1,1,3,3-tetramethyldisiloxane

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 (adaptation not specified)

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 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 deg C.
- Sampling method: DOC analysis - Samples filtered through Gelman 0.45 µm 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% in 28 days 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:

Refer to Endpoint Summary for justification

Reason / purpose for cross-reference:

read-across source

Remarks:

5.2.086

Parameter:

% degradation (inorg. C analysis)

Value:

0

Sampling time:

28 d

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Conclusions:

A biodegradation rate of 0% in 28 days was determined in a reliable study conducted according to an appropriate test protocol, and in compliance with GLP.

Description of key information

Biodegradation in water: screening tests: 0% biodegradation in 28 days (OECD 310), based on read-across from a structurally-related substance.

Key value for chemical safety assessment

Biodegradation in water:

under test conditions no biodegradation observed

Additional information

There are no reliable ready biodegradation data available for H2-L2. H2-L2 hydrolyses rapidly to dimethylsilanol, and more slowly to dimethylsilanediol. Therefore, good quality data for the structurally-related substance, trimethylsilanol (1066-40-6), have been read across.

Dimethylsilanediol, dimethylsilanol, and trimethylsilanol are within an analogue group of substances. Within this analogue group, in general, the substances exhibit no evidence of any significant biodegradation once hydrolysis and subsequent biodegradation of any alkoxy/acetoxy groups has been taken into account..

It is therefore considered valid to read-across the results for trimethylsilanol to fill the data gap for the registered substance. Additional information is given in a supporting report (PFA, 2013g) attached in Section 13 of the IUCLID dossier.

0% degradation in 28d (CO₂ production) was determined for trimethylsilanol.