Dichloride titanium oxide

Endpoint summary

Additional information

Target compound titanium oxychloride is an unstable chemical intermediate which results from the hydrolysis of parent compound titanium tetrachloride.

1. step: TiCl4 + H2O↔TiOCl2 + 2 HCl

2. step: TiOCl2 + H2O↔TiO2 + 2 HCl

Summary reaction: TiCl4 + 2 H2O↔TiO2 + 4 HCl

In water this reaction takes place immediately.

As can be seen from above shown chemical equations, target compound titanium oxychloride only can occur and be stabilised in the chemical equilibrium when hydrochloric acid is being added to the equilibrium. Therefore the conduct of genetic toxicity studies direct on the target compound titanium oxychloride is technically not feasible. For this reason, read-across with studies on the final hydrolysis products titanium dioxid and hydrochloric acid is being proposed.

A classical Ames Test (Ogawa HI et al , 1986, reliability 2) and a Bacillus subtilis recombination assay (Kada T, Hirano K and Shirasu Y, 1980, reliability2) are available as tests for the mutagenicity of TiCl4. Due to the fast hydrolysis of TiCl4 it can beassumed that TiO2 particles and HCl were formed the latter of which was buffered by the used buffer system. So basically TiO2 was tested. Because of this behaviour of TiCl4 further testing of mutagenicity is scientifically unjustified. The hydrolysis products TiO2 and HCl have been shown not to be mutagenic:

Citation from the HCl dossier:

“Hydrochloric acid is not genotoxic in in vitro tests using bacterial or simple eukaryotic cells, while its effects on the pH of the medium precludes the possibility of testing in other in vitro non-bacterial systems. Hydrochloric acid rapidly dissociates almost completely in contact with water, releasing the chloride ion and the hydrogen ion which combines with water to form the hydronium ion. Both chloride and hydronium ions are normally present in body tissue, and gastric juices of animals usually contain hydromium ions in rather high concentrations (e.g. in mammals equivalent to 0.17 N HCl). Further tests on this compound are therefore not necessary; this data requirement is not triggered.”

Citation from the TiO2 dossier:

“Titanium dioxide has been tested in bacterial reverse mutation assays, in vitro gene mutation and clastogenicity tests as well as in vivo. All tests show a negative response, thus titanium dioxide does not require classification for mutagenic properties.”

Short description of key information:
The conduct of toxicity and ecotoxicity studies direct on the unstable target compound titanium oxychloride is technically not feasible. Read-across with studies on the final hydrolysis products titanium dioxid and hydrochloric acid is being proposed. Both hydrolysis products have been tested to be negative for a mutagenic potential.

Endpoint Conclusion: No adverse effect observed (negative)

Justification for classification or non-classification

Parent compound titanium tetrachloride will hydrolyse rapidly in contact with water via target compound titanium oxychloride. The conclusions that can be drawn from studies on bacteria are therefore limited to mutagenic effects in bacteria. As an insoluble precipitate is formed, the bioavailability of the substance to bacteria is questionable, and testing in an aqueous environment is not appropriate. From the absence of mutagenicity of the hydrolysis products TiO2 and HCl which are immediately formed in contact with water it can be concluded that neither parent compound TiCl4 nor target compound TiOCl2 exhibit mutagenic potential.