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Biodegradation in water: screening tests

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Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
May 11 - June 08, 1988
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions. Some modifications were performed such as adding the test substance adsorbed on charcoal particles.
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to
Guideline:
other: Bewertung wassergefährdender Stoffe, Bestimmung des biologischen Abbauverhaltens
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): from municipa sewage treatment plant, Schijndel, Netherlands
- Pretreatment: 4 h aeration with CO2 free air, subsequently mixture at 1:1 ration with tap water, homogenisation for 5 min, afterwards 1 h time to settle. Then 30 mL inoculum were put into the test bottles and aerated for 20 h with CO2-free air
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral nutrient solution, activated sludge and test substance
- Solubilising agent (type and concentration if used): test substance was adsorbed at charcoal particles and as such added to the test solution
- Test temperature: 18.0 - 24.5 °C
- pH: 5.9 - 6.9
- Aeration of dilution water: with CO2-free air (80% oxygen, 20 % nitrogen)

TEST SYSTEM
- Culturing apparatus: closed brown bottles
- Number of culture flasks/concentration: 1
- Measuring equipment: The produced CO2 was measured by titrating the barium hydroxide left against 0.05 N HCl
- Details of trap for CO2 and volatile organics if used: test substance glass bottles were connected to washing bottles with 100 mL 0.025 N barium hydroxide as CO2 absorbant

SAMPLING
- Sampling frequency: after 2, 5, 7, 9, 13, 16, 21 and 28 d

CONTROL AND BLANK SYSTEM
- Inoculum blank: with charcoal particles: 1
Reference substance:
other: sodium acetate
Parameter:
% degradation (CO2 evolution)
Value:
51.6
Sampling time:
28 d
Remarks on result:
other: 10 mg/L
Parameter:
% degradation (CO2 evolution)
Value:
54.4
Sampling time:
28 d
Remarks on result:
other: 20 mg/L
Details on results:
The biodegradation was significant, but did not reach 60%. Since the test substance was added to the flasks adsorbed at charcoal particles, this probably influenced the availability of the test substance to the microorganisms. Therefore, this test condition probably had contributed to the lowering of the degradation rate.
Results with reference substance:
The reference substance was degraded to 65.2% after 28 d.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
disregarded due to major methodological deficiencies
Study period:
May 11 - June 08, 1988
Reliability:
3 (not reliable)
Rationale for reliability incl. deficiencies:
other: Test not valid. Reference substance did not reach pass level of 60% within 14 days
Qualifier:
according to
Guideline:
OECD Guideline 301 B (Ready Biodegradability: CO2 Evolution Test)
Deviations:
no
Qualifier:
according to
Guideline:
EU Method C.5 (Degradation: Biochemical Oxygen Demand)
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): from municipa sewage treatment plant "Waterschap de Aa", Schijndel, Netherlands
- Pretreatment: 4 h aeration with CO2 free air, afterwards 1/2 h time to settle. Then supernatant was decanted. 30 mL inoculum were put into the test bottles and aerated for 24 h with CO2-free air
Duration of test (contact time):
28 d
Initial conc.:
10 mg/L
Based on:
test mat.
Initial conc.:
20 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: mineral nutrient solution, activated sludge and test substance
- Solubilising agent (type and concentration if used): no solubility agent was used, but since the test substance is poorly soluble in water it was quantitatively added to the test media and continuously stirred during the test
- Test temperature: 18.0 - 21.5 °C
- pH: 5.8 - 6.7
- Aeration of dilution water: with CO2-free air (80% oxygen, 20 % nitrogen)

TEST SYSTEM
- Culturing apparatus: closed brown bottles
- Number of culture flasks/concentration: 1
- Measuring equipment: The produced CO2 was measured by titrating the barium hydroxide left against 0.05 N HCl
- Details of trap for CO2 and volatile organics if used: test substance glass bottles were connected to washing bottles with 100 mL 0.025 N barium hydroxide as CO2 absorbant

SAMPLING
- Sampling frequency: after 2, 5, 7, 9, 12, 16, 21 and 28 d

CONTROL AND BLANK SYSTEM
- Inoculum blank: 1
Reference substance:
other: sodium acetate
Parameter:
% degradation (CO2 evolution)
Value:
68
Sampling time:
28 d
Remarks on result:
other: 10 mg/L
Parameter:
% degradation (CO2 evolution)
Value:
70
Sampling time:
28 d
Remarks on result:
other: 20 mg/L
Results with reference substance:
The reference substance was degraded to 77.7% after 28 d. Still the validity criteria of a degradation of the reference substance of 60% 14 days after test start was failed. Thus, the test is considered to be not valid.
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
no data
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Guideline study with acceptable restrictions
Qualifier:
according to
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
oxygen concentration in test bottles below 0.5 mg/L at test end
GLP compliance:
no
Oxygen conditions:
aerobic
Inoculum or test system:
sewage, domestic, non-adapted
Details on inoculum:
- Source of inoculum/activated sludge (e.g. location, sampling depth, contamination history, procedure): effluent of the sewage treatment plant Hochdahl, Germany
- Initial cell/biomass concentration: 10 E+03 to 10 E+04 cells/mL
- Water filtered: yes
- Type and size of filter used, if any:through a corase paper filter, the first 200 mL were discarded
Duration of test (contact time):
30 d
Initial conc.:
2 mg/L
Based on:
test mat.
Initial conc.:
5 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: deionised water was used for the test which is not in line with the guideline.
- Solubilising agent (type and concentration if used): Sodium hydroxide
- Test temperature: 19.9 - 20.1 °C
- pH: 7 - 8
- Aeration of dilution water: aerated until O2 saturation was 8-9 mg O2/L

TEST SYSTEM
- Culturing apparatus: completely filled closed bottles
- Number of culture flasks/concentration: not specified (two parallels were run)

SAMPLING
- Sampling frequency reported: after 5, 15 and 30 days, which is not in line with the guideline
CONTROL AND BLANK SYSTEM
- Inoculum blank: 4
Reference substance:
other: Dodecylsulfate
Parameter:
% degradation (O2 consumption)
Value:
105
Sampling time:
30 d
Remarks on result:
other: 2 mg/L
Parameter:
% degradation (O2 consumption)
Value:
> 72
Sampling time:
30 d
Remarks on result:
other: 5 mg/L
Details on results:
More then 72 % of the test substance was degraded whithin 30 days at a test concentration of 5 mg/L. Due to the good biodegradability the oxygen concentration in this test concentration remained inadequate so that the 72% should be regarded as a minimum value. At a test concentratios of 2 mg/L octanoic acid was completely degraded. 60% were reached within the given 10 day window as required. Thus, the test substance can be regarded as readily biodegradable.
Parameter:
COD
Value:
2.51 mg O2/g test mat.
Results with reference substance:
The reference substance is readily biodegradable since 90 % was degraded after 30 days and over 60 % in the 10 day window. The ThOD of the reference substance was 2.02 mg O2/ mg dodecylsulfate
Interpretation of results:
readily biodegradable

Description of key information

Readily biodegradable: >72% after 30 d (OECD 301D, non GLP) 

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Three studies on the ready biodegradability of octanoic acid are available.

The first study (2004) was performed according to OECD 301D (non GLP) where octanoic acid was tested at concentrations of 2 and 5 mg/L for 30 days. At the test substance concentration of 5 mg/L more than 72% was degraded within 30 days. Due to the good biodegradability, the oxygen concentration at 5 mg/L remained inadequate so that the 72% should be regarded as a minimum value. At test concentration of 2 mg/L octanoic acid was completely degraded while 60% degradation was reached within the 10-day window, as required. Thus, the test substance can be regarded as readily biodegradable. This study was chosen as the key study, since the direct application of the test substance was most appropriate in this OECD 301D test and the validity criteria were met.

In the first supporting study (1988) octanoic acid was assessed according to OECD 301B (modified Sturm Test, GLP). The test substance was added to the flasks adsorbed at charcoal particles. This guideline deviation probably reduced the availability of the test substance to the microorganisms. Nevertheless, the results revealed a degradation of 51.6% - 54.4% clearly indicating the biodegradation potential of octanoic acid.

The ready biodegradability is supported by another OECD 301B test (1991) performed under GLP conditions where octanoic acid was directly added at two concentrations (10 and 20 mg/L). The result showed a degradation of 68% and 70% for 10 mg/L and 20 mg/L, respectively. Moreover, octanoic acid met the criteria for ready biodegradation (10-d window) in the lower concentration. Since the reference substance did not meet the current validity criteria (degradation of 60% within 10 days), the test results have to be interpreted with caution.