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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:
2001-01-09 to 2001-01-11
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Remarks:
Guideline study with restrictions. The study was conducted according to the appropriate OECD test guideline, and in compliance with GLP. Undissolved test substance was observed. Possible physical effects.
Reason / purpose for cross-reference:
reference to other study
Qualifier:
according to guideline
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A stock dispersion was prepared at a nominal loading rate of 100 mg/l by intense stirring for 30 minutes followed by ultra-sonification for 15 minutes. Other treatments were prepared by dilution of the dispersion. A parallel 100 mg/l treatment was prepared by ultra-sonification for 10 minutes followed by stirring for 24 hours and then filtration through a 0.45 μm cellulose nitrate filter.

- Controls: Dilution water

- Evidence of undissolved material: undissolved test material was present in unfiltered test media
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Strain: Clone 5

- Source: Umweltbundesamt, Institut für Wasser-, Boden und Lufthygiene, Berlin, Germany

- Age at study initiation (mean and range, SD): 8-23.5 h

- Feeding during test: none

ACCLIMATION

- Acclimation period: 8 hours

- Acclimation conditions (same as test or not): yes
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
250 mg/l as CaCO3
Test temperature:
21ºC
pH:
7.6-7.9
Dissolved oxygen:
≥7.9 mg/l
Salinity:
not applicable
Nominal and measured concentrations:
Nominal loading rates: 0 (Control), 0.32, 1.0, 3.2, 10, 32 and 100 mg/l and 100 mg/l with filtration.

Details on test conditions:
TEST SYSTEM

- Test vessel: Beaker

- Type: open

- Material, size, headspace, fill volume: glass, 250 ml with 150 ml of test medium

- Aeration: none

- Renewal rate of test solution (frequency/flow rate): static

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 2

- No. of vessels per control (replicates): 2

TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Reconstituted freshwater prepared by adding analytical grade salts to deionised water.

- Alkalinity: 0.8 mmol/l

- Ca/Mg ratio: 4:1

- Culture medium different from test medium: no

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

OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 h light, 8 h dark

- Light intensity: 370-380 lux

EFFECT PARAMETERS MEASURED: mobility after 24 and 48 hours

TEST CONCENTRATIONS

- Spacing factor for test concentrations: 3.1

- Range finding study: yes but results not reported.
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Key result
Duration:
48 h
Dose descriptor:
EL50
Effect conc.:
< 100 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
filtered test medium
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EL50
Effect conc.:
12 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
unfiltered test medium
Basis for effect:
mobility
Remarks on result:
other: 8.7-16.6
Key result
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
3.2 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
unfiltered test medium
Basis for effect:
mobility
Details on results:
- Mortality of control: 0

- Effect concentrations exceeding solubility of substance in test medium: The test substance was not completely soluble and physical effects (surface trapping) were noted in treatments of 3.2 mg/l and higher.
Results with reference substance (positive control):
Not reported
Reported statistics and error estimates:
EL50 values and their confidence intervals were determined by moving-average interpolation. NOELRs were determined directly from the test data.

Table 1. Test results

 Nominal test substance concentration (mg/l)  Mean percentage immobilisation after 24 hours  Mean percentage immobilisation after 48 hours
 0 (Control)  0
 Filtered 100 mg/l stock dispersion  0  80
 0.32  0  0
 1.0  0  10
 3.2  0  0
 10  0  35
 32  65  100
 100  100  100

A 48-h EL50 value of 12 mg/l (8.7 -16.6 mg/l) is reported from the results of the test with unfiltered media based on percentages of immobilised test organisms. Test organisms that were trapped at the surface but still mobile were considered to be unaffected.

Validity criteria fulfilled:
yes
Conclusions:
The test substance was acutely toxic to Daphnia magna over 48 hours (48-h EL50 <100 mg/l). The organisms were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. The test result is considered to be reliable. Exposure to unfiltered test medium gave a 48-h EL50 of 12 mg/l and a NOELR of 3.2 mg/l. The loading rates used were all above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number, with exposure to a 100 mg/l test medium that had been filtered, gave a similar result to that reported in this study (48-h EL50 <100 mg/l). Based on the hydrolysis half-life of the test substance (approx. 22 hours, predicted), it is likely that the organisms were exposed mainly to the hydrolysis products.

Description of key information

48-hour EL50 <100 mg/l (nominal concentration) (single limit test concentration, with filtering of the test substance), mortality of Daphnia magna.

Key value for chemical safety assessment

Additional information

A 48-hour EL50 value of <100 mg/l (nominal concentration) has been determined for effects of the test substance on mortality of Daphnia magna, conducted in accordance with OECD TG 202 and in compliance with GLP (IBACON, 2001c).

The organisms were exposed to a filtered suspension of the test substance prepared at a loading rate of 100 mg/l. Exposure to unfiltered test medium gave a 48-hour EL50 of 12 mg/l and a NOELR of 3.2 mg/l. The loading rates used were all above the water solubility of the substance (<0.1 mg/l). Results of a related study conducted under the same project number, with exposure to a 100 mg/l test medium that had been filtered, gave a similar result to that reported in this study (48-hour EL50 <100 mg/l) (IBACON, 2001d).

Based on the hydrolysis half-life of the test substance (43 hours at pH 7 and 20-25°C, predicted), it is likely that, in the absence of undissolved material, the organisms would be exposed to a mixture of the parent substance and the hydrolysis products. Test solutions were prepared above the limit of water solubility of the parent substance. Undissolved material might have been present in the test solutions as a film on the surface or as hydrolysis resistant micelles of the parent substance and oligomers in the water body. The tests with Daphnia have been conducted in filtered and unfiltered test media. The observations during these tests indicate that higher toxicity is observed in unfiltered test media. Consequently, effects are associated with undissolved test material. A filter is not able to effectively retain all undissolved monomers and oligomers, therefore it is possible that the test organisms in all the tests could have been exposed to undissolved material. Therefore, the results should be treated with caution.

The results are supported by a reliable study with the read-across substance triethoxy(octyl)silane (CAS 2943-75-1). The test substance did not achieve any toxicity when tested at the solubility limit of the substance; the EC50 value was >0.13 mg a.i./l and the NOEC value was ≥0.13 mg a.i./l (nominal concentration) (Springborn Smithers, 2008b). The study was conducted in accordance with OECD TG 202 and in compliance with GLP. The flow-through design of the test means that the test organisms are likely to have been exposed to the parent substance.

Refer to the discussion in the IUCLID Section 6 endpoint summary or Section 7.0 of the CSR for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.