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Short-term toxicity to aquatic invertebrates

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short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
From 2015-12-14 to 2016-01-21
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
according to guideline
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
GLP compliance:
Analytical monitoring:
Details on sampling:
- Concentrations: The concentration of the test item in each sample for GC analysis was determined on the basis of a comparison of the peak area on the chromatogram of the sample solution with that of a standard solution.
- Sampling method: The calibration curve was drawn by using four standard solutions of 1.01, 5.03, 10.1 and 20.1 mg/L prepared according the following way: the test sample (60µL) was taken out by microsyringe and dissolved in hexane to obtain 1010 mg/L solution of the test item, then this solution was diluted to prepare 10.1 mg/L standard solution.
not specified
Test organisms (species):
Daphnia magna
Details on test organisms:

- Species: Clone A
- Source: University of Sheffield, UK (supplied on July 9th,1990)
- Age of parental stock : 14-day old
- Age at study initiation: <24 hours
- Feeding during test : No feeding

- Acclimation conditions (same as test or not): Same as test
- Type and amount of food: Chlorella vulgaris of 0.1-0.2 mgC (organic carbon content)/day per Daphnia
- Feeding frequency: Once a day
- Health during acclimation (any mortality observed): 100% survival rate

Test type:
Water media type:
Limit test:
Total exposure duration:
48 h
Total hardness (as CaCO3) = 28 mg/L
Test temperature:
7.8 to 8.0
Dissolved oxygen:
8.8 to 8.9 mg/L
More than 3 mg/L without aeration at the end of the exposure.
11 mS/m
Nominal and measured concentrations:
Nominal concentrations : 0.854, 1.88, 4.13, 9.09, 20.0 mg/L

Measured concentrations at test initiation: 0.844-19.8 mg/L (94.7-99.8% of nominal concentrations).

Measured concentrations at test termination: 0.850-20.3 mg/L (94.6-102% of nominal concentrations).

The measured concentrations of test item were kept within +/- 20% of the nominal concentration.
Details on test conditions:

- Test vessel: 50 mL Erlenmeyer flask containing 50 mL of the test solution
- Type (delete if not applicable): Closed vessel without headspace
- Aeration: No
- No. of organisms per vessel: 5
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4


- Source/preparation of dilution water: 200 mL of test solution per test level, approximately 50 mL per test vessel.
- Total organic carbon: < 0.5 mg/L
- Particulate matter: < 1 mg/L
- Chlorine: < 0.02 mg/L
- Alkalinity: 29 mg/L
- Conductivity: 11 mS/m


- Adjustment of pH: No
- Photoperiod: 16h-light/8-hour dark
- Light intensity: Room light

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :

Immobility and other symptoms (as lethargic and reduced activity) on the test organisms were observed at 24 and 48 hours after exposure. Immobility was defined as the lack of swimming within 15 seconds after gentle agitation of the test vessel.

Reference substance (positive control):
Potassium dichromate
Key result
48 h
Dose descriptor:
Effect conc.:
6.49 mg/L
Nominal / measured:
Conc. based on:
test mat.
Basis for effect:
Remarks on result:
other: 95% confidence limits (mg/L) = 5.09-8.33

Table 1: Measured concentrations of test item in test solutions in mg/L and (Percentage of measured concentration versus nominal concentration %)

Nominal concentration (mg/L)

At the start

At the end

Geometric mean






0.844 (98.8%)

0.850 (99.5%)

0.847 (99.2%)


1.83 (97.3%)

1.86 (99.1%)

1.85 (98.2%)


4.12 (99.8%)

4.21 (102%)

4.16 (101%)


8.60 (94.7%)

8.60 (94.6%)

8.60 (94.6%)


19.8 (98.9%)

20.3 (101%)

20.0 (100%)

n.d.: <0.406 mg/L

Validity criteria fulfilled:
The 48-hour EC50 value of 6.49 mg/L has been determined for the effects of the test substance on immobility of Daphnia magna.

Description of key information

Short-term toxicity to invertebrates: 48-h EC50 6.49 mg/l (nominal, tert-butyl(dimethyl)silanol), mobility of Daphnia magna.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
6.49 mg/L

Additional information

The registration substance, tert-butyl(chloro)dimethylsilane (CAS 18162-48-6) hydrolyses very rapidly in contact with water to form tert-butyl(dimethyl)silanol (CAS 18173-64-3) and hydrochloric acid. As per the REACH guidance (ECHA 2016, R.16) which states that "for substances where hydrolytic DT50 is less than 12 hours, environmental effects are likely to be attributed to the hydrolysis products rather than to the parent substance itself", the aquatic toxicity assessment including aquatic invertebrates, is based on the properties of the silanol hydrolysis product tert-butyl(dimethyl)silanol (CAS 18173-64-3).

Short-term toxicity to invertebrate tests are available with the registered substance and with the silanol hydrolysis product. Data with the silanol hydrolysis product are used as key since the result is more conservative in respect of the silanol assessment entity than the study with the registered substance.

A 48-h EC50 value of 6.49 mg/l (nominal) has been determined for the effects of tert-butyl(dimethyl)silanol (CAS 18173-64-3) on the mobility of Daphnia magna, in accordance with OECD Test Guideline 202 (CERI-Kurume, 2016). The nominal test concentrations are supported by GC analysis. The measured concentrations ranged between 94.6 -102% of the nominal.

A 48-hour EC50 value of >100 mg/l (nominal) (highest concentration tested) has been determined for the effects of the registration substance on mobility of Daphnia magna, in accordance with OECD Test Guideline 202 (Wacker, 2004). It is likely that the test organisms were primarily exposed to the hydrolysis products of the substance.

The results may be expressed in terms of the silanol hydrolysis product, by adjusting for the respective molecular weights: MW tert-butyl(dimethyl)silanol/MW tert-butyl(chloro)dimethylsilane * EC50 value, thus 132.28/150.73 * >100 mg/l = >88 mg/l as tert-butyl(dimethyl)silanol.

Effects of hydrogen chloride on aquatic organisms are limited to those that result from changes to pH in unbuffered media and are discussed in the endpoint summary: ecotoxicological discussion, consideration of the non-silanol hydrolysis product.