Dimethoxydimethylsilane

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

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

Adequacy of study:

weight of evidence

Justification for type of information:

Please refer to the justification for grouping of substances provided in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Reason / purpose for cross-reference:

read-across source

Remarks on result:

other: An initial rate (12 weeks) of soil biodegradation of 0.36 - 1.70% per week was determined

Remarks:

Lehmann 1998

Remarks on result:

other: An initial rate of soil biodegradation of 0.17 - 2.1% per month was determined.

Remarks:

Sabourin 1996b

Remarks on result:

other: The study showed that DMSD can biodegrade and volatilise from soil. However, the rates of these processes were not well defined.

Remarks:

Lehmann 1994

Remarks on result:

other: Initial rate of soil biodegradation (during first four days of incubation) was 0.16 - 1.9% per month

Remarks:

Sabourin 1996a

Remarks on result:

other: There is no evidence for any significant degradation or conversion of DMSD in soil

Remarks:

Gerin 2016

Transformation products:

not measured

Rates of 14CO2 production were calculated from the first 12 weeks of data since studies show that microbial degradation rates decrease over time under controlled conditions, meaning that initial rates are most representative of field conditions. Rates varied by roughly a factor of 4 for the different soils. Rates increased with microbial biomass for Pipestone (0.36 to 0.42% per week), Londo (0.42 to 0.50% perweek) and Cohoctah soils (0.64 to 0.74% per week). A higher rate of 14CO2 production was found for the Sloan soil (1.59 to 1.70% per week) however, which has the lowest microbial biomass. This suggests that these organisms may be more active in degrading DMSD than organisms in the other soils.

After 30 weeks the 14C was partitioned amoung numerous fractions. Acid extractable 14C is interpreted as soil bound silanols; HPLC analysis indicated DMSD:degradate(s). Base extractable 14C may represent 14C which has been sequestered in the soil humus; HPLC analysis indicated DMSD: degredate(s).

Conclusions:

The studies did not reveal significant degradation of the source substance Dimethylsilanediol (DMSD). Based on these results and the read across justification provided in chapter 13, no significant degradation is expected for the target substance.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP. This study is of limited use due to uncertainty in interpretation of the results (discussed further in Overall remarks).

Principles of method if other than guideline:

Nine soils (some sludge-amended) were tested for their ability to biodegrade 14C-Dimethylsilanediol (DMSD; 100ppm) and 14C-Methylsilanetriol (MST; 10ppm). 5-6g soil (moist) in plastic vials were spiked with DMSD or MST. Each vial placed in centrifuge bottle with another vial containing KOH, which served as CO2 trap. Soils monitored for the production of 14-CO2 over 63d. Incubated at room temperature.
Rate-determining soil simulation biodeg experiment on DMSD. DMSD spiked to Cohoctah soil at 1, 10, 100 ppm and monitored 59d.

GLP compliance:

not specified

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Details on soil characteristics:

SOIL COLLECTION AND STORAGE

- Geographic location: Two soils (Cohotah and Sloan) from Chippewa Nature Centre, Midland, Michigan. Seven soils, both sludge-ammended and non-sludge amended, from farms in Ohio (Groveport, Braun and Kenton).

Details on experimental conditions:

2. EXPERIMENTAL DESIGN

- Soil (g/replicate): 5-6g moist soil

- Control conditions, if used: Sterilized controls - autoclaved and sodium azide (50ul of a 10% solution).

- No. of replication treatments: All soils, live and sterile, were prepared in duplicate.

- Test apparatus (Type/material/volume): 5-6g moist soil in plastic vial and spiked with radiolabelled TS.

- Details of traps for CO2 and organic volatile, if any: Plastic vials containing soil samples placed in a 300 ml centrifuge bottle with another vial containing 5ml of 0.2 M KOH to serve as a CO2 trap.

Test material application
- Volume of test solution used/treatment: Soil samples spiked with either 250 ul of a 2000ppm solution [14C]-DMSD (soil 100ppm wrt DMSD) or 65.8ul of a 760 ppm solution [14C]-MST (soil 10ppm wrt MST).

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: Moisture level adjusted either by adding sterile, deionized water or drying the soil at room temperature, so that after all spiking materials were added the soil moisture would be equivalent to the level at 1 bar.

4. SUPPLEMENTARY EXPERIMENTS: (see Any other information on materials and methods, below)

5. SAMPLING DETAILS
- Sampling intervals: Soils were monitored for the production of 14-CO2 on days 4, 11, 17, 24, 42 and 63.
- Sampling method for soil samples: Radioactivity balance was determined at the completion of experiments. Soil samples extracted with CaCl2 and HCl. Extracts analyzed by LSC; soil dried for a week and then combusted to determine 14-C counts.
- Method of collection of CO2 and volatile organic compounds: In soil bottles, the entire KOH trap removed, capped and a new trap added.

Remarks on result:

other: For results see field "any other information on results incl. tables"

Transformation products:

not measured

Evaporation of parent compound:

not measured

Volatile metabolites:

not measured

Residues:

not measured

DMSD (100ppm): Rates varied depending on soil location. Initial rate during first four days 0.16 - 1.9% per month. Total conversion after 63d 0.33 - 1.35% (initial rate of biodeg slowed over time). Previous addition of sludge to the soil had no statistically significant effect on the rate of biodegradation.

MST (10ppm): Initial rate during first four days for all soils around 0.38% per month. Total conversion after 63d 0.08 - 0.18% (initial rate of biodeg slowed over time). Since none of these rates is >0.4% (the level of possible impurity in [14C]-MST) it is difficult to make any conclusions about the biodeg of [14C]-MST in soil.

MST (100ppm): Initial rate during first six days 0.34% per month. Total conversion after 45d 0.13% (initial rate of biodeg slowed over time). In liquid culture, however, the biodegradation rates of DMSD and MST were similar. These results suggest that rate of MST biodeg in soil is slow due to poor bioavailability of MST due to adsorption to soil.

Adsorption experiment: 50ppm DMSD ~5% adsorbed to soil in first hr, after which no additional loss (up to 70hrs). 10 ppm MST 10% adsorbed to soil in first hr, ~25% adsorbed to soil over 45hrs, after which no additional loss (up to 70hrs). 50ppm MST 10% adsorbed to soil in first hr, 90% adsorbed to soil in 620 hrs. (Control = No loss DMSD to glass vial; 1% or 5% loss MST at 50 and 10ppm.)

Liquid culture: F. oxysporum was able to biodegrade MST at a rate comparable to or faster than the biodeg of DMSD. Arthrobacter was able to biodegrade MST at a rate slightly slower than DMSD.

Rate-determining soil simulation biodeg experiment on DMSD. 1ppm DMSD average initial rate in first 7d 1.4% per month. 10ppm DMSD average initial rate 0.9% per month. 100ppm DMSD average initial rate 0.6% per month. Total biodeg at 59d 1.8%, 1.8% and 1.1% respectively.

Conclusions:

An initial rate of soil biodegradation (during first four days of incubation) of 0.16 - 1.9% per month was determined in a reliable study conducted according to generally accepted scientific principles. It was found that previous addition of sludge to soil had no statistically significant effect on the rate of biodegradation.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP. This study is of limited use due to uncertainty in interpretation of the results (discussed further in Overall remarks).

Principles of method if other than guideline:

Four soils were tested for their ability to biodegrade 14C-Dimthylsilanediol (DMSD). 50g moist soil spiked with radio-labelled TS and ammonium chloride (added to eliminate possibility of nitrogen limitation in the soils) were mixed together in a 500-ml Gledhill flask. Soils incubated at room temperature. Soils monitored for the production of 14CO2 over 290d.

GLP compliance:

not specified

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Details on soil characteristics:

SOIL COLLECTION AND STORAGE

- Geographic location: Four soils taken from either a residential garden or a sludge disposal area. Two soils, a sandy soil from Santa Barbara, California, and a mixture of forest and residential garden soils and composted cow manure from Cobleskill, N.Y., were not beleived to have been previously exposed to PDMS. The remaining two soils were taken from a residential garden (Guilderland, N.Y.) and a sludge disposal area (Glendale, Ohio).

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil (g/replicate): 50g moist soil

- Control conditions, if used: Sterilized controls of both the Cobleskill and the Santa Barbara soils - autoclaved and sodium azide (2ml of a 2.5% solution).

- No. of replication treatments: Duplicates were prepared for each of the four soils.

- Test apparatus (Type/material/volume): 50g moist soil spiked with radiolabelled TS and 100ul of ammonium chloride (50g/l; added to eliminate possibility of nitrogen limitation in the soils) were mixed together in 500-ml Gledhill flasks.

- Details of traps for CO2 and organic volatile, if any: The Gledhill CO2 traps were filled with 10 ml of 0.2 M KOH, although in some cases this was increased to 2 M KOH.

Test material application
- Volume of test solution used/treatment: Soil samples spiked with 2.5 ml of a 2000ppm solution [14C]-DMSD.

3. OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: Oxygen was supplied by diffusion. 12-in 20-gauge needle, connected to an oxygen manifold, was inserted through the septum at the top of the trap.

4. SUPPLEMENTARY EXPERIMENTS: Liquid culture experiments.

5. SAMPLING DETAILS
- Sampling method for soil samples: Radioactivity balance was determined at the completion of experiments. Soil samples extracted with THF, HCl and KOH. Extracts analyzed by LSC; soil combusted to determine 14-C counts.

- Method of collection of CO2 and volatile organic compounds: The entire contents or an aliquot of the KOH trap were withdrawn periodically with a sterile needle. Fresh KOH was added to the traps immediately.

Remarks on result:

other: For results see field "any other information on results incl. tables"

Transformation products:

not measured

Evaporation of parent compound:

not measured

Volatile metabolites:

not measured

Residues:

not measured

Guilderland soil: 2.1% of the total 14-C counts added was converted to 14CO2 in the first month. After 244d 9% had been converted.

Santa Barbara: 0.41% of the total 14-C counts added was converted to 14CO2 in the first month. After 290d, 2.64% had been converted.

Cobleskill: 0.51% of the total 14-C counts added was converted to 14CO2 in the first month. After 290d, 1.5% had been converted.

Glendale: 0.17% of the total 14-C counts added was converted to 14CO2 in the first month. After 255 d, 1.1% had been converted.

The rate of conversion in all of the soils slowed over the course of the experiments

Mixed liquid culture experiments indicated that a fungus (Fusarium oxysporum Schlechtendahl) was likely responsible for the conversion of DMSD to CO2 in liquid cultures inoculated with Guilderland soil. and a bacteria (Arthrobacter sp.) for the conversion in liquid cultures inoculated with Santa Barbara soil.

Conclusions:

An initial rate of soil biodegradation of 0.17 - 2.1% per month was determined in a reliable study conducted according to generally accepted scientific principles.

Reference 4

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

14C-PDMS (1, 10, 100 mg/kg) was placed in 50g Londo sandy clay loam, and the soil was dried to generate the desired silanols in situ. The soil was remoistened and incubated at 25°C, 12% moisture, and 21% O2. Soils monitored for the production of 14CO2 (KOH trap in side flask), other volatiles (carbon plug) over 20 weeks. In addition, extracts from extractions with THF, HCL and KOH were sampled for total 14C (THF extracts also analysed via HPLC-GPC).

GLP compliance:

no

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: London sandy clay loam (0 to 5 cm) was collected in late April of 1992 from a farm in Bay County, Michingan.

- Soil preparation (e.g., 2 mm sieved; air dried etc.): Sieved (2mm) and stored moist at 4 °C until use in July/December.

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil (g/replicate): 50g moist soil weighed into 11 incubation flasks

- Control conditions, if used: Silanol degradation in sterilised soils was not examined because the process of generating silanols required that flasks be open to the air for 2 weeks as the soil dried, and sterility would have been impossible to maintain.

- Details of traps for CO2 and organic volatile, if any: 100 ml 0.2M KOH solution in side flask. A 1.5 x 1.5-cm plug (activated cabon on a polyester support) was inserted in the neck to trap other volatiles.

Test material application
- Volume of test solution used/treatment: 0.5 ml of spiking solution added dropwise to the surface of the soil in incubation flasks to yield 100 mg/kg of PDMS in soil. Soil stirred and flasks left open for 2 weeks at 25 deg C for the soil to dry and generate silanols.

Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

- Other information: At 7 weeks, 1g of ground, dried alfalfa was mixed into the soil in three of the flasks, 1 ml water added, and the KOH traps replaced. A second incubation was begun after obtaining results from the first incubation. Soil added (as above) to 24 flasks, and 1 g alfalfa added to 12 of the flasks. The flasks were maintained moist for 2 weeks to allow microbial activity on the alfalfa to subside, after which PDMS was added as above to yield either 1, 10 or 100 mg PDMS/kg soil. Flasks were then allowed to dry for 2 weeks, remoistened, and incubated as above for 0, 3, 9 and 20 weeks (carbon plugs not used).

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: Flasks attached to O2 manifold.

4. SUPPLEMENTARY EXPERIMENTS:

5. SAMPLING DETAILS
- Sampling intervals: 0, 1, 2, 4, 7, 10, 13 or 19 weeks.

- Sampling method for soil samples: Aliquotes (5g) of soil were extracted 4 times with THF, and the pooled extracts (25 ml) were sampled for total 14-C, while additional extracts (25 ml) were removed for HPLC-GPC. Soils were then extracted overnight with 20 ml of 0.1 M HCL. Certain soils showed low recoveries and so were extracted overnight with 20 ml of 0.5 M KOH. All extracts were sampled in duplicate for total 14C. Soils were then air-dried and ashed. All samples were counted on a Packard 2500 scintillation counter using external standards for quench correction.

- Method of collection of CO2 and volatile organic compounds: Carbon plugs were extracted 4 times with THF for volatile organic 14-C. The KOH trapping solutions were sampled and 14-CO2 was determined via BaCl2 precipitation method.

Remarks on result:

other: For results see field "any other information on results incl. tables"

Transformation products:

not measured

Volatile metabolites:

yes

First incubation: HPLC-GPC analysis indicated that after two weeks the PDMS fragmented into a mixture of large oligomers and low-molecular-weight molecules, with DMSD being the main breakdown product. Analysis via KOH traps implied that the 14C-Si bond was broken in the soil. Other pathways of loss from the soil solution included volatilisation and binding to soil components.

Over half of the 14C was in stabilised forms (large oligomers, HCL-extractable) at the beginning of the microbial degradation phase, the 14C found as volatile silanols, as 14CO2, and as humus-bound (KOH-extractable) probably came from only 40 to 50% of the applied radioactivity. With this in mind, the amount of 14C in the above three fractions after 4 months may represent from 25 to 50% of the original dimethylsilanediol.

Second incubation: HPLC-GPC analysis indicated that PDMS degraded more slowly in soils with alfalfa - probably the polymer has sorbed to the alfalfa preventing it from degrading. This meant that when soils were remoistened to begin the microbial degradation phase, the soils with alfalfa contained much less DMSD than did soils without. Therefore, the data was normalised according to the amount of small silanols actually present in the soil before comparison with data from soils without alfalfa.

At 1 and 10 mg/kg the soils with alfalfa produced higher rates of 14C volatilisation than did soil-only treatments, although at 100 mg/kg the increase was not clear. The secretion of H2O2 and enzymes by some fungi during cellulose metabolism may be responsible for the degradation fo silanols.

Conclusions:

It was determined, in a reliable study conducted according to generally accepted scientific principles, that DMSD could biodegrade and volatilise from soil. However, rates of these processes were not well defined because the 14C-DMSD was generated in-situ from 14C-PDMS and the soil also contained incompletely hydrolysed 14C-PDMS. Moreover, the volatilisation rate inside a flask is probably lower than would be expected in open air.

Reference 5

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Remarks:

The study was well documented and meets generally accepted scientific principles, but was not conducted in compliance with GLP.

Principles of method if other than guideline:

50g moist soil (four soils from sites under different vegetation) incubated in biometer flasks with 0.8 ml 14C-DMSD (89 µg/ml), to give 1mg DMSD/kg soil, for 6 months. Production of 14CO2 was followed via KOH trap in sidearms, and carbon plugs were used to trap volatile DMSD. The incorporation of 14C into the soil was examined via CaCl2, HCL and KOH extractions.

GLP compliance:

no

Test type:

laboratory

Radiolabelling:

yes

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Collected from near Midland, MI, in the summer of 1994. Three (Cohoctah - permanent grass, Pipestone - pine woods, and Sloan - beech, maple woodland) from Chippewa Nature Centre, one (Londo) from Cornfield

- Soil preparation (e.g., 2 mm sieved; air dried etc.): Sieved (2mm) and refridgerated (4 degC) until use.

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil (g/replicate): 50g

- Control conditions, if used: Two additional flasks of Sloan soil were incubated as for test vessels but with addition of 0.5 ml THF as a microbial inhibitor. One 50g sample per soil was ammended with DMSD as above and refrigerated until concurrent analysis with other soils.

- No. of replication treatments: 2

- Test apparatus (Type/material/volume): 50 g moist soil and spiking solution in 16 biometer flasks.

- Details of traps for CO2 and organic volatile, if any: Carbon pugs inserted into necks of flasks to trap volatile DMSD. 100 ml of 0.2 M KOH placed in the sidearms to trap 14CO2.

Test material application
- Volume of test solution used/treatment: 0.8 ml of aqueous DMSD (89 µg/ml) added and soil stirred to yield about 1 mg DMSD/kg soil. 8 flasks also amended with 2g of the appropriate plant litter.

Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: Flasks were attached to an oxygen (O2) supply manifold.

5. SAMPLING DETAILS
- Sampling intervals: Plugs and KOH solutions removed every 3 weeks for analysis for total 14C and 14CO2 (scintillation counter).

- Sampling method for soil samples: Duplicate 5g aliquots extracted with CaCl2,HCl and KOH for 14C analysis. Soils were air-dried and combusted for total 14C. Reversed-phase HPLC was performed on selected water and HCL extracts.

- Method of collection of CO2 and volatile organic compounds: Fresh plugs and KOH solution were placed in the flasks after each sampling.

Remarks on result:

other: For results see field "any other information on results incl. tables"

Transformation products:

not measured

Rates of 14CO2 production were calculated from the first 12 weeks of data since studies show that microbial degradation rates decrease over time under controlled conditions, meaning that initial rates are most representative of field conditions. Rates varied by roughly a factor of 4 for the different soils. Rates increased with microbial biomass for Pipestone (0.36 to 0.42% per week), Londo (0.42 to 0.50% perweek) and Cohoctah soils (0.64 to 0.74% per week). A higher rate of 14CO2 production was found for the Sloan soil (1.59 to 1.70% per week) however, which has the lowest microbial biomass. This suggests that these organisms may be more active in degrading DMSD than organisms in the other soils.

After 30 weeks the 14C was partitioned amoung numerous fractions. Acid extractable 14C is interpreted as soil bound silanols; HPLC analysis indicated DMSD:degradate(s). Base extractable 14C may represent 14C which has been sequestered in the soil humus; HPLC analysis indicated DMSD: degredate(s).

Conclusions:

An initial rate (12 weeks) of soil biodegradation of 0.36 - 1.70% per week was determined in a reliable study conducted according to generally accepted scientific principles.

Reference 6

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

weight of evidence

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

study well documented, meets generally accepted scientific principles, acceptable for assessment

Reason / purpose for cross-reference:

reference to same study

Qualifier:

no guideline followed

Principles of method if other than guideline:

The degradation of Radio-labeled 14C-DMSD was tested in closed microcosms mimicking eight different environmental matrices. The matrices were surface water (Aerobic Surface water), Composite soil suspended in water (Aerobic soil slurry), Composite sludge slurry (Aerobic sludge), Composite sludge slurry + calcium nitrate (Anoxic sludge), Composite sludge slurry + goethite (Ferri-reducing sludge), Composite sludge slurry + iron(II)sulfate (Sulfidogenic sludge), Composite sludge slurry (Methanogenic sludge), Bottom 1 cm layer of solid organic sludge, covered by a 5 cm layer of solid composite soil, at field capacity. Bottom 0.5 cm layer saturated with water (Gradient microcosm). The microbial communities were supplied from environments where microorganisms have high chance to be in contact and possibly degrade silanols. The degradation was followed measuring the 14CO2 and 14CH4, in the headspace and the exhaust gas of the microcosms. The reactors were incubated for 13 to 18 months. sacrifices were performed at 4 times: directly after starting the incubation to characterize the initial situation (d0), after 3 months of incubation (d87- 94), after 6 months of incubation (d180-196) and after a total incubation of 13 months to 18 months (d398-557) depending on the tested condition.

GLP compliance:

no

Remarks:

Study was not conducted for registration purposes. Thus no GLP compliance was necessary.

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Namur (Belgium), Mixture of garden soils
- Pesticide use history at the collection site: not given
- Collection procedures: not given
- Sampling depth (cm): not given
- Storage conditions: at 4°C in darkness
- Storage length: up to 3 month

Soil No.:

#1

Duration:

557 d

Soil No.:

#2

Duration:

540 d

Soil No.:

#1

Initial conc.:

110.35 other: ppm DMSD

Based on:

test mat.

Soil No.:

#2

Initial conc.:

110.35 other: ppm DMSD

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

18–22°C

Soil No.:

#2

Temp.:

18–22°C

Details on experimental conditions:

1. PRELIMINARY EXPERIMENTS:
none
2. EXPERIMENTAL DESIGN
(please see table 1 in "any other information on materials and methods"):
- Soil condition: fresh
- Soil (g/replicate): #1: 41 g wet matter; #2: 171 g wet matter
- Control conditions, if used (present differences from other treatments, i.e., sterile/non-sterile, experimental conditions): same
- No. of replication controls, if used: 2
- No. of replication treatments: 2
- Test apparatus (Type/material/volume): 250 mL GL-45 glass bottles closed with a stainless steel plate cap pressed on a Viton® o-ring with a PBT pierced GL-45 screw cap . The stainless steel plate was crossed by two ¼” outer diameter stainless steel tubes.
- Details of traps for CO2 and organic volatile, if any: 1 M NaOH

Test material application
- Volume of test solution used/treatment: 1 mL
- Application method (e.g. applied on surface, homogeneous mixing etc.): #1: manually shaken, #2: distributed by spiking at multiple positions at the surface layer
Any indication of the test material adsorbing to the walls of the test apparatus: no
Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

3. OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: vented with air

4. SUPPLEMENTARY EXPERIMENTS: none

5. SAMPLING DETAILS
- Sampling intervals: #1: d0, d92, d192, d557; #2: d0, d89, d187, d540
- Sampling method for soil samples: Solid Phase extraction by Tetrahydrofuran (THF)
- Method of collection of CO2 and volatile organic compounds:
Trap for 14 CO2: 1 M NaOH
Trap for 14CH4: CH4 and any volatile carbonaceous molecule was injected into an Oxidizer furnace ((Carbolite, MTT 12/38/850/3508P1 Tritium & Carbon-14 Capture Furnace) and converted to CO2 which was then trapped

Remarks on result:

not measured/tested

Remarks on result:

other: no degradation observed

Remarks on result:

not measured/tested

Transformation products:

not measured

Details on results:

For each condition, the highest amount of radioactivity is recovered in the liquid phase, even at the end of the incubation. The radioactivity recovered from the liquid phase slowly decreases.
At the end of the 13-18 months of incubation, there is a very low but significant cumulated release of 14C marked molecules in the gas samples. The detected non condensable radioactivity can be attributed to volatile 14CDMSD that was not retained by the cold trap. Indeed, even at -70°C, DMSD has a positive vapor pressure (unknown value), and some molecule can escape.
At this stage of the incubation, no clear trend emerges yet from the evolution of radioactivity recovered from the solid phase with time; neither for the total radioactivity nor for the ratio between 14C-DMSD by-products extractable and not extractable by THF.
The HPLC analysis aimed at detecting the presence of different 14C-metabolites of 14C-DMSD. However the results don’t show any evidence for the presence of any metabolite other than 14C-DMSD in the liquid phase, in the THF extract or in the acid extract of the residual solids.

Conclusions:

There is no evidence for any significant degradation or conversion of DMSD in soil conditions. Environmental DMSD degradation, if any, should be sought in another environmental compartments.

Additional information

Dimethoxydimethylsilane (CAS 1112-39-6) hydrolyses rapidly in contact with water (DT50: <0.6 h), to dimethylsilanediol (CAS 1066-42-8) and methanol (CAS 67-56-1). Thus, the environmental fate assessment is based on the hydrolysis products i.e. dimethylsilanediol and methanol rather than the parent substance.

Dimethylsilanediol: Biodegradation of DMSD in soil was investigated in several earlier studies (e.g. Sabourin et al., 1996; Lehman et al., 1998; Sabourin et al., 1999). Various types of soil and duration of tests were applied; however biodegradation rate was no more than a few percent per month.

The biodegradation of DMSD (dimethylsilanediol) was further investigated under any of various water environmental matrices in contact with soil or sediments, in the presence of microorganisms that have high chance to degrade DMSD (CES, 2016). Different sites known or expected to be contaminated by silanols have been selected in order to maximize the probability to obtain samples with various organisms previously exposed and potentially adapted to silanols. The four types of matrices sampled (surface water, sludge, leachate and soil) from each site were mixed together to get four groups with an initial microbial diversity as broad as possible. Eight different conditions that cover a range of environmentally relevant redox conditions were tested in duplicate.

The experimental set-up and procedure was designed to ensure to close the 14C balance as much as possible, by minimizing and checking the 14C losses in order to unequivocally interpret the results. The reactors were incubated for more than one year and sacrifices were performed four times: directly after starting the incubation to characterize the initial situation (d0), after 3 months of incubation (d87-94), after 6 months of incubation (d180-196) and after a total incubation of 13 months to 18 months (d398-557) depending on the tested condition.

As a result of this extensive study, there was no evidence for any significant degradation or conversion of DMSD in any of the aquatic or soil conditions representative for a diversity of environmental conditions.

In consequence, there is no evidence for significant DMSD biodegradation in the soil compartment.

Methanol: The other hydrolysis product methanol is readily biodegradable based on information from the OECD SIDS (OECD, 2004).

In view of the overall evidence on the biodegradation of both hydrolysis products it is not necessary to conduct further simulation tests in soil, or to identify degradation products.

An exposure assessment was performed for the silanol hydrolysis product and it was clearly shown that the risk characterisation ratio (RCR) for the terrestrial compartment, based on the assumption that the hydrolysis product is not biodegradable, is well below 1.