Terbium

Skin sensitisation

Administrative data

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.