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Short-term toxicity to aquatic invertebrates

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Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2002-06-17 to 2002-09-11
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)
Deviations:
yes
Remarks:
The test media were not prepared in accordance with OECD guidance for testing difficult substances.
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Nominal treatments: 0 (Control), 10.0 and 100 mg/L
- Sampling method: One aliquot from the freshly prepared test media of all test concentrations was taken at the start of the test before filling the test vessels. A combined aliquot was collected from the test media of all 4 replicate test vessels at each concentration at the end of the test.
- Sample storage conditions before analysis: Samples were stored at -20 °C prior to analysis.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A stock solution of the test substance was prepared at a nominal loading rate of 100 mg/L by shaking for 30 minutes. Further treatments were prepared by dilution of the resulting stock solution.
- Controls: Dilution water
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Source: IRChA, France
- Age at study initiation: 6-24 hours
- Method of breeding: Laboratory stock culture
- Feeding during test: none

ACCLIMATION
- Acclimation period: at least 1 week
- Acclimation conditions: same as test
- Type and amount of food: log-phase Scenedesmus subspicatus and a small amount of aerated sewage sludge
- Feeding frequency: not reported
- Health during acclimation (any mortality observed): not reported
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
250 mg/l as CaCO3
Test temperature:
20 ± 1 °C
pH:
8.01-8.33
Dissolved oxygen:
87-97% ASV
Nominal and measured concentrations:
Nominal treatments: 0 (Control), 10 and 100 mg/L

The measured DOC concentrations at the start and end of the test were 20% of the theoretical values. The results are therefore expressed and interpreted with reference to nominal concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel:

- Type: open

- Material, size, fill volume: glass, 50 mL with 50 mL of test medium

- Aeration: none

- Renewal rate of test solution: static test

- 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/10 mL

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: reconstituted fresh water

- Alkalinity: 0.8 mmol/L

- Ca/mg ratio: 4:1

- Intervals of water quality measurement: start and end of test

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 hours light, 8 hours dark

- Light intensity: approximately 500 lux

EFFECT PARAMETERS MEASURED: mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 10

- Range finding study

- Results used to determine the conditions for the definitive study: no data
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Details on results:
- Immobilisation of control: 0%
Reported statistics and error estimates:
There were insufficient levels of immobilisation to determine a definitive EC50 value. The NOEC was blow the lowest test concentration.

Table 1. Test results

 Nominal test substance concentration/loading rate (mg/L)  Mean percentage immobilisation after 24 hours  Mean percentage immobilisation after 48 hours
 0 (Control)  0 0
 10  0 10 
 100  0 15

Table 2. Results of analysis of test media

 Nominal test substance concentration/loading rate (mg/L)  Theoretical DOC concentration (mg/L)  Actual DOC concentration at start of test (mg/L)  Actual DOC concentration at end of test (mg/L)
 10  4.0  3.9  4.2
 100 40  41.3  39.8
Validity criteria fulfilled:
yes
Conclusions:
A 48-h EC50 value of >100 mg/L and a NOEC of <10 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna based on nominal concentrations. However it is likely that the test organisms were exposed to the hydrolysis products of the substance.
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
read-across from supporting substance (structural analogue or surrogate)
Adequacy of study:
supporting study
Justification for type of information:
Please refer to the justification for grouping of substances provided in IUCLID Section 13.
Reason / purpose for cross-reference:
read-across source
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 117 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 117 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Conclusions:
A 48-hour EC50 value of >117 mg/L and NOEC of ≥117 mg/L have been determined for the effects of the source substance on mobility of Daphnia magna (OECD 202, GLP). The source substance is the hydrolysis product of the target substance. Since the hydrolysis half life is < 1 h, the results derived for the source substance describe additionally the effects of the the target substance.

Description of key information

EC50 (48 h) > 117 mg/L (OECD 202; Daphnia magna); read across from hydrolysis product (dimethylsilanediol)

Key value for chemical safety assessment

Additional information

Experimental data on the short-term toxicity of dimethoxydimethylsilane (CAS 1112-39-6) to invertebrates are available. Since dimethoxydimethylsilane hydrolyses rapidly to dimethylsilanediol and methanol (DT50 < 0.6 h) data on the hydrolysis product dimethylsilanediol were considered additionally for the assessment.

The experimental study with dimethoxydimethylsilane was performed according to OECD 202 (GLP). Daphnia magna was exposed for 48 hours under static conditions to nominal concentrations of 0, 10 and 100 mg/L (Mitterer, 2003b). For the preparation of test solutions an appropriate amount of test item was added to the test medium and the solution was intensively stirred for 30 min. Due to the fast hydrolysis of the parent substance (DT50 < 0.6 h) the Daphnids were primarily exposed to the hydrolysis product rather than the parent substance. The dissolved organic carbon (DOC) was measured at test start and test end and it was shown that DOC-concentration remained constant during exposure. Immobilization of 15% was recorded after 48 h resulting in an EC50 of > 100 mg/L (nominal).

The result from the parent substance was further supported by experimental data with the silanol hydrolysis product itself. This study was performed according to OECD 202. Daphnia magna was exposed for 48 h under static conditions to dimethylsilanediol. The study was designed as a limit test with a concentration of 120 mg/L (Dow Corning Corporation, 2009b). Since no effects were recorded the EC50 (48 h) was derived to be > 117 mg/L (measured).