Trimethoxyoctylsilane

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

Study period:

2009-10-01 to 2009-10-05

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 203 (Fish, Acute Toxicity Test)

GLP compliance:

yes

Analytical monitoring:

no

Vehicle:

yes

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A dosing stock solution was prepared by mixing 1.87 mL (density 1.07 g/mL) of Trichloro(2,4,4-trimethylpentyl)silane (corresponding to 2 g) with 2.0 mL of tetrahydrofuran (THF) using a Hamilton syringe. The 100 mg test item/L test solution was prepared prior to test initiation by adding 0.485 mL of the dosing stock solution to approximately 1.7 to 1.8 L dilution water using a Hamilton syringe. Prior to addition of the dosing stock solution, the glass beaker containing the dilution water was placed on a magnetic stirrer. This procedure was repeated three times and the resulting solutions combined. The spiked solution was stirred continuously over night. The pH of the solution was then adjusted to 7.0 with 1 N sodium
hydroxide (NaOH). Thereafter, the test solution was further diluted to a final volume of 10 L with dilution water, resulting in a solvent (THF) concentration of 0.10 mL/L. The resulting test solution was mixed for 30 seconds using a glass rod and observed to be clear and colourless, with no visible undissolved test item.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Source: The trout were originally obtained from Forellenzucht P. Hohler-Gasser, a commercial supplier located in Zeiningen, Switzerland.

- Length at study initiation (length definition, mean, range and SD): 34 mm (range 29 to 39 mm)

- Weight at study initiation (mean and range, SD): 0.42 g (range 0.20 to 0.63 g)

- Feeding during test: Fish were not fed during the 24-hour period prior to test initiation and during the exposure period.


ACCLIMATION

- Acclimation conditions (same as test or not): Prior to testing, the fish were maintained in a holding tank (under renewal conditions) under a photoperiod of 16 hours light and 8 hours darkness with a 30 minute transition period. The culture water was modified well water from the municipality of Horn, deionized with a Culligan Reverse Osmosis system. The deionized well water was reconstituted according to the formulation given in the Official Journal of the European Communities.

- Feeding: The fish were fed Hokovit 502, a dry, commercially available food, generally once daily.

- Health during acclimation (any mortality observed): No mortality was observed among the test fish population during the 12-day period prior to testing.

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

160 mg/L as CaCO3

Test temperature:

14.7 to 15.9 °C

pH:

7.04 to 7.65

Dissolved oxygen:

8.43 to 10.43 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control), 0 (Solvent control) and 100 mg/L

Details on test conditions:

TEST SYSTEM

- Test vessel: The test vessels were 12.5 L vessels constructed of stainless steel, each containing 10 L of test solution. The test vessels were placed in a water bath in order to maintain exposure solution temperatures at 15 ± 2°C. The test vessels were loosely covered with a glass plate during the 96-hour exposure.

- Aeration: Test solutions were gently aerated (with oil-free air) throughout the duration of the exposure period.

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

- No. of organisms per vessel: 7

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

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

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

- Biomass loading rate: 0.3 g of biomass per litre of test solution


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: The dilution water used during the definitive test had a pH of 7.64, a total hardness and alkalinity as CaCO3 of 160 and 26 mg/L, respectively, and a specific conductivity of 400 μS/cm.

- Culture medium different from test medium: No

- Intervals of water quality measurement: The pH, dissolved oxygen concentration and temperature were measured at 0, 24, 48, 72 and 96 hours in each test solution. Continuous temperature monitoring was performed in the control solution throughout the exposure period.


OTHER TEST CONDITIONS

- Photoperiod: A 16-hour light, 8-hour dark photoperiod was maintained with an automatic timer.

- Light intensity: The test was illuminated to a light intensity of 200 to 500 lux using fluorescent bulbs.


EFFECT PARAMETERS MEASURED: All test vessels were examined at 0, 24, 48, 72 and 96 hours of exposure for mortality. In addition observations of the physical characteristics of the test solutions (e.g., clear solution, precipitate, film on the surface of the test solution) were made and recorded at each 24-hour interval. Biological observations, including adverse effects on the exposed trout, were performed and recorded at each 24-hour interval. Effects for this study were based on mortality, defined as the lack of movement by the exposed organisms (i.e., absence of gill movement and reaction to gentle prodding).

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but predominantly exposed to hydrolysis product

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 100 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but predominantly exposed to hydrolysis product

Basis for effect:

mortality (fish)

Details on results:

- Behavioural abnormalities: 0

- Mortality of control: 0

- Other adverse effects control: 0

- Abnormal responses: 0

Reported statistics and error estimates:

Since no 50% mortality was observed during the 96 hours of exposure, no 24-, 48-, 72- and 96-hour median lethal concentrations (LC50) were calculated. Based on the nature of the raw data, the LC50 values were empirically estimated as > 100 mg test item/L.

The No-Observed-Effect Concentration (NOEC) during the 96-hour exposure period was determined by visual observation. The NOEC is defined as the highest concentration tested at and below which there were no toxicant-related effects and mortality with respect to the control
organisms.

Sublethal observations / clinical signs:

There were no effects on mortality in the Controls or in the 100 mg/L nominal treatment.

Validity criteria fulfilled:

yes

Conclusions:

A 96-h LC50 value of >100 mg/L and NOEC of ≥100 mg/L have been determined for the effects of the substance on mortality of Oncorhynchus mykiss based on nominal concentration. It is likely that the test organisms were solely exposed to the hydrolysis products of the substance.

Description of key information

Short-term toxicity to fish: 96 hour LC₅₀ >100 mg/L (nominal) (OECD 203), Oncorhynchus mykiss, read across from trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4). The LC₅₀ is equivalent to >78 mg/L when expressed in terms of concentration of the silanol hydrolysis product (2,4,4-trimethylpentyl)silanetriol.

Additional information

There are no reliable short-term fish toxicity data available for trimethoxy(octyl)silane (CAS 3069-40-7), therefore good quality data for an appropriate structural analogue, trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4), have been read across. Both substances have structurally similar silanol hydrolysis products, octylsilanetriol and (2,4,4-trimethylpentyl)silanetriol respectively. The other hydrolysis products are methanol and hydrochloric acid, respectively.

 

A 96 hour LC₅₀ value of >100 mg/L has been determined for the effects of trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) on mortality of Oncorhynchus mykiss based on nominal concentrations of the substance (Springborn Smithers, 2010). The result was obtained under static test conditions. In view of the test media preparation method and exposure regime it is likely that the test organisms were exposed predominantly to the hydrolysis products of the tested substance.

 

The results may be expressed in terms of concentration of the hydrolysis product, (2,4,4-trimethylpentyl)silanetriol, by applying a molecular weight correction: (MW of silanol = 192.3 / MW of parent = 247.7) * concentration of parent = >100 mg/L = >78 mg/L.

 

The study was conducted according to an appropriate OECD test guideline, and in compliance with GLP, and is considered to be reliability 1 (reliable without restrictions).

Read-across from CAS 18379-25-4 to CAS 3069-40-7:

Trimethoxy(octyl)silane is a trialkoxysilane that hydrolyses rapidly under the conditions of the test to form octylsilanetriol and methanol (predicted half-life approximately 4 h at 20-25°C and pH 7).

Trichloro(2,4,4-trimethylpentyl)silane is a trichlorosilane that hydrolyses very rapidly under the conditions of the test to form (2,4,4-trimethylpentyl)silanetriol and hydrogen chloride (half-life based on category read-across < 1 minute at 25°C and pH 4, pH 7 and pH 9). The two silanol hydrolysis products, octylsilanetriol and (2,4,4-trimethylpentyl)silanetriol are both silanetriols with octyl side-chains (one linear, one branched). The physicochemical properties of these substances are comparable, in particular the predicted log K_ow values for the two substances are similar (1.1 for octylsilanetriol and 0.9 for (2,4,4-trimethylpentyl)silanetriol).

The effects of the other hydrolysis products, methanol and hydrogen chloride, are well characterised. Methanol is non-toxic to the environment at concentrations relevant for the assessment and it is considered unlikely that its presence significantly affected the results of the test. The effects of hydrogen chloride on aquatic organisms are limited to those that result from changes to pH in unbuffered media.