across is to assume that titanium carbide, as the substance in question, shows the same systemic effects as titanium dioxide, titanium metal, TiCl3 and TiCl4 which show a higher release of titanium ions compared to titanium carbide, for which release of Ti could not be detected in the T/D test (soluble Ti concentration below the method detection limit of 0.4 µg/L).

The short-term toxicity of titanium dioxide to fish and aquatic invertebrates was determined to be L/EC50 > 100 mg TiO2/L. Algae were slightly more sensitive to titanium dioxide. The lowest 72-h ErC50 of TiO2 in Pseudokirchneriella subcapitata is 61 mg/L, whereas the lowest 72-h ErC10 of 9.9 mg/L is reported for Desmodesmus subspicatus.

Results of a toxicity test on embryo and sac-fry stages of Danio rerio with titanium dioxide are used to assess the chronic fish toxicity of the substance. In the test no deaths were observed at the maximum concentration tested. Thus, the NOEC is 10 mg TiO2/L.

Besides, titanium tetrachloride was tested for toxicity to microorganisms; consequently, read-across to titanium tetrachloride was used for this endpoint. Titanium tetrachloride concentrations of 20 mg/L showed 50 % growth inhibition of Tetrahymena pyriformis after exposure for 6 and 9 h.

 

Due to lower transformation/dissolution results for titanium carbide (the target substance) than the other titanium compounds referenced above (the source substances), the resulting toxicity potential is also be expected to be lower. Therefore, the dose descriptors are expected to be sufficiently high for the target substance, and read-across to the source chemical is adequately protective. In fact, (eco-) toxicologically relevant release of Ti ions from titanium carbide is not expected as the concentration of soluble Ti ions was below the method detection limit (< 0.4 µg/L) in the T/D test. Thus, TiC in considered to be practically insoluble, hence release of Ti ions to any ecotoxicologically relevant extent (and potential subsequent formation of soluble and/or insoluble Ti compounds) is not expected. Therefore, any toxic effects to aquatic organisms are not expected to arise from TiC.