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Ecotoxicological information

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 analogue approach justification provided in 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.
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2008-06-30 to 2008-07-25
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:
- Concentrations: Measurement of the test article concentrations were performed on the batch preparation of each test solution at test initiation. At test termination, water samples were collected for analysis from each test chamber. Water samples (10 mL) were collected from mid- depth of the test chambers using a glass pipette.

- Sampling method: At test termination, water samples were collected for analysis from each test chamber. Water samples (10 mL) were collected from mid- depth of the test chambers using a glass pipette.
Vehicle:
no
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Source: Daphnia magna used in this study were obtained from in-house cultures. The original source of the brood stock was Aquatic BioSystems, Fort Collins, Colorado.

- Age at study initiation: <24 hours

- Feeding during test: Daphnia magna were not fed during the test.


ACCLIMATION

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

- Type and amount of food: Daphnia magna cultures were fed a diet of Selenastrum capricornutum and YCT (yeast, cerophyl and trout chow).
- Feeding frequency:
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
103 mg/L as CaCO3
Test temperature:
20+/-2ºC
pH:
7.4-8.2
Dissolved oxygen:
≥7.5 mg/L (85% of saturation)
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control) and 120 mg/L

Measured concentration at test initiation: 116 mg/L

Measured concentrations at test termination: 120 mg/L

Mean measured concentration: 117 mg/L (99% of the nominal)
Details on test conditions:
TEST SYSTEM

- Test vessels: 600 mL glass beakers containing approximately 500 mL of test solution. Test vessels were impartially placed in an environmental chamber set to maintain a temperature of 20  1C. Each test vessel was covered with a watch glass to reduce evaporation. Test vessels were labeled with the study number, test article concentration and replicate.

- Treatments and replication: Daphnia magna were exposed to one limit concentration of the test article and a negative (dilution water) control. Two replicate test chambers were maintained in each treatment group, with 10 Daphnia magna in each test vessel for a total of 20 Daphnia magna per treatment. The nominal test concentration was selected based on an exploratory range-finding test. The nominal test concentration was 120 mg dimethylsilanediol/L (mg/L). Water samples were collected at test initiation and at test termination for measurement of the test article. Mean measured concentrations were used to estimate EC50 values.

Daphnia magna were indiscriminately assigned to test chambers at test initiation. Indiscriminate distribution was achieved by sequentially adding one to two daphnids at a time to test vessels until each contained 10 daphnids. All transfers were made under the surface of the water. Observations of mortality/immobility and sublethal effects were made at test initiation and approximately 24 and 48 hours after test initiation. Cumulative percent mortality/immobility observed in the treatment group was used to estimate EC50 values at 24 and 48 hours.

- Dilution water: The dilution water was municipal water obtained from Bay City, Michigan. The municipal water was dechlorinated using a carbon filter and aerated prior to use. The pH of the water is periodically adjusted using CO2, as necessary. The water is monitored weekly for hardness, alkalinity, conductivity, pH and total residual chlorine (TRC). The municipal water is also monitored once a year for selected inorganics, total suspended solids (TSS), total organic carbon (TOC) and selected organic compounds. No contaminants have been shown to be present in the municipal water at concentrations that might affect the outcome of this study.

- Environmental conditions: Lighting used to illuminate the test chambers was provided by cool white fluorescent bulbs with a photoperiod of 16 hours light and 8 hours dark. Temperature, dissolved oxygen and pH were measured in the batch solutions prepared at test initiation and in each test vessel at approximately 48 hours. Temperature was measured using a liquid-in-glass thermometer. In addition, temperature of the environmental chamber was measured continuously. The target test temperature was 20+/-2ºC. Measurements of dissolved oxygen were made using a Yellow Springs Instruments dissolved oxygen meter and measurements of pH were made using an Orion pH meter. A sample of dilution water was collected at test initiation for measurements of hardness, alkalinity, conductivity and TRC. Hardness and alkalinity were measured by titration. Conductivity was measured using a Yellow Springs Instruments salinity, conductivity and temperature meter. TRC was measured using a Fisher Chlorine Titrimeter 397.

- Observations: Observations were made to evaluate the number of mortalities and immobile organisms. Immobility was defined as the lack of swimming within 15 seconds after gentle agitation of the test vessel. The numbers of organisms exhibiting sublethal effects (e.g., lethargy, discoloration, etc.) were also evaluated. Observations were made at test initiation and 24 and 48 hours after test initiation (+/-1 hour).
Reference substance (positive control):
no
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
Details on results:
- Immobilisation in control: 0
Reported statistics and error estimates:
The EC50 values were estimated by visual inspection of the mortality/immobility data. Confidence limits could not be calculated because only one concentration was tested.

Daphnia magna in the negative control appeared normal and healthy throughout the test with no mortality/immobility or overt signs of toxicity. After 48 hours of exposure, Daphnia magna exposed to dimethylsilanediol at a concentration of 119 mg/L also appeared normal and healthy with no mortality or immobility. 

Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of >117 mg/L and NOEC of ≥117 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna.

Description of key information

EC50 (48 h) > 117 mg/L (nominal, OECD 202, D. magna; read across from silanol hydrolysis product DMSD)

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Dose descriptor:
EC50
Remarks:
for silanol hydrolysis product (relevant assessment entity)
Effect concentration:
> 117 mg/L

Additional information

Experimental data on the short-term toxicity of dimethoxy(dimethyl)silane (CAS No. 1112-39-6) to invertebrates are available. Since dimethoxy(dimethyl)silane hydrolyses rapidly to dimethylsilanediol and methanol (DT50 < 0.6 h) data on the hydrolysis product dimethylsilanediol were additionally considered for the assessment. The other hydrolysis product, methanol, is well described in the public domain literature. It has a low environmental hazard profile and is therefore not considered contributory to the overall aquatic toxicity of the registered substance (OECD SIDS, 2004). Thus, the ecotoxicity assessment was based on the silanol hydrolysis product dimethylsilanediol (DMSD, CAS No. 1066-42-8).


The experimental study with dimethoxy(dimethyl)silane 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 (bridging study). 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).


 


Reference
OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.