Registration Dossier

Ecotoxicological information

Short-term toxicity to fish

Currently viewing:

Administrative data

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:
2008-04-07 to 2008-04-11
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 203 (Fish, Acute Toxicity Test)
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
yes
Details on sampling:
- Sampling method: Prior to the start of the definitive exposure, water samples were removed from the treatment level and the controls and analysed for triethoxy(octyl)silane concentration. Results of these pretest analyses were used to judge whether sufficient quantities of triethoxy(octyl)silane were being delivered to the test aquaria and whether the appropriate test concentrations were being maintained in order to initiate the definitive exposure.

During the in-life phase of the definitive study, two water samples from the treatment level and the controls were collected and analysed for triethoxy(octyl)silane at 0 hour (test initiation) and 96 hours (test termination). The replicates used for sampling were alternated between intervals. Samples were collected from the approximate midpoint of the test vessel by pipette.

Three quality control (QC) samples each were prepared at each sampling interval and remained with the appropriate set of exposure solution samples throughout the analytical process. These QC samples were prepared in dilution water at nominal concentrations similar to the exposure concentration range. Results of the analyses of the QC samples were used to judge the precision and quality control maintained during the analysis of exposure solution samples.
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

A 1.3 mg a.i./l stock solution was prepared by placing 0.1316 to 0.1341 g (0.1304 to 0.1329 g as active ingredient) in a 100 ml volumetric flask and bringing it to volume with DMF (CAS No. 68-12-2). The resulting stock solution was observed to be clear and colourless with no visible undissolved test substance.

A 0.99 mL/ml solvent stock solution was prepared by bringing 99 ml of DMF to a final volume of 100 ml with deionized water. The resulting stock solution was observed to be clear and colourless.

Prior to test initiation, a Glenco® 50-ml gas-tight syringe in conjunction with a Harvard Syringe Pump was calibrated to deliver 0.0405 ml/cycle of the 1.3 mg a.i./ml triethoxy(octyl)silane stock solution into the diluter system's chemical mixing chamber which also received 0.405 litres of dilution water per cycle. The mixing chamber was positioned over a water-driven magnetic stirrer and was partially submerged within a water bath which continuously mixed the contents of the mixing chamber. The constant mixing aided in the solubilization of the test substance in the dilution water. The concentration of triethoxy(octyl)silane in the solution contained within the mixing chamber was equivalent to that of the nominal test concentration (0.13 mg a.i./l).

The solvent control solution was prepared utilizing a similar system, calibrated to deliver 0.0405 ml/cycle of the solvent control stock solution (0.99 ml/ml) to 0.40 L of dilution water per cycle which was subsequently delivered to the solvent control vessels. The concentration of DMF in the solvent control vessels was equivalent to the concentration of solvent present in the treatment level solution (0.10 ml/l).
Test organisms (species):
Oncorhynchus mykiss (previous name: Salmo gairdneri)
Details on test organisms:
TEST ORGANISM

Juvenile rainbow trout (Oncorhynchus mykiss) was selected as the test organism since it is recommended by the U.S. EPA and commonly used in freshwater acute toxicity tests. The rainbow trout used during this study (SSL Lot No. 08A16) were obtained from Troutlodge, a commercial supplier located in Sumner, Washington. Prior to testing, these fish were held in a 500-litre fiberglass tank under a photoperiod of 16 hours light and 8 hours darkness. The well water which flowed into this holding tank was characterized as having total hardness and total alkalinity ranges as calcium carbonate (CaCO3) of 36 to 44 and 22 to 24 mg/l, respectively, pH of 7.3, a dissolved oxygen concentration range of 9.3 to 9.4 mg/l, 87 to 89% of saturation, the temperature was maintained at 13°C and a specific conductance of 170 micromhos per centimetre (μmhos/cm).

ACCLIMATION

The fish used during the definitive exposure were maintained under these conditions for at least two weeks prior to testing. The fish were fed a dry commercial flaked fish food, ad libitum, daily. Fish were not fed during the 24-hour period prior to test initiation or during the exposure period. No mortality was observed among the test fish population during the 48 hours period prior to testing.


FISH SIZE

A representative sample (N = 30) of the fish from the test population had a mean wet weight of 1.8 g (range 1.1 to 2.4 g) and a mean total length of 54 mm (range 45 to 60 mm).
Test type:
flow-through
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
96 h
Hardness:
36-44 mg/l as CaCO3
Test temperature:
14-16°C
pH:
6.2-7.0
Dissolved oxygen:
5.8-10 mg/l
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control), 0 (Solvent control) and 0.13 mg/l

Additional testing at higher concentrations to define the LC50 value was not performed because the nominal concentration (0.13 mg a.i./l) tested is believed to represent the limit of solubility for the test substance under test conditions maintained.

The mean measured concentration in the treated media ranged from 33 to 57% of nominal concentration and was defined as 0.055 mg a.i./l.
Details on test conditions:
EXPOSURE SYSTEM

The diluter system was calibrated prior to test initiation and at test termination by measuring delivery volumes of test substance and dilution water. The function of the diluter system (e.g., flow rates, stock solution consumption) was monitored daily and a visual check was performed twice each day. The exposure system was in operation for five days prior to initiation of the definitive exposure to allow equilibration of the test substance in the diluter apparatus and exposure vessels. Each glass exposure aquarium measured 30 x 15 x 20 centimetres (cm).

Water depth was maintained at a constant level by an overflow drain 15 cm from the bottom of each aquarium. The total test solution volume was therefore maintained at 6.8 litres. The flow of exposure solution provided approximately 6 solution volume replacements for test days one and two. The rate was increased to 7.7 solution volume replacements for test day three and 10 solution volume replacements for test days four and five as a result of low dissolved oxygen levels in the test aquaria and provided a 90% test solution replacement rate of approximately 6.0 hours. Exposure aquaria were labelled to identify the nominal test substance concentration and designated replicate.

TEST INITIATION

The definitive study was initiated when ten rainbow trout were selected impartially from the holding tank and placed two at a time in each replicate test aquarium. This procedure was repeated until each aquarium contained ten fish for each treatment level and the control (40 fish per treatment and the controls). The resulting test organism loading concentration was 0.26 grams of biomass per litre of solution per day.

DILUTION WATER

The dilution water (well water) used during this study was from the same source as the water used to culture rainbow trout and was characterized as having total hardness and total alkalinity range (as CaCO3) of 40 to 44 mg/l and 22 mg/l, respectively, a pH of 7.0 to 7.1 and a specific conductance range of 180 to 190 μmhos/cm. The TOC concentration of the dilution water source was 0.40 mg/l for April 2008.

BIOLOGICAL MONITORING

All aquaria were examined after 0, 24, 48, 72 and 96 hours of exposure as follows: mortalities were recorded and dead fish removed, biological observations, including adverse effects (e.g., lethargy, loss of equilibrium) of the exposed rainbow trout, and observations of the physical characteristics of the test solutions (e.g., presence of precipitate, film on the solution's surface) were made and recorded. Effects for this study were based on death, defined as the lack of movement by the exposed organisms (i.e., absence of gill movement and reaction to gentle prodding).

WATER QUALITY

Dissolved oxygen concentration, temperature and pH were measured at each 24-hour interval in each treatment level aquaria and the controls. The total hardness, alkalinity and specific conductivity were measured in the 0.13 mg a.i. mg/l treatment and the control at test initiation.
Reference substance (positive control):
no
Key result
Duration:
96 h
Dose descriptor:
LC50
Effect conc.:
> 0.055 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mortality
Key result
Duration:
96 h
Dose descriptor:
NOEC
Effect conc.:
>= 0.055 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mortality
Details on results:
- Mortality of control: 0

- Mortality of solvent control: 0

- Other adverse effects control: None
Reported statistics and error estimates:
No effects were observed in the test and therefore statistical analysis of the results was not required.

Table 1. Results of analysis of test media

 

Nominal

Concentration

(mg a.i./l)

Mean measured concentration (mg/l)

Mean measured concentration as percentage of nominal

0 (Control)

Not applicable

Not applicable

0 (Solvent control)

Not applicable

Not applicable

0.13

0.055

42

 

Table 2. Test results

                                                

Mean measured

Concentration

(mg a.i./l)

Percentage mortality at end of test

0 (Control)

0

0 (Solvent control)

0

0.055

0

 

Validity criteria fulfilled:
yes
Conclusions:
A 96-hour LC50 value of >0.055 mg/l and a NOEC of ≥0.055 mg/l have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss under flow-through test conditions. The result is expressed as mean measured concentration of the test substance over the test period.

Description of key information

Short-term toxicity to fish: 96-hour LC50 >0.055 mg/l (arithmetic mean measured, highest concentration tested) (OECD TG 203), in terms of the substance as tested. The observations in this study are attributed to the exposure of test organisms to a mixture of the parent substance and its hydrolysis products in the test system.

Key value for chemical safety assessment

Additional information

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 test substance over the test period. The flow-through design of the test maximised exposure of the test organisms to the parent substance. However, analytical recoveries of test substance concentrations showed losses of parent test substance, therefore it is likely that the fish were exposed to a mixture of the parent substance and its hydrolysis products.

Supporting data are available for two structurally analogous read-across substances; triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3) and trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4).

A 96-hour LL50 of >100 mg/l has been determined for the effects of triethoxy(2,4,4-trimethylpentyl)silane (CAS 35435-21-3) on mortality of Oncorhynchus mykiss. The data reflect exposure to a mixture of the parent substance and its hydrolysis products.

A 96-hour LL50 of >100 mg/l has been determined for the effects of trichloro(2,4,4-trimethylpentyl)silane (CAS 18379-25-4) on mortality of the Oncorhynchus mykiss.

The data reflect exposure to the hydrolysis products of the test substance.