Iron orthophosphate

Endpoint summary

Additional information

Experimental and appropriate read across data for three trophic levels (fish, aquatic invertebrates, algae) do not reveal short or long term toxicity hazard from the substance up to its water solubility. With exception of algae toxicity, the aquatic toxicity is evaluated based on the dissolution of iron resulted by the transformation/dissolution test according to the OECD guideline 29 and environment reference values (ERV) of a soluble iron (III) source i.e iron chloride (FeCl₃, CAS 7705-08-0). In addition, the environmental toxicity values of Calcium hydrogenorthophosphate (CAS 7757-93-9) are considered for justification of the non-metallic ion PO₄^3-. An extensive read across justification is provided in IUCLID chapter 13.

The results obtained by a transformation/dissolution test according to the OECD 29 show that the substance is poorly water soluble. The 24-hour Dissolution Screening test at loading of 100 mg/L and pH 6 resulted into a water solubility for Iron (III) orthophosphate (anhydrate) of 11.23 µg/L, which is significantly lower than the lowest ERVcompound of 4.03 mg Fe/L (obtained for fish).   

Read across data with calcium hydrogenorthophosphate reveal that no toxicity arises from the non-metallic ion PO₄^3-released from Iron (III) orthophosphate. Short-term tests with a soluble iron (III) form (FeCl₃) resulted into minimum LC50 values of 1.46 and 2.3 mg Fe/L (measured) for fish and aquatic invertebrates respectively. The acute aquatic toxicity reference value is therefore driven by the fish data, which result according to the Guidance on the Application of the CLP Criteria Guidance to Regulation (EC) No 1272/2008 on classification, labelling and packaging (CLP) of substances and mixtures (2017), to a minimum ecotoxicity reference value (ERVcompound) of 4.03 mg/L. The transformation/dissolution test according to OECD guideline 209 showed the dissolution of iron after 7 days was lower than the limit of detection 0.1682 µg Fe/L at the loading of 1 mg/L and pH 6. This value is far below the lowest ERV value revealing that no short-term toxicity is expected by the iron (III) released from the substance up to its water solubility.

In addition, an algal growth inhibition study (OECD 201) has been performed with the substance. 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.

An activated sludge respiration inhibition study (OECD 209) has also been performed with Iron (III) orthophosphate. The effect of the test item on the respiration of activated sewage sludge gave a 3‑hour EC50 of greater than 1000 mg/L. The No Observed Effect Concentration (NOEC) after 3 hours exposure was >= 1000 mg/l. Therefore, exposure of sewage sludge to iron orthophosphate is not considered to be of concern.

Furthermore, the publically available Renewal Assessment Report (2013) for use of ferric phosphate in plant protection products also concludes based on experimental data with the active substance that it is not toxic to aquatic organisms up to a nominal concentration of 100 mg/L. The studies were conducted according to appropriate OECD guidelines and GLP. These results support the above conclusions provided by the read across data.

Literature data on a soluble iron (III) form together with environmental fate considerations give evidence that no long-term toxicity is expected by Iron (III) orthophosphate. The lowest chronic ERVcompound was 0.065 mg Fe/L and was determined for fish. This value is higher than the dissolved iron concentration measured in the 28-d transformation/dissolution test (0.503 µg/L) at a loading of 1 mg/L and pH 6 revealing that no chronic toxicity concerns arise up to the water solubility of the substance at standard environmental conditions. Furthermore, iron phosphate is a common mineral in the environment with low release of its ions, iron and phosphate. Its elements are essential nutrients for life. Environmental background concentrations of iron and phosphate in the environment are high in comparison to the release from the substance.

In conclusion, all evidence indicate that Iron (III) orthophosphate is not hazardous to aquatic organisms.