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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:
30 Nov - 01 Dec 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)
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: Municipal sewage treatment plant, D-31137 Hildesheim

- Pretreatment:
The activated sludge was washed twice with autoclaved tap water. After the second washing the settled sludge was filled up with mineral salts medium and was maintained in an aerobic condition by aeration for 2-4 hours. Thereafter the sludge was homogenized with a blender. The supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 6 days. 10 mL/L were used to initiate inoculation.

- Concentration of sludge: 10 mL/L
- Initial cell/biomass concentration: 10^7 - 10^8 CFU/L
- Water: demineralized
Duration of test (contact time):
28 d
Initial conc.:
22 mg/L
Based on:
test mat.
Initial conc.:
53.9 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Preparation of Test Flasks:
All test solutions were prepared in measuring flasks in demineralised water with the required amounts of mineral medium stock solutions and 10 mL/L inoculum. The test item was weighed out and demineralised water was added. After ultrasonic treatment it was transferred into the measuring flasks.

The reference item was weighed out and transferred into the measuring flasks with demineralised water.

250 mL measuring flasks were used to place 250 mL of the test solutions in the brown glass bottles.

A rubber sleeve with soda lime was hung into the opening of the bottles to absorb evolved CO2. The bottles were closed with Oxi-Top® measuring heads and the measuring system was activated.


Measurements:
The temperature in the incubator was documented continuously throughout the test by a hygrothermograph.
At test start the pH-values of the test solutions in the measuring flasks (before dividing) and at test end the pH-values of the test solutions in the brown glass bottles were determined.
The oxygen consumption was determined continuously from the pressure in the incubation vessels by OxiTop® measuring system at 360 measuring points (every 112 minutes) during the 28 d incubation period.



Reference substance:
benzoic acid, sodium salt
Test performance:
Results of the Functional Control
The pass level of a biodegradation > 60 % was reached on day 4. The validity criterion that the degradation should be > 60 % after 14 d was fulfilled

Results of the Toxicity Control
In the toxicity control the biodegradation achieved 52 % after 14 days. After 28 days the biodegradation came to 56 %. The validity criterion that the test item should not inhibit the biodegradation of the reference item was fulfilled.
Key result
Parameter:
% degradation (O2 consumption)
Value:
0
Sampling time:
28 d
Details on results:
Both test item replicates did not reach the 10 % level (beginning of biodegradation) within the 28 d period of the study. The mean biodegradation on day 28 was 0 %.

Table 1: Biodegradation [%] of the test item in comparison to the functional control and toxicity control

         Biodegradation [%] Study day [d]      
    Replicate  7 14   21  28   
 Test item 22 mg/L  1  1  0  0     0
 Test item 22 mg/L  2  1  0  0     0
 Functional control 45 mg/L    71  78  79     77
 Toxicity control + 22 mg/L test tiem + 45 mg/L reference item    47  52  55     56
Validity criteria fulfilled:
yes
Interpretation of results:
not readily biodegradable
Conclusions:
The test item is 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 Manometrie Respirometry Test for a period of 28 days. The study was conducted from 2016-12 -07 to 2017-01-04, according to OECD guideline 301 F at the test facility. The test item concentration selected as appropriate was 22.0 mg/L, corresponding to a ThOD of 53.9 mg O2/L per test vessel. The oxygen was depleted by the respiration of bacteria and the degradation was followed by measuring the oxygen concentration. The biodegradation rate is therefore expressed as the percentage BOD (biological oxygen demand) and was calculated for each study day.

The mean oxygen depletion in the inoculum control was 9.0 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 on day 4. The biodegradation reached a maximum of 80% degradation on day 19.

 In the toxicity control containing both test and reference item 52% degradation occurred within 14 days.After 28 days the biodegradation came to 56%.The degradation of the reference item was not inhibited by the test item.

Both test item replicates did not reach the 10% level (beginning of biodegradation) within the 28 day period of the study.The mean biodegradation on day 28 was0%.

 The validity criteria of the guideline are fulfilled.

The test item is considered to be not readily biodegrdable within the 28 day period of the study.

Description of key information

The test item is not readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
not biodegradable
Type of water:
freshwater

Additional information

The ready biodegradability of the test item was determined with non-adapted activated sludge in the Manometrie Respirometry Test for a period of 28 days. The study was conducted from 2016-12 -07 to 2017-01-04, according to OECD guideline 301 F at the test facility. The test item concentration selected as appropriate was 22.0 mg/L, corresponding to a ThOD of 53.9 mg O2/L per test vessel. The oxygen was depleted by the respiration of bacteria and the degradation was followed by measuring the oxygen concentration. The biodegradation rate is therefore expressed as the percentage BOD (biological oxygen demand) and was calculated for each study day.

The mean oxygen depletion in the inoculum control was 9.0 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 on day 4. The biodegradation reached a maximum of 80% degradation on day 19.

 In the toxicity control containing both test and reference item 52% degradation occurred within 14 days.After 28 days the biodegradation came to 56%.The degradation of the reference item was not inhibited by the test item.

Both test item replicates did not reach the 10% level (beginning of biodegradation) within the 28 day period of the study.The mean biodegradation on day 28 was0%.

 The validity criteria of the guideline are fulfilled.

The test item is considered to be not readily biodegrdable within the 28 day period of the study.