Ethoxytrimethylsilane

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-07-29 to 2008-08-26

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): A mixed population of sewage sludge microorganisms from the secondary treatment stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

- Preparation of inoculum for exposure: Filtered through coarse filter paper (first approximate 200 ml discarded). Filtrate sparged with CO2-free air for approximately 1 hour whilst maintaining its pH at 6.5 using concentrated orthophosphoric acid. After sparging, the pH was restored to its original value of 8.0 using 7M NaOH and the inoculum allowed to settle for approximately 1 hour prior to removal of an aliquot (2 litres) of the supernatant for use in the test. The supernatant was maintained on aeration using CO2-free air until use.

Duration of test (contact time):

28 d

Initial conc.:

20 mg/L

Based on:

other: Carbon

Parameter followed for biodegradation estimation:

inorg. C analysis

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Test temperature: 20±1 deg C

- Other: Constant shaking at approximately 150 rpm


TEST SYSTEM
- Culturing apparatus: 125 ml glass Wheaton bottles (total volume when full 160 ml) each conatining 107 ml of solution.
- Number of culture flasks/concentration: 45 replicate vessels with concentration 20 mg carbon/l

SAMPLING
- Sampling frequency: Triplicate control, standard material and test material vessels were sacrificed on days 0, 2, 6, 8, 10, 14, 16 and 21 for IC analysis. On day 28, five replicate vessels were sacrificed for IC analysis. Triplicate toxicity control vessels were sacrificed on days 0, 8 and 14 for IC analysis.
- Sampling method: IC analysis - An aliquot (1.0 ml) of concentrated orthophosphoric acid was injected through the septum of each vessel taken for analysis in order to lower the pH of the medium to <3. The vessels were then shaken at approximately 150 rpm (INFORS Version 2 Multitron Incubator) for 1 hour at 20±1 deg C.
- Sampling method: DOC analysis - Samples filtered through Gelman 0.45 um Acrocap filters (approximately 5 ml discarded) prior to DOC analysis.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 45 replicate vessels

- Toxicity control: 11 replicate vessels. Concentration = 40 mg carbon/l

- Standard: 45 replicate vessels. Concentration = 20 mg carbon/l

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (inorg. C analysis)

Value:

0

Sampling time:

28 d

Details on results:

DOC analysis conducted on sample taken from the test material vessels on Day 0 and 28 showed that the replicate test material vessels attained 4% to 8% degradation. The higher degradation rates than those determined IC analysis were considered to be due to sampling/analytical variation.

Results with reference substance:

86% degradation after 14 days and 87% degradation after 28 days. (DOC analysis showed 95-100% degradation after 28 days. The higher degradation rates than those determined by IC analyses were considered to be due to incorporation of sodium benzoate into the microbial biomass prior to degradation and hence CO2 evolution occurring.)

	% degradation at sampling time (days)
	0	2	6	8	10	14	16	21	28
Toxicity control	0	-	-	34		43
Test sample	0	0	-1	0	1	0	0	0	0
Reference substance	0	54	63	70	73	86	82	72	87

 

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

A biodegradation rate of 0% was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Reference 2

Endpoint:

biodegradation in water: ready biodegradability

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 analogue justification provided in IUCLID section 13.

Reason / purpose for cross-reference:

read-across source

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): A mixed population of sewage sludge microorganisms from the secondary treatment stage of the Severn Trent Water Plc sewage treatment plant at Loughborough, Leicestershire, UK, which treats predominantly domestic sewage.

- Preparation of inoculum for exposure: Filtered through coarse filter paper (first approximate 200 ml discarded). Filtrate sparged with CO2-free air for approximately 1 hour whilst maintaining its pH at 6.5 using concentrated orthophosphoric acid. After sparging, the pH was restored to its original value of 8.0 using 7M NaOH and the inoculum allowed to settle for approximately 1 hour prior to removal of an aliquot (2 litres) of the supernatant for use in the test. The supernatant was maintained on aeration using CO2-free air until use.

Duration of test (contact time):

28 d

Initial conc.:

20 mg/L

Based on:

other: Carbon

Parameter followed for biodegradation estimation:

inorg. C analysis

Parameter followed for biodegradation estimation:

DOC removal

Details on study design:

TEST CONDITIONS
- Test temperature: 20±1 deg C

- Other: Constant shaking at approximately 150 rpm


TEST SYSTEM
- Culturing apparatus: 125 ml glass Wheaton bottles (total volume when full 160 ml) each conatining 107 ml of solution.
- Number of culture flasks/concentration: 45 replicate vessels with concentration 20 mg carbon/l

SAMPLING
- Sampling frequency: Triplicate control, standard material and test material vessels were sacrificed on days 0, 2, 6, 8, 10, 14, 16 and 21 for IC analysis. On day 28, five replicate vessels were sacrificed for IC analysis. Triplicate toxicity control vessels were sacrificed on days 0, 8 and 14 for IC analysis.
- Sampling method: IC analysis - An aliquot (1.0 ml) of concentrated orthophosphoric acid was injected through the septum of each vessel taken for analysis in order to lower the pH of the medium to <3. The vessels were then shaken at approximately 150 rpm (INFORS Version 2 Multitron Incubator) for 1 hour at 20±1 deg C.
- Sampling method: DOC analysis - Samples filtered through Gelman 0.45 um Acrocap filters (approximately 5 ml discarded) prior to DOC analysis.

CONTROL AND BLANK SYSTEM
- Inoculum blank: 45 replicate vessels

- Toxicity control: 11 replicate vessels. Concentration = 40 mg carbon/l

- Standard: 45 replicate vessels. Concentration = 20 mg carbon/l

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (inorg. C analysis)

Value:

0

Sampling time:

28 d

Details on results:

DOC analysis conducted on sample taken from the test material vessels on Day 0 and 28 showed that the replicate test material vessels attained 4% to 8% degradation. The higher degradation rates than those determined IC analysis were considered to be due to sampling/analytical variation.

Results with reference substance:

86% degradation after 14 days and 87% degradation after 28 days. (DOC analysis showed 95-100% degradation after 28 days. The higher degradation rates than those determined by IC analyses were considered to be due to incorporation of sodium benzoate into the microbial biomass prior to degradation and hence CO2 evolution occurring.)

	% degradation at sampling time (days)
	0	2	6	8	10	14	16	21	28
Toxicity control	0	-	-	34		43
Test sample	0	0	-1	0	1	0	0	0	0
Reference substance	0	54	63	70	73	86	82	72	87

 

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

A biodegradation rate of 0% was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Not readily biodegradable (0% after 28 d) (OECD 310; RA CAS No. 1066-40-6).

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

There is no data on ready biodegradability for the target substance ethoxytrimethylsilane (CAS No. 1825-62-3) available. However, the target substance ethoxytrimethylsilane hydrolyses within the timescale of a ready biodegradation test to form trimethylsilanol and ethanol (DT50 = 2.2 min at pH 7 and 25 °C). Therefore, a read across to the silanol hydrolysis product trimethylsilanol (CAS No. 1066-40-6) has been applied to support the environmental hazard assessment of ethoxytrimethylsilane (CAS No. 1825-62-3). The second hydrolysis product, ethanol, is readily biodegradable (74% in 5 d, OECD SIDS, 2004). Details on the read across justification can be found in IUCLID Section 13. 

The available study investigating the biodegradation of the silanol hydrolysis product trimethylsilanol (CAS 1066-40-6) was conducted according to OECD guideline 310 and under GLP conditions. The inoculum (non-adapted) activated sludge from a sewage treatment plant) was exposed for 28 days to the test substance and biodegradation was calculated based on inorganic C-analysis. No biodegradation of the substance was recorded after 28 d (0.0%). Thus, the silanol hydrolysis product is not readily biodegradable according to the OECD criteria. 

References:

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