Terbium

Endpoint summary

Key value for chemical safety assessment

Repeated dose toxicity: via oral route - systemic effects

Link to relevant study records

Reference

Endpoint:

short-term repeated dose toxicity: oral

Data waiving:

other justification

Justification for data waiving:

other:

Justification for type of information:

Human and/or environmental exposure to elemental Terbium in massive form can be excluded, since at environmental conditions (air/humidity) practically insoluble substances (oxides, hydroxides) are formed immediately on the surface: Any respective investigations would be of no additional merit for the relevant scientific knowledge with regard to human and/or environmental protection.
Even if Terbiumoxide or –hydroxide (from Terbium in powder form) would be dissolved in the gastric juice, oral toxicity of the formed Terbium(III)-ion is insignificant. Throughout transition to the duodenum (pH 8-9), dissolved Tb(III) will be precipitated to insoluble Terbiumhydroxide. It should be noted that the gastrointestinal absorption of soluble Terbium salts is < 1%. It follows from the above that no relevant systemic expo sure takes place which would justify additional testing with experimental animals. Even though orally ingested Terbium particles may have an incompletely oxidized core, insoluble Terbiumhydroxide/-oxide would be formed immediately in contact with air or water after “flaking off” the oxide layer. From a toxicological point of view, oral application of soluble Terbium salts in order to perform testing with experimental animals is scientifically not justifiable since the potential bioavailability of 100 % of the soluble salts (It should be noted that systemic availability of soluble Terbium salts is < 1 %!) would be equated with the extremely low bioavailability of the metal.
Furthermore the permanent magnets production with Terbium alloys takes place under strictly co
ntrolled 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 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.

Endpoint conclusion

Endpoint conclusion:

no study available

Additional information

Human and/or environmental exposure to elemental Terbium in massive form can be excluded, since at environmental conditions (air/humidity) practically insoluble substances (oxides, hydroxides) are formed immediately on the surface: Any respective investigations would be of no additional merit for the relevant scientific knowledge with regard to human and/or environmental protection.

Even if Terbiumoxide or –hydroxide (from Terbium in powder form) would be dissolved in the gastric juice, oral toxicity of the formed Terbium(III)-ion is insignificant. Throughout transition to the duodenum (pH 8-9), dissolved Tb(III) will be precipitated to insoluble Terbiumhydroxide. It should be noted that the gastrointestinal absorption of soluble Terbium salts is < 1%. It follows from the above that no relevant systemic expo sure takes place which would justify additional testing with experimental animals. Even though orally ingested Terbium particles may have an incompletely oxidized core, insoluble Terbiumhydroxide/-oxide would be formed immediately in contact with air or water after “flaking off” the oxide layer. From a toxicological point of view, oral application of soluble Terbium salts in order to perform testing with experimental animals is scientifically not justifiable since the potential bioavailability of 100 % of the soluble salts (It should be noted that systemic availability of soluble Terbium salts is < 1 %!) would be equated with the extremely low bioavailability of the metal.

Furthermore the permanent magnets production with Terbium alloys takes place under strictly co

ntrolled 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 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.

Justification for classification or non-classification

No relevant systemic exposure of Terbium metal takes place.Therefore no classification is required.