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Short-term toxicity to aquatic invertebrates

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Description of key information

Short-term toxicity to invertebrates: 48 hour EC50: 0.573 mg/l (geometric mean measured concentrations of identified hydrolysis products and condensation products) (OECD TG 202) for the effects of the hydrolysis products on mobility of Daphnia magna, read-across from a test carried out with an analogous/structurally related substance, 3-[chloro(dimethyl)silyl]propyl methacrylate (CAS 24636-31-5). The observations in this study are attributed to the exposure of test organisms to hydrolysis products (3-[hydroxy(dimethyl)silyl]propyl methacrylate) and condensation products (particularly the disiloxane condensation product, 1,1,3,3-tetramethyldisiloxane-1,3-diyl)dipropane-1,3-diyl dimethacrylate), in the test system. This dimeric siloxane is the registration substance.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
0.573 mg/L

Additional information

A 48 hour EC50 value of 0.573 mg/l has been determined for the effects of the hydrolysis products of the tested substance on mobility of Daphnia magna, based on geometric mean measured concentrations and in compliance with OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test).

In view of the test media preparation method, pH adjustment and exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products (monomeric silanol) and both dissolved and undissolved condensation products (siloxane dimer) of the tested substance. The study was supported by analysis of these hydrolysis products which demonstrates the complete hydrolysis of the chlorosilane group and shows that under the conditions of the test a high proportion of the hydrolysis products are present in the form of dimeric siloxane (at a concentration well in excess of its predicted limit of solubility). This dimeric siloxane is the registration substance (target substance).

It is to be expected that at higher concentrations, dimeric siloxane condensation products can form from aqueous solutions of the monomeric silanol. There is some evidence of undissolved material (precipitated products) in the study report for this test, and therefore physical effects may have contributed to some extent to the mobility effects in the test. The use of the E(L)C50 value as a measurement of intrinsic toxicity represents a conservative interpretation of the test findings.