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Ecotoxicological information

Toxicity to aquatic algae and cyanobacteria

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Description of key information

Short-term toxicity to algae: 72 hr EC50 >100 mg/l (nominal) (highest concentration tested) (OECD 202), 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

EC10 or NOEC for freshwater algae:
74 mg/L

Additional information

There are no reliable short-term toxicity to algae 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 72-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 growth rate of Pseudokirchneriella subcapitata. In view of the test media preparation method and exposure regime (3 h stirring prior to start of exposure; static exposure regime; pH 7.4 -8.9) 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, dimeric / 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. 

Test data have also been read-across from 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane (CAS 16068-37-3) which has a structurally similar silanol hydrolysis product, 1,1,1,4,4,4-hexahydroxy-1,4-silabutane, to that of the registration substance.  The other hydrolysis product is ethanol. 4,4,7,7-Tetraethoxy-3,8-dioxa-4,7-disiladecane has a slower hydrolysis half-life (36 h at pH 7) than 1,2-bis[dichloro(methyl)silyl]ethane. However, test solution preparation time during the algae test involved 24 hours stirring, as well as static test conditions, therefore the algae would have been exposed to a mixture of parent substance and hydrolysis products. It is therefore considered conservative to read-across from 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane.

A 72-hour E(L)C50 value of >100 mg/l (highest concentration tested) and EC10 of 92.9 mg/l (nominal) have been determined for the effects of 4,4,7,7-tetraethoxy-3,8-dioxa-4,7-disiladecane (CAS 16068-37-3) on growth rate of Pseudokirchneriella subcapitata. In view of the test media preparation method and exposure regime (24 h stirring prior to start of exposure; static exposure regime; pH 7.82 - 8.23) it is likely that the test organisms were exposed to a mixture of the parent substance and the hydrolysis products.

The results may be expressed in terms of concentration of the hydrolysis product, 1,1,1,4,4,4-hexahydroxy-1,4-silabutane, by applying a molecular weight correction: (MW of silanol = 186.27 / MW of parent = 354.59) * EC50 >100 = >53 mg/l, and EC10 92.9 = 49 mg/l. This value is read across to 1,2-bis[dihydroxy(methyl)silyl]ethane without further correction.

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.