4,4,19,19-tetraethoxy-3,20-dioxa-8,15-dithia-4,19-disiladocosaneand S-(6-{[3-(triethoxysilyl)propyl]thio}hexyl) ethanethioate

Biodegradation in water: screening tests

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in water: ready biodegradability

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2019-11-28 to 2020-03-18

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)

Version / remarks:

1992

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, domestic, non-adapted

Details on inoculum:

Activated sludge from the municipal wastewater treatment plant AZV Breisgauer Bucht was used as inoculum with a concentration corresponding to 30 mg dry solids per litre. Sampling date of activated sludge was 14 January 2020. The dry solid content of the activated sludge was 5.1 g/L. It was determined by weight measurements after drying at 105°C for 4.5 hours (mean of triplicate measurements). The activated sludge was washed twice with tap water by settling the sludge, decanting the supernatant and re-suspending the sludge.

Duration of test (contact time):

28 d

Initial conc.:

20 mg/L

Based on:

TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

The CO2-free air production system consists of an air compressor, three 1000 mL gas wash bottles filled with dry soda lime in series followed by one bottle filled with 0.1 M NaOH (sodium hydroxide). At the end of the system is one gas wash bottle filled with demineralised water, followed by an empty one to catch any drops of condensation water. A color change of the soda lime from white to blue indicates that the CO2 absorption capacity is depleted. The CO2-free air is passed on to an air distributor with two input and 22 output channels and through PE-tubes
Gas wash bottles (2000 mL volume) with lateral connecting pieces for butyl rubber septa were used as reactors. The liquid volume was fixed as 1500 mL each. Mixing was performed by magnetic stirrers with 2 cm stir bars.
The CO2 produced in the reactors was absorbed in two 250 mL gas wash bottles in series each filled with 200 mL 0.2 M NaOH. Sampling was performed through the lateral connecting pieces through the butyl rubber septum using 5 mL PE syringes
In total three reactors containing the test item, three reactors containing only inoculum (blank), three reactors containing the reference compound and one reactor containing test item and reference compound (toxicity control) were set up.
8.8 mL activated sludge was filled up to 1500 mL with 1491.2 mL mineral medium corresponding to 30 mg/L dry solids. The system was sealed and aerated with CO2-free air overnight. The reactors were kept mixed with magnetic stirrers. On the next day, the absorber wash bottles were filled with 0.2 M NaOH and the test substance was added into the test vessels and into the toxicity control vessel. The reference compound was added into the reference vessels and into the toxicity control vessel. In addition, the IC concentration of the sodium hydroxide solution and the IC concentration in the reactor were determined.
The aeration rate was kept at a rate of 30 - 100 mL / min (1.6 - 5.5 bubbles / second) and determined visually daily on working days. The determination by counting the gas bubbles over a defined period using a stop watch was made on days 12 and 28. The CO2-free air production system, the air-tightness of the whole experimental set-up, the aeration of the absorber flasks and the magnetic stirrers were controlled daily on working days.

Reference substance:

benzoic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

4 d

Parameter:

% degradation (CO2 evolution)

Value:

0.1

Sampling time:

7 d

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

11 d

Parameter:

% degradation (CO2 evolution)

Value:

0.3

Sampling time:

14 d

Parameter:

% degradation (CO2 evolution)

Value:

1.3

Sampling time:

21 d

Parameter:

% degradation (CO2 evolution)

Value:

1.9

Sampling time:

28 d

Parameter:

% degradation (CO2 evolution)

Value:

3

Sampling time:

29 d

Results with reference substance:

The reference compound sodium benzoate reached the pass level for ready biodegradability within 4 days

Validity criteria fulfilled:

yes

Interpretation of results:

under test conditions no biodegradation observed

Executive summary:

The substance was tested in a valid readily biodegradation test according OECD 301B. No biodegradation was observed within 28 days.

Description of key information

The substance was tested in a valid readily biodegradation test according OECD 301B. No biodegradation was observed within 28 days.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater