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Short-term toxicity to aquatic invertebrates

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Reference
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1994-11-30 to 1994-12-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EU Method C.2 (Acute Toxicity for Daphnia)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: Test substance concentration was determined in the stock solution used to prepare the test media and in the control as well as all treatments at the start and end of the test.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION
- Method: A 1000 mg/L stock solution in synthetic freshwater was prepared by mixing for 18 hours followed by filtration. The test media were prepared by dilution of the stock solution. The measured DOC concentration in the stock solution was 398 mg/L which was equivalent to 907 mg/L of the test substance.
- Controls: Dilution water
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM
- Common name: Daphnia magna
- Strain: Clone 5
- Source: In-house stock culture
- Age at study initiation: <24 h
- Feeding during test: None

METHOD OF BREEDING
- Method of breeding: Parthenogenetic reproduction
- Breeding conditions: The Daphnia are held in 1 L glass beakers filled with M4-medium (Elendt 1990).
- Maintenance: Every 2 to 3 d, water is renewed, exuviae and juveniles are removed from the beakers.
- Food type: Scenedesmus subspicatus
- Amount of food: As much as is consumed, leaving no residue
- Feeding frequency: Daily
- Other: Red/dark-brown coloring of the organisms is considered healthy.
- Other: Every 4 weeks, juveniles are isolated and used for further breeding.

ACCLIMATION
- Acclimation period: 24 h before test start
- Acclimation conditions (same as test or not): Yes
- Other: 24 h before test start, the mother organisms are isolated. The juveniles that hatch over night are used for the test.
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
The sum of the Ca2+ and Mg2+ ions was 2.5 mmol
Test temperature:
20 +/-1ºC
pH:
7.8
Dissolved oxygen:
8.2 - 8.4 mg/l
Salinity:
not applicable
Nominal and measured concentrations:
Nominal: 0 (control), 54, 91, 163, 272, 481 and 816 mg/l
Measured (0 h): 0, 58, 92, 190, 270, 488, 814 mg/L
Measured (48 h): 0, 57, 90, 166, 266, 475, 785 mg/L
Details on test conditions:
TEST SYSTEM
- Test vessel: Glass cylinder
- Type: Open
- Specifications: Glass vessel, containing 10 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
- Biomass loading rate: 2 mL per organism
- Feeding: None

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: Elendt M4 medium
- Intervals of water quality measurement: end of test

OTHER TEST CONDITIONS
- Photoperiod: Dark

EFFECT PARAMETERS MEASURED:
Immobilization after 24 and 48 h exposure

TEST CONCENTRATIONS
- Spacing factor for test concentrations: 1.7
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 816 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 816 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
- Other adverse effects control: None reported
Results with reference substance (positive control):
EC50 (48 h) > 1.0, < 2.0 mg/l
Reported statistics and error estimates:
The were no toxic effects observed in the highest test concentrations and therefore statistical analysis of the results was not carried out.

ANALYTICAL RESULTS

A deviation of < 20% was obtained for the geometric mean values of the measured concentrations at 0 and 48 h. Therefore, > 80% of the test concentration remained during the testing period and the results were based on the nominal concentrations.

EXPERIMENTAL RESULTS

Table 1. Test results

 Nominal test concentration (mg/l)  Mean percentage immobilisation after 24 hours  Mean percentage immobilisation after 48 hours
 0 (Control)  0  0
 54  0  0
 91  0  0
 163  5  5
 272  5  5
 481  0  0
 816  0  0
Validity criteria fulfilled:
yes
Conclusions:
The 48-h EC50 obtained for the short-term toxicity of the substance toward aquatic invertebrates was >816 mg/L and the NOEC ≥816 mg/L based on nominal concentrations of the substance. However, it is likely that the test organisms were exposed to the hydrolysis products of the substance.

Description of key information

EC50 (48 h) > 816 mg/L (nominal, EU method C2, D. magna, RL 1), equivalent to 607 mg/L when expressed in terms of the silanol hydrolysis product

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Dose descriptor:
EC50
Remarks:
48 h
Effect concentration:
> 607 mg/L

Additional information

A 48-h EC50 value of >816 mg/l and a NOEC of ≥ 816 mg/l (EU Method C.2 (Acute Toxicity for Daphnia) was obtained for the short-term effects of the test substance on the mobility of Daphnia magna based on nominal concentrations.

Since the substance hydrolyses rapidly (half-life approximately 2.6 hours) to propysilanetriol, under ecotoxicity testing conditions, the organisms were predominantly exposed to the hydrolysis product.