Dimethoxydimethylsilane

Toxicity to soil microorganisms

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

toxicity to soil microorganisms

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

Analytical monitoring:

no

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Conclusions:

Based on experimental results the source substance is not expected to cause any significant short or long-term effects on either soil microflora respiration or nitrogen transformation in soil when applied to agricultural soils at levels up to the equivalent of 100 ppm and 300 ppm. The source substance is the hydrolysis product of the target substance. Since the hydrolysis half life is < 1 h, the results derived for the source substance describe additionally the effects of the the target substance.

Reference 2

Endpoint:

toxicity to soil microorganisms

Type of information:

experimental study

Adequacy of study:

key study

Study period:

1996-10-21 to 1997-01-23

Reliability:

2 (reliable with restrictions)

Qualifier:

according to guideline

Guideline:

BBA Part VI, 1-1

GLP compliance:

yes (incl. QA statement)

Remarks:

The Department of Health of the Government of the United Kingdom (14 Jun 1995)

Analytical monitoring:

no

Vehicle:

no

Details on preparation and application of test substrate:

AMENDMENT OF SOIL
- Soil nitrogen tranformation test: Replicate batches of conditioned soil were amended with ground lucerne meal (0.5% w/w). The lucerne meal consisted of dried lucerne, ground to pass a 0.5 mm sieve, and contained 36.7% organic carbon and 2.3% total nitrogen.
- Glucose amendment in biomass determinations (microbial respiration test): 0.6 g/100 g soil dw (sandy loam soil 96/359) and 0.4 g/100 g soil dw (loam 96/368)

APPLICATION OF TEST SUBSTANCE TO SOIL
- Soil microflora respiration test: Replicate batches of conditioned soils were treated with 100 and 300 ppm of test item by even distribution of the liquid over the soil surface followed by thorough mixing.
- Soil nitrogen tranformation test: Replicate batches of conditioned soil were treated with 100 and 300 ppm of test item by even distribution of the liquid over the soil surface followed by thorough mixing.
- Procedure: Two stock solutions of the test item in distilled water were provided by the sponsor. These were a 2350 ppm solution which was used to treat soils at the 300 ppm level and a 2000 ppm stock solution, used to treat soil at the 100 ppm application level.
- Method: In this study, it was critical that the concentration of the test item in the soil water never exceeded 2500 ppm, otherwise the test item would polymerise. It was only possible to treat soil samples by addition of the test item in water when adjusting the moisture content of the soils to the final moisture content, which in this case was at 60 ± 5% of the soil water holding capacity.
At the 300 ppm dosing level, the N-tranformation study required that each soil replicate be treated with 6.38 mL of the 2350 ppm dosing solution to achieve the final application level. Therefore, the soils were required to have a sufficiently low moisture content that the addition of 6.38 mL of test item solution would not cause the moisture content to exceed 60% of the water holding capacity value for each soil. It was therefore determined that the soild should be received at 9 ± 1% in order to fulfill these requirements.
- Other: All treatments were then covered with lids and were then incubated under aerobic conditions.

Test organisms (inoculum):

soil

Remarks:

Exposure duration: 63 and 90 days for the loam and sandy soil respectively.

Test temperature:

21 ± 2 °C

Moisture:

56.13 - 60.04% WHC (loam soil, respiration test)
55.13 - 60.95% WHC (sandy loam soil, respiration test)
54.11 - 60.07% WHC (loam soil, nitrogen transformation test)
53.88 - 60.08% WHC (sandy loam soil, nitrogen transformation test)

Details on test conditions:

TEST SYSTEM
- Test container: 250 mL glass jars (respiration test) and 150 mL glass jars (N-transformation test), sealed with a plastic lid containing two small holes for gas exchange
- Amount of soil per replicate: 100 g dry-weight equivalent (respiration test) and 50 dry-weight equivalent (N transformation test)
- No. of replicates per concentration: 3
- No. of replicates per control: 3

SOIL INCUBATION
- Method: Series of individual subsamples

SOURCE AND PROPERTIES OF SUBSTRATE
- Geographical reference of sampling site: Soils were collected from grassland (Levington Agriculture Limited, 18 Oct 1996)
- History of site: The collection sites had not received pesticide or fertiliser treatments within the 12 months preceding the date of collection.
- Vegetation cover: Grassland
- Treatments with pesticides or fertilizers: None
- Accidental contamination: None
- Sampling: The soils were collected and prepared according to the draft international standards ISO/DIS 10381-6, Soil Quality - Sampling Part 6.
- Sampling date: Soils 96/358 and 96/359 were collected fresh from the field on 14 Oct 1996 whilst soil 96/368 was collected fresh from the field on 29 Oct 1996.
- Other: Due to an error in re-moisturising the loam soil for the respiration study, a second batch of this soil was received on 01 Nov 1996 (soil 96/368).
- Soil taxonomic classification: BBA: Sandy loamy silt (96/358 and 96/368) and silty sand (96/359); USDA: Loam (96/358 and 96/368)
- Soil classification system: BBA and USDA
- BBA soil typology:
- % Fine sand (0.063 - 0.2 mm): 15.2 and 15.4% (sandy loamy silt 96/358 and 96/368), 19.1% (silty sand 96/359)
- % Medium sand (0.2 - 0.63 mm): 8.0 and 8.4% (sandy loamy silt 96/358 and 96/368), 29.9% (silty sand 96/359)
- % Coarse sand (0.63 - 2.0 mm): 2.0 and 2.6% (sandy loamy silt 96/358 and 96/368), 9.2% (silty sand 96/359)
- % Sand total: 25.2 and 26.4% (sandy loamy silt 96/358 and 96/368), and 58.2% (silty sand 96/359)
- % Fine silt (0.002 - 0.006 mm): 4.5 and 4.0% (sandy loamy silt 96/358 and 96/368), 2.5% (silty sand 96/359)
- % Medium silt (0.006 - 0.02 mm): 16.3 and 15.8% (sandy loamy silt 96/358 and 96/368), 9.4% (silty sand 96/359)
- % Coarse silt (0.02 - 0.063 mm): 42.3 and 41.9% (sandy loamy silt 96/358 and 96/368), 22.1% (silty sand 96/359)
- % Clay (< 0.002 mm): 11.7 and 11.8% (sandy loamy silt 96/358 and 96/368), 7.8% (silty sand 96/359) and sandy loam (96/359)
- USDA soil typology:
- % Sand (2 mm - 50 µm): 38.0 and 39.1% (loam 96/358 and 96/368) and 64.9% (sandy loam 96/359)
- % Silt (50 µm - 2 µm): 50.3 and 49.0 (loam 96/358 and 96/368) and 27.3% (sandy loam 96/359)
- % Clay (< 2 µm): 11.7 and 11.8% (loam 96/358 and 96/368) and 7.8% (sandy loam 96/359)
- pH (in water): 6.7 and 6.8 (sandy loamy silt 96/358 and 96/368), 6.6 (silty sand 96/359)
- Initial nitrate concentration for nitrogen transformation test: Loam soil (96/358): 6.73 mg N/kg soil (Day 0, control), 7.22 mg N/kg soil (Day 0, 100 ppm), 7.60 mg N/kg soil (Day 0, 300 ppm); Sandy loam soil (96/359): 5.14 mg N/kg soil (Day 0, control), 4.39 mg N/kg soil (Day 0, 100 ppm), 4.32 mg N/kg soil (Day 0, 300 ppm)
- Maximum water holding capacity (0.001 bar suction (pFO), % w/w soil): 62.4 and 63.9% (sandy loamy silt 96/358 and 96/368) and 44.0% (silty sand 96/359)
- Storage: On receipt, the soils were stored at 21 ± 2 °C for 4 d at a moisture content of 9.29% (sandy loam soil, 96/359), 9.61% (loam soil, 96/358) and 11.34% (loam soil 96/368). Respiration replicates with a dry weight equivalent to 100 g were placed in 250 mL glass jars, whilst nitrogen replicates with a dry weight equivalent to 50 g were weighed into 150 mL glass jars. Each replicate container was sealed with a plastic lid containing two small holes to allow air exchange but minimise moisture loss. These were then stored at 21 ± 2 °C for 4 d (sandy loam 96/359 and loam 96/358) and 3 d (loam 96/368) prior to treatment and adjustment to 60 ± 5% of their water holding capacity (WHC).
- Initial microbial biomass as % of total organic C: Not available

EFFECT PARAMETERS MEASURED:
- Soil microflora respiration (infra-red gas analysis): After 0, 14, 28, 55 and 90 d (sandy loam soil) and after 0, 14, 28 and 63 d (loam soil)
- Soil nitrogen transformation (ammonification/nitrification; colourimetric determination): After 14, 28, 55 and 90 d (sandy loam soil) and after 14, 28 and 63 d (loam soil)

Nominal and measured concentrations:

100 ppm and 300 ppm (nominal)

Reference substance (positive control):

yes

Remarks:

Aretit Flussig (dinoseb acetate, 46.4% w/v)

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Remarks on result:

other: sandy loam soil

Duration:

90 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: sandy loam soil

Duration:

63 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

respiration rate

Remarks on result:

other: loam soil

Duration:

63 d

Dose descriptor:

NOEC

Effect conc.:

>= 300 mg/kg soil dw

Nominal / measured:

nominal

Conc. based on:

test mat.

Basis for effect:

nitrate formation rate

Remarks on result:

other: loam soil

Details on results:

- Effect concentrations exceeding solubility of substance in test medium: No

Results with reference substance (positive control):

- Results with reference substance valid? Yes (Aretit Flussig)
- Relevant effects (respiration rate): Significant differences to control at 0.31 mL CO2/h/100 g soil (Day 28, sandy loam soil) and 0.52 mL CO2/h/100 g soil (Day 28, loam soil)
- Relevant effects (nitrate formation): 67.39 mg N/kg soil (Day 60, sandy loam soil) and 68.77 mg N/kg soil (Day 28, loam soil)

Reported statistics and error estimates:

The data were statistically analysed by analysis of variance. Where a difference between treatments was observed, a suitable mean comparison test was performed to determine statistical significance of each treatment at the 5% level. The programme used was Toxstat Release 3.0 (1989). For treatments with equal numbers of replicates, the Dunnett's test for significance was used. Where unequal numbers of replicates were found between treatments, the Bonferroni T-test was used.

Table 1. Effect on mean microbial respiration rate [mL CO2/ h/ 100 g soil] in a loam soil (96/368)

	mL CO2/ h/ 100 g soil
Treatment	Day 0	Day 14	Day 28	Day 63
Control	1.03	1.00	1.00	1.08
100 ppm	1.23* (+19.42)	1.28* (+28.00)	1.04 (+4.00)	1.09 (+0.93)
300 ppm	1.17 (+13.59)	1.13 (+13.00)	1.07 (+7.00)	1.11 (+2.78)
F ratio	6.00	11.80	1.33	0.05
MSD	0.17	0.17	0.13	0.21

 

Table 2. Effect on mean microbial respiration rate [mL CO2/ h/ 100 g soil] in sandy loam soil (96/359)

	mL CO2/ h/ 100 g soil
Treatment	Day 0	Day 14	Day 28	Day 55	Day 90
Control	0.38	0.41	0.21	0.23	0.34
100 ppm	0.38 (0.00)	0.34 (-17.07)	0.24 (+14.29)	0.19 (-17.39)	0.39 (+14.71)
300 ppm	0.34 (-10.53)	0.39 (-4.88)	0.25 (+19.05)	0.18 (-21.74)	0.35 (+2.94)
F ratio	2.83	4.00	3.75	0.50	0.40
MSD	0.06	0.07	0.05	0.15	0.17

Tables 1 and 2 show means of 3 replicates.

*           = Significance at p = 0.05 level

MSD     = Minimum significant difference (Dunnetts test)

()            = ± variation from control treatment

F ratio  = Ratio of (SST x k(n-1)/SSE x (k-1))

SST       = Sum of squares (treatment)

SSE        = Sum of squares (error)

k            = number of treatments

n            = number of samples per treatment

Table 3. Effect on mean NH4⁺-nitrogen, NO3^—nitrogen and total mineral nitrogen (N-min) concentrations [mg N/kg soil] in a loam soil (96/358)

Treatment		mg N/kg soil
		Day 0	Day 14	Day 28	Day 55
Control	NH4+	7.06	< 0.27	< 0.27	< 0.27
	NO3-	6.73	14.84	46.45	61.78
	NO2	1.66	< 0.27	< 0.27	< 0.27
	N-min	15.45	14.84	46.45	61.78
100 ppm	NH4+	5.77* (-18.27)	< 0.27 (ND)	< 0.27 (ND)	< 0.27 (ND)
	NO3-	7.22 (+7.28)	23.45 (+58.02)	36.10* (-22.28)	57.95 (-6.20)
	NO2	1.00* (-39.76)	< 0.27 (ND)	< 0.27 (ND)	< 0.27 (ND)
	N-min	13.99 (-9.45)	23.45 (+58.02)	36.10 (-22.28)	57.95 (-6.20)
300 ppm	NH4+	6.70 (-5.10)	< 0.27 (ND)	< 0.27 (ND)	< 0.27 (ND)
	NO3-	7.60 (+12.93)	15.04 (+1.35)	49.78 (+7.17)	64.01 (+3.61)
	NO2	1.16* (-30.12)	< 0.27 (ND)	< 0.27 (ND)	< 0.27 (ND)
	N-min	15.46 (+0.06)	15.04 (+1.35)	49.78 (+7.17)	64.01 (+3.61)
F ratio	NH4+	7.87	NA	NA	NA
	NO3-	1.94	4.40	6.69	1.47
	NO2	15.32	NA	NA	NA
MSD	NH4+	0.88	NA	NA	NA
	NO3-	1.16	8.65	10.18	9.35
	NO2	0.33	NA	NA	NA

 

Table 4. Effect on mean NH4⁺-nitrogen, NO3^—nitrogen and total mineral nitrogen (N-min) concentrations [mg N/kg soil] in a sandy loam soil (96/359)

Treatment		mg N/kg soil
		Day 0	Day 14	Day 28	Day 55	Day 90
Control	NH4+	5.23	< 0.26	< 0.26	< 0.26	< 0.26
	NO3-	5.14	2.80	12.75	24.25	44.95
	NO2	0.69	< 0.26	< 0.26	< 0.26	< 0.26
	N-min	11.06	2.80	12.75	24.25	44.95
100 ppm	NH4+	4.26* (-18.55)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)
	NO3-	4.39 (-14.59)	3.00 (+7.14)	17.20 (+34.90)	32.80 (+35.26)	55.05 (+22.47)
	NO2	0.44* (-36.23)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)
	N-min	9.09 (-17.82)	3.00 (+7.14)	17.20 (+34.90)	32.80 (+35.26)	55.05 (+22.47)
300 ppm	NH4+	4.23* (-19.12)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)
	NO3-	4.32 (-15.95)	3.75 (+33.93)	16.19 (+26.98)	31.38 (+29.40)	58.13 (29.32)
	NO2	0.47* (-31.88)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)	< 0.26 (ND)
	N-min	9.02 (-18.44)	3.75 (+33.93)	16.19 (+26.98)	31.38 (+29.40)	58.13 (29.32)
F ratio	NH4+	6.31	NA	NA	NA	NA
	NO3-	1.91	0.35	4.83	2.85	1.78
	NO2	6.73	NA	NA	NA	NA
MSD	NH4+	0.83	NA	NA	NA	NA
	NO3-	1.21	3.14	3.91	10.01	19.07
	NO2	0.19	NA	NA	NA	NA

 

Tables 3 and 4 show means of 4 replicates

(…)        = % variance from control treatments

F ratio  = ratio of sum of squares (treatment) / sum of squares (error)

MSD      = minimum significant difference (Dunnetts test)

LOD      = NO2^--nitrogen and NH4⁺-nitrogen: 0.27 mg/kg; NO3^—nitrogen: 0.54 mg/kg

NA         = Not available

ND        = Not determined

*            = significant (at p = 0.05)

N-min   = Total mineralized nitrogen, i.e. total of ammonium + nitrate + nitrite (if present)

SOIL MICROFLORA RESPIRATION - LOAM SOIL (Table 1)

Day 0: Statistically significant stimulatory effect on microbial respiration at 100 ppm.

After 14 d: Statistically significant stimulatory effect on microbial respiration at 100 ppm.

After 28 d: No statistically significant effects.

After 63 d: No statistically significant effects at either application rate (100 and 300 ppm)

=> No dose-related effects were observed in the loam soil during the course of the respiration study.

SOIL MICROFLORA RESPIRATION - SANDY LOAM (Table 2)

Respiration rates were lower on Day 28 and 55, which was probably due to a reductionin oxygen availability in the moist soils.

The study was continued to 90 d. After 90 d, no statistically significant effects greater than ± 15% were observed at either application rate.

=> No dose-related effects were observed in the sandy loam soil during the course of the respiration study.

SOIL NITROGEN TRANSFORMATIONS - LOAM SOIL (Table 3)

Day 0: Statistically signifcant effects on ammonium and nitrite concentrations at the 100 ppm application level. At the 300 ppm level, a statistically significant effect was observed for nitrite concentrations only.

After 14 d: Ammonium and nitrite concentrations were below the detectino limits (0.27 mg/kg) at both application levels.

After 28 d: A statistically significant effect was observed on nitrate concentrations at the 100 ppm application level. No statistically significant effects were observed at the 300 ppm application level.

After 55 d: No statistically significant effects in excess of ± 15% were observed at either application level.

=> No dose-related effects were observed in the loam soil during the course of the nitrogen transformation study.

SOIL NITROGEN TRANSFORMATIONS - SANDY LOAM (Table 4)

Day 0: Statistically significant effects on ammonium and nitrite levels were observed at both application levels, indicating a temporary inhibitory effect of the test item on nitrogen transformation processes.

After 14 d: Ammonium and nitrite levels were below the detection limit of 0.26 mg/kg at both treatment levels.

After 28 d: A statistically signifcant stimulatory effect was observed on nitrate concentrations at the 100 ppm application level. No statistically significant effects were observed at the application level of 300 ppm.

After 55 d: No statistically significant effects greater than ± 15% were observed for both nitrate and total mineral nitrogen concentrations at both application levels.

After 90 d: Non-statistically significant effects in excess of ± 15% were observed at both application levels.

OVERALL CONCLUSION

The test item is not expected to cause any significant long-term effects on either soil microflora respiration or nitrogen transformation in soil when applied to agricultural soils at levels up to the equivalent of 100 and 300 ppm.

Conclusions:

DMSD is not expected to cause any significant short or long-term effects on either soil microflora respiration or nitrogen transformation in soil when applied to agricultural soils at levels up to the equivalent of 100 ppm and 300 ppm.

Description of key information

NOEC (90 d) ≥ 300 mg/kg soil dw (nominal, BBA Part VI (1-1), soil; read across from silanol hydrolysis product DMSD)

Key value for chemical safety assessment

Long-term EC10 or NOEC for soil microorganisms:

300 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 and methanol. 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). 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 terrestrial toxicity was assessed based on read-across to the silanol hydrolysis product dimethylsilanediol.

One study is available for the hydrolysis product dimethylsilanediol investigating the effect of the test item on soil microflora. A short-term respiration test and a soil nitrogen transformation test were performed. The respiration test was conducted after 0, 14, 28, 55 and 90 d (sandy loam soil) and after 0, 14, 28, and 63 d (loam soil). On each occasion, aliquots of soil were amended with a non-limiting quantity of glucose and the carbon dioxide evolution was measured over the subsequent 24 -h period with an infrared gas analyser. Values for the substance induced respiration rate were converted to soil microbial respiration (mL CO2/ h/ 100 g soil).
The effects on nitrogen transformations, ammonification and nitrification were investigated by determining ammonium-N, nitrate-N and nitrite-N concentrations in soil amended with ground lucern grass. Aliquots of soil were extracted with 2 M KCl within 3 h and after 14, 28, 55 and 90 d (sandy loam soil) and 14, 28 and 63 d (loam soil). The concentrations of inorganic nitrogen species in the extracts were determined colourimetrically. Treatment levels of 100 and 300 ppm were applied, respectively.
No statistically significant effects were observed at both application levels for the respiration test and the soil nitrogen transformation test, respectively. In consequence, dimethylsilanediol is not expected to cause any significant long-term effects on either soil microflora respiration or nitrogen transformation when applied to agricultural soils at levels up to 300 ppm.

 

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