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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:
03 May - 01 June 2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP compliant , guideline study. Available as an unpublished report. Acceptable without restriction.
Reason / purpose:
reference to same study
Qualifier:
according to
Guideline:
OECD Guideline 301 A (Ready Biodegradability: DOC Die Away Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.4-A (Determination of the "Ready" Biodegradability - Dissolved Organic Carbon (DOC) Die-Away Test)
Deviations:
no
GLP compliance:
yes (incl. certificate)
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Not applicable
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic (adaptation not specified)
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): - Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): Sourced from predominatly domestic wastewater treatment plant (ARA Ergolz II, Fullinsdorf / Switzerland)
- Storage conditions: Room temperature. Aeration.
- Storage length: 1 day
- Preparation of inoculum for exposure: Washed twice with tap water by centrifugation, supernatant liquid phase decanted.
- Concentration of sludge: 30 mg dry material per litre.
Duration of test (contact time):
28 d
Initial conc.:
47 - 47.4 mg/L
Based on:
DOC
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Composition of medium: Purified water with dissolved analytical grade salts
- Test temperature: 22 - 24 °C
- pH: 7.2-7.4
- pH adjusted: yes
- Aeration of dilution water: Test media was constantly stirred, flasks were prepared as to allow for exchange of air between flasks and surrounding atmosphere.
- Suspended solids concentration: 30 mg dry material per litre.
- Continuous darkness: yes

TEST SYSTEM
- Culturing apparatus: 2000 mL Erlenmeyer flasks, 1000 mL test medium per flask. Flasks loosely covered with aluminium foil.
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: Test media was constantly stirred, flasks were prepared as to allow for exchange of air between flasks and surrounding atmosphere.
- Measuring equipment: Samples analysed for DOC by means of a TOC-analyser with automatic sampler [combustion/non-dispersive IR gas analysis method]
- At each sampling point water evapouration losses were determined and compensated for and deposits on the test vessels resuspended

SAMPLING
- Sampling frequency: At 0, 3 (not toxicity control), 7, 10, 14, 21 (not toxicity or prodecure control) and 28 days
- Sampling method: 10 mL samples taken. Samples filtered through 0.45 µm filter (first 3-4 mL of filtrate discarded)

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes.
- Abiotic sterile control: No
- Toxicity control: Yes (47mg/L test item plus 50mg/L reference item)
- Procedure control: Yes (reference item)

Degradation was calculated by comparing DOC removal in the test flasks to that in the inoculum controls.
Reference substance:
benzoic acid, sodium salt
Parameter:
% degradation (DOC removal)
Value:
98
Sampling time:
10 d
Parameter:
% degradation (DOC removal)
Value:
99
Sampling time:
28 d
Details on results:
Results are given as the average of the degradation in the two replicates.
Results with reference substance:
100% degradation of the reference item within 7 days was observed in the procedure control

Table 1. Percentage degradation in the Test Flasks

Time (days) Percentage biodegradation (corrected for the innoculum controls)
Test Item Procedure Control Toxicity Control
Replicate No. Replicate No. Replicate No.
1 2 mean 1 2 mean 1
0 0 0 0 0 0 0 0
3 1 0 1 99 98 98 n.d.
7 99 98 99 100 99 100 99
10 99 98 98 n.d. n.d. n.d. n.d.
14 99 98 98 99 100 99 99
21 99 99 99 n.d. n.d. n.d. n.d.
28 99 99 99 98 100 99 99

n.d. = not determined

Validity criteria fulfilled:
yes
Remarks:
The suitability of the activated sludge was confirmed as the reference substance degraded by 100% within 7 days.
Interpretation of results:
readily biodegradable
Conclusions:
The substance is ready biodegradable.
Executive summary:

In a GLP compliant, OECD guideline test the test substance degraded sufficiently that it can be considered readily biodegradable. The 10 -day window was met with 98% of the test substance degrading by day 10. The results from the toxicity control show that test substance is not inhibitory to activated sludge.

Description of key information

readily biodegradable, OECD 301A

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable
Type of water:
freshwater

Additional information

A recent guideline study is available which is considered to be reliable and adequate, and is carried forward for use in risk assessment, classification and labelling.