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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
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reference:
Composition 0
Qualifier:
according to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Version / remarks:
2006, corrected 2014
GLP compliance:
yes
Test material information:
Composition 1
Specific details on test material used for the study:
SOURCE OF TEST MATERIAL
- Source and lot/batch No.of test material: Batch No. 648300
- Purity & test date: 99.9%, Jul 26, 2017
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge: freshly obtained from a municipal sewage treatment plant: 'Waterschap Aa en Maas', 's-Hertogenbosch, The Netherlands, receiving predominantly domestic sewage
- Storage conditions: The freshly obtained sludge was used immediately
- Concentration of sludge: The concentration of suspended solids was determined to be 4.9 g/L in the concentrated sludge. Before use, the sludge was allowed to settle (58 minutes) and the liquid was decanted for use as inoculum at the amount of 10 mL/L of mineral medium.
Duration of test (contact time):
28 d
Initial conc.:
20 mg/L
Based on:
IC (inorganic carbon)
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: Mineral medium
- Test temperature: 20 and 21°C
- pH: 7.4-7.8
- Continuous darkness: Incubation was conducted in the dark (on an orbital shaker)

TEST SYSTEM
- Culturing apparatus: Well sealed glass serum vessels
- Number of culture flasks/concentration: Triplicate test vessels for each treatment for each time interval. Five test vessels for analysis at the end of the test
- Method used to create aerobic conditions: Sealed vessels with a headspace of air
- Measuring equipment: Shimadzu TOC-VCPH total organic carbon analyser combined with a Shimadzu ASI-V autosampler.

SAMPLING
- Sampling frequency: At Day 1,7,14,21, and 28 for Inoculum Blank and Test Item groups. At Day 1,7,14 for Procedure Control and Toxicity Control groups. At Day 1 and 28 for Abiotic Control group

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes
- Abiotic sterile control: Yes
- Toxicity control: Yes
Reference substance:
benzoic acid, sodium salt
Test performance:
Acceptability of the Test
- the reference item was biodegraded by at least 60% (87%) within 14 days.
- the mean amount of TIC present in the inoculum blanks at the end of the test was < 3 mg C/L (1 mg C/L).

Since all criteria for acceptability of the test were met, this study was considered to be valid.
Key result
Parameter:
% degradation (CO2 evolution)
Value:
0
Sampling time:
28 d
Details on results:
Assuming 100% mineralization of the test item to CO2, the Theoretical maximum IC production (ThIC) in excess of that produced in the inoculum blanks equals the Total Organic Carbon (TOC) added to each test vessel at the start of the test. The TOC content of TAOBN was determined to be 60.6%. Thus, the ThIC of TAOBN was calculated to be 0.61 mg/mg.

In the toxicity control more than 25% biodegradation occurred within 14 days (38%, based on ThIC). Therefore, the test item was assumed not to inhibit microbial activity.
Results with reference substance:
The refence item achived 87% degradation in 14 days.
Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
Conclusions:
The test item was not readily biodegradable under the conditions of the Headspace Test presently performed. The test item was assumed not to inhibit microbial activity.
Executive summary:

The objective of the study was to evaluate the organic test item for its ready biodegradability in an aerobic, aqueous inoculated medium. The test was performed in sealed vessels with a headspace of air.

The CO2 evolution resulting from the aerobic biodegradation of the test item was determined by measuring the inorganic carbon (IC) produced in the test vessels in excess of that produced in inoculum blank. Biodegradation was expressed as a percentage of the ThIC, based on the quantity of test item (as C) initially added. The relative biodegradation values calculated from the measurements performed during the test period revealed no biologically relevant biodegradation of the test item (0% after 28-days, based on the ThIC). In conclusion, the test item is designated as not readily biodegradable.

 

In the toxicity control more than 25% biodegradation occurred within 14 days and the reference substance achieved 87% degradation within 17 days. Therefore, the test item was assumed not to inhibit microbial activity and the test system was viable.

Description of key information

Not readily biodegradable, 0% degradation in 28 days under the conditions of OECD 310.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed
Type of water:
freshwater

Additional information

The objective of the study was to evaluate the organic test item for its ready biodegradability in an aerobic, aqueous inoculated medium. The test was performed in sealed vessels with a headspace of air.

The CO2 evolution resulting from the aerobic biodegradation of the test item was determined by measuring the inorganic carbon (IC) produced in the test vessels in excess of that produced in inoculum blank. Biodegradation was expressed as a percentage of the ThIC, based on the quantity of test item (as C) initially added. The relative biodegradation values calculated from the measurements performed during the test period revealed no biologically relevant biodegradation of the test item (0% after 28-days, based on the ThIC). In conclusion, the test item is designated as not readily biodegradable.

 

In the toxicity control more than 25% biodegradation occurred within 14 days and the reference substance achieved 87% degradation within 17 days. Therefore, the test item was assumed not to inhibit microbial activity and the test system was viable.