Registration Dossier

Ecotoxicological information

Endpoint summary

Administrative data

Description of key information

Additional information

Reliable short-term toxicity data are available for the toxicity of the registered substance to freshwater fish, invertebrates and algae showing no effects at the limit of solubility.

 

A 96-hour LC50 value of >0.055 mg/l has been determined for the effects of the registered substance on mortality of Oncorhynchus mykiss under flow-through test conditions. The result is expressed as mean measured concentration of the substance over the test period.

 

A 48-hour EC50 value of >0.049 mg/l has been determined for the effects of the registered substance on mobility of Daphnia magna under flow-through test conditions. The result is expressed as mean measured concentration of the substance over the test period.

 

A 72-hour EC50 value of >0.13 mg/l and NOEC value of ≥0.13 mg/l have been determined for the effects of the registered substance on growth rate of Pseudokirchneriella subcapitata. The results are expressed relative to nominal test substance concentration because measured concentrations had declined to below the limit of quantification after 24 hours. The test substance is subject to hydrolysis and it is therefore likely that, under the static test conditions, the test organisms were exposed to the hydrolysis products of the substance.

 

Reliable long-term toxicity data are available for the toxicity of the registered substance to freshwater invertebrates.

A 21-day EC10 value of 0.25 mg/l and NOEC value of 0.25 mg/l have been determined for the effects of triethoxy(octyl)silane (CAS 2943-75-1) on reproduction of Daphnia magna based on nominal concentrations. The EC10 and NOEC values are 0.189 mg/l and 0.199 mg/l, respectively, based on geometric mean measured concentrations. The test was designed to maximise exposure to the parent test substance, although hydrolysis was observed. The test organisms were predominantly exposed to the parent test substance.

A Fish, Early Life Stage (FELS) toxicity test is currently ongoing with the registration substance. The final report is expected in July 2020.

 

Data are also available with triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3), which is a structural analogue in terms of parent compound and silanol hydrolysis product to the registered substance (i.e. a branched rather than linear octyl side chain).

Short-term toxicity data are available with fish, invertebrates and algae presenting L(E)L50 values of >100, <100 mg/l, >100 mg/l respectively. A NOELR of 32 mg/l and a NOEC of 0.28 mg/l based on mean measured concentration were also determined in the algal study.

 

A 21-day long-term toxicity study with Daphnia magna is also available with triethoxy(2,4,4-trimethylpentyl)silane, in which a NOEC value of 32 mg/l based on nominal, and 0.058 mg/l based on measured concentration of the parent test substance triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3), were determined. The study was conducted at a concentration 25 fold higher than the limit of solubility of the substance. However, the length of the test media preparation (96 h), suggests that the organisms were exposed to high concentrations of the hydrolysis product from the start of the study. The solution was not analysed for concentration of hydrolysis product and it is not possible to determine whether the observed effects are due to the parent compound, the hydrolysis product or the presence of undissolved test material. The results of the study should be treated with caution.

 

Long-term toxicity data for aquatic invertebrates are available for trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4), which hydrolyses very rapidly to (2,4,4-trimethylpentyl)silanetriol, a structural analogue of the hydrolysis product of the registered substance. A 21 day NOEC value of 32 mg/l (measured TOC) and a LOEC of 65 mg/l (measured) have been determined for the effects of the test substance on mortality of Daphnia magna. No effects on reproduction were determined in test concentrations below the LOEC for mortality. The report authors note that it cannot be excluded that the effects of the test item were at least partly caused by undissolved test item, which could not be removed by the preparation method used during the test period. However, given the high NOEC value derived, the study confirms the low toxicity of the hydrolysis product and forms the basis for indicative PNECaquatic for use in equilibrium partitioning calculations for assessment of the sediment and soil compartments.