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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:
2010
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: Well described GLP study conducted in accordance with OECD guideline 301 D and giving reliable information on dimethyloctadiene biodegradability.
Reason / purpose for cross-reference:
reference to same study
Qualifier:
according to guideline
Guideline:
OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test)
Deviations:
yes
Remarks:
ammonium chloride was omitted from the medium to prevent oxygen consumption due to nitrification/ activated sludge instead of effluent/ extract/mixture was used as inoculum
GLP compliance:
yes (incl. QA statement)
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): wastewater treatment plant Nieuwgraaf in Duiven, The Netherlands
- Pretreatment: the activated sludge was pre-conditionned to reduce the endogeous respiration rates. 400 mg dry weight/L of activated sludge was aerated for one week.
Duration of test (contact time):
28 d
Initial conc.:
2 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
TEST CONDITIONS
- Composition of medium: per liter of deionized water: 8.5mg KH2PO4, 21.75mg K2HPO4, 33.3mg Na2HPO4.2H2O, 22.5mg MgSO4.7H2O, 27.5mg CaCl2, 0.25mg FECl3.6H2O
- Additional substrate: silica gel
- Test temperature: within the prescribed temperature range of 22 to 24°C
- pH: 6.8 (control, control with silica and test)
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Number of culture flasks/concentration: 10 bottles containing only inoculum, 10 bottles containing inoculum and silica gel, 10 bottles containing inoculum and silica gel dosed with test substance, 6 bottles containing sodium acetate and inoculum
- Measuring equipment: an oxygen electrode (WTW TrioXmatic EO 200) and meter (WTW OXI 530) to electrochemically determine the dissolved oxygen concentrations, a Knick 765 calimatic pHmeter to measure pH, a sensor connected to a data logger to measure and record the temperature
- Test performed in closed vessels due to significant volatility of test substance

SAMPLING
- Sampling frequency: weekly
- Sampling method: Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at day 7, 14, 21, and 28.
- Sample storage before analysis: the bottles were closed and incubated in the dark

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes
- Abiotic sterile control: no
- Toxicity control: no inhibition of the biodegradation due to the "high" initial concentration of the test substance is expected
Reference substance:
acetic acid, sodium salt
Test performance:
The validity of the test is demonstrated by an endogenous respiration of 1.0 mg/L at day 28. Sodium acetate was degraded 83% of its ThOD after 28 days. The validity of the test is also shown by oxygen concentrations >0.5 mg/L in all bottles during the test period.
Parameter:
% degradation (O2 consumption)
Value:
71
Sampling time:
28 d
Details on results:
The pass level of 60% was reached after 10 to 11 days upon achieving 10% biodegradation. Dimethyloctadiene therefore fulfilled the 14-day time window (10-day for other OECD 301 tests) criterion for ready biodegradable compounds. The 14-day window is considered acceptable for the Closed Bottle test because the number of bottles to evaluate the 10-day window causes the test to become too unwieldy (OECD, 1992).
Results with reference substance:
See following Tabe(s) in "Any other information on results incl. tables" section :
Table 1: Dissolved oxygen concentrations (mg/L) in the closed bottles
Table 2: Oxygen consumption (mg/L) and the percentages biodegradtion of the test substances, dimethyloctadiene (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test

Table 1: Dissolved oxygen concentrations (mg/L) in the closed bottles.

Time (days)

Oxygen concentration (mg/L)

Ocs

Ot

Oc

Oa

0

8.6

8.6

8.6

8.6

 

8.6

8.6

8.6

8.6

Mean

8.6

8.6

8.6

8.6

7

7.8

6.2

8.0

3.9

 

8.0

6.1

7.9

3.9

Mean

7.9

6.2

8.0

3.9

14

7.8

3.6

7.7

3.4

 

7.6

3.3

7.8

3.2

Mean

7.7

3.5

7.7

3.3

21

7.7

3.3

7.8

 

 

7.6

3.1

7.6

 

Mean

7.7

3.2

7.7

 

28

7.6

2.7

7.5

 

 

7.6

2.9

7.6

 

Mean

7.6

2.8

7.6

 

Ocs: Mineral nutrient solution without test material but with inoculum and silica gel.

Ot: Mineral nutrient solution with test material (2.0 mg/L), silica gel, and inoculum.

Oc: Mineral nutrient solution with only inoculum

Oa: Mineral nutrient solution with sodium acetate (6.7 mg/L) and with inoculum

Table 2: Oxygen consumption (mg/L) and the percentages biodegradation of the test substance, dimethyloctadiene (BOD/ThOD) and sodium acetate (BOD/ThOD)

in the Closed Bottle test.

Time (days)

Oxygen consumption (mg/L)

Biodegradation (%)

Test substance

Acetate

Test substance

Acetate

0

0.0

0.0

0

0

7

1.7

4.1

25

76

14

4.2

4.5

62

83

21

4.5

 

66

 

28

4.8

 

71

 

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
Dimethyloctadiene is classified as readily biodegradable (biodegradation: 71% in 28 days)
Executive summary:

The test was carried out according to OECD 301D Ready biodegradability in closed bottles

The test substance was applied to closed bottles with preconditionned activated sludge (origin: wastewater treatment plant Nieuwgraaf in Duiven, NL). The closed bottles were incubated for 28 days at 23°C ± 1°C and the oxygen consumption during this period was measured.

The BOD values were related to Theorical oxygen demand (ThOD) and percentage biodegradability in water was estimated.

Reference substance was Sodium acetate.

Oxygen consumption after 28 days incubation was 4.8 mg O2/L test substance

% BOD of ThOD after 28 days of incubation was 71%

The test substance did not inhibit bacterial respiration at the tested concentration. Abiotic degradation was not recorded.

Potential for biodegradation in water was determined in this study.

It is therefore considered that the test substance is readily biodegradable according to the criteria of the OECD 301 D guideline.

Description of key information

Dimethyloctadiene is readily biodegradable in a GLP study conducted according to the criteria of the OECD 301 D guideline.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A test has been carried out according to OECD 301D Ready biodegradability in closed bottles

The test substance was incubated for 28 days at 23°C ± 1°C in closed bottles with preconditioned activated sludge and the oxygen consumption during this period was measured.

% BOD of ThOD after 28 days of incubation was 71%

The test substance is readily biodegradable according to the criteria of the OECD 301 D guideline.

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