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Description of key information

Short description of key information on bioaccumulation potential result: 
No reliable results are available for basic toxicokinetics of synthetic rutile. Therefore, read-across is proposed to available data on TiO2. No substantial accumulation of titanium was observed in tissues following oral administration of titanium dioxide.
Short description of key information on absorption rate:
No reliable results are available for dermal absorption of synthetic rutile. Therefore, read-across is proposed to available data on TiO2. Titanium dioxide has been shown not to penetrate human skin to any appreciable degree, so that the dermal absorption of titanium dioxide through human skin is considered negligible.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential

Additional information

Read across concept

Synthetic rutile consists primarily of a titanate phase (solid solution) most of which is titanium in an oxidised form. Upon ingestion, a low rate of dissolution in the GI tract is assumed, based on the experimental verified inertness of the material. Any material being released from Synthetic rutile under physiological conditions will be in the form of ionic titanium, which is similarly the case for titanium dioxide, thus read-across from repeated dose oral toxicity data on titanium dioxide is considered feasible without any restrictions.

Furthermore, transformation/dissolution testing according to “OECD 29 Environmental Health and Safety Publications, Series on testing and assessment, Guidance document on transformation/ dissolution of metals and metal compounds in Aqueous media” has shown that synthetic rutile compared to titanium dioxide has a similar release rate of titanium ions (please refer to the respective entry under the endpoint water solubility).

In a toxicokinetic study rats were exposed with diets reinforced with different forms of titanium dioxide at approx. 200 ppm (equivalent to ca. 30 mg/kg bw) for 7 days. The main route of excretion was via the faeces accounting for means of 39 – 63% daily dose. For each collection interval (0 - 24, 24 – 48, 48 – 72 hours) there was no statistical evidence to suggest differences in patterns of excretion between different forms of titanium dioxide. The results suggest that there is no substantial accumulation of titanium in tissues following administration of diets with different forms of titanium dioxide.

In vitro bioaccessibility data on titanium released from titanium dioxide were determined when exposed to synthetic biological media of varying pH and composition. Only a small fraction of titanium was released/dissolved from the titanium dioxide powder during exposure to any of the media matrices of varying acidity and composition. A trend with somewhat higher release rates with increasing acidity and exposure period was evident. The test results suggest that there is no substantial accumulation of titanium in tissues following administration of diets with different forms of titanium dioxide.

Discussion on absorption rate:

Read across concept

Synthetic rutile consists primarily of a titanate phase (solid solution) most of which is titanium in an oxidised form. Upon ingestion, a low rate of dissolution in the GI tract is assumed, based on the experimental verified inertness of the material. Any material being released from Synthetic rutile under physiological conditions will be in the form of ionic titanium, which is similarly the case for titanium dioxide, thus read-across from repeated dose oral toxicity data on titanium dioxide is considered feasible without any restrictions.

Furthermore, transformation/dissolution testing according to “OECD 29 Environmental Health and Safety Publications, Series on testing and assessment, Guidance document on transformation/ dissolution of metals and metal compounds in Aqueous media” has shown that synthetic rutile compared to titanium dioxide has a similar release rate of titanium ions (please refer to the respective entry under the endpoint water solubility).

 

The absorption of titanium dioxide through porcine skin has been measured in an in vitro percutaneous study. Under the present testing conditions the total dermal absorption is estimated to 0 %, for the two tested titanium dioxide samples, retention in the skin was estimated to be 0.1-0.5%. Therefore, based on this study a value of 0% for dermal absorption is suggested. This value is supported by various supportive data in which the retention of titanium dioxide from sunscreen formulations in human skin has been investigated. It has been shown that titanium dioxide is retained in the outmost layers of the stratum corneum.

Furthermore, titanium dioxide was tested in various percutaneous absorption tests which have been reviewed by the Scientific Committee on cosmetic products and non-food products (SCCNFP/0005/98, 2000) and which concluded “extensive tests for percutaneous absorption, mostly in vitro, indicate that absorption does not occur, either with coated or uncoated material; one experiment found some evidence that a little of the material could be found in the openings of the follicles. [...] The toxicological profile of this material does not give rise to concern in human use, since the substance is not absorbed through the skin. In view, also, of the lack of percutaneous absorption, a calculation of the margin of safety has not been carried out.”