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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:
08-03-2016 to 18-07-2016
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 is of the aqueous phase of non-adapted activated sludge from the municipal sewage treatment plant in Hildesheim, Germany. The activated sludge was washed twice with chlorine free tap water. After the second washing the settled sludge was re-suspended in mineral salts medium and was maintained in an aerobic condition by aeration for 2 hours. Thereafter the sludge was homogenized with a blender. After sedimentation the supernatant was decanted and maintained in an aerobic condition by aeration with air for 5 days. 10 mL/L were used to initiate inoculation.
Colony forming units in the test vessels: approx. 107 - 108 CFU/L
Duration of test (contact time):
28 d
Initial conc.:
48 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
The test solutions were prepared in measuring flasks and were placed in brown glass bottles as incubation vessels (inoculum control and functional control) or were prepared directly in brown glass bottles (test item and toxicity control):
• two for the inoculum control (C1, C2)
• one for the functional control (R1)
• two for the test item (P1, P2)
• one for the toxicity control (T1)

Separate replicates of test item and toxicity control were prepared for measurement of the pH-value at test start:

• one for the test item (PpH)
• one for the toxicity control (TpH)

The inoculated test medium, consisting of the required volumes of mineral medium stock solutions, ultrapure water and inoculum, were prepared in a measuring flask. 250 mL of this solution were filled in the brown glass bottles of the inoculum control, using a 250 mL measuring flask.

For the functional control, the reference item was weighed out and transferred into a measuring flask, the required vol-umes of mineral medium stock solutions, ultrapure water and inoculum, were added. 250 mL of this solution was filled in the brown glass bottle of the functional control, using a 250 mL measuring flask.

For the test item replicates the test item was weighed out for each replicate and directly transferred into the test vessel with 250 mL inoculated medium, using a 250 mL measuring flask.

For the toxicity control, the test item was weighed out and directly transferred into the test vessel with 250 mL of the reference item medium (see above), using a 250 mL measuring flask.
Reference substance:
benzoic acid, sodium salt
Test performance:
Toxicity Control: In the toxicity control the biodegradation achieved 47% after 14 days. After 28 days the biodegradation came to 50%. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled

The validity criteria were fulfilled according to the guideline:

• The percentage degradation of the functional control reached the pass level of 60 % within 3 days (validity criterion: 60 % after 14 days).
• The mean oxygen depletion in the inoculum control was 7.7 mg oxygen/L on day 28 (validity criterion: < 60 mg oxygen/L).
• The pH-value of all test replicates was in the range of 6.0 - 8.5 at the end of the test.
• The difference of extremes of replicate values of removal of the test item at the end of the test was less than 20 % (3 % difference on day 28).
• The percentage degradation of the toxicity control reached the pass level of 25 % within 2 days (validity criterion: 25 % after 14 days).
Key result
Parameter:
% degradation (O2 consumption)
Value:
2
Sampling time:
28 d
Results with reference substance:
Functional control: The pass level for ready biodegradation (> 60% degradation) was reached within 3 days. The validity criterion that the degradation should be > 60% after 14 d was fulfilled. The adaptation phase changed to degradation phase within 1 day (degradation > 10%) and the biodegradation came to a maximum of 100% on day 13.
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
Both test item replicates did not reach the 10% level (beginning of biodegradation) until test end. The mean biodegradation on day 28 was 2%. The test item is classified as not readily biodegradable within the 28 day period of the study
Executive summary:

The ready biodegradability of the test item was determined with non-adapted activated sludge in the Manometric Respirometry Test for a period of 28 days. The study was conducted according to OECD guideline 301 F and EC D.4-D. The test item concentration selected as appropriate was 48 mg/L, corresponding to a ThOD of 75.8 mg O2/L per test vessel. The degradation was followed by measuring the oxygen concentration. The mean oxygen depletion in the inoculum control was 7.7 mg O2/L on day 28.

In order to check the activity of the test system sodium benzoate was used as functional control. The pass level > 60% was reached within 3 days. The biodegradation reached a maximum of 100 % degradation on day 13.

In the toxicity control containing both test and reference item 47% degradation occurred within 14 days. After 28 days the biodegradation came to 50%. The degradation of the reference item was not inhibited by the test item.

The mean biodegradation on day 28 was 2%. The validity criteria of the guideline are fulfilled. The test item is classified as not readily biodegradable within the 28 day period of the study.

Description of key information

The ready biodegradability of the test item was determined with non-adapted activated sludge in the Manometric Respirometry Test for a period of 28 days. The study was conducted according to OECD guideline 301 F and EC D.4-D. The test item concentration selected as appropriate was 48 mg/L, corresponding to a ThOD of 75.8 mg O2/L per test vessel. The degradation was followed by measuring the oxygen concentration. The mean oxygen depletion in the inoculum control was 7.7 mg O2/L on day 28.

In order to check the activity of the test system sodium benzoate was used as functional control. The pass level > 60% was reached within 3 days. The biodegradation reached a maximum of 100 % degradation on day 13.

In the toxicity control containing both test and reference item 47% degradation occurred within 14 days. After 28 days the biodegradation came to 50%. The degradation of the reference item was not inhibited by the test item.

The mean biodegradation on day 28 was 2%. The validity criteria of the guideline are fulfilled. The test item is classified as not readily biodegradable within the 28 day period of the study.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information