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Toxicity to aquatic algae and cyanobacteria

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Description of key information

ErC50 (72h) >100 mg/L for green alga Desmodesmus subspicatus (OECD TG 201)

Key value for chemical safety assessment

Additional information

In accordance with Annex XI, section 1.5 of Regulation (EC) No 1907/2006 (REACH) a read across approach may be used when substances have similarities based on the likelihood of common breakdown products via physical and biological processes, which result in structurally similar chemicals. As mentioned in the hydrolysis summary, polyphosphoric acid is hydrolysed to orthophosphate in environmental conditions. Thus a read across from orthophosphoric acid to pyrophosphoric acid is justified. In addition, studies performed with pyrophosphate salts can also be used. Pyrophosphate salts are ionic in nature and therefore dissociate readily into cations and anions in water. Cations as potassium and sodium are essential micronutrients that are ubiquitous in the enviroment. As such, their uptake is tightly regulated and is therefore not considered to pose a risk for ecotoxicity. In environmental conditions, the pyrophosphate anion is unstable and a number of different processes result to an ultimate breakdown product of orthophosphate.

The toxicity of orthophosphoric acid to Desmodesmus subspicatus was studied according to OECD TG 201 and GLP requirements (Vryenhoef & Mullee, 2010). In this limit study, green algae were exposed to an aqueous solution of phosphoric acid at 100 mg/L under static test conditions for 72h. The pH was adjusted to neutral (pH 7.5). The choice for doing a limit test was based on a preliminary test in which the algae were exposed to concentrations of 0.1, 1, 10 and 100 mg/L with and without pH adjustment. When the pH was not adjusted, the ErC50 was 75 mg/L and the NOEC=10 mg/L. The pH of the 100 mg/L test solution was 3.0 while the pH of the 10 mg/L test solution was 6.3 -6.4. When the pH was adjusted, the result obtained in the final limit test are: ErC50>100 mg/L and NOEC=100 mg/L, based on nominal concentrations.

As a supporting study, a toxicity test performed on Desmodesmus subspicatus with a pyrophosphate salt (disodium dihydrogenpyrophosphate) has been investigated and gave a ErC50_72h of greater than 100 mg/L (Vryenhoef & Mullee, 2010).