3-(dimethoxymethylsilyl)propyl methacrylate

Short-term toxicity to aquatic invertebrates

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), read across from a structurally-related substance, 3-(chlorodimethylsilyl)propyl methacrylate (CAS 24636-31-5), for the effects of the hydrolysis products on mobility of Daphnia magna. The observations in this study are attributed to the exposure of test organisms to hydrolysis products and condensation products in the test system.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

0.573 mg/L

Additional information

There are no reliable data for this endpoint available for the registration substance, therefore good quality data for an appropriate structural analogue, 3-(chlorodimethylsilyl)propyl methacrylate (CAS 24636-31-5), have been read across. Both substances have structurally similar silanol hydrolysis products, 3-[dihydroxy(methyl)silyl]propyl methacrylate and 3-[hydroxy(dimethyl)silyl]propyl methacrylate respectively. The other hydrolysis products are methanol and hydrochloric acid, respectively. In the test with 3-(chlorodimethylsilyl)propyl methacrylate (CAS 24636-31-5), the observations are attributed to the exposure of test organisms to 3-[hydroxy(dimethyl)silyl]propyl methacrylate (monomeric silanol) and 1,1,3,3-tetramethyldisiloxane-1,3-diyl)dipropane-1,3-diyl dimethacrylate (CAS 18547-93-8, EC 242-419-3) (siloxane dimer) in the test system. There is no basis to expect that hydrochloric acid significantly influenced the results of this test. The toxicity of hydrochloric acid and methanol are discussed further in the ecotoxicological information overview endpoint summary (additional information).

A 48 hour EC₅₀ value of 0.573 mg/l has been determined for the effects of the hydrolysis products of the test 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).

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.