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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

One key study to assess the toxicity of the analogous substance manganese hydrogen phosphate to algae exists. On this basis manganese (Mn2+) are considered to be toxic to aquatic freshwater algae. 

Key value for chemical safety assessment

EC10 or NOEC for freshwater algae:
9.9 mg/L

Additional information

RESULTS

Exposure of Pseudokirchneriella subcapitata to the test item gave the following results (based on Growth Rate):

EC50 (mg/L): >20*

No Observed Effect Concentration (NOEC) (mg/L): 9.9

Lowest Observed Effect Concentration (LOEC) (mg/L): 20

Analysis of the test preparations at 0 and 72 hours showed measured test concentrations to range from 1.2 to 21 mg/L and so the results are based on the 0-Hour measured test concentrations only.

* It was not possible to calculate an EC50 value as no concentration tested resulted in 50% inhibition.

JUSTIFICATION FOR READ-ACROSS

An assessment of the environmental toxicity has been made on the basis of a read-across between analogous Mn2+ containing substances.

 

All substances used as source chemicals for read-across contain Mn2+ and are very soluble in water. Due to the inorganic nature and high solubility of these materials (manganese sulphate, manganese chloride, and manganese hydrogen phosphate) the anions and cations may be considered separately. Chloride, sulphate or phosphate anions are naturally occurring components of all biological fluids and as such are not considered to have any influence on the effective toxicity of Mn2+ nor any toxicity in their own right and can be disregarded when assessing the toxicity of these materials.

Any toxicological effects will be as a result of the presence of Mn2+ and therefore an assessment of the relative toxicity of soluble inorganic manganese salts with non-toxic anions can be made on the basis of data from similar substances, such as:

 

- Manganese bis(dihydrogen phosphate)

- Manganese hydrogen phosphate

- Manganese sulphate

- Manganese chloride

 

 

When considering a testing strategy for manganese phosphates, tests have been performed on manganese hydrogen phosphate as that contributes the greater amount of Mn2+ on a %w/w basis (36.4% as compared to 22% in manganese bis(dihydrogen phosphate) these results will be directly read across to manganese bis(dihydrogen phosphate) as they are representative of a worst-case for manganese phosphates.

 

Further, where results from studies on manganese sulphate or manganese chloride are reported as units of manganese (e.g. mg Mn/L) a molecular weight calculation has been performed to translate the value into units of manganese hydrogen phosphate. This value will then be used for manganese bis(dihydrogen phosphate) as a worst-case.