Dichloride titanium oxide

Endpoint summary

Additional information

Titanium oxychloride is an unstable chemical compound which results from the hydrolysis of 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. Therefore, under environmentally relevant conditions titanium tetrachloride hydrolyses rapidly according to above stated two steps to hydrogen chloride and titanium oxychloride, which hydrolyzes to titanium dioxide and again hydrogen chloride. As target compound titanium oxychloride only can get stabilised in aqueous medium when hydrochloric acid is being added, direct aquatic toxicity testing of the target substance itself is technically not feasible.

A review of aquatic ecotoxicity data sources for parent compound titanium tetrachloride located only a single result for the substance. A 9-hour IC50 (inhibitory concentration) of 20 mg/L has been determined by Sauvant et al (1995) for effects on population growth of a ciliate protozoan (Tetrahymena pyriformis). In the setting of this test the effects of titanium tetrachloride are clearly related to the pH effect caused by the hydrogen chloride released in a fourfold molar amount during the rapid hydrolysis.

The other transformation product, titanium dioxide (CAS 13463-67-7), is considered inert and non-poisonous in the relevant isomolar levels. The hydrogen chloride will dissociate fully in hydronium ions and chlorides, of which the latter is not a harmful substance. Thus observed effects in organisms exposed in unbuffered aqueous media may be due to pH.

In water with no buffering capacity the addition of a concentration of 0.47 mg/L of titanium tetrachloride would be sufficient to lower the pH (increase the acidity) from a value of 7.0 to a value of 5.0. The concentration required to achieve this change would rise to approximately 5.2 mg/L in poorly buffered water (10 mg/L as CaCO3). In moderately buffered water (250 mg/L as CaCO3) a shift from pH 7.0 to pH 5.0, that might be biologically intolerable, would only occur when the added concentration of titanium tetrachloride exceeded ca. 119 mg/L, which is above the regulatory cut-off limit for acute aquatic toxicity. Acidity effects are not true toxic effects and accordingly considered not relevant for assessment.

The titanium dioxide and pH effect levels diverge by more than three orders of magnitude with regard to aquatic micro-organisms (Daniels 2008 and Egeler & Goth 2009). It seems unlikely that tolerable pH drops could have any influence on the biological activity of titanium dioxide.

In consequence the effects of the transformation products of titanium tetrachloride were assessed by read across from titanium dioxide as well with regard to micro-organisms.

The assessment of the titanium dioxide effects revealed no indication of any hazard to the aquatic life of the analogue material titanium tetrachloride. As no effect levels were reached no threshold concentrations were derived and no starting points for the calculation of aquatic PNECs is given.

It is concluded that neither the parent compound titanium tetrachloride, nor the target compound titanium oxychloride nor the final hydrolysis transformation products (namely titanium dioxide) exhibit acute effects to aquatic invertebrates at the level of their water solubility in addition with undissolved microdisperse matter in excess; thus they do not pose risk to aquatic life.