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Bioconcentration refers to the accumulation of a substance dissolved in water by an aquatic organism (definition from section R.7.10.1.1 of ECHA's guidance document on "Information requirements and chemical safety assessment" R7c p. 9). As the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide is a solid inorganic multi-constituent substance which undergoes dissociation and hydrolysis in aqueous media, this means that Mg2 +, OH- and hydrogen peroxide are the species to be taken into account when assessing its potential to bioconcentrate.

 

* H2O2: Hydrogen peroxide is reactive and a polar substance with a short half-life, and the log KOW value of hydrogen peroxide is estimated at approximately –1.5. These properties indicate negligible potential of bioconcentration of hydrogen peroxide (cf., European Union Risk Assessment Report: hydrogen peroxide; European Chemicals Bureau, Institute for Health and Consumer Protection, 2nd Priority List Volume 38; EUR 20844 EN; page 35).

Moreover, the enzyme catalase is almost ubiquitously distributed in biotic systems enabling the organisms to convert hydrogen peroxide into water and oxygen.

 

* Mg(OH)2: Exposure to magnesium hydroxide actually comes down to exposure to magnesium ions and hydroxyl ions. There will be no intake of magnesium hydroxide as such from an aquatic medium, nor will magnesium hydroxide prevail under its original form in the organisms. Moreover, both the intake of the essential element magnesium and the internal pH of an organism are actively regulated (homeostasis). Therefore, this endpoint is considered not to be relevant for magnesium hydroxide, and a bioconcentration test in fish is not deemed required.

 

In conclusion, the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide is an inorganic multi-constituent substance that hydrolyses in water. The constituents and hydrolysis products are not bioaccumulative. Studies to determine the bioaccumulation of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide are therefore not needed.

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