1,1,3,3-tetramethyldisiloxane

Short-term toxicity to aquatic invertebrates

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

read-across from supporting substance (structural analogue or surrogate)

Adequacy of study:

weight of evidence

Justification for type of information:

See Section 13 RAAF reports for the justification of read-across.

Reason / purpose for cross-reference:

read-across source

Remarks:

6.1.3.042

Reason / purpose for cross-reference:

read-across source

Remarks:

6.1.3.165

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

905 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

dimethylsilanol

Basis for effect:

other: mortality and immobilization

Remarks on result:

other: not calculable

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

124

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

dimethylsilanol

Basis for effect:

other: mortality and immobilization

Remarks on result:

other: 51-203

Key result

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

< 60 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

dimethylsilanol

Basis for effect:

other: mortality and immobilization

Key result

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

> 117 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Remarks:

DMSD

Basis for effect:

mortality

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of 124 mg/L and NOEC of <60 mg/L have been determined for the effects of the test substance on mobility/mortality of Daphnia magna based on mean measured concentrations.

Reference 2

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2004-03-23 to 2004-03-25

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 202 (Daphnia sp. Acute Immobilisation Test)

Qualifier:

according to guideline

Guideline:

EPA OPPTS 850.1010 (Aquatic Invertebrate Acute Toxicity Test, Freshwater Daphnids)

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Concentrations: Negative Control, 63, 125, 250, 500 and 1000 mg/L

- Sampling method: Measurement of test concentrations in each test chamber at test initiation, on Day 1 (old solution) and test termination.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION

- Method: Direct addition of test article to dilution water.

- Controls: Dilution water

Test organisms (species):

Daphnia magna

Details on test organisms:

TEST ORGANISM

- Source: Source: Wildlife International, Ltd. cultures

-Age at study initiation: <24 hours old

- Culture: Adult daphnids were cultured in water from the same source and at approximately the same temperature as used during the test. Daphnids in the cultures were held for 14 days prior to collection of the neonates for testing. The adults showed no signs of disease or stress during the holding period.

- Test organisms: Neonate daphnids were obtained for testing from four individual adult daphnids that had already produced at least one previous brood and had produced at least three young per adult per day over the 7-day period prior to the test. At test initiation, the juvenile daphnids were collected from the cultures and indiscriminately transferred one and two at a time to transfer containers until each transfer chamber contained 10 daphnids. Transfer chambers were indiscriminately assigned to test chambers, and then the daphnids were released into the test chambers. All transfers were made below the water surface using wide-bore pipettes.

- Feeding: Daphnids in the cultures were fed daily a mixture of yeast, Cerophyll® and trout chow, as well as a suspension of the freshwater green alga, Selenastrum capricornutum. The adults were fed prior to test initiation, but neonates were not fed during the test.

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

48 h

Post exposure observation period:

None

Hardness:

126 mg/L as CaCO3

Test temperature:

19.2 to 20.5 ºC

pH:

8.5 to 8.6

Dissolved oxygen:

≥8.6 mg/L (96% of saturation)

Salinity:

Not applicable

Nominal and measured concentrations:

Nominal concentrations: Negative Control, 63, 125, 250, 500 and 1000 mg/L

Mean measured concentrations:
The results are reported and interpreted with reference to the mean measured concentrations.

Details on test conditions:

TEST SYSTEM

- Test vessel:

- Type: open

- Material, size, headspace, fill volume: 250 mL glass beakers containing 20 mL of test solution.

- Aeration: none

- Renewal rate of test solution: Daily

- No. of organisms per vessel: 10

- No. of vessels per concentration (replicates): 2

- No. of vessels per control (replicates): 2

- Biomass loading rate: 1 daphnia/2 ml


TEST MEDIUM / WATER PARAMETERS

- Source/preparation of dilution water: Well water

- Total organic carbon: < 1 mg/L

- Alkalinity: 179 mg/L as CaCO3

- Conductivity: 290 mhos/cm

- Culture medium different from test medium: No

- Intervals of water quality measurement: Daily


OTHER TEST CONDITIONS

- Adjustment of pH: no

- Photoperiod: 16 hours light:8 hours dark

- Light intensity: Wavelength similar to natural sunlight, 131 lux


EFFECT PARAMETERS MEASURED: Mobility daily


TEST CONCENTRATIONS

- Spacing factor for test concentrations: 2

Reference substance (positive control):

no

Duration:

24 h

Dose descriptor:

EC50

Effect conc.:

> 905 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

other: mortality and immobilization

Remarks on result:

other: not calculable

Duration:

48 h

Dose descriptor:

EC50

Effect conc.:

124 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

other: mortality and immobilization

Remarks on result:

other: 51-203

Duration:

48 h

Dose descriptor:

NOEC

Effect conc.:

< 60 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

other: mortality and immobilization

Details on results:

Biological observations: After 48 hours of exposure, mortality/immobility in the 60, 116, 207, 447 and 905 mg/L treatment groups was 30%, 65%, 45%, 80% and 85%, respectively.

Was control response satisfactory: Yes

Reported statistics and error estimates:

Statistical methods: Probit Analysis

Table 1. Cumulative immobilization:

Mean measured concentration (mg/l)	Number dead/Number immobile 0 hours	Number dead/number immobile/number exposed 24 hours	Number dead/number immobile/number exposed 48 hours
negative control	0/0/20	0/0/20	0/1/20
60	0/0/20	0/0/20	0/6/20
116	0/0/20	0/0/20	7/6/20
207	0/0/20	0/0/20	8/1/20
447	0/0/20	0/2/20	10/6/20
905	0/0/20	0/4/20	8/9/20

Validity criteria fulfilled:

yes

Conclusions:

A 48-hour EC50 value of 124 mg/L and NOEC of <60 mg/L have been determined for the effects of the test substance on mobility/mortality of Daphnia magna based on mean measured concentrations.

Reference 3

Endpoint:

short-term toxicity to aquatic invertebrates

Type of information:

experimental study

Adequacy of study:

weight of evidence

Study period:

2008-06-30 to 2008-07-25

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

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+/-2ºC

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 labeled 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+/-2ºC. 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

Key result

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 magna exposed 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 aquatic invertebrates: 48-h EC50: 124 mg/l (measured, arith. mean) (OECD 202), read-across from an analogous/structurally related substance trimethylsilanol (CAS 1066-40-6).

Key value for chemical safety assessment

Fresh water invertebrates

Fresh water invertebrates

Effect concentration:

124 mg/L

Additional information

A 48-hour EL₅₀value of >100 mg/l has been determined for the effects of 1,1,3,3-tetramethyldisiloxane (CAS 3277-26-7), on mobility of Daphnia magna when tested with adjustment of test medium pH and based on nominal test substance loading rate. The results are above the limit of solubility of the substance, however, due to the rapid hydrolysis and length of test media preparation, the organisms would have been exposed to a fully solubilised hydrolysis product. The back calculated DOC concentration corresponds to an EL₅₀ of >42 mg/l. It is possible that the discrepancy may be explained by the volatilisation of the parent substance from the test medium. The substance has an estimate Henry’s Law Constant value of 1.86E⁺⁵ Pa m³ mol-1 at 25°C.

While the data are considered to be reliable, due to the very rapid hydrolysis of the parent substance, good quality data have been read across from trimethylsilanol (CAS 1066-40-6), based on the substance being an analogue of the intermediate hydrolysis product, dimethylsilanol. Data are also available with dimethylsilanediol (CAS 1066-42-8), the registered substance’s ultimate hydrolysis product.

In the tests with trimethylsilanol and dimethylsilanediol, the observations are attributed to the exposure of test organisms to the test substances. Data from tests carried out with the read-across substances report the following results:

-        A 48-hour EC₅₀value of 124 mg/l has been determined for the effects of trimethylsilanol on mobility/mortality of Daphnia magnabased on measured (arithmetic mean) concentrations.

-      A 48-hour EC₅₀value of >117 mg/l has been determined for the effects of dimethylsilanediol on mobility of Daphnia magna, based on measured (arithmetic mean) concentrations.

The study with trimethylsilanol presents a slightly unusual dose-response curve, where at 48-hours the immobility and mortality rates observed at 116 mg/l are higher than those at 207 mg/l concentrations. It is possible this causes the high confidence intervals (51-203) observed in the study. It is the opinion of the reviewer that because at 24 hours no unusual observations were observed and the other study concentrations appear to follow a normal dose-response curve, the study is considered to be valid and the data are used in the risk assessment.

Trimethylsilanol (TMS, CAS 1066-40-6) has the potential to condense to form hexamethyldisiloxane (HMDS, CAS 107-46-0), which would then contribute to the species present in the test system. HMDS is classified as Aquatic Acute 1 H400 and Aquatic Chronic 2 H411 [1] and therefore its presence may impact the toxicity results. However, the estimated concentration of HMDS is 0.04, 0.2, 0.3, 0.6 and 0.9 mg/l at 100, 200, 300, 400 and 500 mg/l of TMS respectively, and there was no reporting of undissolved test material or droplets being formed, which would otherwise clearly indicate the formation of HMDS. In addition, the log K_ow of trimethylsilanol (1.62) is such that effects may be observed at high concentrations in short-term studies. Therefore the effects seen in the short-term toxicity to invertebrate study may be attributable to TMS alone and the study is considered to be conservative and reliable for the purpose of this assessment.

The registered substance also releases hydrogen during its final hydrolysis. Hydrogen is not thought to contribute to the toxicity of the substance and is discussed further in the ecotoxicological information overview endpoint summary (additional information).

Refer to the discussion in the Section 6 endpoint summary (Section 7.0 of CSR) for further discussion of the approach to chemical safety assessment for this registration substance, and justification for read-across used.

[1] https://echa.europa.eu/information-on-chemicals/cl-inventory-database/-/discli/notification-details/32082/948794