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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:
1993-05-25 to 1993-05-27
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)
Version / remarks:
1982
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
The dissolved organic carbon analysis (DOC) concentration of the stock solution used to prepare the test media was determined and used as the basis for setting the treatment levels.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method:The test substance was dissolved at 1 g/l in VE water and stirred for 18 h. The resulting stock solution was filtered and served as the initial solution for testing. 
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Common name: Daphnia magna

- Strain: Clone 5

- Source: Stock culture

- Age at study initiation (mean and range, SD): <24 h

- Method of breeding: Parthenogenetic reproduction

- Feeding during test: None

ACCLIMATION

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

- Type and amount of food: Scenedesmussubspicatus, sufficient to be consumed each day leaving no residue

- Feeding frequency: daily
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Hardness:
synthetic freshwater: ratio Ca2+ : Mg2+ = 4 : 1 Na+ : K+ = 10 : 1 (CaCl2.2H2O = 294 mg/L, MgSO4.7H2O = 123 mg/L, NaHCO3 = 63 mg/L, KCl = 5.5 mg/L)

Test temperature:
20±1ºC
pH:
7.4-7.5 at end of test
Dissolved oxygen:
6.9-8.2 mg/L at end of test
Salinity:
Not applicable
Nominal and measured concentrations:
The DOC content of the stock solution was determined to be 378.5 mg/l, corresponding to a test material concentration of 1046 mg/l.

Nominal concentrations based on DOC measured concentration in the stock solution: 0 (Control), 115, 167, 230, 335, 471, 669 and 941 mg/L

Details on test conditions:
TEST SYSTEM

The test vessels were glass cylinders graduated to 10 ml. 

Each concentration had 4 replicate vessels and each vessel contained 5 test organisms.  

The age of the test organisms was <24 hours and they were not fed during the test. 

Vessels were kept in the dark at 20ºC and not aerated during the  test.

The Daphnia were observed for immobilization after 24 and 48 hours of exposure.  

The synthetic water used for the study had the following components: CaCl2 x 2 H20 = 294 mg/l MgSO4 x 7 H20 = 123 mg/l NaHCO3 = 63 mg/l KCl = 5.5 mg/l
Reference substance (positive control):
yes
Remarks:
Potassium dichromate.
Key result
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
669 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
869 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Key result
Duration:
48 h
Dose descriptor:
EC100
Effect conc.:
> 941 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Key result
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
> 941 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Immobilisation of control: 0
Results with reference substance (positive control):
EC50: >0.9, <1.9 mg/L
Reported statistics and error estimates:
The EC50 value was determined by Probit analysis. TheNOEC was determined by visual examination of the raw data.

Immobile organisms were observed only at the test substance concentration of 941 mg/l:

Concentration

24 hour

48 hour

Mobile

Immobile

%

Mobile

Immobile

%

Control

20

0

0

20

0

0

115

20

0

0

20

0

0

167

20

0

0

20

0

0

230

20

0

0

20

0

0

335

20

0

0

20

0

0

471

20

0

0

20

0

0

669

20

0

0

20

0

0

941

19

1

5

7

13

65



Oxygen content and pH at the end of the test:
conc (mg/l)  O2 (mg/L)          pH
Control (0)       8.2                7.5
115                7.3                 7.5
167                7.2                 7.4
230                7.1                 7.4
335                6.9                 7.4
471                7.2                 7.4
669                7.4                 7.4
941                6.9                 7.4

Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of 869 mg/L and a NOEC of 669 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna. It is likely that the test organisms were exposed to the hydrolysis products of the substance.

Description of key information

48-hour EC50 869 mg/l (measured based on DOC in the stock solution) (OECD guideline 202). The observations in this study are attributed to the exposure of test organisms to the silanol hydrolysis product, (3-chloropropyl)silanetriol, in the test system. The EC50 is equivalent to 685 mg/l when expressed in terms of the silanol hydrolysis product.

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates
Effect concentration:
685 mg/L

Additional information

A 48-hour EC50 value of 869 mg/l (measured) has been determined for the effects of the registered substance (3-chloropropyl)trimethoxysilane (CAS 2530-87-2) on mobility of Daphnia magna (Hüls, 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 nominal test concentrations are supported by DOC analysis of the stock solution. The results may be expressed in terms of concentration of the silanol hydrolysis product, (3-chloropropyl)silanetriol, by applying a molecular weight correction: (MW of silanol = 156.64 / MW of parent = 198.72) * 869 mg/l = EC50 685 mg/l.

 

Above a concentration of approximately 1000 mg/l, dimeric / oligomeric, cyclic or cross-linked condensation products could potentially form over time in the aqueous test media. There was no mention of undissolved material (parent substance or precipitated products) in the study report for this test. 

In a supporting short-term toxicity to aquatic invertebrates test, conducted according to OECD TG 202 and in compliance with GLP, a 48 hour NOEC and EC10 were concluded to be 4.64 and 10 mg/l respectively, and an EC50 >100 mg/l, based on the mobility of Daphnia magna.

The measured concentrations at the start and after 48-hours were below 70% (in the first set) and 60% (in the second test set) of the nominal concentrations. This depended on undissolved test substance or water-insoluble condensation products, respectively. The undissolved test substance or water-insoluble condensation products tend to adsorb on the surface of the glass vessels used and were not detected by the DOC-method. Although not dissolved, the test substance was available in the stock solution of the nominal concentration of 100 mg/L. Because the reported DOC measurements are below the limit of quantitation, the reported biological results are related to the nominal concentrations. Due to the presence of undissolved test materials and DOC recoveries below the limit of quantitation, the results should be treated with caution (LPT, 2003).

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion of the approach to chemical safety assessment for this registration substance.

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