Diethoxy(methyl)silane

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 °C
- Other: Constant shaking at approximately 150 rpm


TEST SYSTEM
- Culturing apparatus: 125 ml glass Wheaton bottles (total volume when full 160 ml) each containing 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 °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 the attached justification below and the overall justification for grouping of substances attached in IUCLID Section 13.

Reason / purpose for cross-reference:

read-across source

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.

Interpretation of results:

under test conditions no biodegradation observed

Description of key information

Not readily biodegradable: 0% after 28 d (CO2  evolution, OECD 310)

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

There are no reliable data available on the biodegradation of diethoxy(methyl)silane (CAS 2031-62-1). In accordance with Regulation (EC) No 1907/2006 Annex XI, 1.5 “Grouping of substances and read across” and in accordance with the Read across assessment framework (RAAF, ECHA 2017) a read across from the analogue substance trimethylsilanol (CAS 1066-40-6) has been applied to support the environmental hazard assessment of diethoxy(methyl)silane (CAS 2031-62-1). Details on read across justifications can be found in the attached justification in the respective target entry and in the overall justification for grouping of substances attached in IUCLID Section 13.

The available study (2008) investigating the biodegradation of the analogue substance trimethylsilanol (CAS 1066-40-6) was conducted according to OECD 310, 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 substance is not readily biodegradable according to the OECD criteria. 

On the basis of the read across data, diethoxy(methyl)silane is not assumed to be readily biodegradable. Diethoxy(methyl)silane will hydrolyse successively to methylsilanediol and methylsilanetriol as well as ethanol. Ethanol is known to be readily biodegradable (OECD 2004) while no significant biodegradation is expected for the silanol hydrolysis products.

References

OECD (2004): SIDS Initial Assessment Report for SIAM 19, Berlin, Germany, 19-22 October 2004, Ethanol, CAS 64-17-5.

[Type of water: freshwater]