Triethoxy(2,4,4-trimethylpentyl)silane

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Remarks:

Guideline study with acceptable restrictions. The study was conducted according to an appropriate OECD test guideline. It was not compliant with GLP.

Reason / purpose for cross-reference:

reference to other study

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

Deviations:

no

GLP compliance:

no

Analytical monitoring:

no

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A water-soluble fraction of the test substance was prepared by adding 100 mg/l of the substance to dilution water and stirring for 24 hours. The medium was then filtered (0.45 μm cellulose nitrate) and the filtrate used as the test medium.

- Controls: Dilution water

- Evidence of undissolved material: In a previous test conducted under GLP it was observed that undissolved test material was present at a loading rate of 100 mg/l and it was suspected that this may have been responsible for mortality observed in the test.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Common name: Rainbow trout

- Source: Forellenhof, Fredelsloh, Germany

- Length at study initiation (length definition, mean, range and SD): 5.3 +/-0.3 cm

- Weight at study initiation (mean and range, SD): 1.7 +/-0.4 g

- Feeding during test: none

ACCLIMATION

- Acclimation period: >5 weeks

- Acclimation conditions (same as test or not): yes

- Type and amount of food: Tetra Min, TETRA-Werke, Melle, Germany

- Feeding frequency: not reported

- Health during acclimation (any mortality observed): <3% mortality in the 5 weeks prior to the test

Test type:

semi-static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

250 mg/l as CaCO3

Test temperature:

14-16ºC

pH:

7.6-8.1

Dissolved oxygen:

≥8.2 mg/l

Salinity:

not applicable

Nominal and measured concentrations:

Nominal loading rates: 0(Control) and 100 mg/l.

Details on test conditions:

TEST SYSTEM

- Test vessel: Aquaria

- Type: open

- Material, size, headspace, fill volume: 20 litre with 15 litre test medium volume

- Aeration: yes

- Renewal rate of test solution (frequency/flow rate): Daily

- No. of organisms per vessel: 7

- No. of vessels per concentration (replicates): 1

- No. of vessels per control (replicates): 1

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted freshwater was prepared by adding analytical grade salts to deionised water.

- Alkalinity: 0.8 mmol/l

- Ca/Mg ratio: 4:1

- Culture medium different from test medium: no

- Intervals of water quality measurement: Daily

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 h light, 8 h dark

- Light intensity: 480-510 lux

EFFECT PARAMETERS MEASURED: mortality after 2, 24, 48, 72 and 96 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: limit test

Reference substance (positive control):

no

Key result

Duration:

96 h

Dose descriptor:

LL50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Key result

Duration:

96 h

Dose descriptor:

NOELR

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

- Mortality of control: 0

Reported statistics and error estimates:

Not applicable

Sublethal observations / clinical signs:

No toxic effects were observed in the only tested loading rate of 100 mg/l.

Validity criteria fulfilled:

yes

Conclusions:

A 96-h LL50 >100 mg/L, and NOELR >= 100 mg/l, have been determined for the test substance based on mortality of Oncorhynchus mykiss. The fish were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. The loading rate of 100 mg/l was far above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number but with unfiltered test media resulted in mortalities of the test substance that were attributed to the effects of the undissolved test substance. A parallel exposure to a 100 mg/l test medium that had been filtered gave a similar result to that reported in this study (96-h LL50 >100 mg/l). Based on the hydrolysis half-life of the test substance (approx. 22 hours, predicted), it is likely that the organisms were exposed mainly to the hydrolysis products.

Description of key information

96-hour LL₅₀ >100 mg/l (nominal concentration) (highest concentration tested), mortality of Oncorhynchus mykiss.

Additional information

A 96-hour LL₅₀ value of >100 mg/l has been determined for effects of the test substance on mortality of Oncorhynchus mykiss, conducted in accordance with OECD TG 203 but not in compliance with GLP (IBACON, 2001a). The fish were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. The loading rate of 100 mg/l was far above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number but with unfiltered test media resulted in mortalities of the test organisms that were attributed to the effects of the undissolved test substance. A parallel exposure to a 100 mg/l test medium that had been filtered gave a similar result to that reported in this study (96-hour LL₅₀ >100 mg/l) (IBACON, 2001b).

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 could be exposed to a mixture of the parent substance and the hydrolysis products. 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. The tests with fish have been conducted in filtered and unfiltered test media. The observations during these tests indicate that toxicity is observed in unfiltered test media only. 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 the tests with filtered test media could have been exposed to lower amounts of undissolved material.

The results are supported by a reliable study with the read-across substance triethoxy(octyl)silane (CAS 2943-75-1), which is a structural analogue of the registration substance. The test substance did not achieve any toxicity when tested at the solubility limit of the substance; the 96-hour LC₅₀ value was >0.13 mg a.i./l (nominal concentration) (Springborn Smithers, 2008a). The study was conducted in accordance with OECD TG 203 and in compliance with GLP. The flow-through design of the test means that the test organisms are likely to have been exposed to the parent substance.

Refer to the discussion in the IUCLID Section 6 endpoint summary or Section 7.0 of the CSR for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.