tert-butylbenzene

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:

2018

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:

adopted 17. Jul. 1992

Deviations:

not specified

Qualifier:

according to guideline

Guideline:

EU Method C.4-C (Determination of the "Ready" Biodegradability - Carbon Dioxide Evolution Test)

Version / remarks:

adopted 30. May 2008

Deviations:

not specified

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge (adaptation not specified)

Remarks:

Activated sludge from a biologic sewage treatment plant was used as inoculum. The cho-sen plant treats mostly domestic sewage.

Details on inoculum:

- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): The sludge was taken from the activation basin of the ESN (Stadtentsorgung Neustadt) sewage treatment plant, Im Altenschemel, 67435 NW-Lachen-Speyerdorf.
Date of collection: 28. Sep. 2018, batch no: 20180928.
- Pretreatment: The sludge was filtrated, washed and re-suspended. It was then aerated until use. And the dry matter was determined.
- Concentration of sludge: The dry matter was determined to contain 4940 mg of sus-pended solids/L.
- Water filtered: no
- Type and size of filter used, if any: The sludge was filtrated, washed with test medium (2x)

Duration of test (contact time):

28 d

Initial conc.:

20 other: 20 mg organic carbon/L

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition of medium: The medium was freshly prepared. 10 mL of solution a were mixed with 800 mL water, then 1 mL of solutions b, c and d were added and filled up to 1 L with H2O demin (volumes were adapted to final volume needed in the test).
- Test temperature: 20.1 – 22.8 °C without direct lighting
- pH: 6.9-7.6
- pH adjusted: no
- Suspended solids concentration: 4940 mg of suspended solids/L
- Continuous darkness: yes

TEST SYSTEM
- Measuring equipment: Analyses of the emitted CO2 were made by IC measurement using the carbon analyser TOC multi N/C 2100S, Analytik Jena. Each sample was measured in duplicate or triplicate, respectively (depending on the variation between the measured values).
- Test vessels: The test vessels were aerated with purified (by activated charcoal), CO2-scrubbed, mois-tened air. 2000 mL-SCHOTT-flasks were used as test vessels, 100 mL scrubber flasks as absorbent vessels.

SAMPLING
From each front scrubber flask, 9 samples were taken in order to determine the emitted CO2 (on day 0, 3, 7, 9, 11, 14, 17, 23 and 29). The sample volume was 1 mL. The resulting change in the volume of the front flask was considered in the calculation of emitted CO2 (see also chapter 8.3.1).
On day 28, 5 mL HCl 2 M was added to each test flask in order to drive off dissolved CO2. On day 29, samples from both scrubber flasks were taken.

CONTROL AND BLANK SYSTEM:
- Positive control: Aniline (Phenylamine, C6H5NH2, CAS-No. 62-53-3).
Apparatus blanks 2, containing mineral medium only
Blank Controls 2, containing mineral medium and inoculum
Positive control flasks 2, containing positive control, mineral medium and inoculum
Test flasks 2, containing test item, mineral medium and inoculum
Abiotic control 1, containing test item, mineral medium and HgCl2
Toxicity control 1, containing test item, positive control, mineral medium and inoculum

Reference substance:

aniline

Key result

Parameter:

% degradation (CO2 evolution)

Value:

11

Sampling time:

28 d

Details on results:

•The test item tert-Butylbenzene is considered as “not readily biodegradable“.
•The degree of biodegradation reached 11 % after 28 days.
•The 10-day-window began on day 22, the end is unevaluable, because the end of the test was day 28.
•Degradation missed 60 % within 28 days, too. Therefore, the test item is considered as “not ultimately biodegradable within 28 days”, as well.
•The abiotic degradation reached 0.9 %.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

The test item tert-Butylbenzene was tested using a concentration of nominally 20 mg organic carbon/L tert-Butylbenzene in test medium following OECD 301B and EU-Method C.4-C.

Aniline was chosen as positive control.
Activated sludge was used as inoculum (concentration in the test 25.0 mg dry matter/L). The test was left running for 28 days.
All validity criteria were met. Degradation of the positive control surpassed the pass level of 60 % after 10 days.

The following data were determined for the test item tert-Butylbenzene:
10-day-window: start day 22
degradation at the end of 10-day-window unevaluable end of the test day 28
degradation at the end of the test 11 %
pass level following guideline: 60 % at the end of 10-day-window for pure substances
respective 60 % at the end of the test for mixtures

Therefore, when applying the 10-day-window, the test item tert-Butylbenzene is not readily biodegradable following OECD 301B and EU C.4-C respectively. As degradation missed 60% in the course of the test, tert-Butylbenzene is considered as not ultimately biodegradable, as well.

Executive summary:

All validity criteria were met.

Degradation behaviour of positive control and toxicity control was normal. Abiotic degradation was not observed. Both replicates of the test item showed very good correspondence.

If degradation in the toxicity flask is below 25 % after 14 days, the test item can be considered as toxic towards the inoculum. As degradation in the toxicity flask was 42.6 % after 14 days, the test item can be stated as “not toxic towards the inoculum in a concentration of 22.8 mg/L”.

 

Ready biodegradability is defined in the guidelines as degradation surpassing 60% within 10 days after reaching a level of 10 %. The 10-day-window began on day 22, the end was unevaluable, because the end of the test was day 28. Therefore, when applying the 10-day-window, the test itemtert-Butylbenzeneisnotreadily biodegradablefollowing OECD 301B and EU C.4-C respectively. As degradation missed 60% in the course of the test,tert-Butylbenzeneis considered asnot ultimately biodegradable, as well.

No observations were made which might cause doubts concerning the validity of the study outcome.

The result of the test can be considered valid.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater