1,1,3,3-tetramethyldisiloxane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

fish early-life stage toxicity

Data waiving:

other justification

Justification for data waiving:

other:

Reference 2

Endpoint:

fish early-life stage toxicity

Type of information:

experimental study

Adequacy of study:

key study

Study period:

23 October to 24 November 2020

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

OECD Guideline 210 (Fish, Early-Life Stage Toxicity Test)

Deviations:

yes

Remarks:

water temperature ranged from 23.4 - 27.9°C throughout exposure period (exceeding range in guidance). This is not believed to influence the results or their interpretation.

Principles of method if other than guideline:

One further protocol deviation occurred during the study: the protocol states that following the completion of hatch, daily observations will be recorded on larval or juvenile fish mortality, behavior, and appearance. On test day 15, the estimated counts were recorded; however, the observations for behavior and appearance were inadvertently omitted, and not recorded in real time. As the observations were normal on the test day prior to and following this omission, the lack of this one observation does not have a negative impact on the results or interpretation of the study

GLP compliance:

yes

Analytical monitoring:

yes

Details on sampling:

- Concentrations: every treatment concentration and control
- Sampling method: Exposure samples were removed from the approximate midpoint of each replicate beaker solution using a pipette.
- Sample storage conditions before analysis: subsamples of the exposure solutions were also collected at each sampling interval and stored frozen as archive samples. Storage conditions of exposure samples for analysis not reported.

Vehicle:

no

Details on test solutions:

PREPARATION AND APPLICATION OF TEST SOLUTION (especially for difficult test substances)
- Method: a 12.0 mg/ml primary stock solution was prepared prior to exposure initiation. The primary stock solution was used to prepare the high embryo exposure solution (12 mg/L). Subsequent exposure solutions were prepared as dilutions of the 12 mg/L high embryo exposure solutions.
- Eluate: not applicable
- Differential loading: not applicable
- Controls: dilution water
- Test concentration separation factor: 2
- Evidence of undissolved material (e.g. precipitate, surface film, etc.): no visible undissolved test substance following preparation
- Other relevant information:

Test organisms (species):

Pimephales promelas

Details on test organisms:

TEST ORGANISM
- Common name: fathead minnow
- Strain: not reported
- Source: brood stock at test laboratory (Smithers)
- Age at study initiation (mean and range, SD): approximately 20 weeks old
- Length at study initiation (length definition, mean, range and SD): not reported
- Weight at study initiation (mean and range, SD): not reported
- Method of breeding: Spawning substrates were introduced to the brood stock aquaria at the end of the working day the evening prior to initiation (day 0). The following morning, spawning substrates were removed from the brood stock aquaria, and the embryos were placed in a tub of dilution water at test temperature to harden for 1 hour.
- Feeding during test: larvae were fed from day 5 onwards, 3 times daily.
- Food type: brine shrimp nauplii (Artemia salina)
- Amount: ad libitum
- Frequency: 3 times daily

ACCLIMATION - not applicable as embryos were used

QUARANTINE (wild caught) - not applicable

Test type:

semi-static

Water media type:

freshwater

Limit test:

no

Total exposure duration:

28 d

Remarks on exposure duration:

28 days post hatch, 32 days total exposure

Hardness:

68-150 mg/l as CaCO3

Test temperature:

23.4 - 27.9°C

pH:

6.9 - 7.8

Dissolved oxygen:

5.88 - 7.96

Salinity:

not reported

Conductivity:

480 - 1200

Nominal and measured concentrations:

Nominal: control, 0.75, 1.5, 3.0, 6.0, 12 mg/l
Measured: control, 0.78, 1.5, 3.0, 6.2, 12 mg/l

Details on test conditions:

TEST SYSTEM
- Emybro cups (if used, type/material, size, fill volume): not used
- Test vessel: 250 ml beakers for the embryo stage of the exposure. 3L beakers were used for the fry exposure.
- Type (delete if not applicable): not specified whether open or closed
- Material, size, headspace, fill volume: fill volume was 200 ml for the embryo stage, 2.5L for the fry stage, material not specified
- Aeration: Gentle, oil-free aeration within the fry exposure beakers was initiated on the day of release to maintain the dissolved oxygen concentration at the desired level (i.e., >60% of saturation).
- Type of flow-through (e.g. peristaltic or proportional diluter): test design was semi static renewal
- Renewal rate of test solution (frequency/flow rate): exposure solutions including the control were prepared daily for the embryo portion of the exposure (0-5 days). Exposure solutions for the fry stage of the exposure were prepared three times weekly (28 days). The volume of each exposure beaker was renewed three times weekly, at a rate of 80% of the total volume per renewal.
- No. of fertilized eggs/embryos per vessel: 30 eggs per vessel, then 20 organisms per replicate once hatched
- No. of vessels per concentration (replicates): 4
- No. of vessels per control (replicates): 4
- Biomass loading rate: did not exceeed 0.12 g/organism or 0.94 g/L at any time.

TEST MEDIUM / WATER PARAMETERS
- Source/preparation of dilution water: unadulterated water from 100 meter bedrock well and dechlorinated town of Wareham well water.
- Total organic carbon: 0.78 and 0.87 mg/l for the months of the exposure
- Particulate matter: tested semi annually, none present in concentrations considered toxic, in agreement with ASTM (2007)
- Metals: tested semi annually, none present in concentrations considered toxic, in agreement with ASTM (2007)
- Pesticides: tested semi annually, none present in concentrations considered toxic, in agreement with ASTM (2007)
- Chlorine: 145 mg/l (chloride)
- Alkalinity: as CaCO3: 58-78 mg/l and 21-26 mg/l
- Ca/mg ratio: not reported
- Salinity: not reported
- Culture medium different from test medium: no
- Intervals of water quality measurement: weekly

OTHER TEST CONDITIONS
- Adjustment of pH: none
- Photoperiod: 16 hours light/8 hours dark
- Light intensity: for the embryo portion of the exposure, 800-1100 lux. For the fry portion, 970-1300 lux.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) : hatch success, mortality, total length and wet weight, record of abnormalities

VEHICLE CONTROL PERFORMED: not applicable - no vehicle used

RANGE-FINDING STUDY
- Test concentrations: control - 12 mg/l
- Results used to determine the conditions for the definitive study: 90-98% hatch success, 95-100% live/normal larvae at hatch, 74-88% mean larval survival, 11.66-12.89 mm, 0.0109 - 0.0138g

POST-HATCH DETAILS
- Begin of post-hatch period: 5 days
- No. of hatched eggs (alevins)/treatment released to the test chamber: 20
- Release of alevins from incubation cups to test chamber on day no.: not specified

FERTILIZATION SUCCESS STUDY
- Number of eggs used: 30
- Removal of eggs to check the embryonic development on day no.: 4

Reference substance (positive control):

not specified

Duration:

32 d

Dose descriptor:

NOEC

Effect conc.:

>= 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Duration:

32 d

Dose descriptor:

LOEC

Effect conc.:

> 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Duration:

32 d

Dose descriptor:

EC10

Effect conc.:

> 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Details on results:

- Mortality/survival at embryo and larval stages: 74-80% hatching success, 91-96% larval survival
- Overall mortality/survival: 91-96% larval survival, overall mortality not calculated due to removal of extra embryos after hatching (from maximum 30 embryos to 20)
- Days to hatch and numbers hatched: 4 days
- Data for length and weight of surviving fish: length: 20.99 - 23.23 mm, weight: 0.1093 - 0.1196 g
- Type of and number with morphological abnormalities: one deformed fish per concentration for the control, 0.78, 1.5, 3.0 mg/l and four deformed fish in 12 mg/l treatment. There was no treatment related response for any endpoint, therefore the occurence of deformed fish did not affect the results or interpretation of the exposure.
- Type of and number with behavioural abnormalities: observed, but none reported
- Other biological observations:
- Effect concentrations exceeding solubility of substance in test medium: none observed
- Incidents in the course of the test which might have influenced the results: none reported

Reported statistics and error estimates:

Software used was CETIS version 1.9. Fisher's exact test with Bonferroni-Holm's adjustment was used to determine treatment effects, Shapiro WIlks' test for normality was conducted to evaluate normality of continuous data, Bartlett's equality of variance test evaluated the homogeneity of continuous data, Dunnett's Multiple COmparison test established treatment effects for the biological endpoints.

Table 1. Mean measured concentrations of DMSD in the exposure

Nominal concentration (mg/l)	Measured concentration (mg/l)										Mean measured (SD)	Percent of nominal	% CV
	Day 0 (new)	Day 4/0 (aged)	Day 4/0 (new)	Day 12/8 (aged)	Day 12/8 (new)	Day 19/15 (aged)	Day 19/15 (new)	Day 26/22 (new)	Day 26/22 (aged)	Day 32/28 (aged)
Control	<MDL (<0.10)	<MDL	<MDL	<MDL	<MDL	<MDL	<MDL	<MDL	<MDL	<MDL	NA (NA)	NA	NA
0.75	0.68	0.87	0.63	0.74	0.89	0.78	0.72	0.75	0.91	0.81	0.78 (0.092)	100	12
1.5	1.2	1.7	1.2	1.5	1.5	1.3	1.4	1.5	1.7	1.6	1.5 (0.16)	98	11
3.0	2.9	3.4	2.5	3.0	2.6	2.9	2.8	3.3	3.4	2.9	3.0 (0.31)	99	11
6.0	5.8	7.1	4.9	6.5	7.1	5.8	5.1	6.4	7.4	5.8	6.2 (0.87)	100	14
12	11	14	11	14	10	10	12	12	14	14	12 (1.6)	100	13

Table 2. Summary of biological observations of Pimephales promelas fry and embryo after exposure to DMSD

Nominal concentration	Mean measured concentration (mg/l)	Mean embryo hatching success (%)	Live, normal larvae at hatch (%)	Mean larval survival (%)	Mean larval length (mm)	Mean larval wet weight (g)
Control	Control	98	99	74	12.89	0.0138
0.75	0.78	93	100	84	12.10	0.0115
1.5	1.5	98	98	74	12.21	0.0131
3.0	3.0	90	98	85	12.04	0.0117
6.0	6.2	92	97	88	11.66	0.0109
12	12	91	95	75	12.17	0.0124

Validity criteria fulfilled:

yes

Remarks:

With some exceptions. Mean control hatching success was >70%, mean control survival at exposure termination was >75%, dissolved oxygen was >60%, concentrations of the test substance were maintained at +/-20% of nominal. See Conclusions for deviations

Conclusions:

32-day EC10, NOEC and LOEC values of >12, ≥12 and >12 mg/l have been determined for the effects of dimethylsilanediol on larval development (as embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight) of Pimephales promelas based on mean measured concentrations.

The OECD 210 guidance specifies the water temperature should be maintained at 25 +/- 1.5°C, however water temperature ranged from 23.4 - 27.9°C throughout the exposure period. The maximum temperature was likely due to the probe coming in close contact to the water bath heater for a short period. The lower temperature was only outside the specified range by 0.1°C. It is concluded these deviations did not affect the results of the study or their interpretation.

Reference 3

Endpoint:

fish early-life stage toxicity

Type of information:

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

Adequacy of study:

key study

Justification for type of information:

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

Reason / purpose for cross-reference:

read-across source

Duration:

32 d

Dose descriptor:

NOEC

Effect conc.:

>= 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Duration:

32 d

Dose descriptor:

LOEC

Effect conc.:

> 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Duration:

32 d

Dose descriptor:

EC10

Effect conc.:

> 12 mg/L

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

larval development

Remarks:

embryo hatching success, live normal larvae at hatch, larval survival, total length and wet weight

Description of key information

Dimethylsilanediol: Long-term toxicity to fish: 32-d EC₁₀, NOEC and LOEC: >12, ≥12 and >12 mg/l (measured, arith. mean) (OECD 210), read-across from data on the ultimate hydrolysis product dimethylsilanediol (CAS 1066-42-8).

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

EC10

Effect concentration:

> 12 mg/L

Additional information

No data are available for the registered substance 1,1,3,3-tetramethyldisiloxane (CAS 3277-26-7), which hydrolyses very rapidly to dimethylsilanol during the intermediate hydrolysis. The substance further hydrolyses to dimethylsilanediol (CAS 1066-42-8), however the final hydrolysis rate is >48 hours, therefore as indicated by the REACH guidance (ECHA 2016, R.16), the aquatic chemical safety assessment and PNECs are based on the intermediate hydrolysis product, for which short-term aquatic toxicity data have been read across from the structural analogue trimethylsilanol (CAS 1066-40-6) (structural analogue of dimethylsilanol).

Based on the short-term aquatic data set on trimethylsilanol, the most sensitive trophic level is invertebrates, although no toxicity was observed below 100 mg/l. For the purpose of chemical safety assessment, a freshwater PNEC has been derived by applying an assessment factor of 1000 to the short-term data.

Short-term and long-term aquatic toxicity data are also available on the ultimate hydrolysis product dimethylsilanediol, where no effects were reported at the highest concentrations tested.

Dimethylsilanol

In accordance with Column 2 of REACH Annex IX, there is no need to further investigate the effects of this substance in a long-term aquatic toxicity to fish study because, as indicated in guidance R.7.8.4.3 (ECHA 2016), the quantitative chemical safety assessment (conducted according to Annex I of REACH) indicates that the Risk Characterisation Ratio is below 1 and therefore the risk is already adequately controlled and further testing is not justifiable.

Overall it is concluded that the risk characterisation conclusion is sufficiently conservative in respect of any uncertainties and therefore further in vivo testing is not considered necessary or justified on ethical grounds.   

Dimethylsilanediol

A 32-day EC₁₀of >12 mg/l has been determined for the effects of dimethylsilanediol (CAS 1066-42-8) on larval development ofPimephales promelasbased on mean measured concentrations.The data are used to derive indicative sediment and soil PNECs for the ultimate hydrolysis product, using the Equilibrium Partitioning Method.

Details on how the PNEC and the risk characterisation ratio have been derived can be found in IUCLID Section 6.0 and Chapters 9 and 10 of the Chemical Safety Report, respectively.