4-tert-Butoxystyrene

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:

2008

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:

July 17, 1992

Deviations:

no

GLP compliance:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

activated sludge, non-adapted

Details on inoculum:

- Source of activated sludge (e.g. location, sampling depth, contamination history, procedure): freshly obtained from a municipal sewage treatment plant receiving predominantly domestic sewage.
- Storage conditions: The freshly obtained sludge was kept under continuous aeration until further treatment.
- Concentration of suspended solids in concentrated sludge: 4.2 g/l.
- Preparation of inoculum for exposure: before use, the sludge was allowed to settle (65 minutes) and the liquid was decanted for use as inoculum at 10 ml per liter of mineral medium.

Duration of test (contact time):

28 d

Initial conc.:

12 mg/L

Based on:

TOC

Parameter followed for biodegradation estimation:

CO2 evolution

Details on study design:

TEST CONDITIONS
- Composition and preparation of pre-incubation medium: mineral components according to OECD 301B, Milli-RO water (ca. 80% total volume) and inoculum (1% final volume). The medium was aerated overnight allowing the system to be purged of CO2.
- The test substance and positive control were added to the bottles containing pre-incubation medium (ca. 80% of total volume). The volumes of suspensions were made up to 2 litres with Milli-RO water.
- Preparation of test solution:
Butoxystyrene was not sufficiently soluble to allow preparation of an aqueous solution at a concentration of 1 g/l. Therefore, weighed amounts of 29 mg butoxystyrene were pre-treated in 250 ml Milli-RO water with ultrasonic waves (15 minutes) to accelerate dissolution and to ensure homogeneity. The resulting suspension was added to each test bottle.
- Test temperature: 22±2°C
- pH: 7.4±0.2.
- pH adjusted: yes
- Aeration: test media were aerated and stirred continuously during the test period.

TEST SYSTEM
- Test vessel: 2 litre all-glass brown coloured bottles.
- Number of culture flasks/concentration:
2 test suspension bottles containing 29 mg/2 l test substance (12 mg TOC/l).
2 inoculum blank bottles
1 positive control bottle containing 40 mg/l sodium acetate (12 mg TOC/l).
1 toxicity control bottle containing 29 mg/2 l test substance (12 mg TOC/l) and 40 mg/l sodium acetate (12 mg TOC/l).
- Method used to create aerobic conditions:
Synthetic air (CO2 < 1 ppm) in a mixture of oxygen (21%) and nitrogen (79%) was sparged through at a rate of ca. 30-100 ml/min.
- Measuring equipment:
Three CO2-absorbers (bottles filled with 100 ml 0.0125 M Ba(OH)2) were connected in series to the exit air line of each test bottle. The CO2 produced in each test bottle reacted with the barium hydroxide in the gas scrubbing bottle and precipitated out as barium carbonate. The amount of CO2 produced was determined by titrating the remaining Ba(OH)2 with 0.05 M standardized HCl.

SAMPLING
- Sampling frequency:
Titrations were made every second or third day during the first 10 days, and thereafter at least every fifth day until the 28th day.
- Sampling method:
Each time the CO2-absorber nearest to the test bottle was removed for titration; each of the remaining two absorbers was moved one position in the direction of the test bottle. A new CO2-absorber was placed at the far end of the series.

CONTROL AND BLANK SYSTEM
- Inoculum blank: containing only inoculum.
- Positive control: containing reference substance and inoculum.
- Toxicity control: containing test substance, reference substance and inoculum.

Reference substance:

acetic acid, sodium salt

Parameter:

% degradation (CO2 evolution)

Value:

0

Sampling time:

9 d

Parameter:

% degradation (CO2 evolution)

Value:

1

Sampling time:

14 d

Parameter:

% degradation (CO2 evolution)

Value:

1

Sampling time:

23 d

Key result

Parameter:

% degradation (CO2 evolution)

Value:

2

Sampling time:

29 d

Details on results:

The relative degradation values calculated from the measurements performed during the test period revealed no significant degradation of butoxystyrene.

Value:

3 other: mg CO2/mg

Remarks on result:

other: ThCO2 of butoxystyrene

Results with reference substance:

The positive control substance was degraded by at least 60% within 14 days.
In the toxicity control more than 25% degradation occurred within 14 days. Therefore, the test substance was assumed not to inhibit microbial activity.

Validity criteria fulfilled:

yes

Interpretation of results:

not readily biodegradable

Conclusions:

Butoxystyrene was not readily biodegradable under the conditions of the modified Sturm test that was performed.

Executive summary:

The ready biodegradability of butoxystyrene was assessed in a CO₂ evolution test (modified Sturm test). Butoxystyrene was tested in duplicate at 29 mg per 2 litres, corresponding to 12 mg TOC/l. The organic carbon content was based on the molecular formula. The Theoretical CO₂ production (ThCO₂) of butoxystyrene was calculated to be 3.00 mg CO₂/mg.

Since butoxystyrene was not sufficiently soluble to allow preparation of an aqueous solution at a concentration of 1 g/l, weighed amounts of 29 mg butoxystyrene were pre-treated in 250 ml Milli-RO water with ultrasonic waves (15 minutes) to accelerate dissolution and to ensure homogeneity.

The resulting suspension was added to each test bottle containing medium with microbial organisms and mineral components. The final volume was made up to 2 litres with Milli-RO water. The test solutions were continuously stirred during the test, to ensure optimal contact between the test substance and the test organisms.

The relative degradation values calculated from the measurements performed during the test period revealed no significant degradation of butoxystyrene. In the toxicity control, butoxystyrene was found not to inhibit microbial activity.

Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, butoxystyrene was not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:

not biodegradable

Type of water:

freshwater

Additional information

A study was conducted to determine the ready biodegradability of the test substance butoxystyrene according to OECD Guideline 301B (CO₂ evolution test) and in compliance with GLP. Butoxystyrene was tested in duplicate at 29 mg per 2 litres corresponding to 12 mg TOC/l. The theoretical CO₂ production (ThCO₂) of butoxystyrene was calculated to be 3.00 mg CO₂/mg. The reference substance used was sodium acetate at a concentration of 40 mg/l corresponding to 12 mg TOC/L.

Since butoxystyrene was not sufficiently soluble to allow preparation of an aqueous solution at a concentration of 1 g/l, weighed amounts of butoxystyrene were pre-treated in Milli-RO water with ultrasonic waves for 15 minutes to accelerate dissolution and to ensure homogeneity. The resulting suspension was added to each test bottle containing medium with mineral components and inoculated with activated sludge. The final volume was made up to 2 litres with Milli-RO water.

The test vessels were aerated by the passage of CO₂-free air and incubated under aerobic conditions for 28 d. The test solutions were continuously stirred during the test.

The relative degradation values calculated from the measurements performed during the test period revealed no significant degradation of butoxystyrene. 

Since all criteria for acceptability of the test were met, this study was considered to be valid. In conclusion, butoxystyrene was not readily biodegradable.