Tetrairon tris(pyrophosphate)

Endpoint summary

Additional information

Summary of degradation

Tetrairon tris(pyrophosphate) is aninorganic phosphate and therefore a ready biodegradation test is not applicable.

One key study is submitted to show the hydrolysis of a soluble pyrophosphate (tetrapotassium pyrophosphate). However the data does not necessarily reflect a ‘real world’ situation as phosphates and essential cations such as K+ are rapidly assimilated by microorganisms in soil and waters. The key study reports the estimated half-life’s at 25°C of the test material were determined to be; 527 days at pH 4 and > 1 year at pH 7 and 9. Under the physiologically relevant conditions of pH 1.2, 37.0 ± 0.5°C, the half-life of the test material was determined to be 26.1 hours. The substance was shown to following the following mechanism of hydrolysis:

Pyrophosphate anion + water → 2 x orthophosphate anion

In reality and due to the pKa’s of orthophosphoric acid and the nature of the phosphate ion it is likely that in natural waters the hydrolysis product will be either orthophosphoric acid and monopotassium dihydrogen orthophosphate (which may also dissociate to phosphate ions and sodium ions).

Results for the preliminary test indicate that the rate of hydrolysis increases with a decrease in pH.

For soluble pyrophosphates the rate of hydrolysis in natural waters is far greater in natural waters than in distilled water. Pyrophosphates will not persist in natural waters. Biotic degradation and assimilation by algae and/or microorganisms will occur at a faster rate than hydrolysis in distilled water. The breakdown products of such reactions are the ubiquitous orthophosphate anion.

As tetrairon tris(pyrophosphate) is considered to be of very low water solubility, extensive hydrolysis is not expected. Up to the limits of solubility tetrairon tris(pyrophosphate) may break down to form iron cations (Fe^{3 +}) and pyrophosphate anions (which will subsequently hydrolyse to orthophosphate as discussed above). Both are natural components of soils. Soil and sediment degradation studies are not considered to be scientifically feasible as there is no available analytical method that could differentiate between the contributions to the analysable solution originating from the test material and that originating from the required soil / sediment matrix / solution matrix due to the ubiquitous nature of theFe³⁺/Fe²⁺and PO₄^3-ions.

 

Data on volatilisation is not available. Tetrairon tris(pyrophosphate) is a stable inorganic solid and therefore can be considered to be non-volatile.

 

No experimental data on bioaccumulation exist. However, bioaccumulation is not expected as accumulation in fats is not possible.

Tetrairon tris(pyrophosphate) may be degraded to pyrophosphate (then further to orthophosphate) and ferric (Fe^{3 +}) ions in biological systems. In order for ferric ions to be bioavailable they must be reduced to ferrous (Fe²⁺) ions. Iron and orthophosphate ions are ubiquitous in the environment. Further both are natural ionic components of blood and cellular fluids and as such their metabolism is homeostatically regulated and therefore the potential for bioaccumulation is considered to be minimal. In addition, no risk of secondary poisoning is anticipated for the same reasons.

 

Eutrophication

tetrairon tris(pyrophosphate) is not anticipated to contribute to eutrophication as it is of very low solubility in water and as such the bioavailability of phosphorus (as phosphate) is significantly reduced. In addition, iron is often used in phosphate removal processes in order to prevent eutrophication as free iron will fix phosphate causing it to become insoluble.

 

Assessment of PBT/vPvB properties; comparison with the criteria of Annex XIII (Regulation (EC )No. 1907/2006).

 

According to the Guidance on Information Requirements and Chemical Safety Assessment, Chapter R.11: PBT Assessment, the PBT and vPvB criteria of Annex XIII to the regulation do not apply to inorganic substances. Therefore, tetrairon tris(pyrophosphate) is not considered to require any further assessment of PBT properties.