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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

A 72-h EC50 value of >100 mg/l and NOEC of =100 mg/l have been determined for the effects of the test substance on growth rate of Scenedesmus subspicatus. It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

The results from a second reliable test are also available. A 72-h EC50 value of >536 mg/l and NOEC of 322 mg/L were determined in the test.

Key value for chemical safety assessment

Additional information

A 72-h EC50 value of >100 mg/l and NOEC of =100 mg/l have been determined for the effects of the test substance on growth rate of Scenedesmus subspicatus. Test media were prepared by direct addition with stirring for 35 minutes. However in view of the exposure period it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

In a second reliable test, a 72-h EC50 value of >536 mg/l and NOEC of 322 mg/L were determined. In this test, the registration substance would have been fully hydrolysed during preparation of stock solution (which was also filtered prior to the exposure period). There is potential for oligomerisation to have occurred during preparation of the stock, however, high recoveries at the end of the test indicate that precipitation did not occur to a significant extent. At the loading levels corresponding to the NOEC and EC50 the concentration of monomeric silanol should have been stable in the test medium. It is therefore appropriately conservative to derive an indicative PNEC for the silanol hydrolysis product from the second study result for use in chemical safety assessment.

Both of these reliable studies provide useful weight of evidence for the hazard assessment.