Triethoxy(2,4,4-trimethylpentyl)silane

Endpoint summary

Additional information

Reliable short-term toxicity tests results are available for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for the registration substance. The relevant short-term values are:

Fish: LC₅₀ (96-h): >100 mg/l (based on nominal concentrations). Test solution preparation included 24 hours of stirring followed by filtration. It is therefore likely that the test organisms were exposed to a mixture of the parent substance and its hydrolysis products, with the parent substance dominating at the beginning of the test, then the hydrolysis products increasingly dominating with time.

Daphnia: EC₅₀ (48-h): 12 mg/l (unfiltered test solution) and <100 mg/l (filtered test solution) (based on nominal concentrations). Test solution preparation for the unfiltered test solution was less than one hour, therefore it is likely that the organisms were predominantly exposed to the parent substance. Test solution preparation for the filtered test solution included 24 hours of stirring. It is therefore likely that the test organisms were exposed to a mixture of the parent substance and its hydrolysis products, with the parent substance dominating at the beginning of the test, then the hydrolysis products increasingly dominating with time. Effect concentrations exceeded the solubility of parent substance in the test medium: The test substance was not completely soluble and physical effects (surface trapping) were noted in treatments of 3.2 mg/l and higher.

Algae: ErC₅₀ (72-h): >100 mg/l (based on nominal concentrations), >1.2 (based on measured concentrations of parent substance); NOEC: 32 mg/l (based on nominal concentrations), 0.28 mg/l (based on measured concentrations). Test solution preparation included 96 hours of stirring followed by filtration. It is therefore likely that the test organisms were predominantly exposed to the hydrolysis products.

For the fish, Daphnia and algae studies, test solutions were prepared above the limit of water solubility of the parent substance. Undissolved material might have been present in the test solutions as a film on the surface or as hydrolysis resistant micelles of the parent substance and oligomers in the water body. Tests with fish and Daphnia have been conducted in filtered and unfiltered test media. The observations during these tests indicate that higher toxicity is observed in unfiltered test media. Consequently, effects are associated with undissolved test material. However, a filter is not able to effectively retain all undissolved monomers and oligomers, therefore it is possible that the test organisms in all the tests could have been exposed to undissolved material.

Loading rates above 0.1 mg/l are above the water solubility of the substance (<0.1 mg/l).

 

Reliable supporting short-term toxicity tests results are also available for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for the analogous substance triethoxy(octyl)silane (CAS 2943-75-1). These data are read across to support the measured data with the registration substance because they are carried out at the limit of solubility of the test substance and the results are not confounded by the possibility of undissolved test material. The relevant short-term values are:

Fish: LC₅₀ (96-h): >0.055 mg/l (based on nominal concentrations).

Daphnia: EC₅₀ (48-h): >0.049 mg/l (based on nominal concentrations).

Algae: ErC₅₀ (72-h): >0.13 mg/l; NOEC: ≥0.13 mg/l (based on nominal concentrations). 

There are no long-term data for fish with triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3) but results are available from a long-term study with invertebrates (Daphnia magna) where effects were observed in the highest test concentration only (100 mg/l nominal). 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 appropriate 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 filtration processes. 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 in the effect concentration. Instead a long-term study with Daphnia magna has been read across from trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) because both substances share the same silanol hydrolysis product. Effects were seen in the highest test concentration only. Due to the high reactivity of the chlorosilane(hydrolysis half-life <1 minute at pH 7), the no effect concentration was determined by DOC analysis (which would measure both parent and hydrolysis products). This resulted in a measured NOEC of 32 mg/l. The test organisms would have been exposed to the hydrolysis products of the substance, (2,4,4-trimethylpentyl)silanetriol and hydrochloric acid.

A NOEC is also available for algae (Pseudokirchneriella subcapitata) but with the same problems as reported in the long-term test with Daphnia. As minor effects were only seen in the highest concentration and this concentration was based on both loading rate and analytical data of the parent substance above the water solubility limit this NOEC should not be used for risk assessment purposes. This is supported by an algae test with the read across substance triethoxy(octyl)silane (CAS 2943-75-1) that determined the NOEC to be greater than the water solubility limit.

The long-term values relevant for risk assessment are:

Invertebrate: NOEC (21-d): 32 mg/l.

Algae: NOEC (72-h): Non-toxic at solubility limit.

There is no evidence from the results of the short-term tests that fish would be expected to be more susceptible to the substance than invertebrates or algae. Therefore, an assessment factor of 50 is applied to the NOEC obtained in the long-term invertebrate test.

Therefore, PNEC_{aqua(freshwater)} is 32/50 = 0.64 mg/l.

Currently, the available chronic data reflect exposure of the test organisms to the hydrolysis products of the registration substance. Consequently, in order to assess the toxicity of the parent substance, long-term aquatic toxicity tests are being conducted in accordance with ECHA Final Decision TPE-D-2114455990-41-01/F. The OECD TG 210 Fish, Early Life-Stage Toxicity test and the OECD TG 211 Daphnia Reproduction test are ongoing. The substance dataset and risk assessment will be updated once results of the chronic studies are available and the studies are finalised. An update is planned to be completed within three months from when the last final report is received. The draft reports are expected in January/February 2021, with the final reports following in March/April 2021.

An activated sludge respiration inhibition 3-hour EC₅₀ value of >100 mg/l (nominal) was determined in a reliable study.

Refer to the IUCLID Section 6 endpoint summary or CSR Section 7.0 for further discussion of the approach to chemical safety assessment and justification for read across.