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Short-term toxicity to fish

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Description of key information

No experimental data are available that assess the short-term toxicity of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide to fish. Nevertheless, a 96h-LC50 value can be derived from reliable information that is available for hydrogen peroxide.
The 96h-LC50 for the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide is 73.4 mg/L.

Key value for chemical safety assessment

Fresh water fish

Fresh water fish
Effect concentration:
73.4 mg/L

Additional information

No experimental data are available that assess the short-term toxicity of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide to fish. Nevertheless, for this endpoint reliable information is available for hydrogen peroxide (H2O2) and magnesium hydroxide (Mg(OH)2), the primary hydrolytic degradation products of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide.

 

For magnesium hydroxide, the short-term toxicity test with Pimephales promelas (Fathead minnow) (Heinen, 2005) was carried out according to the EPA-821-R-02-012 guidance. A control plus six test substance concentrations were tested, ranging from 24.22 mg/L to 775 mg/L. The test substance contained 61% of magnesium hydroxide in an aqueous suspension. Survival of the fish after 96 hours ranged from 35% in the highest dose group to 100% in the lowest dose group. The LC50 was calculated to be 511.31 mg/L based on the test material containing 61% magnesium hydroxide. This value was recalculated towards an LC50 for pure magnesium hydroxide: 306.79 mg/L.

 

The key study assessing the acute toxicity of hydrogen peroxide to fish as identified in the REACH registration dossier for hydrogen peroxidedates from 1989 and is performed according to US EPA guidelines (Shurtleff, 1989). In this semi-static experiment, Pimephales promelas (fathead minnow) were exposed for 96 hours to nominal hydrogen peroxideconcentrations of 0.5, 5, 25, 50 and 250 ppm. The test solutions were replaced every day. The 96h-LC50 was found to be 16.4 mg/L (95% confidence interval: 13.1 -20.5 mg/L), and the 96h-NOEC value was 5 mg/L. As the 96h-LC50 value for hydrogen peroxide is lower than the value found for magnesium hydroxide, the former was selected for the assessment of the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide.

From this 96h-LC50 value a corresponding 96h-LC50 value can be calculated for the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide, by taking into account the applicable chemical reaction (i.e. the amount of hydrogen peroxideformed is equimolar to the amount of magnesium peroxidepresent in the reaction mass) and the composition of the reaction mass (i.e. the reaction mass contains ca. 37% magnesium peroxide).

Thus: 100 mg of the reaction mass contains 37 mg of magnesium peroxide,which corresponds to 0.66 mmol of magnesium peroxide. Therefore, 0.66 mmol (= 22.35 mg) of hydrogen peroxideis formed upon dissolution of 100 mg of the reaction mass.

 

As a consequence, the 96h-LC50 for the reaction mass of magnesium carbonate and magnesium hydroxide and magnesium oxide and magnesium peroxide can be calculated from the 96h-LC50 for hydrogen peroxide (16.4 mg/L):

100 mg/L reaction mass         yields              22.35 mg/L hydrogen peroxide

73.4 mg/L reaction mass        yields              16.4 mg/L hydrogen peroxide

==> the 96h-LC50 (reaction mass) = 73.4 mg/L