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Ecotoxicological information

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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; NOEC: ≥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 hydrolysis products, with the parent substance dominating at the beginning of the test, then the hydrolysis products increasingly dominating from halfway through.

 

Daphnia: EC50 (48-h): 12 mg/l (unfiltered test solution) and <100 mg/l (filtered test solution); NOEC: 3.2 mg/l (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 hydrolysis products, with the parent substance dominating at the beginning of the test, then the hydrolysis products increasingly dominating from halfway through. Effect concentrations exceeded the solubility of 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); 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.

 

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. 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.

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

 

 

Reliable short-term toxicity tests results are also available for freshwater fish (Oncorhynchus mykiss), invertebrates (Daphnia magna) and algae (Pseudokirchneriella subcapitata) for the read-across substance triethoxyoctylsilane (CAS 2943-75-1). The relevant short-term values are:

 

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

Daphnia: EC50 (48-h): >0.049 mg/l; NOEC:≥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 but results are available from a long-term study with invertebrates (Daphnia magna) with effects in the highest 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 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. 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 D. magna from trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) was used as the hydrolysis products are the same. Effects were also 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.

 

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 triethoxyoctylsilane (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, PNECaqua(freshwater) is 32/50 = 0.64 mg/l.

Long-term testing on aquatic invertebrates has been proposed for the analogous substance triethoxyoctylsilane (CAS 2943-75-1). The test proposal has been read-across to this substance. The approach to PNEC derivation may be reviewed once these data have been read-across, and therefore the PNEC is subject to change.

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

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