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Environmental fate & pathways

Biodegradation in water: screening tests

Administrative data

Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2011
Report Date:
2011

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)

Test material

Reference
Name:
Unnamed
Type:
Constituent

Study design

Oxygen conditions:
aerobic
Inoculum or test system:
sewage, predominantly domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): from a wastewater treatment plant (ARA Ergolz II, Füllinsdorf, Switzerland)
- Preparation of inoculum for exposure: Prior to use, the sludge was first thoroughly mixed and then diluted with test water to a concentration of 1 g per liter (dry weight basis). Based on the determined dry weight of this diluted activated sludge, defined amounts were added to test water to obtain a final concentration of 30 mg dry material per liter.
- Pretreatment: The sludge was washed twice with tap water by centrifugation and the supernatant liquid phase was decanted. A homogenized aliquot of the final sludge suspension was weighed, thereafter dried and the ratio of wet to dry weight was calculated. Based on this ratio, calculated amounts of wet sludge were suspended in test water to obtain a concentration equivalent to 4 g (±10%) dry material per liter. During the holding period of three days prior to use, the sludge was aerated at room temperature.
- Water filtered: no
Duration of test (contact time):
28 d
Initial test substance concentration
Initial conc.:
101 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The test design and test system are consistent with the testing guidelines and should provide a rational basis to assess the ready biodegradability of the test item under aerobic conditions.

TEST CONDITIONS
- Test temperature: 22 °C, maintained with a built-in thermostat and checked once per week
- pH: The pH was adjusted from 7.8 to 7.4 with a diluted hydrochloric acid solution. Prior to test start, the pH was measured in each test flask before the addition of the activated sludge inoculum. At the end of incubation, the pH was measured again in each test flask.
- pH adjusted: yes
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: Apparatus: The test flasks (500 mL reaction vessels, labeled with the necessary information to ensure unmistakable identification) were incubated under continuous stirring in a SAPROMAT D12 (Voith GmbH, Heidenheim, Germany). Oxygen consumption was recorded manually by taking a daily reading at least on each working day.
- Number of culture flasks/concentration: 2replicates with test item; 101 mg/L
- Measuring equipment: Electro-chemical analysis process: The biodegradation process consumes the dissolved oxygen in the test medium and generates CO2. The CO2 is adsorbed by soda lime, which results in a decrease of the total pressure in the airtight test flasks. The pressure drop is detected and converted into an electrical signal by means of an electrode type manometer. The consumed oxygen is replaced by electrolytically generated oxygen from a copper sulfate solution.
- Other: The final test volume was 250 mL per test flask.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes (2 replicates)
- Toxicity control: yes (1 replicate, 100 mg/L)
- Other: Procedure control: yes (2 replicates, 100 mg/L)
Reference substance
Reference substance:
benzoic acid, sodium salt

Results and discussion

Preliminary study:
No information about a preliminary study are available.
Test performance:
No unusual observations during test period observed.
% Degradation
Key result
Parameter:
% degradation (O2 consumption)
Value:
>= 21 - <= 24
Sampling time:
28 d
Remarks on result:
other: 24% without nitrification, 21% with nitrification
Details on results:
The percent biodegradation of the test item was calculated based on the theoretical oxygen demand of 1.91 mg O2/mg test item without nitrification (ThODNH4) and 2.16 mg O2/mg test item with nitrification (ThODNO3).
The biochemical oxygen demand (BOD) of V380 in the test media slowly increased from about Exposure Day 7 until test termination after 28 days. At the end of the 28-day exposure period, the mean biodegradation of V380 amounted to 24% without nitrification or 21% with nitrification.

BOD5 / COD results

Results with reference substance:
The percent biodegradation of the reference item sodium benzoate was calculated based on the theoretical oxygen demand of 1.67 mg O2/mg (ThOD).
In the procedure controls, the reference item sodium benzoate was degraded by an average of 95% by Exposure Day 14, and reached complete biodegradation (101%) by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Applicant's summary and conclusion

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
V380 was found to be slightly biodegradable (21 - 24%) under the test conditions within 28 days. However, the pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-day window within the 28-day period of the test was not reached.
Executive summary:

The test item was investigated for its ready biodegradability in a manometric respirometry test over 28 days according to EU method C.4 -D and OECD guideline 301 F.

The percent biodegradation of the test item was calculated based on the theoretical oxygen demand of 1.91 mg O2/mg test item without nitrification (ThODNH4) and 2.16 mg O2/mg test item with nitrification (ThODNO3).

The biochemical oxygen demand (BOD) of the test item in the test media slowly increased from about Exposure Day 7 until test termination after 28 days. At the end of the 28-day exposure period, the mean biodegradation amounted to 24% without nitrification or 21% with nitrification.

Consequently, the substance was found to be slightly biodegradable (21 - 24%) under the test conditions within 28 days. However, the pass level for ready biodegradability, i.e. biodegradation of at least 60% of the ThOD in a 10-day window within the 28-day period of the test was not reached.

In the toxicity control, containing both the test item and the reference item sodium benzoate, the substance had no inhibitory effect on the activity of activated sludge microorganisms at the tested concentration of 100 mg/L.

In the procedure controls, the reference item sodium benzoate was degraded by an average of 95% by Exposure Day 14, and reached complete biodegradation (101%) by the end of the test (Day 28), thus confirming suitability of the activated sludge.

Thus, all validity criteria of the test method were met.