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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
Study period:
23/01/2006 - 05/01/2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 306 (Biodegradability in Seawater)
Deviations:
no
GLP compliance:
yes (incl. QA statement)
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: marine
Details on inoculum:
- Source of inoculum/activated sludge: Natural seawater collected from Anglesey Sea Zoo (North Wales), on collection the temperature was 15 °C, pH 7.95 and 100% dissolved oxygen.
- Storage conditions: Stored in darkness, 15 (+- 2) °C and gently aerated
- Water filtered: yes, coarse filtered
Duration of test (contact time):
>= 0 - <= 28 d
Initial conc.:
7 mg/L
Based on:
test mat.
Initial conc.:
9 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
DOC removal
Details on study design:
TEST CONDITIONS
- Composition of medium: nutrient fortified seawater
- Additional substrate: positive control included reference material (sodium benzoate)
- Test temperature: 18 - 19.5 °C
- pH: 7.95
- pH adjusted: no
- Aeration of dilution water: prior to definite test for aging only
- Continuous darkness: yes


TEST SYSTEM
- Culturing apparatus: BOD bottles of nominal 272 ml volume
- Number of culture flasks/concentration: 2 replicate flasks per time period tested per test material concentration (7 and 9 mg/ L). The same for the positive control (2.5 mg/ L sodium benzoate). For the blank control 3 replicates per time point measured were included.
- Test performed in open system: closed bottle method, sealed


SAMPLING
- Sampling frequency: 24 hour intervals
- Sampling method: dissolved oxygen content measured

CONTROL AND BLANK SYSTEM
- Inoculum blank: Nutrient fortified seawater
- Toxicity control: Nutrient fortified seawater with reference substance (sodium benzoate)
Reference substance:
benzoic acid, sodium salt
Test performance:
The reference material had a degradation figure of > 100 % after 28 days demonstrating that the inoculum was biologically active.
Key result
Parameter:
% degradation (DOC removal)
Value:
54.6
Sampling time:
28 d
Remarks on result:
other: 7 mg/ L test substance
Parameter:
% degradation (DOC removal)
Value:
41.7
Sampling time:
28 d
Remarks on result:
other: 9 mg/ L test substance
Details on results:
Dissolved oxygen was measured for the test substance and the controls
- DOC 7.0 mg/ L test substance (average): 7.69, 6.82, 5.57, 4.72, 4.56 and 4.43 mg O2/ L for 0, 3, 7, 14, 21 and 28 days, respectively
- DOC 9.0 mg/ L test substance (average): 7.68, 6.40, 4.61, 3.40, 2.82 and 4.46 mg O2/ L for 0, 3, 7, 14, 21 and 28 days, respectively
- DOC 2.5 mg/ L sodium benzoate: 7.74, 3.61, 3.00, 2.82, 2.36 and 2.34 mg O2/ L for 0, 3, 7, 14, 21 and 28 days, respectively
- DOC blank (nutrient fortified seawater only): 7.68, 7.02, 6.55, 6.54, 6.35 and 6.50 mg O2/ L for 0, 3, 7, 14, 21 and 28 days, respectively
Key result
Parameter:
COD
Value:
0.565 other: mg mg-1
Results with reference substance:
Reference substance (Sodium benzoate) had >100% degradability at 28 days
Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The study showed 54.6% biodegradability for 7.0 mg/L test material and 41.7% biodegradability at 9 mg/ L test material at 28 days. These results show the test substance has good potential for biodegradation.
Executive summary:

The study assesses the potential for 25% M528 -7 (W/W) neutralised with DEA in deionised water to readily biodegrade in water. The study was conducted under GLP in accordance with OECD guideline 306: Biodegradability in seawater, using a closed bottle method. All validity criteria were met. Testing was conducted using natural seawater that was coarse filtered, aged via aeration and darkness prior to testing and fortified with nutrients. The inoculum shown to have suitable biological activity based on the reference material results. Test substance experiments were performed with 2 replicates per concentration, per time period. For the degradability negative control dissolved oxygen was at an average of 7.68, 7.02, 6.55, 6.54, 6.35 and 6.50 mg O2/ L for 0, 3, 7, 14, 21 and 28 days (3 replicates). For the positive control (reference substance, sodium benzoate) the degradability was 83.1%, 86.5%, 90.5%, 97% and >100% for 3, 7, 14, 21 and 28 days (2 replicates).

The definitive test showed that at 7.0 mg/L the test substance readily biodegradability was 54.6% at day 28, while at the test concentration of 9 mg/L the readily biodegradability was 41.7% at Day 28. The results from this study show that the test substance show a good potential to biodegrade but it is not deemed to be readily biodegradable.

Description of key information

The study assesses the potential for 25% M528 -7 (W/W) neutralised with DEA in deionised water to readily biodegrade in water. The study was conducted under GLP in accordance with OECD guideline 306: Biodegradability in seawater, using a closed bottle method. All validity criteria were met. Testing was conducted using natural seawater that was coarse filtered, aged via aeration and darkness prior to testing and fortified with nutrients. The inoculum show to have suitable biological activity based on the reference material results. Test substance experiments were performed with 2 replicates per concentration, per time period. For the degradability negative control dissolved oxygen was at an average of 7.68, 7.02, 6.55, 6.54, 6.35 and 6.50 mg O2/ L for 0, 3, 7, 14, 21 and 28 days (3 replicates). For the positive control (reference substance, sodium benzoate) the degradability was 83.1%, 86.5%, 90.5%, 97% and >100% for 3, 7, 14, 21 and 28 days (2 replicates).

The test showed that at 7.0 mg/L the test substance readily biodegradability was 54.6% at day 28, while at the test concentration of 9 mg/L the readily biodegradability was 41.7% at Day 28. The results from this study show that the test substance show a good potential to biodegrade but it is not deemed to be readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable
Type of water:
marine water

Additional information