Dimethoxydimethylsilane

Long-term toxicity to fish

Link to relevant study record(s)

Reference

Reference 1

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 2

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:

Please refer to the analogue approach justification provided in Section 13.

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:

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

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

Conclusions:

32-day EC10, NOEC and LOEC values of >12, ≥12 and >12 mg/L have been determined for the effects of dimethylsilanediol, the silanol hydrolysis product of the registered substance, 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.

Description of key information

EC10 (32 d) > 12 mg/L (meas. arithm. mean, OECD 210, P. promelas;  read across from silanol hydrolysis product DMSD

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Dose descriptor:

EC10

Remarks:

for silanol hydrolysis product DMSD (relevant assessment entity)

Effect concentration:

> 12 mg/L

Additional information

Dimethoxy(dimethyl)silane (CAS No. 1112-39-6) hydrolyses rapidly in contact with water (DT50 < 0.6 h), to dimethylsilanediol (DMSD, CAS No. 1066-42-8) and methanol (CAS No. 67-56-1). The ECHA guidance R.16 states that “for substances where hydrolytic DT50 is less than 12 h, environmental effects are likely to be attributed to the hydrolysis product rather than to the parent itself” (ECHA, 2016). The ECHA guidance R.16 also suggests that in case the hydrolysis half-life is less than 12 h, the breakdown products, rather than the parent substance, should be evaluated for aquatic toxicity. Methanol is well described in the public domain literature. It has a low environmental hazard profile and is therefore not considered contributory to the overall aquatic toxicity of the registered substance (OECD SIDS, 2004). Thus, the ecotoxicity assessment was based on the silanol hydrolysis product dimethylsilanediol (DMSD, CAS No. 1066-42-8). Details on the read-across approach are provided in the attached document in IUCLID Section 13.

One experimental study for the long-term toxicity of the silanol hydrolysis product DMSD toward fish is available, which was conducted according to OECD guideline 210 and GLP.
In a semi-static test with a daily renewal rate during the embryo stage (0 to 5 d) and a three times weekly renewal rate in the fry stage of exposure (28 d), Pimephales promelas was exposed to the nominal concentrations of 0.75, 1.5, 3.0, 6.0 and 12 mg/L for 28 d. A control was run in parallel.
Test solutions were prepared by dilution of a 12 mg/L stock solution and there was no visible undissolved test substance.
The test concentrations were analytically verified by LC-MS in fresh media and in aged media at test solution renewal.
The mean measured test concentrations of DMSD in the exposure vessels was within 98 to 100% of nominal and an EC10 (32 d) of > 12 mg/L (measured arithmetic mean) was obtained for the chronic toxicity of DMSD toward fish, indicating no effects up to the highest concentration tested.

 

Reference
OECD SIDS, 2004. Methanol - SIDS Initial Assessment Report For SIAM 19, Berlin, Germany: UNEP Publications.