Manganese bis(dihydrogen phosphate)

Short-term toxicity to aquatic invertebrates

Description of key information

One key study is available to assess the toxicity of Mn2+ (in the form of manganese chloride). 2 species of aquatic invertebrates are used (C.dubia and H.azteca). Testing was performed under soft, medium-hard and hard water conditions. 
The value considered for assessment of the toxicity of manganese hydrogen phosphate was seleced on the basis that it represents a worst-case scenario (soft water).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

15.66 mg/L

Additional information

Calculation of an EC50 value relevant for Manganese hydrogen phosphate (see 'read-across justification for further information)

The lowest 48 h EC50 value in the studies performed with manganese chloride was found to be 5.7 mg Mn/L (C.dubia, soft water). In the study with H.azteca a lower value of 3 mg Mn/L was recorded, however this was over a 96h time period and as such the 48 h EC50 is more relevant for classification and labelling. In addition, H.azteca are not the standard test species for this type of experiments as studies for regulatory purposes are more common performed with Daphia. Therefore the C.dubia value has been translated into a value relevant to manganese hydrogen phosphate by a molecular weight calculation.

READ-ACROSS JUSTIFICATION

 

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.

For the derivation of PNECs it was decided to use the worst-case data performed on a manganese phosphate (algal growth study, manganese hydrogen phosphate) as the starting point due to the fact that the bulk of the data for the environment is literature data and whilst for the Mn ion this could be considered to be reliable data it was not performed to current guidelines or under the conditions of GLP and as such it is considered that calculating a PNEC based on the most recent data on the most relevant substance would give the most reliable value to be taken forward into risk assessment. Classification has been based on an assessment of all data; including data for the Mn ion and represents a worst-case for the environment.