Potassium methylsilanetriolate

Endpoint summary

Additional information

A 48-hour EC₅₀ value of >100 mg/l and NOEC of <10 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna. In solution, potassium methylsilanetriolate is fully dissociated to potassium and methylsilanetriolate. At lower pH (pH ≤9) methylsilanetriol is formed from methylsilanetriolate. Therefore it is likely that the test organisms were primarily exposed to methylsilanetriol.

There are no test data for short-term toxicity to fish and toxicity to algae and cyanobacteria, and there is uncertainty in the interpretation of the short-term invertebrate data. However a 96-hour LC₅₀ value of >500 mg/l and NOEC of ≥500 mg/l have been determined for the effects of a read-across substance, triethoxy(methyl)silane (CAS 2031-67-6), on mortality of Brachydanio rerio, and a 48 -hour EC₅₀ value of >500 mg/l and NOEC of >=500 mg/l for the same substance in Daphnia magna.

The results may be expressed in terms of concentration of the hydrolysis product, methylsilanetriol, by applying a molecular weight correction, therefore the E(L)C₅₀ for both the fish and invertebrate tests is >264 mg/l as methylsilanetriol.

Similarly, a 72-hour EC₅₀ value of >120 mg/l and NOEC of ≥120 mg/l have been determined for the effects of a read-across substance, trimethoxy(methyl)silane (CAS 1185-55-3), on growth rate of Pseudokirchneriella subcapitata. It is likely that in both cases the test organisms were primarily exposed to the hydrolysis products of the substance.

The results may be expressed in terms of concentration of the hydrolysis product, methylsilanetriol, by applying a molecular weight correction, therefore the EC₅₀ for the algal test is >83 mg/l as methylsilanetriol.

There are no long-term studies in fish or invertebrates for the registered substance. A reliable study with a suitable read-across substance (trichloro(ethyl)silane, CAS 115-21-9) is available. A 21-day NOEC value of ≥100 mg/l has been determined for the effects of the test substance on survival and reproduction of Daphnia magna when expressed in terms of nominal concentrations. When expressed in terms of mean measured TOC concentration in the test medium the NOEC was ≥10 mg/l. It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance. When expressed in terms of the silanol hydrolysis product, by correcting for molecular weight, the 21-day NOEC value is ≥45 mg/l as ethylsilanetriol.

All ecotoxicity data are interpreted and discussed in terms of concentrations of potassium methylsilanetriolate or its silanol products. Water present in the registration substance is not taken into account in loading rates. Under dilute conditions at neutral pH and ambient temperature, the substance is predominantly in the form of monomeric silanol and the approach to completing the registration data set takes this into account.