Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Reliable short-term toxicity tests results are available for freshwater invertebrates (Daphnia magna) (based on read-across from a test with a structural analogue, in which test organisms were exposed to a combination of the registration substance and to the common hydrolysis product of both the source and target substance, formed under the study conditions) and algae (Pseudokirchneriella subcapitata) (based on a test conducted with the registration substance). The relevant short-term values are:

Daphnia: EC50 (48 h): 0.573 mg/l (expressed in terms of geometric mean measured concentration of the hydrolysis products, sum of 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))

Algae: EC50 (72 h): >11 mg/l; ErC10 >11 mg/l  (expressed in terms of geometric mean measured concentration of test material).

With regard to the invertebrate study, the very rapid hydrolysis of the test substance (24636-31-5) (half-life <5 min at pH 7 and 20-25 °C) is consistent with the analytical evidence that the test organisms in each test were exposed primarily to the hydrolysis products, 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 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 (which is the subject of this registration). 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.

With regard to the algal study, undissolved test material is thought to have been present, and as such the test result is interpreted to indicate lack of effects up to the limit of solubility.

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