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Ecotoxicological information

Toxicity to soil microorganisms

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Description of key information

Titanium carbide was not tested for toxicity to soil micro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. Due to lower transformation/dissolution results for titanium carbide (the target substance) than for titanium dioxide (the source substance), the resulting toxicity potential would also be expected to be lower, so read-across is appropriate. Therefore, the dose descriptors are expected to be sufficiently high for the target substances and read-across to the source chemical is adequately protective. A hazard for soil microorganisms is not identified.

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Additional information

In the available supporting (yet unreliable) study regarding the REACH endpoint “toxicity to soil microorganisms”, toxicity o f TiO2 to soil bacteria was determined in the Biolog test over 7 consecutive days. No effects could be observed. The authors report the EC50 (7 d) to be > 100 mg TiO2/L. This result may in principle be used in a read-across approach to cover the endpoint requirements for the REACH registration of TiC. Toxic effects to soil microorganisms arise from exposure via soil pore water. Due to lower transformation/dissolution results for titanium carbide (the target substance) than titanium dioxide (the source substance), the resulting toxicity potential of TiC is also 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. 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 soil microorganisms are not expected to arise from TiC.

A corresponding key study regarding toxicity to soil microorganisms is not available. However, additional testing is not required as in accordance with REACH Annex IX, 9.4, column 2, the equilibrium partitioning method (EPM) based on aquatic data may be applied to assess the hazard to soil organisms in the absence of reliable toxicity data for soil microorganisms. However, a hazard for aquatic organisms was not identified. Consequently, no hazard is identified for soil microorganisms via the EPM. In addition, the available supporting study does not indicate toxic effects to soil microorganisms when exposed to Ti. Besides, experiments with soil macroorganisms and terrestrial plants do not indicate a hazard for the soil compartment.