Hexamethylcyclotrisiloxane

Short-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to fish

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2007-02-16 to 2007-02-20

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.1075 (Freshwater and Saltwater Fish Acute Toxicity Test)

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 D3 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 3.1932 g of D3 in a 200-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 0.500 mL/mL solvent stock solution was prepared by bringing 125 mL of acetone to a final volume of 250 mL with distilled water. The resulting solution was clear and colourless.

Prior to test initiation, a 50 mL Glenco® gas-tight syringe in conjunction with a Harvard syringe pump was calibrated to deliver 0.040 mL/cycle of the 16 mg/mL stock solution into the diluter system's mixing chamber which also received 0.40 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

- Chemical name of vehicle (organic solvent, emulsifier or dispersant): Acetone

- Concentration of vehicle in test medium (stock solution and final test solution(s) including control(s)): 0.1 mL/L

- Evidence of undissolved material (e.g. precipitate, surface film, etc): None

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Common name: Rainbow trout

- Source: Test organisms were obtained from a commercial Hatchery. Prior to testing, the fish were held in a 500-L fiberglass tank under a photoperiod of 16 hours light and 8 hours dark. The temperature in the holding tank was 11 °C. The water which flowed into the fish holding tank was characterized as having total hardness and alkalinity ranges as CaCO3 of 44 to 66 mg/L and 20 to 23 mg/L, respectively, a pH of 7.1 to 7.6, and a specific conductivity of 190 to 210 µmhos/cm.

- Length at study initiation (length definition, mean, range and SD): A representative sample (N = 30) of the fish from the test population had a mean total length of 33 mm (range 29 to 39 mm).

- Weight at study initiation (mean and range, SD): A representative sample (N = 30) of the fish from the test population had a mean wet weight of 0.32g (range 0.21 to 0.46 g)

- Feeding during test: None


ACCLIMATION

- Type and amount of food: The fish were fed a dry commercial flaked fish food (Trout Chow), ad libitum, daily. Feeding was stopped 48-hours prior to the start of the test.

Test type:

flow-through

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

Total hardness and alkalinity ranges as CaCO3 of 44 to 46 mg/L and 20 to 23 mg/L

Test temperature:

12-15 ºC

pH:

6.8 - 7.2

Dissolved oxygen:

6.7-11 mg/L

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 test medium: 15.8 mg/L

The test results are reported and evaluated with reference to nominal concentration.

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 was  constructed of glass and silicone sealant, and was designed to provide a  single concentration of test substance, a dilution water control and a  solvent control.  Duplicate vessels were established for each control and  four replicates were estabilished for the treatment level. 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 colorless.  A Glenco®  50-mL gas-tight syringe in conjunction with a Harvard Syringe Pump was  calibrated to deliver 0.040 mL/cycle of 16 mg/mL test substance solution into the  diluter's chemical mixing chamber which received 0.40 L of dilution water  per cycle.  The mixing chamber was continuously mixed.  The concentration  of test substance in the solution contained withing 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 63 to 81 footcandles (680 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 ranges (as  CaCO3) of 44 to 46 mg/L and 22 to 23 mg/L, respectively, a pH of 6.9 to  7.4 and a specific conductance of 210 to 220 µmhos/cm.  The total organic  carbon content (TOC) was 0.58 mg/L.  

The dilution water control vessels  had a dissolved oxygen concentration of 11 mg/L at test initiation and a  range of 8.8 to 9.4 mg/L during the test.  

The pH measured in the  dilution water control vessel replicates was 7.2 at test initiation and  ranged from 6.8 to 6.9 at test termination.

Reference substance (positive control):

yes

Remarks:

Acetone

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 1.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC0

Effect conc.:

> 1.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 1.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

LC100

Effect conc.:

> 1.6 mg/L

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

- Mortality of control: 0

Reported statistics and error estimates:

There were no toxic effects observed in the test and therefore statistical analysis of the results was not required.

Sublethal observations / clinical signs:

Table 1. Test results

Treatment	Percentage mortality after 96 hours
0 (Control)	0
0 (Solvent control)	0
1.6 mg/L test substance	0

Validity criteria fulfilled:

yes

Conclusions:

A 96-hour LC50 value of > 1.6 mg/L and NOEC of ≥ 1.6 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss. A concentration of 1.6 mg/L corresponds to the approximate water solubility of the substance.

Reference 2

Endpoint:

short-term toxicity to fish

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 203 (Fish, Acute Toxicity Test)

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: The test article concentration was measured in each test chamber at test initiation (before the addition of the fish) and at test termination.

- Sampling method: Water samples (10 mL) were collected from mid-depth of the test chambers using a glass pipette.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: The nominal test concentration was 120 mg/L. Appropriate aliquots (3.6 g) of the test article were added directly to 30-L of aerated dilution water in the test chambers. The mixtures were stirred using a glass pipette for approximately 1 minute. The negative control was dilution water only. All test solutions appeared clear and colourless.

Test organisms (species):

Oncorhynchus mykiss (previous name: Salmo gairdneri)

Details on test organisms:

TEST ORGANISM

- Common name: Rainbow trout

- Source: Thomas Fish Company, Anderson, California on June 27, 2008. The identity of the species was verified by the supplier.

- Length at study initiation (length definition, mean, range): 49 mm (46-52 mm)

- Holding conditions: The fish were held at a temperature of 11.6 to 11.7 ºC.

- Type and amount of food: During holding, rainbow trout were fed finfish starter #2 obtained from Zeigler Brothers, Gardners, PA. The trout chow is analyzed annually for selected contaminants. No contaminants had been shown to be present in the trout chow at concentrations that might affect the outcome of this study. Feeding was discontinued at least 48 hours prior to test initiation and the fish were not fed during the test.

- Health during acclimation (any mortality observed): no mortality

Test type:

static

Water media type:

freshwater

Limit test:

yes

Total exposure duration:

96 h

Hardness:

111 mg/L as CaCO3

Test temperature:

12 ± 1 ºC

pH:

7.6-8.4

Dissolved oxygen:

≥ 8.7 mg/L

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: 0 (Control) and 120 mg/L

Measured concentrations at test initiation: 120-126 mg/L

Measured concentrations at test termination: 128-131 mg/L

Mean measured test concentration: 126 mg/L (105 % of nominal)

Details on test conditions:

TEST SYSTEM

- Test vessel: Test chambers were 38-L glass aquaria containing approximately 30 L of test solution. Test chambers were impartially placed in a temperature-controlled environmental chamber set to maintain a temperature of 12 ± 1 ºC. Each test chamber was loosely covered with a piece of plexiglass. Test chambers were labelled with the study number, test article concentration and replicate.

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 3

- No. of vessels per control (replicates): 3

- Biomass loading rate: 0.28 g/L


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: The dilution water was municipal water obtained from Bay City, Michigan. The water was dechlorinated using a carbon filter and aerated prior to use.

- Culture medium different from test medium: No

- Intervals of water quality measurement: The laboratory water is monitored weekly for hardness, alkalinity, conductivity, total residual chlorine and pH. The water is 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 water at concentrations that might affect the outcome of this study.


OTHER TEST CONDITIONS

- Light intensity: Lighting used to illuminate the test vessels was provided by cool white fluorescent bulbs with a photoperiod of 16 hours light and 8 hours dark. Light intensity at test initiation was 34 foot-candles.


EFFECT PARAMETERS MEASURED: Mortality after 24, 48, 72 and 96 hours


TEST CONCENTRATIONS

- Spacing factor for test concentrations: Limit test

- Results used to determine the conditions for the definitive study:

Reference substance (positive control):

no

Duration:

96 h

Dose descriptor:

LC50

Effect conc.:

> 126 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Duration:

96 h

Dose descriptor:

NOEC

Effect conc.:

>= 126 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality (fish)

Details on results:

- Mortality of control: 0

Reported statistics and error estimates:

The 24, 48, 72 and 96-hour LC50 values were estimated by visual inspection of the mortality data. Confidence limits could not be calculated because only one concentration was tested.

Sublethal observations / clinical signs:

No toxic effects were observed in the Control or treated test media.

Validity criteria fulfilled:

yes

Conclusions:

A 96-hour LC50 of > 126 mg/L and a NOEC of ≥ 126 mg/L have been determined for the effects of the test substance on mortality of Oncorhynchus mykiss.

Description of key information

Short-term toxicity to fish: 96-hour LC₅₀ >1.6 mg/l (nominal) (highest concentration tested), mortality of Oncorhynchus mykiss.

Additional information

A 96-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 mortality of Oncorhynchus mykiss (Springborn Laboratories, 2007). The test was conducted in accordance with EPA OPPTS 850.1075 (Freshwater and Saltwater Fish Acute Toxicity Test) 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).

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 the L3-diol (half-life 23 min, pH 7 and 25°C). The pH during the test was maintained at pH 7.2. Sonication during mixing would have increased the rate of hydrolysis. With replacement of 90% test solution in 6 hours this would mean that the fish were mainly exposed to the L3-diol. As the pH was kept 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 fish at the limit of solubility of the parent substance (D3, water solubility 1.6 mg/l).

 

For evaluation of the effects of the final hydrolysis product of the registration substance, a 96-hour E(L)C₅₀ value of >126 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 of Oncorhynchus mykiss (HES Dow Corning, 2009). The test was conducted in accordance with OECD TG 203 and in compliance with GLP.