Terbium

Genetic toxicity: in vitro

Administrative data

Endpoint:

in vitro gene mutation study in bacteria

Data waiving:

other justification

Justification for data waiving:

other:

Justification for type of information:

For genetic toxicity of Terbium (powder form), the Terbium ion will have to be made bioavailable to the target gene in sufficient concentration to cause the mutagenic effect. This requires that Terbium will have to be bioavailable by absorption via relevant routes of exposure. After oral uptake, throughout transition to the duodenum (pH 8-9), dissolved Tb(III) would be precipitated to insoluble Terbiumhydroxide. It should be noted that the gastrointestinal absorption of soluble Terbium salts is < 1%. It is therefore unlikely to occur with the insoluble Terbium which is not soluble in the digestive tract. Terbium is insoluble in water and not fat soluble, consequently it is not expected to be absorbed through the skin. In particular also Terbium cations will not be absorbed dermally.
Furthermore 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.
In addition the in vitro 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. The readily formed oxides and hydroxides are insoluble in water. 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 registration obligations.