Tetramethylsilane

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1998-08-25 to 1998-08-27

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

The concentration of test substance in the Control and only test concentration was determined at the start and end of the test.

Vehicle:

no

Details on test solutions:

The test substance was added to dilution medium so that the initial loading was approximately 2 mL/L. The mixture was strongly agitated for 10 minutes using a magnetic agitator. After subsequent slower agitation without droplet distribution of the test substance for about 5 minutes, and after pre-drainage of about 500 mL, the test solution was drawn from the bottom of the vessel.

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Strain: Clone 5

- Source: Laboratory stock culture

- Age at study initiation (mean and range, SD): <24 hours
:
- Method of breeding: Parthenogenetic reproduction

- Feeding during test: None


ACCLIMATION

- Acclimation conditions: same as test

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

48 h

Hardness:

250 mg/L as CaCO3

Test temperature:

20+/-1ºC

pH:

7.7-7.8

Dissolved oxygen:

8.1-8.6 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Control and 103 mg/L (calculated from measured concentration)

Details on test conditions:

TEST SYSTEM

- Test vessel: Head-space containers, sealed with septum, filled to 20 mL.

- Type (delete if not applicable): closed

- Aeration: none

- No. of organisms per vessel: 5

- No. of vessels per concentration (replicates): 4

- No. of vessels per control (replicates): 4

- Biomass loading rate: 1 daphnid/4 mL


TEST MEDIUM / WATER PARAMETERS

- Culture medium different from test medium: No, Elendt M4 medium

- Intervals of water quality measurement: Daily


OTHER TEST CONDITIONS

- Adjustment of pH: No

- Photoperiod: 24 h darkness

- Light intensity: darkness


EFFECT PARAMETERS MEASURED (with observation intervals if applicable): Mobility after 24 and 48 hours


TEST CONCENTRATIONS

- Spacing factor for test concentrations: Limit test

Reference substance (positive control):

no

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 103 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mobility

Remarks on result:

other: reported as >103 mg/l but the reliability of the analysis cannot be judged therefore should be reported as >LoS

Details on results:

- Immobilisation of control: 0%

Reported statistics and error estimates:

No effects were observed in the test and therefore statistical analysis of the results was not carried out.

Table 1. Results of analysis of test media

Test medium	Measured initial concentration (mg/L)	Measured concentration after 48 hours (mg/L)	Concentration for evaluation of results (mg/L)*
Control	<1	<1	<1
Initial solution	109	107	103

*Taking into account dilution by introduction of test organisms

Table 2. Test results

Test concentration (mg/L)	Mean percentage immobilisation after 24 hours	Mean percentage immobilisation after 48 hours
0 (Control)	0	0
103	0	0

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of >103 mg/L and NOEC of ≥103 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna.

Description of key information

Short-term toxicity to aquatic invertebrates: 48-hour EC₅₀ based on mobility of Daphnia magna: not toxic at the limit of solubility.

Additional information

A short-term toxicity to freshwater invertebrates study is available with the registered substance, tetramethylsilane (CAS 75-76-3; EC No. 200-899-1).

A 48-hour EC₅₀ value of >103 mg/l (arithmetic mean measured concentration) (highest concentration tested) was reported for the effects of tetramethylsilane on mobility of Daphnia magna (Hüls, 1998), conducted in accordance with OECD TG 202 and in compliance with GLP.

 

The substance is highly volatile therefore the study was conducted in headspace containers sealed with a septum in an attempt to minimise volatilisation of tetramethylsilane during the 48-hour exposure. The test substance solution was made by preparing an initial concentration of approximately 2 ml of test substance in 1 litre of water (equivalent to a concentration of approximately 1300 mg a.i./l), followed by agitation and draining of 500 ml of the solution. The measured concentrations indicate that test substance concentrations were stable over the course of the test. However, the study report contains no details on the analytical method and, as such, the reliability of the measurements cannot be assessed. The water solubility of the substance is estimated to be 19.6 mg/l and data from the fish and algal studies (Springborn Smithers 2010) indicate that the maximum achievable concentrations under ecotoxicity testing conditions may be much lower. Therefore, the measured concentrations were well above the expected limit of water solubility. As no effects were observed and the measured concentrations of test substance were above the limit of solubility of the substance, the EC50 value should therefore be reported as not toxic at the limit of solubility (EC50 >LoS).

 

A second short-term toxicity to Daphnia magna study was conducted with tetramethylsilane. A 48-hour EC₅₀ value of >100 mg/l (nominal concentration) was reported for the effects of the test substance on mobility of Daphnia magna, conducted in accordance with OECD TG 202 and in compliance with GLP (LPT, 2003). The test concentrations were measured by DOC analysis. The measured actual concentrations of the start and 48-hour samples of the test set were below 5% of the theoretical concentrations. The explanation given by the laboratory for this was that during the sample preparation for the DOC analysis, loss of substance was possible due to the high vapour pressure of the test substance. However, although the test was conducted in ampoules covered with a glass top with no contact with air, the test solutions were prepared by intense stirring for 30 minutes. The test substance has such high volatility, it is possible that it was lost from the test solution during this mixing period.

The reported biological results are therefore reported in terms of nominal concentrations, although it is not clear if any test substance remained in solution during the study.

Both studies showed no effects on aquatic invertebrates. Because measures were taken in the first study to minimise losses of test substance, the results of first study are therefore selected as key.

 

Refer to IUCLID Section 6 endpoint summary, Section 7.0 of CSR, for further discussion of the approach to chemical safety assessment for this registered substance.