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Toxicity to terrestrial arthropods

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Titanium carbide was not tested for toxicity to soil macro-organisms and read-across to titanium dioxide (TiO2) was used for this endpoint. In a feeding study with Porcellio scaber TiO2 applied at concentrations up to 3000 mg/kg food did not increase mortality compared to control.

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The effects of nano-size titanium dioxide (TiO2; anatase, 15 nm) on the terrestrial isopod Porcellio scaber (Isopoda, Crustacea) was investigated after 3-d dietary exposure. TiO2 was applied at concentrations of 1, 10, 100, 1000, 2000, and 3000 mg/kg food. Evaluated endpoints included weight change, feeding rate, food assimilation efficiency, and survival (= higher-level endpoints), as well as activities of antioxidant enzymes, such as catalase (CAT) and glutathione-S-transferase (GST) (= lower-level endpoints).

Exposure concentrations of 0.5, 2,000, and 3,000 mg non-sonicated TiO2 /kg food led to a decrease in CAT and GST activities, but intermediate concentrations (1, 10, 100, and 1,000 mg/kg food) did not result in significant changes of enzyme activities.

Higher-level endpoints (e.g. mortality) were not affected up to the highest tested concentration of TiO2 in food (3000 mg/kg).

Due to lower transformation/dissolution results for titanium carbide (the target substance) than titanium dioxide, the resulting toxicity potential of TiC 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. (Bioelution results (KMHC, 2012) are in this case of minor relevance as woodlice digest food by enzymatic degradation during gut passage without influence of gastric fluids.)

Thus, TiC in considered to be practically insoluble and thus non-bioavailable in the gut. Therefore, any toxic effects to terrestrial woodlice via food are not expected to arise from TiC.