Registration Dossier

Diss Factsheets

Administrative data

Description of key information

Study scientifically not justified.

Key value for chemical safety assessment

Acute toxicity: via oral route

Endpoint conclusion
Endpoint conclusion:
no study available

Acute toxicity: via inhalation route

Endpoint conclusion
Endpoint conclusion:
no study available

Acute toxicity: via dermal route

Endpoint conclusion
Endpoint conclusion:
no study available

Additional information

Human and/or environmental exposure to elemental Dysprosium 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 Dysprosiumoxide or –hydroxide (from Dysprosium in powder form) would be dissolved in the gastric juice, oral toxicity of the formed Dysprosium(III)-ion is insignificant which is supported by literature data (LD50 of soluble DyCl3: 7,650 mg/kg). Throughout transition to the duodenum (pH 8-9), dissolved Dy(III) will be precipitated to insoluble Dysprosiumhydroxide. It should be noted that the gastrointestinal absorption of soluble Dysprosium salts is < 1%. It follows from the above that no relevant systemic exposure takes place which would justify additional testing with experimental animals.

Even though orally ingested Dysprosium particles may have an incompletely oxidized core, insoluble Dysprosiumhydroxide/-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 Dysprosium 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 Dysprosium salts is < 1 %!) would be equated with the extremely low bioavailability of the metal.

The skin provides a sturdy, flexible, and self-repairing barrier to the exterior environment, protecting the internal body organs and fluids from external influences. The major barrier to permeation within the skin is the Stratum corneum, the outermost cornified layer, consisting of corneocytes. These corneo-cytes comprise mainly scleroprotein keratin. Permeation of a chemical through the Stratum corneum is basically a diffusion process in which active transport plays no role. The layer with the highest resistance to diffusion is the rate-limiting membrane. For many compounds, the lipophilic Stratum corneum is the primary or rate-limiting barrier.

Dysprosium metal is insoluble in water and not fat soluble, consequently Dysprosium is not expected to be absorbed through the skin.

In particular also Dysprosium cations will not be absorbed dermally.

Furthermore the permanent magnets production with Dysprosium 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 (dermal,oral, inhalation) during production of the magnets is unlikely to occur.

 

In addition the study is technically not feasible: Application of Dysprosium in massive form, which would be a prerequisite for toxicological and eco-toxicological studies, is practically not feasible. For this purpose at least Dysprosium 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” Dysprosium metal (powder form), which is a prerequisite for the requested biological tests. Appropriate application of „free“ Dysprosium 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 Dysprosium is due to its high reactivity (high reduction potential) with water and air not existent at ambient conditions. In air Dysprosium metal is converted to Dysprosium oxide. In contact with water Dysprosium hydroxide is immediately formed.These reaction products are exempted from REACH registration obligations.

Justification for classification or non-classification

No classification of Dysprosium metal regarding acute toxicity is required.