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A 48-h EC50value of >100 mg/l has been determined for the effects of the test substance on mobility of Daphnia magna.It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

There are no short-term data for fish and aquatic algae with the registered substance. However data are available for astructurally-analogous substances,dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) and (3-chloropropyl)diethoxymethylsilane (CAS 13501-76-3). A 96-h LC50value of >107 mg/l has been determined for effects on mortality of Cyprinus carpio withdichloro(3-chloropropyl)methylsilane and a 72-hour EC50value of 437 mg/l and NOEC of approximately 57 mg/l have been determined for effects on growth rate of Desmodesmus subspicatus (tested as Scenedesmus subspicatus) with (3-chloropropyl)diethoxymethylsilane.

Read-across justification:

(3-chloropropyl)dimethoxymethylsilane and the substances used as surrogates for read-across are part of a class of compounds which act via a non-polar narcosis mechanism of toxicity. Substances in this group include alkoxy- and chloro- silanes having secondary features that do not affect the toxicity of the substances. The registered substance hydrolyses rapidly in water and therefore the selection of surrogate substance is based on the silanol hydrolysis products, their log Kowas well as the groups present on the side chains.

Dichloro(3-chloropropyl)methylsilane is a dichlorosilane with a chloropropyl side chain that will hydrolyse to (3-chloropropyl)methylsilanediol very rapidly (<1 min, at pH 7 and 25C, read-across).(3-chloropropyl)diethoxymethylsilane and (3-chloropropyl)dimethoxysilane are dialkoxysilanes with an alkyl side chain. While there is some uncertainty about the hydrolysis half-life of the structurally analogous substance, (3-chloropropyl)diethoxymethylsilane, the available ecotoxicological data suggests that the hydrolysis rate is <12 hours.Namely, the amount of DOC present at the start of the studies in relation to the water solubility of the parent substance and the hydrolysis product (36 and 6000 mg/l respectively),the length of the test media preparation (stirring for 18 hours) and the study regimes (static and semi-static),indicate that the substance present in solution was the hydrolysis product, chloropropyl(methyl)silanediol..Therefore the assessment of (3-chloropropyl)dimethoxymethylsilane (CAS 18171-19-2), dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1) and (3-chloropropyl)diethoxymethylsilane (CAS 13501-76-3) will consider exposure to hydrolysis product (3-chloropropyl)methylsilanediol under the conditions of the ecotoxicity test. The other hydrolysis products are methanol, hydrochloric acid and ethanol, respectively. Methanol and ethanol are non-toxic to the environment at the concentrations relevant to this assessment and it is considered unlikely that their presence would significantly affect the results of ecotoxicity tests. The effects of hydrochloric acid are restricted the effects of pH and further consideration is given below.

Effects on aquatic organisms arising from exposure to hydrochloric acid are thought to result from a reduction in the pH of the ambient environment (arising from an increase in the H+concentration) to a level below their tolerable range. The studies with the substance used as surrogate do not seem to have affected the outcome of the study as the pH of the studies were in the tolerable range.

It is considered appropriate to read-across fromdichloro(3-chloropropyl)methylsilane (CAS 7787-93-1)and (3-chloropropyl)diethoxymethylsilane (CAS 13501-76-3) to (3-chloropropyl)dimethoxymethylsilane (CAS 18171-19-2).Additional information is given in a supporting report <REFERENCE IN PROGRESS> attached in Section 13 of the IUCLID 5 dossier.

The short-term aquatic toxicity studies for dichloro(3-chloropropyl)methylsilane (CAS 7787-93-1)and (3-chloropropyl)diethoxymethylsilaneused stock solutions at a concentration of 1000 mg/l. At this concentration the silanol hydrolysis product (which is formed in significant quantities over the time-scale of the media preparation) can undergo condensation reactions to give siloxane and siloxanol dimers, oligomers and polymers.

The stock solutions used for the test medium were filtered and no condensation products were reported and after filtration, the measured DOC (dissolved oxygen concentrations) were within 20% of the nominal concentration. However polymerisation products, such as oligomers, could still be present in the stock solution as filtration is limited to solid, high viscous particles. It is considered reasonable to assume that the concentrations corresponding to theLC50or EC50values predominantly represent the concentration of the test substance’s hydrolysis product (and not the polymer).

While the stock solution preparation was not carried out under ideal conditions for this substance, the studies do indicate that the registered substance is of low short-term toxicity to the tested organisms.