Dimethoxydimethylsilane

Toxicity to soil macroorganisms except arthropods

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

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

Vehicle:

no

Duration:

56 d

Dose descriptor:

NOEC

Effect conc.:

>= 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

LOEC

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

EC50

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

56 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

LOEC

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

EC50

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Conclusions:

A 56-day EC50 value of >3.8 mg/kg soil dry weight and NOEC of ≥3.8 mg/kg soil dry weight have been determined for the effects of the test substance on reproduction of Eisenia fetida. 28-day EC50 and NOEC values of ≥3.8 and >3.8 mg/kg soil dry weight respectively, have been determined for the effects of the test substance on adult survival and adult weight of Eisenia fetida.

Reference 2

Endpoint:

toxicity to soil macroorganisms except arthropods: long-term

Type of information:

experimental study

Adequacy of study:

key study

Study period:

F0 exposure: 19 October - 16 November 2021. F1 exposure: 17 November - 15 December, 2021. Last day of data collection: 22 February 2022.

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 222 (Earthworm Reproduction Test (Eisenia fetida/Eisenia andrei))

GLP compliance:

yes (incl. QA statement)

Analytical monitoring:

yes

Details on sampling:

- Concentrations: control and 5.0 mg/kg soil dry weight
- Sampling method: triplicate soil samples were removed on days 0, 2, 28 (before and after adults were removed), and 56 from the control and 5.0 mg/kg treatment using a soil core method. One extra test vessel was prepared at initiation and used for every analytical sample interval.
- Sample storage conditions before analysis: Directly after sampling, the cores were placed in glass bottles with Teflon-lined caps prior to analytical processing.

Vehicle:

no

Details on preparation and application of test substrate:

A soil dosing trial was conducted prior to the definitive test to confirm the dosing methods to be used for terrestrial toxicity testing with dimethylsilanediol. A primary dosing stock solution was prepared in deionized water for application of the test substance to the sandy loam (earthworm matrix) to a dosing stock concentration of 0.47 mg/mL. The resulting dosing stock solution was observed to be clear and colorless with no visible undissolved test substance following approximately 5 minutes of stirring using a magnetic stir plate and Teflon-coated stir bar. The test substance was applied to the sandy loam (earthworm matrix) to a nominal treatment level of 5.0 mg/kg dry weight. Following dosing, the soil/test substance was mixed for approximately 10 minutes using a Hobart mixer. The results indicated that the dosing methods in natural soil are successful in reaching the target concentration levels and support the earthworm and seedling emergence definitive studies.

- Method of application to filter paper (if used): not used
- Method of mixing into soil (if used): a stock solution was directly added to wet artificial soil and mixed thoroughly for 10 minutes using a Hobart mixer.
- Method of application to soil surface (if used): not used
- Controls: control soil was prepared in the same manner but was not dosed with the test substance.
- Chemical name of vehicle (organic solvent, emulsifier or dispersant): no vehicle used.
- Concentration of vehicle in test medium (stock solution and final test solution): no vehicle used.
- Evaporation of vehicle before use: No vehicle used

Test organisms (species):

Eisenia fetida

Animal group:

annelids

Details on test organisms:

TEST ORGANISM
- Common name: earthworm
- Source: earthworms were cultured at the test laboratory from adults purchased from Carolina Biological Supply Company, Burlington, North Carolina.
- Age at test initiation (mean and range, SD): All earthworms used to initiate this exposure were mature with clitellum and were 3 to 5 months old.
- Weight at test initiation (mean and range, SD): control earthworms: 0.3212 g (SD 0.0131 g) and 5.0 mg/kg earthworms: 0.3322 g (SD 0.0182 g)

ACCLIMATION
- Acclimation period: not reported
- Acclimation conditions (same as test or not): Prior to exposure initiation, earthworms were transferred to artificial soil (Lot No. 101821A) for acclimation to conditions consistent with those used during the definitive test
- Health during acclimation (any mortality observed): Earthworms used for testing were healthy and uniform in size. No mortality reported.

Study type:

laboratory study

Substrate type:

artificial soil

Limit test:

yes

Total exposure duration:

56 d

Test temperature:

The temperature largely remained between 18 and 22ºC, with the exception of a maximum temperature of 23ºC recorded on day 9. Additionally, temperature values of 48-58ºC were recorded on days 13 and 14. However, given that the test organisms would not survive temperatures above 30ºC, the recorded temperatures are likely to be a result of faulty equipment and do not represent the temperature on those days. In addition, the recorded temperature before and after the temperature deviation period on days 13 and 14 were 20 and 19 ºC, respectively, and support that the temperature was not recorded accurately during this time as the chamber can’t heat up or cool down by approximately 40 ºC that rapidly. Thus, it is likely that the test temperature on days 13 and 14 was still maintained within the appropriate temperature range and the high temperatures were not accurately recorded.

pH:

5.8 - 6.8

Moisture:

34 - 36%

Details on test conditions:

TEST SYSTEM
- Test container (material, size): 1000 mL glass beakers, each test vessel was covered with transparent plastic wrap held in place with an elastic band and perforated for gas exchange to prevent the test soil from becoming anoxic during the 56-day exposure.
- Amount of soil or substrate: 520 g (dry weight) of treated or control soil.
- No. of organisms per container (treatment): 10
- No. of replicates per treatment group: 8 plus one analytical vessel
- No. of replicates per control: 8 plus one analytical vessel
- No. of replicates per vehicle control: no vehicle used.

SOURCE AND PROPERTIES OF SUBSTRATE (if soil)
- Soil taxonomic classification: not reported
- Soil classification system: not reported
- Composition (if artificial substrate): 70% fine sand, 20% kaolin clay and 10% sphagnum peat moss.
- Organic carbon (%): not reported
- Maximum water holding capacity (in % dry weight): not reported
- CEC: not reported
- Pretreatment of soil: Periodic analysis of representative samples of the artificial soil components and cattle manure used during the earthworm culture and testing were analyzed for the presence of pesticides, PCBs, and toxic metals by Eurofins Lancaster Laboratories Environmental, Lancaster, Pennsylvania. Results of these analyses established that the laboratory well water, manure, and artificial soil did not contain any contaminants that would adversely affect the test organisms in agreement with ASTM (2007) standard practice
- Storage (condition, duration): not reported
- Stability and homogeneity of test material in the medium: recoveries of stability QC samples were all within 15% of their original results which serves as confirmation of stability during storage.

OTHER TEST CONDITIONS
- Photoperiod: not reported
- Light intensity: light intensity of the test area measured on days 0, 7, 14, 28, 42, and 56 ranged from 400 to 690 lux.

EFFECT PARAMETERS MEASURED (with observation intervals if applicable) :
Food consumption: observations of food consumption were recorded weekly, beginning on day 7, until test day 28.
Earthworm weight: the pooled earthworm weight was determined for earthworms (F0) added to each replicate vessel at test initiation (day 0), and at the termination of the F0 generation phase (day 28). Earthworm (F0) weights were measured to the nearest 0.0001 g using an analytical balance after rinsing the earthworms with laboratory well water and blotting them dry.
Mortality and health: earthworm mortality and health (e.g., color changes, lethargy, and softness) assessments were also performed on day 28. Mortality was defined as a lack of visible movement after mechanical stimulation (i.e., gentle touching) was applied to the anterior end of the organisms. Any earthworms that were unaccounted for were presumed dead and decomposed.
Reproduction: juveniles were counted on day 56 and approximately 24 hours after. At the end of the study, no earthworms remained in the soil of any replicates from the control or treatment level.

VEHICLE CONTROL PERFORMED: not applicable, as no vehicle used.

TEST CONCENTRATIONS
- Spacing factor for test concentrations: not applicable, one concentration tested (5.0 mg/kg soil dry weight)
- Justification for using less concentrations than requested by guideline: limit test
- Range finding study: not performed.

Nominal and measured concentrations:

Nominal: control and 5.0 mg/kg soil dry weight.
Measured: control and 3.8 mg/kg soil dry weight

Duration:

56 d

Dose descriptor:

NOEC

Effect conc.:

>= 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

LOEC

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

EC50

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 3.8 mg/kg soil dw

Nominal / measured:

meas. (arithm. mean)

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

56 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

LOEC

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

56 d

Dose descriptor:

EC50

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

reproduction

Duration:

28 d

Dose descriptor:

NOEC

Effect conc.:

>= 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

LOEC

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Duration:

28 d

Dose descriptor:

EC50

Effect conc.:

> 5 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

mortality

Remarks:

and growth

Details on results:

- Mortality at end of exposure period: controls: 99% survival, treatment group: 98%.
- Total mass of adults at beginning of test:
- Changes in body weight of live adults (% of initial weight) at end of exposure period: 44% weight change in controls, 40% change in treatment group. See table 1.
- No. of offspring produced: see table 2.
- No. of unhatched cocoons: none reported
- Morphological abnormalities: none reported
- Behavioural abnormalities: none reported
- Other biological observations: None reported

Results with reference substance (positive control):

- Results with reference substance valid? Yes, conducted with benomyl.
- Relevant effect levels: No 28-day mortality effects in highest concentration tested (5.0 mg/kg dry weight). On test day 28, the average weight change was 4.3, 25, 25, and 5.9% among adult earthworms exposed to the 0.63, 1.3, 2.5, and 5.0 mg/kg treatment levels, respectively. Following 56 days of exposure, 59 offspring per vessel were produced in the solvent control groups. An average of 64, 58, 46, and 7.5 offspring per vessel were produced among earthworms exposed to the 0.63, 1.3, 2.5, and 5.0 mg/kg treatment levels, respectively. As the 5.0 mg/kg treatment level had a significant effect compared to the solvent control, this result is within the range of expected significant values (1 to 5 mg/kg) for reproduction for benomyl, recommended by the testing guideline, and demonstrated that the test system was sensitive for detecting adverse effects of toxicant exposure.

Reported statistics and error estimates:

Fisher’s Exact Test was used to determine significant effects for survival. Wilcoxon’s Rank Sum Test was used to determine significant effects for adult weight and reproduction. All statistical conclusions were made at the 95% level of certainty except in the case of the basic assumption tests, e.g., Shapiro-Wilks’ Test and Bartlett’s Test, in which the 99% level of certainty was applied. The 28 day LC50 value for the adult survival and the 56 day EC10 and EC50 values for reproduction were all empirically estimated to be >5.0 mg/kg based on nominal values. As per the protocol, EC values for weight were not determined.

Table 1. Mean Percent Survival, Mean Weight of Live Organisms, and Percent Weight Change for the F₀ Generation

Nominal Concentration (mg/kg)	Replicate	Day 28 Survival (%)	Mean Individual Earthworm Weight^a (g)		Mean Percent Weight Change (SD)^bcd
			Day 0	Day 28
Control	1	100	0.3149	0.4708	50
	2	100	0.3179	0.4558	43
	3	100	0.3035	0.4950	63
	4	100	0.3194	0.4405	38
	5	100	0.3495	0.4983	43
	6	100	0.3249	0.4665	44
	7	100	0.3177	0.4329	36
	8	90	0.3215	0.4476	39
	Mean (SD)	99 (4)	0.3212 (0.0131)	0.4634 (0.0240)	44 (8.6)
5.0	1	100	0.3197	0.4803	50
	2	100	0.3669	0.4629	26
	3	100	0.3209	0.4660	45
	4	100	0.3427	0.4968	45
	5	90	0.3074	0.4580	49
	6	90	0.3277	0.4516	38
	7	100	0.3416	0.4170	22
	8	100	0.3310	0.4800	45
	Mean (SD)	98 (5)	0.3322 (0.0182)	0.4641 (0.0239)	40 (11)

a. Mean individual weights were determined by dividing the group weight for each replicate by the number of surviving adults for that replicate.

b. Mean percent weight change were determined by dividing the day 0 and 28 weight difference by the day 0 weight ((individual mean replicate weight, day 28 - individual mean replicate weight, day 0) / individual mean replicate weight, day 0) × 100.

c. SD = Standard Deviation

d. Values based on unrounded data and not on the rounded values presented in this table.

Table 2. Number of surviving offpsring per replicate

Nominal Concentration (mg/kg)	Replicate	Total Number of Surviving Offspring per Replicate^a
		Day 57^b- Total
Control	1	85
	2	111
	3	89
	4	115
	5	128
	6	121
	7	129
	8	122
	Mean (SD^c)	113 (17)
5.0	1	118
	2	91
	3	74
	4	96
	5	131
	6	65
	7	119
	8	72
	Mean (SD)	96 (25)

a. Adults (F₀) were removed on day 28 and cocoons present in the soil were allowed to hatch and mature until exposure day 56. 

b. Juvenile worms were extracted from treated and control soils over approximately 24 hours after termination on day 56. Numbers of juveniles were subsequently counted and constitute the total for each replicate.

c. SD = Standard Deviation

Table 3. Measured and nominal concentrations of the test substance on days 0, 2 and 28

Nominal test concentration (mg/kg)	Measured concentration				Mean measured concentration (mg/kg)	SD (mg/kg)	Percent of nominal (%)
	Day 0	Day 2	Day 28^a	Day 28^b
Control	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)	NA	NA	NA
	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)
	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)	<0.50^d(NA^e)
5.0	4.2 (85)	5.3 (110)	3.6 (73)	2.7 (54)	3.8	8.6	77
	4.2 (84)	4.3 (87)	3.8 (76)	2.7 (54)
	4.3 (86)	4.8 (95)	3.6 (72)	2.6 (53)
Mean	42 (85)	4.8 (96)	3.7 (73)	2.7 (53)

a. Results from samples taken before adult removal. 

b. Results from samples taken after adult removal.

c. Mean measured concentration, standard deviation (SD), and percent of nominal (in parentheses) values werecalculated using the actual analytical (unrounded) results and not the rounded values presented in this table. 

d.Concentrations expressed as less than values were below the method detection limit (MDL). The MDL is dependent upon thelowest concentration calibration standard andthe dilution factorofthe controls.

e. NA = Not Applicable

Validity criteria fulfilled:

yes

Remarks:

In the control group, mortality was 1% at day 28 (<10%) and ≥85 juveniles per replicate were produced by test termination (≥30). The % CV for reproduction in the control was 15% and did not exceed 30%.

Conclusions:

A 56-day EC50 value of >3.8 mg/kg soil dry weight and NOEC of ≥3.8 mg/kg soil dry weight have been determined for the effects of the test substance on reproduction of Eisenia fetida. 28-day EC50 and NOEC values of ≥3.8 and >3.8 mg/kg soil dry weight respectively, have been determined for the effects of the test substance on adult survival and adult weight of Eisenia fetida.

Description of key information

EC50 (28 d) > 3.8 mg/kg soil dw (meas. arithm. mean, OECD 222, E. fetida; read across from silanol hydrolysis product DMSD)

NOEC (28 d) ≥ 3.8 mg/kg soil dw (meas. arithm. mean, OECD 222, E. fetida; read across from silanol hydrolysis product DMSD)

Key value for chemical safety assessment

Short-term EC50 or LC50 for soil macroorganisms:

3.8 mg/kg soil dw

Long-term EC10, LC10 or NOEC for soil macroorganisms:

3.8 mg/kg soil dw

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 ecotoxicity of the registered substance (OECD SIDS, 2004). Thus, the ecotoxicity assessment is based on read-across to the silanol hydrolysis product dimethylsilanediol (DMSD, CAS No. 1066-42-8). Details on the read-across can be found in the analogue justification attached in IUCLID Section 13.

 

For the toxicity to soil macroorganisms, one experimental study is available for the silanol hydrolysis product and analogue substance dimethylsilanediol (CAS No. 1066-42-8), which was conducted according to OECD guideline 222 and in compliance with GLP.
In a limit test conducted as a laboratory study, earthworms (Eisenia fetida) were exposed to the nominal concentration of 5.0 mg/kg soil dw for 56 d in artificial soil (pH 5.8 to 6.8 and 34 to 36% moisture). A primary dosing stock concentration of 0.47 mg/mL was prepared by stirring on a magnetic stir plate for approximately 5 min, which was clear and colorless without any visible undissolved test substance. The test substance was then applied to the sandy loam (earthworm matrix) to a nominal treatment level of 5.0 mg/kg soil dw. Following dosing, the soil/test substance was mixed for approximately 10 min using a Hobart mixer.
A control was run in parallel Analytical monitoring of the control and test concentration was performed by LC-MS on days 0, 2, 28 and 56 after test start. The measured nominal concentration of exposure was 3.8 mg/kg soil dw, indicating that the dosing method was appropriate.
At test end, no effects on Eisenia fetida were observed (98% survival), resulting in an EC50 (56 d) of > 3.8 mg/kg soil dw and a NOEC (56 d) of ≥ 3.8 mg/kg soil dw, for the effects of dimethylsilanediol (DMSD, CAS No. 1066-42-8) on adult survival and weight of Eisenia fetida.

 

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