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Toxicity to aquatic algae and cyanobacteria

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Description of key information

One key study is available to assess the toxicity of the analogous substance iron orthophosphate to aquatic algae. This study has been conducted to an appropriate guideline (OECD Method 201) and under the conditions of GLP. Therefore no further testing is required.

Key value for chemical safety assessment

Additional information

Exposure of Pseudokirchneriella subcapitata to the test item gave EC50 values of greater than 100% v/v saturated solution. The No Observed Effect Concentration was determined to be 100% v/v saturated solution.

This study is submitted for the following reasons:

In accordance with Regulation (EC) No. 1907/2006 (REACH) Annex XI, section 2 testing for a specific endpoint may be omitted if it is technically not possible to conduct the study as a consequence of the properties of the substance. Tetrairon tris(pyrophosphate) is an insoluble inorganic material and is not considered to be bioavailable in aquatic environments. This is demonstrated by the fact that iron is often added to effluents containing soluble phosphates in order to remove phosphorus (via making the phosphate insoluble) and prevent eutrophication in water bodies.

As a result of the physicochemical properties, administration of precise and consistent dose levels is not considered to be possible and as such aquatic toxicity testing is not considered to be technically possible. As such a study on a similar substance (iron orthophosphate is submitted). Read-across is justified on the following basis:

 Both substances are relatively insoluble inorganic ferric (Fe3+) compounds. In conditions where the substances have limited solubility/bioavailability; ionisation to the Fe cation and the orthophosphate cation (iron orthophosphate) or pyrophosphate cation (tetrairon tris(pyrophosphate) will occur. In biological systems (i.e. in the presence of alkaline phosphatase) the pyrophosphate will be broken down into orthophosphate. It is considered that the Fe3+ cation is of most relevance when considering the toxicity of the test material and as iron orthophosphate is slightly more soluble this substance is a good candidate for read-across.