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Description of key information

In conclusion, as worst case estimate oral and dermal absorption values at 1% are assumed for risk assessment purposes, and 2% (i.e. twice the oral absorption) for inhalation absorption.

Key value for chemical safety assessment

Bioaccumulation potential:
no bioaccumulation potential
Absorption rate - oral (%):
1
Absorption rate - dermal (%):
1
Absorption rate - inhalation (%):
2

Additional information

 

Introduction

The physico-chemical properties and the results of in vitro studies, as well as acute and repeated dose toxicity studies performed with ditantalum pentaoxide or structurally related substances have been used to determine a toxicokinetic profile.

 

Physicochemical properties

The substance ditantalum pentoxide is a white powder inorganic substance. It has the molecular formula O₅Ta₂ and a molecular weight of 441.893 g/mol. In this oxide is the inorganic element, Tantalum, is in its highest possible oxidation state, +5. Ditantalum pentoxide is an inert material and is practically insoluble in water (water solubility <0.005 mg/L at both 10 and 20 °C). Its melting point has been reported to be 1800 °C as a minimum.

 

Absorption

Oral absorption

Based on the physical form, high molecular weight and insolubility in water, all suggesting minimal, if any, oral absorption, supported by the extremely high oral LD0values reported in literature (Cochran 1950), the lack of systemic effects at the limit dose of 1000 mg/kg bw/day in a repeated-dose toxicology study performed with the structurally related substance tantalum pentachloride (TaCl5), and similarity with the inorganic element of the substance, tantalum, oral absorption at 1% is assumed for risk assessment purposes.

 

Dermal absorption

No studies investigating the absorption of ditantalum pentaoxide through the skin are available. Given its practical insolubility and that it is a solid, dermal absorption is expected to be minimal. The molecular weight is very close to the threshold of 500 g/mol for which a default dermal absorption value of 10% is generally accepted however, as dermal absorption is unlikely to be higher than oral absorption, the same value of 1% will be used for risk assessment purposes.

 

Inhalation absorption

Based on the lack of systemic effects following 4-h inhalation at the highest technically achievable concentration of 3.89 mg/L, with approximately 90% of the particulate representing the respirable fraction (<7 μm in aerodynamic diameter), and literature data, in vitro and in vivo following direct instillation into the trachea (Clayton 1981, Delphant 1955, Matthay 1976), indicating benign reactions and reversibility related to clearance by macrophages, inhalation absorption at 2% (i.e. twice the oral absorption) is assumed for risk assessment purposes.

 

Distribution

Based on the relatively high molecular weight and extremely low water solubility, together with the fact that no target organ was identified following repeated oral dosing at the limit dose of 1000 mg/kg bw/day with tantalum pentachloride, it is unlikely that ditantalum pentaoxide will be widely distributed within the body.

 

Metabolism

No information is available on the fate of the possibly absorbed material however, given the nature of the substance and its physico-chemical properties, no metabolism is expected to occur.

 

Elimination

Literature data suggest that the test material is poorly absorbed in the alimentary tract where it is rapidly excreted in the faeces. When exposed via the lungs the test material is rapidly absorbed, the excretory pathway via this route of exposure has not been reported, although clearance by macrophages has been reported elsewhere (Venugopal, 1978).

 

Conclusion

As worst-case estimates, oral and dermal absorption values at 1% are assumed for risk assessment purposes, and 2% (i.e. twice the oral absorption) for inhalation absorption.