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Short-term toxicity to fish

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Description of key information

No studies on the short-term toxicity of magnesium carbonate to fish are available and testing is scientifically unjustified.
The key study was conducted on an analogous substance and assesses the short-term toxicity of magnesium chloride to Pimephales promelas (fathead minnow). The 96 h LC50 was 2120 mg/L which demonstrates that magnesium chloride is not acutely toxic to fish at the concentrations tested.
The results from this study can be read across to magnesium carbonate and hence the equivalent LC50 value for magnesium carbonate is equal to 1875 mg/L.

Key value for chemical safety assessment

Additional information

Rationale for read across:

Magnesium chloride is significantly more soluble in water than magnesium carbonate (~1667 g/L versus 110 mg/L) and therefore represents the worst case in terms of bioavailability in natural waters. Although magnesium carbonate is less soluble, both magnesium chloride and magnesium carbonate are expected to dissociate to their ionic forms in water and therefore the toxicity results can be read across.

The key study (Mount, 1997) assessed the acute toxicity of magnesium chloride to Pimephales promelas (fathead minnow) at various different concentrations. No adverse effects were reported in the study and the 96 h LC50 for magnesium chloride was found to be 2120 mg/L. The equivalent LC50 value for magnesium carbonate is equal to 1875 mg/L. Based on the lack of toxicity seen with magnesium chloride and the high calculated LC50 value, the carbonate salt would also be expected to be not acutely toxic to fish.

The concentration of magnesium carbonate that might cause acute toxicity would be greater than the maximum solubility of magnesium carbonate in water (110 mg/L at 20 °C).

Magnesium is naturally abundant in the environment meaning that aquatic organisms are constantly exposed to magnesium without suffering from any adverse or detrimental effects. Indeed, each of the Mg2+, Cl- and CO3^2- ions are ubiquitous and are not considered to pose a risk of ecotoxicity. Magnesium is present in all natural waters and is a major contributor to water hardness. Water from areas rich in magnesium-containing rocks may contain magnesium in the concentration range 10 to 50 mg/L. The sulfates and chlorides of magnesium are very soluble, and water in contact with such deposits may contain several hundred milligrams of magnesium per litre.

The abundance of magnesium in the aquatic environment and the lack of toxicity in the presented study demonstrate that any further testing is scientifically unjustified.