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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

One key study exists on an analogous substance. This study had been conducted in accordance with a recommended guideline (OECD 201, EU Method C.3) and under the conditions of GLP. As such, no further testing is considered necessary.

Key value for chemical safety assessment

EC50 for freshwater algae:
97.1 mg/L
EC10 or NOEC for freshwater algae:
97.1 mg/L

Additional information

NOEC (toxicity) = 97.1 mg DAP/L (no inhibition of algal growth observed in study) / NOEC (stimulation) = 3.57 mg DAP/L

No adverse inhibitory effects were observed. There was some growth stimulation at 6.25 mg/L and above. This was consistent with the known stimulatory effect of phosphate compounds. The reported NOEC reflects this stimulatory response and is not considered to be an adverse effect.

Read-across in accordance with Annex XI, Section 1.5 of Regulation (EC) No. 1907/2006 (REACH) is justified on the following basis:

Polyphosphoric acids, ammonium salt (also known as ammonium polyphosphate) is a mixture of oligomeric species of ammonium phosphate. When analysed the substance appears to consist mainly of ammonium orthophosphates, ammonium diphosphate and ammonium triphosphate.

The proposed source chemical (diammonium hydrogenorthophosphate) has the following (EC number 231-987-8) is very soluble in water (> 10000 mg/L). In aqueous media soluble inorganic orthophosphates will dissociate to their ionic constituents; in this case ammonium and orthophosphate ions. The target chemical is also a highly soluble inorganic phosphate (>10000 mg/L). In aqueous media the oligomeric species of ammonium phosphate will dissociate to ammonium cations and pyrophosphate, pyrophosphate and triphosphate anions. The pyrophosphate and triphosphate anions are unstable in aqueous solutions with the degree of instability varying according to pH. In distilled water they will hydrolyse slowly via abiotic mechanisms to orthophosphate. In natural waters a number of different processes can occur; abiotic hydrolysis, biotic degradation (as a result of the action of phosphatases which cleave triphosphates and pyrophosphates into orthophosphate subunits) and assimilation by organisms in the water. Thus the target substance (ammonium polyphosphates) and the source substance (diammonium hydrogenorthophosphate) will be primarily absorbed as the same inorganic ions: ammonium and orthophosphate and are expected to behave in a similar manner under test conditions.

All (bio) transformation products of the source chemical are common to the target chemical and as such the data is considered to be adequate and reliable for use in the assessment of ammonium polyphosphate for the ecotoxicity hazard assessment.