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Toxicity to microorganisms

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Description of key information

EC50 (3h) > 1000 mg/L and NOEC (3h) ≥ 1000 mg/L (OECD 209), RA

Key value for chemical safety assessment

Additional information

Since no studies investigating the toxicity to microorganisms of Silicon orthophosphate (CAS No. 12037-47-7) are available for this endpoint, in accordance to Regulation (EC) No. 1907/2006 Annex XI, 1.5 Grouping of substances and read-across, a read-across was conducted based on the products of dissociation. The read across is explained within the read across justification in section 13.

Silicon orthophosphate (CAS No. 12037-47-7) is readily soluble in water, dissociating into silicon and phosphate ions. Consequently, the chemical assessment is based on the products of dissociation. The substances which were chosen for the read across approach yield the same ions as the target substance (either ionic silicon or ionic orthophosphate) when dissolved in water. Data from dipotassium hydrogenorthophosphate (CAS: 7758 -11 -4) are used to cover the toxicity to algae of the phosphate moiety of the substance. Dipotassium hydrogenorthophosphate (CAS: 7758 -11 -4) was tested in a GLP study according to OECD guideline 209 using predominantly domestic activated sludge as inoculum (Clarke, 2010). After a contact time of 3 h, no inhibition of microbial respiration occurred up to 1000 mg/L which was the highest test concentration. Therefore, an EC50 (3h) > 1000 mg/L and a NOEC ≥ 1000 mg/L was stated.

No data are available for the silicon moiety. However, based on the absence of aquatic toxicity of synthetic amorphous silica and silicates in general, and since silicon dioxide is known to be utilized by aquatic organisms such as diatoms, radiolarians and silicoflagellates and thus beeing a part of the environment, the absence of toxicity for activated sludge in sewage treatment plants can be safely assumed. This assumption is supported by public assessments for synthetic amorphous silica and silicates, such as: OECD (2004).SIDS Synthetic amorphous silica and silicates.

Furthermore with regard on the given uses within this dossier there is no emission to a sewage treatment plant to be expected.