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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Link to relevant study record(s)

Description of key information

No studies are available on magnesium carbonate.
The acute toxicity of magnesium chloride hexahydrate to algae has been investigated in a GLP study performed in accordance with OECD Test Guideline 201. The test was performed as a limit test using 100 mg/L. The 72 h NOEC was 100 mg/L and the EC50 was >100 mg/L. The results from this study can be read across to magnesium carbonate and hence the equivalent 72 h EC50 is >65 mg MgCO3/L and the NOEC is 65 mg MgCO3/L.

Key value for chemical safety assessment

Additional information

Rationale for read across:

Magnesium chloride hexahydrate is significantly more soluble in water than magnesium carbonate and therefore represents the worst case in terms of bioavailability in natural waters. Although magnesium carbonate is less soluble, both magnesium chloride hexahydrate and magnesium carbonate are expected to dissociate to their ionic forms in water and therefore the toxicity results can be read across. Mg2+, Cl- and CO32 - ions are all ubiquitous in the aquatic environment 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. This natural abundance of magnesium ions in the environment means that aquatic organisms including algae are constantly exposed to magnesium without suffering from any adverse or detrimental effects. This lack of toxicity is supported by the presented study, summarised below. Any further testing is scientifically unjustified.

A GLP guideline study was performed which assessed the acute toxicity of magnesium chloride hexahydrate (Eurofins-GAB GmbH, 2010) to algae in a limit test. The 72 h EC50 for magnesium chloride hexahydrate was found to be >100 mg/L and the NOEC was 100 mg/L, the highest concentration tested. No toxic effects were noted. The concentrations of magnesium were measured in each test solution. The EC50 based on the mean measured concentrations of magnesium is therefore equal to >18.5 mg/L and the NOEC is 18.5 mg/L. Based on these values the NOEC and EC50 for magnesium carbonate can be estimated to be 65 mg/L and >65 mg/L, respectively.

The lack of toxicity seen in this study therefore suggests that magnesium carbonate would not be acutely toxic up to the limit of its solubility in water (110 mg/L at 20 °C).