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Ecotoxicological information

Toxicity to soil macroorganisms except arthropods

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Description of key information

Titanium carbide was not tested for toxicity to soil macro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. In an earthworm reproduction test with Eisenia fetida the NOEC of bulk TiO2 was found to be greater than or equal to the highest concentration tested (≥1000 mg TiO2/kg dry soil).

Key value for chemical safety assessment

Additional information

A study according to OECD 222 was conducted to assess the effects of TiO2 nanoparticles as well as TiO2 bulk material on the reproduction of the earthworm Eisenia fetida in soil at limit a concentration of 1000 mg/kg. The exposure of Eisenia fetida to TiO2 nanoparticles caused a clear reduction (about 50 %) of reproductive success, whereas the reproduction of Eisenia fetida exposed to the same concentration of TiO2 bulk material did not cause any adverse effects on reproduction.

 

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 would also be expected to be lower. Therefore, the dose descriptors are expected to be sufficiently higher for the target substances 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. (Bioelution results (KMHC, 2012) are in this case of minor relevance as earthworms digest food by enzymatic degradation during gut passage without influence of gastric fluids.)

Therefore, any toxic effects to terrestrial earthworms via soil pore water and/or TiC incorporated with food/soil are not expected to arise from TiC.

Besides, TiC is not manufactured in the nano form. Therefore, toxic effects attributable to nano-sized TiO2 are considered not relevant for the assessment of bulk TiC. Therefore, toxic effects for soil macroorganisms are not expected to arise from TiC.