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Toxicity to aquatic algae and cyanobacteria

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Description of key information

Short-term toxicity to algae: 72-h EC50 >89 mg/l and NOEC of >=89 mg/l (measured) (highest concentration tested) (Circular on Test Methods of New Chemical Substances (Japan), Alga growth inhibition test), read-across from an analogous substance, trimethoxy(vinyl)silane (CAS 2768-02-7). The EC50 is equivalent to 64 mg/l when expressed in terms of the silanol hydrolysis product. This result is considered in weight of evidence together with a 7 day EC50 value of 210 mg/l and NOEC of ca. 25 mg/l (nominal) (US EPA 67014-73-0) read-across from an analogous substance, trimethoxy(vinyl)silane (CAS 2768-02-7). The EC50 is equivalent to 150 mg/l when expressed in terms of the silanol hydrolysis product

Key value for chemical safety assessment

Additional information

There are no reliable toxicity to algae data available for tris(isopropenyloxy)(vinyl)silane (CAS 15332-99-7), therefore good quality data for an appropriate structural analogue, trimethoxyvinylsilane (CAS 2768-02-7), have been read across.

Both substances share the same silanol hydrolysis product, vinylsilanetriol. The other hydrolysis products are propen-2-ol/acetone and methanol, respectively.

A 72-h EC50 value of >89 mg/l and NOEC of >=89 mg/l (measured, time weighted mean concentration) (highest concentration tested) have been determined for the effects of trimethyl(vinyl)silane (CAS 2768-02-7) on growth rate of Pseudokirchneriella subcapitata (MoE 2006b).

In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, vinylsilanetriol, by applying a molecular weight correction: (MW of silanol = 106.15 / MW of parent = 148.24) * >89 = >64 mg/l as vinylsilanetriol.

This result is considered as weight of evidence together with a 7 day EC50 value of 210 mg/l and NOEC of ca. 25 mg/l (nominal concentration) determined for the effects of trimethyl(vinyl)silane (CAS 2768-02-7) on final yield of Pseudokirchneriella subcapitata (Dow Corning Corporation 1979). In view of the test media preparation method/exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance. The results may be expressed in terms of concentration of the hydrolysis product, vinylsilanetriol, by applying a molecular weight correction: (MW of silanol = 106.15 / MW of parent = 148.24) * 210 = 150 mg/l as vinylsilanetriol.

OECD 201 guidelines state that algal growth has to be exponential throughout the test period. Exponential growth may be more difficult to maintain during a 7 day test compared to a standard 72 hour test. The study report for this test gives little raw data but does show a graph of cell concentration over time. It is not possible to definitively determine whether exponential growth was maintained throughout the test, as the graph shows that there is a possible slight levelling off of growth between days 4 and 7.

The result from this test may therefore be considered as a conservative value because it cannot be definitely stated that the algae was in exponential growth phase throughout the whole of the test.

A limit test result was determined in the Ministry of Environment test, representing the lowest EC50 seen in a standard-duration study. A definitive EC50 value was determined in the Dow Corning study.

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

References:

Dow Corning Corporation (1979). Acute static toxicity of Dow Corning Q9-6300 Silane to Daphnia, Bluegill, Rainbow trout and two species of algae. Testing laboratory: Dow Corning Biological Services Department, Dow Corning Corporation. Owner company: Dow Corning. Study number: TX-1636. Report date: 1979-12-21.

Ministry of the Environment, Government of Japan (2006b). Alga, growth inhibition test in Pseudokirchneriella subcapitata by silane, ethenyltrimethoxy-. Mitsubishi Chemical Safety Institute Ltd., Yokohama Laboratory, Yokohama, Japan. Study reference no. A050111. Study owner Ministry of the Environment, Government of Japan. Report date 2006-05-24.