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Ecotoxicological information

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:
1995-09-26 to 1995-09-28
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: 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/L and the fresh stock solution used to prepare the test media.

- Sampling method: Concentrations of test substance hydrolysis products determined in fresh media at all concentrations after preparation and again before renewal after 24 hours. The concentrations of the fresh stock solution used to prepare the test media was also determined.

- Sample storage conditions before analysis: not reported
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Test media prepared by dilution of a 1000 mg/L stock solution prepared by mixing for 18 h followed by filtration. TOC concentration of stock solution determined and used as the basis for determining the nominal test concentrations.

- Test concentrations (Nominal): Control, 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/L
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: 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:
The sum of the Ca2+ and Mg2+ ions: 2.5 mmol
Test temperature:
20 +/-1 degree C
pH:
7.5 - 7.9
Dissolved oxygen:
8.8 - 9.6 mg/L
Salinity:
not applicable
Nominal and measured concentrations:
- Test concentrations (Nominal): Control, 0.64, 1.3, 2.7, 5.4, 11, 21 and 43 mg/L

- Test concentrations (at start of test): Control,
- Test concentrations at end of test: Control,
- The measured concentrations that were >LOD were within +/-20% of nominal. The results are therefore presented and interpreted with reference to nominal concentrations.
Details on test conditions:
TEST SYSTEM

- Test vessel: glass cylinder

- Type: open

- Material, size, headspace, fill volume: cylinder 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


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 (with observation intervals if applicable) : Immobilization after 24 and 48 h exposure


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2
Reference substance (positive control):
yes
Remarks:
Potassium dichromate
Key result
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
6.7 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Remarks on result:
other: 4.9 - 9.1
Key result
Duration:
24 h
Dose descriptor:
EC50
Effect conc.:
20 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Remarks on result:
other: 12 - 36
Key result
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
2.7 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Remarks:
but exposure is to hydrolysis products
Basis for effect:
mobility
Results with reference substance (positive control):
- Results with reference substance valid?

- EC50/LC50: >1 mg/L, <2.0 mg/L
Reported statistics and error estimates:
EC50 and confidence interval determined by Probit analysis

Table 1. Results of analysis of test media

 Nominal test concentration (mg/L)  Measured concentration at start of test (mg/L)  Measured concentration at end of test (mg/L)
 0 (Control)  -  -
 0.64  <LOD  <LOD
 1.3  <LOD  <LOD
 2.7  Unreliable value  2.3
 5.4  Unreliable value  6.3
 11  12.4  9.7
 21  20.9  20.4
 43  37.7  39.8

Table 2. Test results

 Nominal test concentration (mg/L)  Mean percentage immobilisation after 24 hours  Mean percentage immobilisation after 48 hours
 0 (Control)  5  5
 0.64  0  0
 1.3  0  0
 2.7  0  5
 5.4  15  50
 11  50  85
 21  40  90
 43  70  95
Validity criteria fulfilled:
yes
Conclusions:
A 48-h EC50 value of 6.7 mg/L and a NOEC of 2.7 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna based on nominal concentrations of the substance. The test substance hydrolyses in water and it is therefore 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 6.7 mg/l (measured as TOC) (EC Guideline 92/69/EWG C2), mobility of Daphnia magna. The EC50 is equivalent to 5.3 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
Effect concentration:
5.3 mg/L

Additional information

A 48-hour EC50 value of 6.7 mg/l (measured as TOC) has been determined for the effects of the registration substance on mobility of Daphnia magna, conducted in accordance with EU Method C.2 (Acute Toxicity for Daphnia) and in compliance with GLP (Hüls 1995). 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.

It is evident from the low recovery (as DOC) that a significant proportion of the test material was removed by filtration, and at the loading concentration used in preparation of stock, it is expected that oligomers and/or cross-linked aggregates may have been present to some extent, which would be consistent with this. While this is an uncertainty, it is considered that the study results in terms of geometric mean measured concentrations are suitable to be used (with caution), with effects attributed in principle to intrinsic ecotoxicity of silanol.

The results may be expressed in terms of concentration of the hydrolysis product, 3-(trihydroxysilyl)propanethiol, by applying a molecular weight correction: (MW of silanol = 154.26 / MW of parent = 196.34) * 6.7 = 5.3 mg/l.

The reliability of two other EC50 values of 4 and 84 mg/l, that were obtained from the open literature, could not be determined.

To support the proposed long-term read-across data, short-term aquatic toxicity data with 3-(triethoxysilyl)propanethiol (CAS 14814-09-6, EC No. 238-883-1) are included, for comparison of aquatic effects between the registered and read-across substances.

A 48-hour EC50 value of 2.71 mg/l has been determined for the effects of 3-(triethoxysilyl)propanethiol (CAS 14814-09-6) on mobility of Daphnia magna, conducted in accordance with OECD TG 202 and in compliance with GLP (Noack 2020). This value is equivalent to 1.75 mg/l when expressed in terms of the silanol hydrolysis product, 3-(trihydroxysilyl)propanethiol).

During the test with 3-(triethoxysilyl)propanethiol (CAS 14814-09-6), it is likely that the Daphnia were exposed predominantly to the parent substance, especially at the beginning of the tests, with increasing amounts of hydrolysis products towards the end of the test media renewal period.

Refer to IUCLID Section 6, CSR Section 7.0, for further discussion of the approach to chemical safety assessment for this registration substance.