Registration Dossier

Diss Factsheets

Environmental fate & pathways

Biodegradation in water: screening tests

Currently viewing:

Administrative data

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:
From May 26 to June 25, 2016
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 F (Ready Biodegradability: Manometric Respirometry Test)
Version / remarks:
1992
Qualifier:
according to guideline
Guideline:
EU Method C.4-D (Determination of the "Ready" Biodegradability - Manometric Respirometry Test)
Version / remarks:
2008
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
Inoculum: non-adapted activated sludge from the aeration tank of the ARA Werdhölzli (CH-8048 Zürich), a municipal biological waste water treatment plant. 30 mg/l dry matter in the final mixture.
Duration of test (contact time):
ca. 28 d
Initial conc.:
ca. 38.8 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The activated sludge was used after sampling from the treatment plant without adaptation. However, the sludge was pre-conditioned for 7 days (aerated but not fed) to reduce the amount of O2 consumed by the blank controls.
Prior to the test the sludge was washed twice with tap water and once with mineral medium. After centrifugation, the sludge was suspended in test medium at a concentration twice of the final concentration.
The test item was applied by direct addition in the test vessels, so as to give a final test concentration of about 100 mg ThOD/l (i.e. about 39 mg/l test item).
The reference item was dissolved in the test medium at a concentration twice of the final concentration to be achieved for the test. This stock solution was diluted with the sludge suspension 1:1 (v:v) to give a final test concentration of about 100 mg ThOD/l (i.e. about 60 mg/l reference item).
In the toxicity control a mixture of about 100 mg ThOD /l of test item and about 100 mg ThOD/l of reference item was tested (total 200 mg ThOD/l; application by direct addition and by stock solution, respectively).
In the abiotic sterile control about 100 mg ThOD/l of test item was tested (application by direct addition).
The following test flasks were set up:
T: Test suspension: containing inoculum, test medium and test item (two replicates)
B: Blank control: containing inoculum and test medium (two replicates)
R: Procedure control containing inoculum, test medium and sodium benzoate as ready biodegradable reference item (two replicates)
C: Abiotic sterile control: containing test item, ultra-pure water and 0.2 mM HgCl2 as sterilizing agent to prevent microbial decomposition (one replicate)
X: Toxicity control: containing inoculum, test medium, test item and sodium benzoate as ready biodegradable reference item (one replicate)
Before the test start, the pH value was checked and if necessary adjusted to 7.2 (±0.2) with NaOH or HCl (except in flask C; and in flask T and X only if the test item is soluble).
The test vessels were stirred by an inductive stirring system for a maximum test period of 28 days. During the test the O2 uptake was continuously measured with a manometric BOD measuring device. Temperature was recorded with a data logger.
At the end of the test, the pH was measured in all flasks except the abiotic sterile control (C).
Total eliminationwas determined in each test vessel (T, B and R) based on the theoretical carbon content and the analysis of the dissolved organic carbon (DOC) concentrations at the end of the test.
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (O2 consumption)
Value:
ca. 0
Sampling time:
28 d
Remarks on result:
other: Potential toxic effect
Parameter:
% degradation (DOC removal)
Value:
ca. 66
Sampling time:
28 d
Remarks on result:
other: Elimination by adsorption to the sludge, and/or just reflects the limited solubility of the test item
Details on results:
The procedure control sodium benzoate reached 88% biodegradation after 14 days, thus confirming suitability of inoculum and test conditions.
The respective concentrations of organic carbon at the beginning (as mg TOC/l) and at the end (as mg DOC/l) of the test after 28 days were, respectively:
23.6* and 6.74 / 11.3 for test unit 1 / test unit 2
<0.5 and 1.04 for the blank control (mean of two replicates)
35.0* and 1.23 for the procedure control (mean of two replicates)

* theoretical value calculated based on the carbon content and the test concentration

The total elimination calculated based on dissolved organic carbon (DOC) measurements reached 66% for the test substance and 99% for sodium benzoate. For the test substance, this data suggests that the elimination mostly occurred through adsorption to the sludge, and/or just reflects the limited solubility of the test item.
Results with reference substance:
88 % of biodegradation after 14 days

Additional controls

Toxicity control

Strictly according to the test guideline OECD 301, the test item was not judged to have any significant inhibitory effecton the microbial populationat the applied initial test concentration of 38.5 mg/l, since the biodegradation of the mixture (test item + reference item sodium benzoate) exceeded 25 % within 14 days.

However, the lag-phase of about 4 days tends to confirm the toxic effects observed in the main test vessels.

Abiotic sterile control

the test substance was not abiotically degraded (by processes using O2) during the whole test period of 28 days in the absence of microorganisms as confirmed by the lack of oxygen consumption.


Validity of the test

All validity criteria were fulfilled.

At the end of the test the pH values of the blank controls were 7.0 and 7.1 and the pH values of the procedure control were 7.2 and 7.1, respectively. The pH values of the test units were 7.1 and 7.0 and the pH of the toxicity control was 7.2, respectively. All pH values were therefore in the required range at the end of the test.

The temperature was in the acceptable range during the whole incubation period.

Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
Not ready biodegradable.
Executive summary:

Method

The biodegradability of the test substance exposed to microorganisms derived from activated sludge of a municipal sewage treatment plant was investigated under aerobic static exposure conditions, following the test guideline OECD 301 F.

Discussion

No biodegradability of the test substance based on O2consumption was observed after 28 days as compared to the theoretical oxygen demand (ThOD). The negative BOD values however suggest a potential toxic effect of the test substance towards the activated sludge, which is partially confirmed by the toxicity control.

The procedure control sodium benzoate reached 88% biodegradation after 14 days, thus confirming suitability of inoculum and test conditions.

The total elimination calculated based on dissolved organic carbon (DOC) measurements reached 66 % for the test substance and 99 % for sodium benzoate. For the test substacnce, this data suggests that the elimination mostly occurred through adsorption to the sludge, and/or just reflects the limited solubility of the test item.

Conclusion

The test substance is not biodegradable in the Manometric Respirometry Test 301 F within 28 days of incubation.

Description of key information

Not readily biodegradable

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

The biodegradability of the test substance exposed to microorganisms derived from activated sludge of a municipal sewage treatment plant was investigated under aerobic static exposure conditions, following the test guideline OECD 301 F.

No biodegradability of the test substance based on O2 consumption was observed after 28 days as compared to the theoretical oxygen demand (ThOD). The negative BOD values however suggest a potential toxic effect of the test substance towards the activated sludge, which is partially confirmed by the toxicity control.

The procedure control sodium benzoate reached 88 % biodegradation after 14 days, thus confirming suitability of inoculum and test conditions.

The total elimination calculated based on dissolved organic carbon (DOC) measurements reached 66% for the test substance and 99% for sodium benzoate. For the test substacnce, this data suggests that the elimination mostly occurred through adsorption to the sludge, and/or just reflects the limited solubility of the test item.