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Short-term toxicity to aquatic invertebrates

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Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2007-01-16 to 2007-01-18
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EPA OPPTS 850.1010 (Aquatic Invertebrate Acute Toxicity Test, Freshwater Daphnids)
Version / remarks:
(Flow-through conditions)
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
On day -1, a quality control (QC) sample was prepared at the same nominal concentration as the stock solution. The QC sample and a sample from the stock solution were analysed for the substance concentration.
Vehicle:
yes
Details on test solutions:
PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: A 16 mg/mL diluter stock solution was prepared prior to the start of the test by placing 0.3996 g of D3 in a 25-mL volumetric flask and bringing to volume with acetone. The resulting stock solution was clear and colourless with no visible undissolved substance. In addition, a 0.98 mL/mL solvent stock solution was prepared by bringing 246 mL of acetone to a final volume of 250 mL with deionised water. The resulting solution was clear and colourless.

Prior to test initiation, a 10 mL Glenco® gas-tight syringe in conjunction with a Harvard syringe pump was calibrated to deliver 0.203 mL/cycle of the 16 mg/mL stock solution into the diluter system's mixing chamber which also received 0.203 L of dilution water per cycle. The concentration of D3 in the mixing chamber was equivalent to the nominal test concentration of 1.6 mg/L. The mixing chamber was positioned over a water-driven magnetic stir plate and was partially submerged within an ultrasonic water bath. The sonication aided in the solubilisation of the test substance in the dilution water.

The solvent control solution was prepared in a similar way to produce a final exposure concentration of 0.10 mL/L.

- Controls: Dilution water control and Solvent control
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 used in the test.

- Feeding: Daphnids were fed a unicellular green algae (Ankistrodesmus falcatus, 4 x 10E7 cells/mL) at a rate of 1.0  to 2.0 mL per vessel daily 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:
yes
Total exposure duration:
48 h
Hardness:
Total hardness and alkalinity (as CaCO3) of  160 mg/L and 100 mg/L, respectively.
Test temperature:
19-21 ºC
pH:
7.8 - 8.0
Dissolved oxygen:
8.5-9.3
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control), 0 (Solvent control) and 1.6 mg/L

Measured concentration in stock solution used to prepare the test media: 15.2 mg/L

The test results are reported and interpreted with reference to nominal concentrations
Details on test conditions:
TEST SYSTEM

The test was conducted using an intermittent-flow proportional diluter and a set of eight exposure vessels.  The exposure system consisted of  two replicate test vessels each for the dilution water control, solvent  control and test solution.  

Test vessels consisted of 1600 mL square  glass battery jars which had two holes drilled in each side 15 cm from  the bottom.  The holes were covered with Nitex® 40-mesh screen for  drainage.  The total test solution volume was maintained at 1400 mL.  

A 16 mg/mL dilutor stock solution was prepared in acetone and analyzed to  confirm the test substance concentration in this solvent stock.  The solvent stock  solution was delivered into the diluter's mixing chamber via syringe.   The resulting solution was observed to be clear and colourless.  A Glenco®  10-mL gas-tight syringe in conjunction with a Harvard Syringe Pump was  calibrated to deliver 0.0203 mL/cycle of 16 mg/mL test substance solution into the  diluter's chemical mixing chamber which received 0.203 L of dilution  water per cycle.  The mixing chamber was continuously mixed.  The  concentration of test substance in the solution contained within the mixing chamber  was equivalent to the nominal concentration of 1.6 mg/L.  Dilutor flow  was maintained at a rate to deliver approximately 10 solution  replacements per day.

The exposure vessels were maintained in an area illuminated with  fluorescent bulbs at an intensity of 75 to 81 footcandles (810 to 870  lux)  with a 16 hour light and eight hour dark photoperiod.  Sudden  transitions between light and dark periods were avoided.  

Dilution water  was characterized as having total hardness and alkalinity (as CaCO3) of  160 mg/L and 100 mg/L, respectively, a pH of 7.8 and a specific  conductance of 500 µmhos/cm.  The total organic carbon content (TOC) was  0.30 mg/L.  

The dilution water control vessels had a dissolved oxygen  concentration range of 8.8 to 8.9 mg/L at test initiation and a range of  9.2 to 9.3 mg/L during the test.  

The pH measured in the dilution water  control vessel replicates was 7.9 at test initiation and 7.8 at test  termination.
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 1.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC0
Effect conc.:
>= 1.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 1.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Duration:
48 h
Dose descriptor:
EC100
Effect conc.:
> 1.6 mg/L
Nominal / measured:
nominal
Conc. based on:
test mat.
Basis for effect:
mobility
Details on results:
- Immobilisation of control:0
Reported statistics and error estimates:
There were no effects of the test substance on mobility of the test organisms and therefore statistical analysis of the results was not required.

Table 1. Test results

 Treatment  Mean percentage immobilisation after 24 hours   Mean percentage immobilisation after 48 hours
 0 (Control)  0  0
 0 (Solvent control)  5  5
 1.6 mg/L  0  0
Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of > 1.6 mg/L and NOEC of ≥ 1.6 mg/L have been determined for the effects of the test substance on mobility of Daphnia magna. A concentration of 1.6 mg/L corresponds to the approximate water solubility of the substance.
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
1991
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Principles of method if other than guideline:
Method: other
GLP compliance:
yes
Analytical monitoring:
yes
Details on sampling:
The levels of test substance were determined in the test substance-saturated water at the start of the test and in at least one test  bottle at each dose level at test termination.
Details on test solutions:
Five grams of the test material were placed on the surface of approximately eight liters of dechlorinated municipal water.  The sealed saturator system was designed such that D3 saturated water could be withdrawn from the bottom without disturbing the surface water.  The system was gently agitated with a stir bar for several days prior to the start of the test.  
Test organisms (species):
Daphnia magna
Details on test organisms:
Daphnia magna utilized in the test were less than 24-h old and obtained from egg-bearing, ephippia-free in-house daphnids cultured on unicellular green algae.   The dilution water was unhardended (harness typically 60-80 mg/L as CaCO3) dechlorinated municipal water.  Daphnia cultures were maintained in the same water that was hardened to 200-220 mg/L. 
Test type:
static
Water media type:
freshwater
Limit test:
no
Total exposure duration:
48 h
Test temperature:
22 ± 2 °C
pH:
6.04-6.48
Dissolved oxygen:
8.2 - 12.5 mg/L
Nominal and measured concentrations:
The highest test concentration used in the test was the concentration obtained by the saturator system (129 μg/L).  This water was mixed with dilution water such that levels of 0 % (control), 6.25 %, 12.5 %, 25 %, 50 % and 100 % test-substance-saturated water were used.  

Measured concentrations (µg/L) at 48-h were: Control  = non-detectable,  6.25 %  = 6.8, 12.5 %  = 21,    25 %  = 30,     50 %  = 59,  100 %  = 129, 132
Details on test conditions:
TEST SYSTEM

The test substance-saturated and dilution water were unhardended (hardness typically 60-80 mg/L as CaCO3) dechlorinated municipal water.  

The test was conducted at 22 ± 2 °C in duplicate 500 mL glass bottles filled to capacity with test solution and sealed with screw top lids throughout the study.  

Ten daphnia were added to each test vessel.  Each vessel was examined for mortalities and other untoward effects at 2, 24, and 48-h.

Dissolved oxygen and pH were determined at the end of the test in a number of vessels. 
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 129 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: It is likely that the test organisms were predominantly exposed to the hydrolysis products of the test substance.
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 129 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: It is likely that the test organisms were predominantly exposed to the hydrolysis products of the test substance.
Duration:
48 h
Dose descriptor:
EC100
Effect conc.:
> 129 µg/L
Nominal / measured:
meas. (not specified)
Conc. based on:
test mat.
Basis for effect:
mobility
Remarks on result:
other: It is likely that the test organisms were predominantly exposed to the hydrolysis products of the test substance.

Table 1. Test results

 Nominal test substance concentration (% dilution of stock solution)  Percentage immobility at end of test
 0 (Control)  0
 6.25  0
 12.5  0
 25  5
 50  0
 100

                            
Analytical results were:
Four replicate samples of saturator water were analyzed at 0-h.  The results were 1130,  1210, 1140, and 1130 µg/L.

Analyses of test vessels (µg/L) at 48-h were:
Control  = non-detectable 
6.25 %  = 6.8
12.5 %  = 21   
25 %  = 30    
50 %  = 59 
100 %  = 129, 132

Dissolved oxygen levels ranged from 8.2 mg/L in the controls to 11.0 mg/l at 100 % due to presence of algae in the dilutor.  

Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of > 129 μg/L and NOEC of ≥ 129 μg/L have been determined for the effects of the test substance on mobility of Daphnia magna. A concentration of 1.6 mg/L corresponds to the approximate water solubility of the substance. It is likely that the test organisms were exposed primarily to the hydrolysis products of the substance.
Endpoint:
short-term toxicity to aquatic invertebrates
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2008-06-30 to 2008-07-25
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Guideline study with GLP and analysis of exposure concentrations
Qualifier:
according to guideline
Guideline:
OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)
GLP compliance:
yes (incl. QA statement)
Analytical monitoring:
yes
Details on sampling:
- Concentrations: Measurement of the test article concentrations were performed on the batch preparation of each test solution at test initiation. At test termination, water samples were collected for analysis from each test chamber. Water samples (10 mL) were collected from mid- depth of the test chambers using a glass pipette.

- Sampling method: At test termination, water samples were collected for analysis from each test chamber. Water samples (10 mL) were collected from mid- depth of the test chambers using a glass pipette.
Vehicle:
no
Test organisms (species):
Daphnia magna
Details on test organisms:
TEST ORGANISM

- Source: Daphnia magna used in this study were obtained from in-house cultures. The original source of the brood stock was Aquatic BioSystems, Fort Collins, Colorado.

- Age at study initiation: < 24 hours

- Feeding during test: Daphnia magna were not fed during the test.


ACCLIMATION

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

- Type and amount of food: Daphnia magna cultures were fed a diet of Selenastrum capricornutum and YCT (yeast, cerophyl and trout chow).
Test type:
static
Water media type:
freshwater
Limit test:
yes
Total exposure duration:
48 h
Hardness:
103 mg/L as CaCO3
Test temperature:
20 ± 2 ºC
pH:
7.4-8.2
Dissolved oxygen:
≥ 7.5 mg/L (85 % of saturation)
Salinity:
Not applicable
Nominal and measured concentrations:
Nominal concentrations: 0 (Control) and 120 mg/L

Measured concentration at test initiation: 115 mg/L

Measured concentrations at test termination in Replicates A and B: 118 mg/l and 119 mg/l, respectively.

Mean measured concentration: 117 mg/L (98 % of the nominal)
Details on test conditions:
TEST SYSTEM

- Test vessels: 600 mL glass beakers containing approximately 500 mL of test solution. Test vessels were impartially placed in an environmental chamber set to maintain a temperature of 20 ± 1 °C. Each test vessel was covered with a watch glass to reduce evaporation. Test vessels were labelled with the study number, test article concentration and replicate.

- Treatments and replication: Daphnia magna were exposed to one limit concentration of the test article and a negative (dilution water) control. Two replicate test chambers were maintained in each treatment group, with 10 Daphnia magna in each test vessel for a total of 20 Daphnia magna per treatment. The nominal test concentration was selected based on an exploratory range-finding test. The nominal test concentration was 120 mg dimethylsilanediol/L (mg/L). Water samples were collected at test initiation and at test termination for measurement of the test article. Mean measured concentrations were used to estimate EC50 values.

Daphnia magna were indiscriminately assigned to test chambers at test initiation. Indiscriminate distribution was achieved by sequentially adding one to two daphnids at a time to test vessels until each contained 10 daphnids. All transfers were made under the surface of the water. Observations of mortality/immobility and sublethal effects were made at test initiation and approximately 24 and 48 hours after test initiation. Cumulative percent mortality/immobility observed in the treatment group was used to estimate EC50 values at 24 and 48 hours.

- Dilution water: The dilution water was municipal water obtained from Bay City, Michigan. The municipal water was dechlorinated using a carbon filter and aerated prior to use. The pH of the water is periodically adjusted using CO2, as necessary. The water is monitored weekly for hardness, alkalinity, conductivity, pH and total residual chlorine (TRC). The municipal water is also monitored once a year for selected inorganics, total suspended solids (TSS), total organic carbon (TOC) and selected organic compounds. No contaminants have been shown to be present in the municipal water at concentrations that might affect the outcome of this study.

- Environmental conditions: Lighting used to illuminate the test chambers was provided by cool white fluorescent bulbs with a photoperiod of 16 hours light and 8 hours dark. Temperature, dissolved oxygen and pH were measured in the batch solutions prepared at test initiation and in each test vessel at approximately 48 hours. Temperature was measured using a liquid-in-glass thermometer. In addition, temperature of the environmental chamber was measured continuously. The target test temperature was 20 ± 2 ºC. Measurements of dissolved oxygen were made using a Yellow Springs Instruments dissolved oxygen meter and measurements of pH were made using an Orion pH meter. A sample of dilution water was collected at test initiation for measurements of hardness, alkalinity, conductivity and TRC. Hardness and alkalinity were measured by titration. Conductivity was measured using a Yellow Springs Instruments salinity, conductivity and temperature meter. TRC was measured using a Fisher Chlorine Titrimeter 397.

- Observations: Observations were made to evaluate the number of mortalities and immobile organisms. Immobility was defined as the lack of swimming within 15 seconds after gentle agitation of the test vessel. The numbers of organisms exhibiting sublethal effects (e.g., lethargy, discoloration, etc.) were also evaluated. Observations were made at test initiation and 24 and 48 hours after test initiation (± 1 hour).
Reference substance (positive control):
no
Duration:
48 h
Dose descriptor:
EC50
Effect conc.:
> 117 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
other: mortality/immobility
Duration:
48 h
Dose descriptor:
NOEC
Effect conc.:
>= 117 mg/L
Nominal / measured:
meas. (arithm. mean)
Conc. based on:
test mat.
Basis for effect:
other: mortality/immobility
Details on results:
- Immobilisation in control: 0
Reported statistics and error estimates:
The EC50 values were estimated by visual inspection of the mortality/immobility data. Confidence limits could not be calculated because only one concentration was tested.

Daphnia magna in the negative control appeared normal and healthy throughout the test with no mortality/immobility or overt signs of toxicity. After 48 hours of exposure, Daphnia magnaexposed to dimethylsilanediol at a concentration of 117 mg/L also appeared normal and healthy with no mortality or immobility. 

Validity criteria fulfilled:
yes
Conclusions:
A 48-hour EC50 value of > 117 mg/L and NOEC of ≥ 117 mg/L have been determined for the effects of the test substance on mortality/immobility of Daphnia magna.

Description of key information

Short-term toxicity to invertebrates: 48-hour EC50 >1.6 mg/l (nominal) (highest concentration tested), mobility of Daphnia magna.

Key value for chemical safety assessment

Additional information

A 48-hour E(L)C50 value of >1.6 mg/l (nominal) (highest concentration tested) has been determined for the effects of hexamethylcyclotrisiloxane (D3, CAS 541-05-9; EC No. 208-765-4) on mobility of Daphnia magna (Springborn Laboratories, 2007). The test was conducted in accordance with EPA OPPTS 850.1010 (Aquatic Invertebrate Acute Toxicity Test, Freshwater Daphnids) and in compliance with GLP. In view of the test media preparation method and flow-through exposure regime it is likely that the test organisms were exposed predominantly to the initial intermediate hydrolysis product of the tested substance, 1,1,3,3,5,5-hexamethyltrisiloxane-1,5-diol (CAS 3663-50-1; EC No. 222-920-3; L3-diol) (half-life for loss of L3-diol approximately 200 hours at pH 7 and 25°C).

The short-term toxicity to fish test with D3 was carried out at the limit of water solubility for D3 (1.6 mg/l) under flow-through conditions. D3 will rapidly hydrolyse to L3-diol (half-life 23 mins, pH 7 and 25°C). The pH during the test was maintained at pH 7.8 and sonication during mixing would have increased the rate of hydrolysis. With replacement of 90% test solution in 6 hours this would mean that the Daphnia were mainly exposed to the L3-diol. As the pH was kept relatively neutral, there would be very little time for further hydrolysis of the L3-diol to 1,1,3,3-tetramethyldisiloxane-1,3-diol (CAS 1118-15-6; EC No. 214-258-9; L2-diol) or dimethylsilanediol (DMSD, CAS 1066-42-8; EC No. 213-915-7) (half-life for loss of L3-diol approximately 200 hours at pH 7 and 25°C).

No effects were seen in the test, therefore it can be said that the L3-diol is not toxic to invertebrates at the limit of solubility of the parent substance (D3, 1.6 mg/l).

In a second test with D3, a 48-hour E(L)C50 value of >0.129 mg/l (measured) (highest concentration tested) has been determined for effects on mobility of Daphnia magna (Dow Corning, 1991). The test was not conducted in accordance with any guideline but was in compliance with GLP. The test solutions were prepared using a 625 mg/l stock solution of D3 and stirring for several days. It is therefore likely that the D3 had hydrolysed and the test organisms were exposed to the hydrolysis products. This is supported by the low analytical recoveries of D3 at the end of the test (90% reduction of D3 at 48 hours). Due to the solubility of the hydrolysis products, this test indicates that L3-diol, L2-diol and DMSD are not toxic above the limit of solubility of the parent substance. However, the concentrations of the hydrolysis products were not analytically verified.

 

A 48-hour E(L)C50 value of >117 mg/l (measured, arithmetic mean) (highest concentration tested, limit test) has been determined for the effects of dimethylsilanediol (DMSD, CAS 1066-42-8) on mortality/immobility of Daphnia magna. This substance is the final hydrolysis product of D3.