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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:
2007-02-28 to 2007-03-02
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
"Analytical monitoring: During the in-life phase of the definitive study, one water sample (alternating between replicates A and B) from each treatment level and the control solution was collected and extracted at 0 hour (test initiation) and 48 hours (test termination).  
Vehicle:
no
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: During the definitive study, 3-(triethoxysilyl)propiononitrile (density 0.974 g/mL, 946 mg a.i./L) was delivered directly into the diluter's mixing chamber via syringe. The resulting solution was observed to be clear and colorless with an oily film of undissolved test substance on the solution's surface. A Glenco®  50-mL gas-tight syringe in conjunction with a Harvard Syringe Pump was calibrated to deliver 46.58 µL/cycle of the 946 mg a.i./L 3-(triethoxysilyl)propiononitrile solution into the diluter system's chemical mixing chamber which also received 0.387 L of dilution water per  cycle. The mixing chamber was positioned over a water-driven magnetic stirrer and was partially submerged within an ultrasonic water bath which continuously mixed the contents of the mixing chamber. The concentration of 3-(triethoxysilyl)propiononitrile in the solution contained within the mixing chamber was equivalent to that of the highest nominal test concentration (120 mg a.i./L) and was proportionally diluted (50%) to produce the remaining nominal test concentrations (60, 30, 15 and 7.5 mg  a.i./L).
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Source: Springborn Smithers culture facility.  

- Culture conditions: Daphnids were cultured in 1.0-L glass vessels containing 0.80 L of water. 

- Culture medium: Water used to culture the daphnids was from the same source as the dilution water.  

- Feeding: Daphnids were fed a unicellular green algae (ankistrodesmus falcatus, 4 x 10E7 cells/mL) at a rate of 0.5  to 1.5 mL per vessel daily green algae depending on the age of the adult organisms in the culture vessel and 0.5 mL of a combination of yeast, cereal leaves and flaked fish food (YCT) daily.

- Age of test organisms: Daphnids were obtained by removing all immature daphnids from the culture vessel, thus isolating mature gravid daphnids < 24 hours prior to initiating the test. Young produced by these organisms were subsequently pipetted into the test beakers. Age at study initiation < 24 hours.
Test type:
flow-through
Water media type:
freshwater
Limit test:
no
Test temperature:
19 to 21 ºC
pH:
7.0 at test initiation and 7.1 at test termination
Dissolved oxygen:
9.8 to 9.9 mg/L at test initiation and 9.4 to 9.5 at test termination
Nominal and measured concentrations:
Nominal test concentrations: 0 (control), 7.5, 15, 30, 60 and 120 mg/L.

Mean measured concentrations:  5.7, 15, 21, 45 and 100 mg/L

Method of calculating mean measured concentrations (i.e., arithmetic mean, geometric mean, etc.):  Arithmetic mean.  

The results are presented and interpreted with reference to mean measured concentrations.
Details on test conditions:
TEST SYSTEM

- Exposure system: The toxicity test was conducted using an exposure system consisting of an  intermittent-flow proportional diluter and a set of 12 exposure vessels. The exposure system was designed to provide five concentrations of the test substance and a dilution water control. Test vessels were  impartially placed in a water bath containing circulating water designed to maintain the test solution at a temperature of 20 ± 1 ºC. A 16-hour  light, 8-hour dark photoperiod was maintained. Two replicate vessels were established for each treatment level and the control.

- Test temperature range: 19 to 21 ºC

- Exposure vessel type (e.g., size, headspace, sealed, aeration, # per treatment): Each test vessel (1600-mL square glass battery jars) had two 2-cm holes drilled in the sides,15 cm from the bottom, which were covered with Nitex® 40 mesh screen for drainage. The total test solution volume was maintained at 1400 mL.  

- Test design (number of replicates, individuals per replicate, concentrations): Twenty daphnids were impartially selected and distributed to each concentration and the control (two replicates, ten daphnids per replicate vessel).

- Replication: Two replicate test vessels were established for each treatment level and a dilution water control.  

- Aeration: No aeration was provided to the test vessels.

- Dilution water source: Laboratory well water. oDilution water chemistry (hardness, alkalinity, pH, TOC):  The dilution water had a total hardness and alkalinity as CaCO3 of 44 mg/L and 21 mg/L, respectively, a pH range of 6.8 to 7.3 and a specific conductivity range of 210 to 240 µmhos/cm. The TOC concentration of the dilution water was 0.58 and 0.48 mg/L for the months of February and March 2007, respectively.  

- Lighting (quality, intensity, and periodicity): The test area was illuminated with fluorescent bulbs. The test area received a regulated photoperiod of 16 hours of light and 8 hours of darkness. Sudden transitions from light to dark and vice versa were avoided. Light intensity was measured once during the test.

- Control group: dilution water control

- Water chemistry in test (D.O., pH), in the control, and at least one concentration where effects were observed: Measured daily throughout the test.

- Element (unit) basis (i.e., immobilization): Immobilization
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 100 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 100 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 120 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Reported statistics and error estimates:
There were no significant effects on immobility during the test and therefore statistical analysis of the results was not required.

Table 1. Test results

 Mean measured test substance concentration (mg/L)  Percentage immobilisation after 24 hours   Percentage immobilisation after 48 hours
 0 (Control)  0  5
 5.7  0  10
 15  0  0
 21  0  0
 45  0  0
 100  0  0


Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of >100 mg/L and NOEC of =100 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 a solution that was predominantly of the test substance but also contained its hydrolysis products.

Description of key information

48 h EC50 >100 mg/l, D. magna, read-across from CAS 919-31-3, measured value based on parent substance.

Key value for chemical safety assessment

Additional information

There are no reliable short-term toxicity to invertebrate data available for 3-(trimethoxysilyl)propiononitrile (CAS 2526-62-7), therefore, good quality data for an appropriate structural analogue, 3-(triethoxysilyl)propiononitrile (CAS 919-31-3), have been read across. Both substances share the same silanol hydrolysis product, 3-(trihydroxysilyl)propiononitrile. The other hydrolysis products are methanol and ethanol, respectively. In the test with 3-(triethoxysilyl)propiononitrile (CAS 919-31-3), the observations are attributed to the exposure of test organisms to 3-(triethoxysilyl)propiononitrile in the test system. There is no basis to expect that ethanol significantly influenced the results of the test. The toxicity of ethanol is discussed further in the ecotoxicological information overview endpoint summary (additional information).

 

A 48-hour EC50 value of >100 mg/l and NOEC of =100 mg/l have been determined for the effects of the read-across substance 3-(triethoxysilyl)propiononitrile on mobility of Daphnia magna (highest concentration tested, measured concentration), in accordance with test guidance OECD 202 (Springborn Smithers, 2007). However, due to the rapid hydrolysis rate of the tested substance and the test system being flow-through, it is likely that the test organisms were exposed to both the test substance and its hydrolysis product. This is confirmed by the fact that the parent substance’s measured concentrations are lower than the nominal concentrations (but within 20% of nominal). Results expressed relative to nominal concentrations are EC50 >120 mg/l.

During the test with the read-across substance, the test organisms are likely to have been predominantly exposed to the parent substance. The read-across is therefore supported by a Daphnid 48 h EC50 QSAR prediction for the silanol hydrolysis product, 3-(trihydroxysilyl)propiononitrile, using ECOSAR v2.0 for the prediction of the aquatic toxicity of neutral organics. A predicted value of 990000 mg/l was determined.