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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
4 March - 2 April 2004
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Although a toxicity control was missing, the respiration inhibition test indicated that the EC50 value to activated sludge is > 1000 mg/L. Therefore it can be assumed that the test substance was not inhibiting the inoculum activity at the tested concentration.
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
GLP compliance:
yes
Specific details on test material used for the study:
- Solubility in water: poorly soluble in water (information of the sponsor)
- TOC content: 48.85% (measurement by IFU Gewerbliches Institut für Fragen des Umweltschutzes GmbH, Grießheimer Weg 7a, D-79423 Heitersheim, Germany)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
Activated sludge from the municipal wastewater treatment plant Breisgauer Bucht was used as inoculum with a concentration corresponding to 30 mg dry solids per litre. The treatment plant clarifies predominantly domestic wastewater of the region of Freiburg and has a capacity of 600.000 inhabitant equivalents.
Dry solids of the activated sludge was determined as 5.9 g/L by weight measurements after 2 h drying at 105°C (mean of triplicate measurements). The activated sludge was washed twice by settling the sludge, decanting the supernatant and resuspending the sludge in aerated tap water.
Duration of test (contact time):
28 d
Initial conc.:
41 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
other: TOC
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
The C02-free air production system consists of an air compressor, two 1000 mL gas wash bottles filled with dry soda lime followed by one bottle filled with 0.1 M NaOH (sodium hydroxide) and one filled with 0.05 M Ba(OH)2 as an indicator for CO2. At the end of the system was one gas wash bettle filled with demineralised water followed by an empty one to catch any drops of condensation water. A colour change of the soda lime from white to blue indicates, that CO2 absorption capacity is depleted. The CO2-free air is passed on to an air distributer with two input and 22 output channels and through PE-tubes.

ln total three reactors containing the test item, three reactors containing only inoculum (blank) and three reactors containing the reference compound were set up.

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 a magnetic stirrer with 2 cm stir bars. 61.4 and 61.5 mg of the test item were added directly into the three test vessels, corresponding to a TOC concentration of 20 mg/L TOC. Because of the insolubility the test item was put on a polyethylene film (0.22 mm, type 400, prewashed with ethanol and demineralised water), to simplify the addition of the test item. From the reference compound 5.15 mL of a 10 g/L stock solution was added to the two reference vessels.

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.

There was no toxicity control or abiotic control.
Reference substance:
benzoic acid, sodium salt
Remarks:
5.15 mL of a stock solution of 10 g/L of the reference item were added into the reference vessels (corresponding concentration: 20 mg/L TOC).
Key result
Parameter:
% degradation (CO2 evolution)
Value:
5
Sampling time:
28 d
Details on results:
The degradation extent at the end of the test (28 days after acidification) was 5.8 %. Therefore the test item was not biodegradable within 28 days.
The mean CO2-evolution of the blank flasks was 41.0 mg/L in 28 days after acidification.
Before adding the test item, the inorganic carbon content in the reactor was determined, but insignificant amounts of inorganic carbon were found. The inorganic carbon concentration of the NaOH in the second CO2-absorber flasks in line, used as protective flasks was below 10 ppm only and was not considered in the data processing, because CO2 absorption from room air was the source of it.
The temperature range was 20.5 °C to 22.0 °C throughout the whole study.
Results with reference substance:
The reference compound sodium benzoate reached the pass Ieveis for ready biodegradability within 4 days.
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Under the test conditions negligible biodegradation was observed. Therefore, the test substance is not ready biodegradable.
Executive summary:

The ready biodegradability was examined in a OECD 301 B test in accordance with GLP.

Under the test conditions negligible biodegradation was observed (5% in 28d). Therefore, the test substance is not ready biodegradable.

The validity criteria were fulfilled.

Although a toxicity control was missing, the respiration inhibition test indicated that the EC50 value to activated sludge is > 1000 mg/L. Therefore it can be assumed that the test substance was not inhibiting the inoculum activity at the tested concentration, and thus reliability 1 was assigned.

Description of key information

The ready biodegradability was examined in a OECD 301 B test in accordance with GLP.
Under the test conditions negligible biodegradation was observed. Therefore, the test substance is not ready biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The ready biodegradability was examined in a OECD 301 B test in accordance with GLP.

Under the test conditions negligible biodegradation was observed (5% in 28d). Therefore, the test substance is not ready biodegradable.

The validity criteria were fulfilled.

Although a toxicity control was missing, the respiration inhibition test indicated that the EC50 value to activated sludge is > 1000 mg/L. Therefore it can be assumed that the test substance was not inhibiting the inoculum activity at the tested concentration, and thus reliability 1 was assigned.