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Short-term toxicity to aquatic invertebrates

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Description of key information

EL50 (48 h): <1 mg/l (nominal) based on: mobility of Daphnia magna. Evidence of physical fouling was seen in the test at both loading levels and therefore effects seen are attributed to physical effects caused by undissolved test substance or precipitated by-products.

Key value for chemical safety assessment

Additional information

A 48-h EL50 value of <1 mg/l and NOELR of <1 mg/l have been determined for effects on mobility of Daphnia magna. Under the test conditions a proportion of the test substance would have hydrolysed. It is likely that the observed effects on the test organisms resulted, at least in part, from exposure to undissolved test material or precipitate, even though steps were taken to avoid this in the test procedure. The results of this test were selected as key in preference to those of a second test of equal reliability, because they gave a more conservative 48-h EL50.

A 48-hour EL50 value of >10 mg/L and NOELR of ≥10 mg/L have been determined for the effects of CAS 211519-85 -6 on mobility of Daphnia magna. It is likely that, because of the prolonged test medium preparation phase, the test organisms were exposed to the hydrolysis products of the substance. The test substance is a multiconstituent reaction mass of 4,4,15,15-tetraethoxy-3,16-dioxa-8,9,10,11-tetrathia-4,15-disilaoctadecane and 4,4,14,14-tetraethoxy-3,15-dioxa-8,9,10-trithia-4,14-disilaheptadecane and 4,4,13,13-tetraethoxy-3,14-dioxa-8,9-dithia-4,13-disilahexadecane. One constituent is the submission substance (CAS 56706-10-6) and all constituents are structurally very similar, therefore, it is valid to read-across the results of this test to the hydrolysis product of CAS 56706-10-6.

Based on the test media preparation methods and exposure regime, it is likely that the organisms would have been exposed to a mixture of the monomeric silanol hydrolysis product and siloxane oligomers. Insoluble oligomers may have precipitated out of solution to an extent during the media preparation and in the course of the test. The test results have been interpreted in this context. This is reflected in the observation of turbidity in test media, although no analytical verification was performed.

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