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Short-term toxicity to fish

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Description of key information

Short-term toxicity to fish: 96 hr EC50 >100 mg/l (nominal) (highest concentration tested) (OECD 203), read-across from a structurally related substance, 1,6-bis(trimethoxysilyl)hexane (CAS 87135-01-1). The observations in this study are attributed to the exposure of test organisms to the hydrolysis products in the test system. The EC50 is equivalent to >74 mg/l when expressed in terms of the silanol hydrolysis product.

Key value for chemical safety assessment

Additional information

There are no reliable short-term toxicity to fish data available for 1,2-bis[dichloro(methyl)silyl]ethane (CAS 3353-69-3), therefore good quality data for an appropriate structural analogue,1,6-bis(trimethoxysilyl)hexane (CAS 87135-01-1), have been read across. Both substances have structurally similar silanol hydrolysis products, 1,2-bis[dihydroxy(methyl)silyl]ethane and 1,6-bis(trihydroxysilyl)hexane respectively. The other hydrolysis products are hydrogen chloride and methanol, respectively. In the test with 1,6-bis(trimethoxysilyl)hexane, the observations are attributed to the exposure of test organisms to 1,6-bis(trihydroxysilyl)hexane in the test system. There is no basis to expect that methanol significantly influenced the results of the test. The toxicity of methanol is discussed further in the ecotoxicological information overview endpoint summary (additional information).

 

A 96-hour E(L)C50 value of >100 mg/l and NOEC of ≥100 mg/l (nominal) (highest concentration tested) have been determined for the effects of 1,6-bis(trimethoxysilyl)hexane (CAS 87135-01-1) on mortality of Oncorhynchus mykiss. In view of the test media preparation method and exposure regime (3 h stirring prior to start of exposure; static exposure regime; pH 7.9 -8.4) it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance, although a low proportion of parent substance may have been present at the beginning of the exposure period.

 

The results may be expressed in terms of concentration of the hydrolysis product, 1,6-bis(trihydroxysilyl)hexane, by applying a molecular weight correction: (MW of silanol = 242.38 / MW of parent = 326.54) * >100 = >74 mg/l. This value is read across to 1,2-bis[dihydroxy(methyl)silyl]ethane without further correction.

 

Above a concentration of approximately 1000 mg/l, oligomeric, cyclic or cross-linked condensation products could potentially form over time in the aqueous test media. No evidence of undissolved material (parent substance or precipitated products) is indicated in the study report for this test. 

Short-term toxicity to fish data are available with 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane (CAS 16068-37-3). Its silanol hydrolysis product is structurally similar to the silanol hydrolysis product of the registration substance. However, this data has not been used to read across to 1,2-bis[dichloro(methyl)silyl]ethane due to the significantly longer hydrolysis half-life of 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane. The short test solution preparation time and semi-static conditions of the fish test with 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane meant the organisms were predominantly exposed to the parent substance. In addition, the observation made during this test, of undissolved test material in the test solution makes the reliability of this test uncertain. It would therefore be considered too conservative to read-across the results of this test as the chemical safety assessment focuses on the silanol hydrolysis product of the registration substance.

 

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.

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