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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:
02 Jul - 31 Jul 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to
Guideline:
OECD Guideline 310 (Ready Biodegradability - CO2 in Sealed Vessels (Headspace Test)
Qualifier:
according to
Guideline:
other: EN ISO 14593 (1999): Water quality - Evaluation of ultimate aerobic biodegradability of organic compounds in aqueous medium - Method by analysis of inorganic carbon in sealed vessels (CO2 headspace test)
GLP compliance:
yes (incl. certificate)
Remarks:
Staatliches Gewerbeaufsichtsamt Hildesheim, Germany
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): activated sludge from a municipal sewage treatment plant (Hildesheim, Germany)
- Laboratory culture: no
- Pretreatment: washed twice with chlorine-free tap water; sludge was allowed to settle and resuspended in mineral salts medium and maintained under aerobic conditions for 2.5 h by aeration; sludge was homogenized with a blender; after sedimentation the supernatant was decanted and maintained in an aerobic condition by aeration with CO2-free air for 5 d.
- Colony-forming units (CFU): 10E+05 - 10E+08 CFU/L
Duration of test (contact time):
28 d
Initial conc.:
21.21 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
Details on study design:
TEST CONDITIONS
- Composition of medium: according to guideline
- Additional substrate: no
- Test temperature: 20 ± 1 °C (up tp 26 °C on day 25)
- pH adjusted: no
- Continuous darkness: low light conditions

TEST SYSTEM
- Culturing apparatus: headspace flasks, 120 mL (fill volume: 80 mL; headspace to liquid ratio: 1:2)
- Number of culture flasks/concentration: 3 (5 repliactes at the end)
- Method used to create aerobic conditions: constantly shaken (150 - 200 rpm)
- Measuring equipment: CO2 was determined by IC analysis with a carbon analyser according to DIN EN 1484.
- Test performed in closed vessels due to significant volatility of test substance: yes
- Other: The inoculated test medium was prepared in a test flask (80 mL). 2 µL of the test substance were added to the test item flasks (+ toxicity control) by pipetting them into a glass ring and giving it into the test vessels. Sodium hydroxide solution (0.74 mL 7 mol/L solution to 80 mL medium) was injected to each vessel sampled. The vessels were shaken on an overhead shaker for 1 h at test temperature. Suitable samples were analysed.

SAMPLING
- Sampling frequency: Analysis was carried out at test start, twice in the first two weeks and thereafter every 7 d.
- Sample storage before analysis: analysed directly

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, three bottles
- Abiotic sterile control: no
- Toxicity control: yes, three bottles
- Other: reference susbtance: yes, three bottles
Reference substance:
benzoic acid, sodium salt
Key result
Parameter:
% degradation (CO2 evolution)
Value:
76
Sampling time:
28 d
Remarks on result:
other: 95% CI: 75 - 77%
Details on results:
Within the 10-day time window the 60% level was passed. Therefore, the substance is regarded as readily biodegradable according to the OECD criteria.
The toxicity control attained 65% after 14 d and 87% after 28 d. Thus, the test substance is not considered to be inhibitory to the inoculum.
Results with reference substance:
The reference substance was degraded to 92% after 14 d and 94% after 28 d (95% CI: 92 - 96%), 60% pass level was reached.

Table 1: CO2 production and biodegradation of the test item

 

CO2 production in mg C/L

 

 

Day

Replicate 1

Replicate 2

Replicate 3

Replicate 5

Replicate 5

MP

Net MP

Degr. [%]

0

2.46

2.47

2.46

 

 

0.46

-

-

1

1.43

1.40

1.47

 

 

0.55

0.00

0

3

2.03

2.11

1.93

 

 

0.87

0.00

0

7

2.18

2.06

2.01

 

 

0.98

0.00

0

10

5.85

2.42

3.02

 

 

2.38

0.86

5

14

10.59

11.28

10.55

 

 

9.71

8.61

54

21

12.59

12.06

12.90

 

 

11.49

10.38

65

28

14.29

14.62

14.20

14.30

14.50

13.57

12.02

76

MP: mean values (NaOH corrected)

Net MP: netto mean production (corrected for inoculum control values)

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The substance is readily biodegradable according to the OECD criteria (76%, CO2 evolution after 28 d, meeting the 10-day window; OECD 310).

Description of key information

One experimental study is available investigating the ready biodegradability of the test substance. The study was performed according to the OECD 310 (GLP). Activated sludge from a municipal sewage treatment plant was used as inoculum. 76% degradation of the test substance was recorded based on CO2 evolution after 28 d. Since the 10-day window was met the test substance is considered to be readily biodegradable. The toxicity control (containing both, reference substance and test substance) attained 65% and 87% degradation after 14 and 28 d, respectively. Thus, the test substance is not considered to be inhibitory to the inoculum.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information