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Data on the toxicity of the target substance diphosphoric acid, compound with 1,3,5-triamine (1:2) are not available. The assessment is based on data available for the read across substances melamine (CAS 108-78-7), calcium hydrogenorthophosphate (CAS 7757-93-9) and tetrapotassium pyrophosphate (CAS 7320-34-5).The source substances calcium hydrogenorthophosphate and tetrapotassium pyrophosphate were contemplated to assess the toxicity of the diphosphoric acid moiety. The read across approach is in accordance with Regulation (EC) No. 1907/2006, Annex XI, 1.5. Further justification is given in the analogue justification attached to IUCLID section 13.

Read across data are available for three trophic levels (fish, aquatic invertebrates, algae). The available data give no indication of acute or chronic toxicity within the range of the water solubility (WS: 385.6 ± 1.1 mg test item/L based on P and 233.1 ± 2.4 mg/L based on non purgeable carbon).

Data on the acute aquatic toxicity of melamine (CAS 108-78-1) are available for fish, aquatic invertebrates and algae. The toxicity to freshwater fish was assessed in a weight of evidence approach. The available studies tested the toxicity of the substance on the standard test species Oryzias latipes, Oncorhynchus mykiss, Leuciscus idus and Poecilia reticulate, respectively. The determined LC50 values, either after 48 hours or 96 hours of exposure, were in the range of >500 - >4400 mg/L.

One reliable study investigating the acute toxicity of melamine (CAS 108-78-7) to Daphnia magna is available. The determined LC50 (48 h) value was > 1000 mg/L based on mortality (EC50 (48 h) < 180 - 200 mg/L based on behaviour).

Two studies on the toxicity of melamine to algae are available. Both studies investigated a possible growth inhibition of green algae induced by melamine. The determined EC50 (96 h) in a toxicity test with Pseudokirchneriella subcapitata was 325 mg/L (NOEC (96 h): 98 mg/L). In the second study with Scenedesmus pannonicus an EC50 (90.5 h) of 940 mg/L (meas. initial) was determined. The NOEC (90.5 h) was 320 mg/L (nominal).

The acute aquatic toxicity of the pyrophosphate ion was assessed by read across to available studies on calcium hydrogenorthophosphate (CAS 7757-93-9) and tetrapotassium pyrophosphate (CAS 7320-34-5).

For calcium hydrogenorthophosphate (CAS 7757-93-9) no acute or chronic toxicity was observed. The study on the acute toxicity to Oryzias latipes determined a LC50 (96 h) > 13.5 mg/L based on the mean measured concentrations. Whereas in a study conducted with Pseudokirchneriella subcapitata an EC50 (72 h) >4.4 mg/L (measured) was determined based on the algal growth rate (nominal: EC50 (72 h) >100 mg/L).

In the available study on tetrapotassium pyrophosphate (CAS 7320-34-5) Daphnia magna was exposed to a nominal test substance concentration of 100 mg/L for 48 hours. At test termination an EC50 (48 h) >100 mg/L (nominal) was determined.

Studies investigating the chronic toxicity of the read across substance melamine (CAS 108-78-1) are available for fish and aquatic invertebrates. Detrimental effects on hatching and development of fish were not observed. The recorded NOEC was >1000 mg/L. A study investigating the effects of melamine (CAS 108-78-7) on reproduction and survival of Daphnia magna a NOEC of 18 mg/L was determined.

The toxicity to activated sludge microorganisms was assessed in a weight of evidence approach using available data for melamine (CAS 108-78-1) and calcium bis(dihydrogenorthophosphate) (CAS 7758-23-8) to assess the toxicity of the melamine compound and of the pyrophosphate compound. The available test determined no detrimental effects of the substances on microorganisms.