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Environmental fate & pathways

Adsorption / desorption

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Description of key information

Dysprosium metal is converted to the insoluble Dysprosium hydroxide in aqueous solution. Therefore adsorption is not expected to be relevant. 

Key value for chemical safety assessment

Additional information

According to column 2 of REACH Annex IX the study does not need to be conducted if based on the physicochemical properties the substance can be expected to have a low potential for adsorption (e.g. the substance has a low octanol water partition coefficient). Dysprosium metal is converted to the insoluble Dysprosium hydroxide in aqueous solution. Therefore adsorption is not expected to be relevant. 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 REACH 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. Due to its reductive power and vigorous reaction with water appropriate application of Dysprosium metal (powder form) is technically not possible. In aqueous solution „free“ Dysprosium metal is converted to Dysprosiumhydroxide. Dysprosiumhydroxide is insoluble in water. Furthermore the study is scientifically unjustified: Human and/or environmental exposure to elemental Dysprosium in massive form can be excluded, since at environmental conditions (presence of 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. In aqueous solution „free“ Dysprosium metal (powder form) is converted to Dysprosiumhydroxide. Dysprosiumhydroxide is insoluble in water. 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 aqueous compartments during production of the magnet articles is unlikely to occur. During the manufacturing processes of elemental Dysprosium metal (electrolysis/molten salt process) direct or indirect exposure to Dysprosium (metal form) is considered unlikely since the Dysprosium metal dust will immediately react under the extreme heat conditions of these processes to form Dysprosium oxide which may be emitted as a component of the fume or dust. 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 in 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.