Triethoxy(2,4,4-trimethylpentyl)silane

Short-term toxicity to aquatic invertebrates

Description of key information

A 48-h EL₅₀ of <100 mg/l (highest concentration tested, with filtering of the test substance) has been determined for the effects of the test substance on mortality of Daphnia magna based on nominal concentrations, in accordance with test guideline OECD 202. In a parallel test, a 48 hr EL₅₀ of 12 mg/l and a NOEC of 3.2 mg/l (without filtering of the test substance) have been determined for the effects of the test substance on mortality of Daphnia magna based on nominal concentrations and in accordance with test guideline OECD 202.

Additional information

A 48-h EL₅₀ of <100 mg/l has been determined for effects of the test substance based on mortality of Daphnia magna.

The organisms were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. The test result is considered to be reliable. Exposure to unfiltered test medium gave a 48-h EL₅₀ of 12 mg/l and a NOELR of 3.2 mg/l. The loading rates used were all above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number, with exposure to a 100 mg/l test medium that had been filtered, gave a similar result to that reported in this study (48-h EL₅₀ <100 mg/l).

Based on the hydrolysis half-life of the test substance (43 hours at pH 7 and 20-25°C, predicted), it is likely that in the absence of undissolved material the organisms would be mainly exposed to a mixture of the parent and the hydrolysis products. 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.

The results are supported by a reliable study with the read-across substance triethoxyoctylsilane (CAS 2943-75-1). The test substance did not achieve any toxicity when tested at the solubility limit of the substance i.e. the EC₅₀ value was >0.13 mg a.i./l and the NOEC value was ≥0.13 mg a.i./l (nominal concentration). Based on the hydrolysis half-life of the test substance (30-h, predicted), it is likely that the organisms were exposed to a mixture of the parent and 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.