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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:
1993-06-22 to 1993-06-24
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
Principles of method if other than guideline:
DIN 38412 Part 1; EG Guideline 92/69/EWG
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
The DOC concentration of the filtered stock solution used to prepare the test media was determined.
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The test substance was added to dilution water to provide a nominal concentration of 1 g/l and stirred for 18 hours. The solution was filtered and the DOC content determined to be 534 mg/L, which is equivalent to 1093 mg/L of the test substance. This solution served as the primary stock solution of the test substance for preparation of the other test concentrations. The test began immediately after preparation of the test solution.
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: Parthenogenic reproduction

- Feeding during test: None

ACCLIMATION

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

- Type and amount of food: Scenedesmus subspicatus, 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:
Water hardness was reported  as 2.5 mmol/L and alkalinity was reported as 0.8 mmol/L.
Test temperature:
20ºC
pH:
The control pH was 7.5 units and the test vessel pH ranged from 7.5 to 8.7 units. 
Dissolved oxygen:
The control DO was 8.4 mg/L and the test vessel DO ranged from 7.8 to 8.7 mg/L.
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations (based on measured concentrations in stock solution):  0, 8.7, 16.4, 28.4, 54.7, 94.0, 174.9, 306.0, 546.5, and 983.7 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 dilution water was synthetic fresh water with a hardness of approximately 294 mg/L as CaCO3.
Reference substance (positive control):
yes
Remarks:
potassium dichromate
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
94 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
331 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: 249-441
Details on results:
- Mortality of control: 0
Results with reference substance (positive control):
24 h EC50 lies between 0.9 and 1.9 mg/L
Reported statistics and error estimates:
EC50 values were calculated by Probit analysis. The NOEC was determined by visual examination of the raw data

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
 8.7  0  0
 16.4  5  5
 28.4  0  0
 54.7  0  0
 94.0  5  10
 174.9  19  19
 306.0  45  50
 546.5  40  60
 983.7  62  100
Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of 331 mg/L and NOEC of 94 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: 331 mg/l, mobility of Daphnia magna; equivalent to 205 mg/l as 3-aminopropylsilanetriol.

Key value for chemical safety assessment

EC50/LC50 for freshwater invertebrates:
205 mg/L
EC50/LC50 for marine water invertebrates:
360 mg/L

Additional information

The only available test data for short-term toxicity of 3-(trimethoxysilyl)propylamine (CAS 13822-56-5) to invertebrates are of non-assignable reliability, taken from a secondary data source. An EC50 value of 302 mg/l was reported.

Reliable data are however available from appropriate structural analogues, 3-aminopropyltriethoxysilane (CAS 919-30-2) and 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6), which react in water to the same hydrolysis product as the registration substance, 3-aminopropylsilanetriol.

A 48-hour EC50 value of 331 mg/l (nominal concentration) has been determined for the effects of 3-aminopropyltriethoxysilane (CAS 919-30-2) on mobility of Daphnia magna, in accordance with OECD Test Guideline 202.

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 results may be expressed in terms of concentration of the hydrolysis product, 3-aminopropylsilanetriol, by applying a molecular weight correction: (MW of silanol = 137.21 / MW of parent = 221.37) * 331 mg/l = 205 mg/l. This value is read across to 3-(trimethoxysilyl)propylamine (CAS 13822-56-5) without further correction.

A 48-hour LC50 of 580 mg/l have also been determined for the effects of the same read-across substance on mortality of the marine invertebrate Acartia tonsa. The test substance is susceptible to hydrolysis and it is therefore likely that the test organisms were exposed to the hydrolysis products of the substance. The LC50 is equivalent to 360 mg/l expressed in terms of concentration of the hydrolysis product.

These findings are supported by a 48-hour EC50 in Daphnia magna of >100 mg/l, determined for 3-(trimethoxysilyl)propyl isocyanate (CAS 15396-00-6). For this substance the isocyanate group is very rapidly hydrolysed to the corresponding amine, which is structurally identical to the registration substance (half-life <1 minute at pH 7), and further hydrolysis of the alkoxy groups proceeds at a slower rate (half-life of 2.6 hours at pH 7 and 20-25 °C, estimated) to 3-aminopropylsilanetriol and methanol.

 

Refer to the IUCLID Section 6 endpoint summary (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.