Triethoxy(2,4,4-trimethylpentyl)silane

Long-term toxicity to aquatic invertebrates

Description of key information

A 21-d NOEC of 32 mg/l has been determined for the effects of read-across substance trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) on the mortality of Daphnia magna.

Key value for chemical safety assessment

EC10, LC10 or NOEC for freshwater invertebrates:

32 mg/L

Additional information

A 21-d No Observable Effect Loading Rate (NOELR) of 32 mg/l and Lowest Observable Effect Loading Rate (LOELR) of 100 mg/l have been determined for the effects of the test substance on reproduction of Daphnia magna. A NOELR value result has been used in this instance because the loading rate of the test substance in the test solution was well above the test substance solubility. The NOELR refers to the point at which no effects were observed in relation to the amount of test substance put into the test solution, rather than the actual concentration of the test substance in the test solution, where a NOEC value would be used instead. A NOEC of 0.058 mg/l was defined on the basis of measurements of the parent substance in the no effect concentration. However it is not indicative to use this value for risk assessment purposes as (i) the concentration of the equally relevant hydrolysis products were not considered by the analytical method and did therefore not contribute to the measured value of the no effect concentration, (ii) the effect concentration was clearly above the water solubility limit (< 0.1 mg/l) of the parent substance in terms of nominal (100 mg/l) and measured (376 µg/l) values and it is not expected that the undissolved substance could easily be hydrolysed or be removed by a filtration processes (see discussion in short-term toxicity to invertebrates data). Based on the available data it is therefore not possible to (i) quantify a reasonable no effect concentration (NOEC) for the silane and its hydrolysis products and (ii) to separate physical from systemic effects at the effect concentration. Instead a long-term study with Daphnia magna from trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) is used to derive the hazard assessment, as its silanol hydrolysis product is the same as that of the registration substance. Effects were seen in the highest concentration only. Due to the high reactivity of the chlorosilane the no effect concentration was determined as the sum of the parent substance and its hydrolysis products by DOC analysis. This resulted in a measured NOEC of 32 mg/l.

While the data are considered to be sufficient to derive a reliable hazard assessment for the silanol hydrolysis product of the registered substance, a long-term toxicity test with Daphnia magna has been proposed with the analogous substance triethoxyoctylsilane (CAS 2943-75-1). The study proposal is being read-across to the registered substance to determine effects of the parent substance.

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.