Triethoxy(2,4,4-trimethylpentyl)silane

Toxicity to aquatic algae and cyanobacteria

Description of key information

A 72-h EC₅₀ of >1.2 mg/l and a NOEC of 0.28 mg/l have been determined for the effects of the test substance on growth rate and biomass of Pseudokirchneriella subcapitata based on initial measured concentrations, in accordance with test guideline OECD 201. However loading rates above 0.1 mg/l are above the limit of solubility of the substance (<0.1 mg/l) and it cannot be excluded that undissolved test material was present. The results are considered to be > limit of solubility.

Additional information

A 72-h EC₅₀ of >1.2 mg/l and a NOEC of 0.28 mg/L have been determined for the effects of the test substance on growth rate and biomass of Pseudokirchneriella subcapitata based on initial measured concentrations. A 72-h NOELR of 32 mg/l and LOELR of 100 mg/l have been determined for the effects of the test substance on growth rate and biomass (yield) of Pseudokirchneriella subcapitata based on nominal concentrations. Loading rates above 0.1 mg/l are above the water solubility of the substance (<0.1 mg/l).

Based on the hydrolysis half-life of the test substance (43 hours at pH 7 and 20-25°C, predicted), and the 96 hour preparation of the test stock solution, it is likely that in the absence of undissolved material the organisms would be exposed mainly to the hydrolysis products of the test substance. Undissolved material might have been present in the test solutions as film on the surface or as hydrolysis resistant micelles of the parent substance and oligomers in the water body. The observations during the tests with fish, Daphnia and algae indicate that the dosage of the test item and the filtration step are hypersensitive parameters for the occurrence of undissolved material. A filter is not able to retain effectively undissolved monomers and oligomers. Therefore the results should be treated with caution.

The results are supported by a reliable study with the read-across substance triethoxyoctylsilane. A 72-h EC₅₀ of >0.13 mg/l and a NOEC of ≥0.13 mg/l have been determined for the effects of the test substance on growth rate and biomass (yield) of Pseudokirchneriella subcapitata. Based on the hydrolysis half-life of the test substance (30 hours, predicted), it is likely that the test organisms were exposed to a mixture of the parent and its hydrolysis products.

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.