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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:
weight of evidence
Study period:
04/2010-09/2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP, Guideline study with deviations that have been assessed with respect to study validity criteria and considered to have no influence on the results of the study.
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
yes
Remarks:
Alkalinity of dilution water 74 to 90 mg/L as CaCO3; water quality of replicates measured. Deviations fully evaluated.
GLP compliance:
yes (incl. certificate)
Analytical monitoring:
no
Details on sampling:
Samples from each exposure solution and the control were removed and analyzed for TOC as an indication of the consistency of test substance concentration in each solution over the course of the study. Samples were removed from each treatment level and control at test initiation and at the 24 hour renewal interval (freshly prepared solutions) and at 24 and 48 hours (aged solutions) for TOC analysis. Samples removed from freshly prepared solutions were removed from the intermediate mixing vessels, prior to division into replicate vessels. Samples removed from aged solutions were a composite of replicate solutions for each treatment level or control.
Vehicle:
no
Details on test solutions:
A 100 mg a.i./L stock solution was prepared prior to test initiation and at the 24-hour renewal period by placing, for example, 0.3617 g (0.3610 g as active ingredient) of test substance in a 3.5-L intermediate vessel and bringing it to volume with dilution water. The resultant solution was mixed using a Teflon®-coated stir bar and magnetic stir plate for approximately 48 hours to ensure hydrolysis of the parent material. The resulting stock solution was observed to be clear and colorless with no visible undissolved test substance.
Test solutions were mixed with a glass rod for approximately one minute prior to division into replicate exposure vessels. Following mixing, all test solutions were observed to be clear and colorless with no visible undissolved test substance. Each test solution was divided into four replicate vessels, each containing approximately 290 mL of solution and zero headspace. A set of control solutions was also prepared containing dilution water only. A similar procedure was used to prepare test solutions at the 24-hour solution renewal.
Test organisms (species):
Daphnia magna
Details on test organisms:
Daphnids, < 24 hours old.
Source: laboratory cultures maintained at test laboratory facility.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Remarks on exposure duration:
test solution renewal at 24 h
Hardness:
Total hardness of dilution water as CaCO3: 180 mg/L
Total alkalinity of dilution water as CaCO3: 82 mg/L
Test temperature:
Temperature: 19 to 21 ºC
pH:
pH: 7.9 to 8.2
Dissolved oxygen:
Dissolved oxygen: 7.0 to 8.3 mg/L
Nominal and measured concentrations:
Nominal test concentrations: 1.0, 2.6, 6.4, 16, 40 and 100 mg a.i./L
Details on test conditions:
Photoperiod of 16 hours light and 8 hours darkness at a light intensity range of 690 to 890 lux
Specific conductivity: 650 μmhos/cm
Reference substance (positive control):
yes
Remarks:
reference study
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
> 100 mg/L
Nominal / measured:
nominal
Conc. based on:
act. ingr.
Basis for effect:
mobility
Details on results:
Definitive Test:
-Following 48 hours of exposure (test termination), no toxicant-related immobilization or adverse effects were observed among daphnids exposed to the control or to any treatment level tested.
- Following 48 hours of exposure, 5% immobilization was observed among daphnids exposed to the control. ASTM (2002) recognizes the limitations of acute toxicity testing, i.e., response less than or equal to 10% is allowable in a control population and is considered within the expected range of naturally occurring variability. No immobilization or adverse effects were observed among daphnids exposed to the any of the treatment levels tested.- Since no concentration tested resulted in ≥ 50% immobilization, the 48-hour EC50 value for Daphnia magna and 2,4,6,8-tetramethylcyclotetrasiloxane was empirically estimated to be > 100 mg a.i./L, the highest concentration tested. The highest concentration producing 0% immobilization was 100 mg a.i./L. The lowest concentration producing 100% immobilization was > 100 mg a.i./L.
- Additional testing to further define the 48-hour EC50 value was not performed since the highest nominal test concentration, 100 mg a.i./L, represented the highest nominal test concentration required by the testing guideline.
Results with reference substance (positive control):
A 24-hour reference test was conducted with daphnids (< 24 hours old) from the laboratory culture. The reference test is used to evaluate the sensitivity of the daphnid population at the testing laboratory. The 24-hour reference test was conducted from 23 to 24 February 2010 and the results established that the 24-hour EC50 value for Daphnia magna and potassium dichromate was 3.1 mg/L. This result was within the expected range for D. magna exposed to potassium dichromate.
Reported statistics and error estimates:
Since no concentration tested resulted in ≥ 50% immobilization, EC50 values were empirically estimated to be greater than the highest concentration tested.

Preliminary Testing:

- A preliminary range-finding exposure was conducted at the test laboratory during which daphnids were exposed under static-renewal conditions to nominal 2,4,6,8-tetramethylcyclotetrasiloxane concentrations of 0.0010, 0.010, 0.10, 1.0, 10 and 100 mg a.i./L, and a solvent control. Two test vessels, each containing five daphnids, were established for each treatment level and the solvent control. No extended mixing was employed during the preliminary exposure. Since a small amount of undissolved material was observed in the stock solution directly after preparation, individual, concentrated solvent stocks (acetone) were prepared and used to prepared exposure solutions. Following 48 hours of exposure, 10 and 60% immobilization was observed in the 0.010 and 10 mg a.i./L treatment levels tested. Following 48 hour of exposure, two daphnids in the 1.0 and 10 mg a.i./L treatment levels were observed to be stuck in the surface tension of the water and two daphnids exposed to the 10 mg a.i./L were observed to be on the bottom of the test vessel. No immobilization or adverse effects were observed among daphnids exposed to the solvent control or any of the remaining treatment levels tested. Based on these results and consultation with the study sponsor, nominal concentrations of 1.0, 2.6, 6.4, 16, 40 and 100 mg a.i./L were selected for the definitive static-renewal exposure. Since the parent material was found to undergo rapid hydrolysis, a 48 hour mixing period was incorporated into the study design in order to ensure hydrolysis. Due to the change in study design and the intent to test the hydrolysis products, no solvent was required for use during the definitive exposure to solubilize the test substance.

Protocol Deviations:

1. The protocol states that the dilution water will typically have a range for alkalinity of 110 to 130 mg/L as CaCO3. During this exposure, as well as the two weeks prior, the alkalinity of the dilution water was found to range from 74 to 90 mg/L as CaCO3. The slight fluctuation from the range outlined in the protocol is attributed to seasonal variability in the source water. Since control performance met criteria for an acceptable study, this slight fluctuation is not considered to have had a negative impact on the results or interpretation of this study.

2. The protocol states that the water quality parameters will be measured in one representative test vessel for the aged solutions. During this study the water quality parameters were measured in a composite of replicates A through D. As the composite solution represents the water quality of the aged solutions and is a standard practice in acute testing, this deviation is not considered to have had a negative impact on the results or interpretation of this study.

Validity criteria fulfilled:
yes
Conclusions:
The 48-hour EC50 value for Daphnia magna and the test substance was empirically estimated to be > 100 mg a.i./L, the highest nominal concentration tested.
Executive summary:

The purpose of the study was to investigate the acute toxicity (EC50) of the hydrolysis products for 2,4,6,8 -tetramethylcyclotetrasiloxane to daphnids (Daphnia magna) under static-renewal test conditions. The results of the study are based on nominal concentrations of the parent material. Since no concentration tested ≥ 50% immobilization, the 48-hour EC50 value for Daphnia magna and the test substance was empirically estimated to be > 100 mg a.i./L, the highest nominal concentration tested. The highest concentration producing 0% toxicant-related imobilization was 100 mg/a.i./L. The lowest concentration producing 100% immobilization was > 100 mg a.i./L. Additional testing to further define the 48-hour EC50 value was not performed since the highest nominal test concentration, 100 mg a.i./L, represented the highest nominal test concentration required by the testing guideline.

Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
weight of evidence
Study period:
1994-04-27 to 1994-04-29
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
EU Method C.2 (Acute Toxicity for Daphnia)
Deviations:
no
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
- Concentrations: 500 mg/l nominal treatment

- Sampling method: Samples of test media were taken at the start and end of the test

- Sample storage conditions before analysis: Refrigerated
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 500 mg/l nominal concentration of the test substance was prepared by stirring overnight.

- Controls: Dilution water
Test organisms (species):
Daphnia magna
Details on test organisms:

- Type and amount of food: Chlorella vulgaris at 500000 cells/ml

- Feeding frequency: Daily
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
204 mg/l as CaCO3
Test temperature:
20.3 - 21.7ºC
pH:
7.4 - 8.1
Dissolved oxygen:
99 - 100% ASV
Nominal and measured concentrations:
Nominal: 0(Control), 500 mg/l

Measured concentration at start of test: 405 mg/l

Measured concentration at end of test: 436 mg/l

Mean measured concentration: 420 mg/l

Mean measured concentration as a percentage of nominal: 84.1%

The test results are presented and interpreted with reference to nominal concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel: Conical flasks

- Type: closed

- Material, fill volume: Glass, 150 ml of test medium

- Aeration: none

- No. of organisms per vessel: 5

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

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


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted freshwater prepared by mixing (1:1) treated mains water and proprietary mineral water (Ashbourne, Still Natural Water (Nestle, UK. Limited).

- Culture medium different from test medium: no

- Chlorine: <0.1 mg/l (Total)

- Alkalinity: 134 mg/l as CaCO3

- Conductivity: 404 μS/cm

OTHER TEST CONDITIONS

- Adjustment of pH: no

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : Immobilization after 24 and 48 h
Reference substance (positive control):
no
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 500 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis product
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 500 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Details on results:
- Mortality of control: 0
Reported statistics and error estimates:
No toxic effects were observed in the test media, the test results were therefore not subject to statistical analysis.
Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of >500 mg/l and NOEC of ≥500 mg/l have been determined for the effects of the test substance on mobility of Daphnia magna 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 invertebrates: 48 hour EC50 >100 mg/l (nominal, highest concentration tested) in accordance with OECD Guideline 202 (Daphnia sp. acute immobilisation test);

48 hour EC50 >500 mg/l (nominal, highest concentration tested) (EU Method C.2 (Acute toxicity for Daphnia)), read across from triethoxy(methyl)silane (CAS 2013-67-6). The observations in this study are attributed to the exposure of test organisms to the hydrolysis products in the test system. The EC50 is equivalent to >264 mg/l when expressed in terms of the silanol hydrolysis product, methylsilanetriol.

Key value for chemical safety assessment

Additional information

Toxicity to aquatic invertebrates was studied in a valid Daphnia sp. acute immobilisation test with Daphnia magna according to OECD 202 under GLP. Test concentrations ranged from 1 to 100 mg/l (nominal concentrations) Because of rapid hydrolysis of the test substance, the stock solution was allowed to hydrolyse for 48 hours prior to test initiation under conditions that prevented evaporation of the test substance. No effects on Daphnia survival or mobility were observed. Under the conditions of the test, the hydrolysis products of the test substance did not induce toxicity to Daphnia Magna. A 48 hour EC50 value of >100 mg/l was determined.

 

To further assess the toxicity of the hydrolysis product methylsilanetriol, good quality data have been read across from triethoxy(methyl)silane (CAS 2031-67-6). HD4 and triethoxy(methyl)silane rapidly hydrolyse to the same hydrolysis product; methylsilanetriol. The other hydrolysis products are hydrogen gas and ethanol, respectively. In the test 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 48 hour EC50 value of >500 mg/l (nominal, highest concentration tested) has been determined for the effects of triethoxy(methyl)silane (CAS 2013-67-6) on mobility of Daphnia magna (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.