2,4,6,8-tetramethylcyclotetrasiloxane

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:

1994-04-26 to 1994-04-30

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EU Method C.1 (Acute Toxicity for Fish)

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

not specified

Details on sampling:

- Concentrations: 500 mg/L

- Sampling method: Samples of test media were taken from all treatments at the start and end of the first (0-24h) and third (48-72h) test periods.

- Sample storage conditions before analysis: refrigerated

Vehicle:

not specified

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A stock solution was prepared by mixing the substance overnight with dilution water used in the test

- Controls: Dilution water

Test organisms (species):

Danio rerio (previous name: Brachydanio rerio)

Details on test organisms:

TEST ORGANISM

- Common name: Zebrafish

- Source: Tropical Waters (Feltham, UK)

- Age at study initiation (mean and range, SD):

- Length at study initiation (length definition, mean, range and SD): 3.4 cm (3.1 - 3.7 cm)

- Weight at study initiation (mean and range, SD): 0.38 g (0.3 - 0.45 g)

- Feeding during test: None

ACCLIMATION

- Acclimation period: 12 days

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

- Type and amount of food: TetraMin® Tropical Flake

- Feeding frequency: dependent upon size and temperature

- Health during acclimation (any mortality observed): Cumulative mortality must no exceed 5% in the 7-day period prior to the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

96 h

Hardness:

40.8 - 41.3 mg/L

Test temperature:

20 - 21ºC

pH:

7.0 - 7.5

Dissolved oxygen:

62 - 100% ASV

Nominal and measured concentrations:

Nominal: Control, 31.25, 62.5, 125, 250 and 500 mg/L.

Measured concentrations in fresh media (excluding Control) at start of test: 27.2, 58.5, 119, 249 and 499 mg/L.

Measured concentrations in old media (excluding Control) after 24 h exposure: 30.7, 63.4, 124, 248 and 497 mg/L.

Measured concentrations in fresh media (excluding Control) at 48 h: 32, 64.6, 124, 241 and 490 mg/L.

Measured concentrations in old media (excluding Control) after 24 h exposure: 28.1, 59.9, 117, 232 and 492 mg/L.

Mean measured concentrations: 29.4, 61.5, 121, 242 and 494 mg/L.

Mean measured concentrations as a % of nominal: 94.1, 98.4, 96.6, 96.9 and 98.9.

Details on test conditions:

TEST SYSTEM

- Test vessel: Culture vessels

- Type: sealed

- Material: Glass

- Aeration: none

- Renewal rate of test solution (frequency): daily

- No. of organisms per vessel: 10

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

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

- Biomass loading rate: 0.38 g/L

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Laboratory mains supply

- Chlorine: <0.1 mg/L (Total)

- Alkalinity: 14 mg/L CaCO3

- Conductivity: 128 μS/cm

- Culture medium different from test medium: no

- Intervals of water quality measurement:

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 h (light)/8 h (dark)

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2.0

Reference substance (positive control):

no

Key result

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis product

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 500 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Remarks:

but exposure is to hydrolysis product

Basis for effect:

mortality (fish)

Details on results:

- Behavioural abnormalities: At the end of the testfish exposed to the 250 mg/L nominal test concentration were showing mild behavioural effects and those exposed to 500 mg/L severe behavioural effects.

Reported statistics and error estimates:

There were no lethal effects at the highest test concentration and therefore statistical analysis of the results was not carried out.

Validity criteria fulfilled:

yes

Conclusions:

A 96-hour LC50 value of >500 mg/L and NOEC of ≥500 mg/L have been determined for the effects of the test substance on mortality of Brachydanio rerio based on nominal concentration of the substance. However it is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

Description of key information

Short-term toxicity to fish: 96 hour LC₅₀ >500 mg/l (nominal) (EU Method C.1 (Acute toxicity for fish)), read across from an analogous/structurally related substance, triethoxy(methyl)silane (CAS 2031-67-6). The observations in this study are attributed to the exposure of test organisms to the hydrolysis products in the test system. The LC₅₀ is equivalent to >264 mg/l when expressed in terms of the silanol hydrolysis product, methylsilanetriol.

Additional information

There are no reliable short-term fish toxicity data available for 2,4,6,8-tetramethylcyclotetrasiloxane (HD4, CAS 2370-88-9), therefore good quality data have been read across from triethoxy(methyl)silane (CAS 2031-67-6). The substances share the same silanol hydrolysis product, methylsilanetriol. The other hydrolysis products are hydrogen gas and ethanol, respectively. In the tests with triethoxy(methyl)silane (CAS 2031-67-6) the observations are attributed to the exposure of test organisms to methylsilanetriol in the test system. There is no basis to expect that ethanol significantly influenced the results of the test. The toxicity of ethanol is discussed further in the ecotoxicological RAAF document attached in Section 13 of IUCLID.  

A 96 hour LC₅₀ value of >500 mg/l (nominal, highest concentration tested) has been determined for the effects of triethoxy(methyl)silane (CAS 2031-67-6) on mortality of Danio rerio (Hazleton, 1994). 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, methylsilanetriol, by applying a molecular weight correction: (MW of silanol = 94.14 / MW of parent = 178.31) * >500 = >264 mg/l. This value is read across to methylsilanetriol without further correction.