Terbium

Endpoint summary

Description of key information

The study is technically not feasible.

Key value for chemical safety assessment

Skin sensitisation

Link to relevant study records

Reference

Endpoint:

skin sensitisation: in vitro

Data waiving:

study technically not feasible

Justification for data waiving:

other:

Justification for type of information:

The study is technically not feasible: Application of Terbium in massive form, which would be a prerequisite for toxicological and eco-toxicological studies, is practically not feasible. For this purpose at least Terbium powder would be required (see Annex XI (2)).
The Lanthanide elements own a very high affinity for oxygen; they exhibit the highest free energy for
oxide formation of all elements in the periodic table, accounting for the exceptional thermodynamic stability of the oxides. In consequence the metals will react with air, building up an oxide layer on the surface. This implies the technical unfeasibility of exposure to “free” Terbium metal (powder form), which is a prerequisite for the requested biological tests. Appropriate application of „free“ Terbium metal is not possible since the particles would react in contact with water and air. Based on the strong reductive properties of Terbium powder, classification as skin- and eye irritant is justifiable.
In addition the permanent magnets production with Terbium alloys takes place under strictly controlled conditions (vacuum, inert gas; see technological process) in order to ensure the high quality of the permanent magnets. Therefore exposure of humans during production of the magnets is unlikely to occur. Furthermore according to REACH annex V, section 1 "substances which result from a chemical reaction that occurs incidental to exposure of another substance or article to environmental factors such as air, moisture, microbial organisms or sunlight" are exempted from the obligation to register. The ignoble metal Terbium is due to its high reactivity (high reduction potential) with water and air not existent at ambient conditions. In air Terbium metal is converted to Terbium oxide. In contact with water Terbium hydroxide is immediately formed. These reaction products are exempted from REACH.

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information:

The study is technically not feasible: Application of Terbium in massive form, which would be a prerequisite for toxicological and eco-toxicological studies, is practically not feasible. For this purpose at least Terbium powder would be required (see Annex XI (2)).

The Lanthanide elements own a very high affinity for oxygen; they exhibit the highest free energy for

oxide formation of all elements in the periodic table, accounting for the exceptional thermodynamic stability of the oxides. In consequence the metals will react with air, building up an oxide layer on the surface. This implies the technical unfeasibility of exposure to “free” Terbium metal (powder form), which is a prerequisite for the requested biological tests. Appropriate application of „free“ Terbium metal is not possible since the particles would react in contact with water and air.

Based on the strong reductive properties of Terbium powder, classification as skin- and eye irritant is justifiable; additional testing is therefore not necessary.

In addition the permanent magnets production with Terbium alloys takes place under strictly controlled conditions (vacuum, inert gas; see technological process) in order to ensure the high quality of the permanent magnets. Therefore exposure of humans during production of the magnets is unlikely to occur. Furthermore according to REACH annex V, section 1 "substances which result from a chemical reaction that occurs incidental to exposure of another substance or article to environmental factors such as air, moisture, microbial organisms or sunlight" are exempted from the obligation to register. The ignoble metal Terbium is due to its high reactivity (high reduction potential) with water and air not existent at ambient conditions. In air Terbium metal is converted to Terbium oxide.In contact with waterTerbium hydroxide is immediately formed. These reaction products are exempted from REACH.

Justification for classification or non-classification

Testing is not technically feasible because of Tb reactivity in air or water. Given that dissolution is widely

considered to be required prior to percutaneous absorption, this may be interpreted as a likely indication of

low bioavailability via the dermal exposure route. No classification for Terbium metal is required.