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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:
27 October - 25 November 2011
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Reason / purpose:
reference to same study
Reason / purpose:
reference to other study
Qualifier:
according to
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 (omission does not result in nitrogen limitation); river water instead of an effluent/extract/mixture was used as inoculum
Principles of method if other than guideline:
Not applicable
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:
other: river water, near to a domestic wastewater treatment plant (3 km upstream)
Details on inoculum:
- Source of inoculum: River water was sampled from the Rhine near Heveadorp, The Netherlands. The nearest plant (Arnhem-Zuid) treating domestic wastewater biologically was 3 km upstream.
- Preconditioning: The river water was aerated for 7 days before use to reduce the endogenous respiration (van Ginkel and Stroo, 1992). River water without particles was used as inoculum. The particles were removed by sedimentation after 1 day while moderately aerating.
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: River water spiked per liter of deionised water: 8.5 mg KH2PO4, 21.75 mg K2HPO4, 33.3 mg Na2HPO4.2H2O, 22.5 mg MgSO4.7H2O, 27.5 mg CaCI2, 0.25 mg FeCI3.6H2O
- Source/preparation of dilution water: Deionised water containing no more than 0.01 mg/L Cu was prepared in a water purification system.
- Test temperature: 22-24 °C
- pH (at start of test): 8.2; pH (at end of test): 8.1 (controls) and 7.9 (test)
- Continuous darkness: Yes

TEST SYSTEM
- Culturing apparatus: 0.30 L BOD (biological oxygen demand) bottles with glass stoppers
- 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, and 6 bottles containing sodium acetate and inoculum
- Test performed in closed vessels: Yes

MEASURING EQUIPMENTS:
- Dissolved oxygen concentrations were determined electrochemically using an oxygen electrode (WTW TrioXmatic EO 200) and meter (WTW OXI 530) (Retsch, Ochten, The Netherlands)
- pH was measured using a Eutech Cyberscan pH11 pH meter (Eutech Instruments, Nijkerk, The Netherlands).
- Temperature was measured and recorded with a sensor connected to a data logger.

SAMPLING
- Sampling frequency: Two duplicate bottles of all series were withdrawn for analyses of the dissolved oxygen concentration at Days 0, 7, 14, 21 and 28.

CONTROL AND BLANK SYSTEM
- Inoculum blank: Yes; containing inoculum only
- Procedure control: Yes; containing reference substance (sodium acetate) with inoculated medium
- Toxicity control: No; test material was considered to be non-toxic to micro-organisms as inhibition of the endogenous respiration of the inoculum was not detected.
- Other: Containing inoculum and silica gel
Reference substance:
acetic acid, sodium salt
Remarks:
6.7 mg/L; source: Acros organics, Belgium; purity: > 99 %
Preliminary study:
No data
Test performance:
No data
Key result
Parameter:
% degradation (O2 consumption)
Value:
90
Sampling time:
28 d
Details on results:
Initial test material concentration: 2 mg/L
- Theoretical oxygen demand (ThOD) = 2.9 mg/mg
- % biodegradation on Day 2: > 10 %
- % biodegradation on Day 7: > 60 %
- % biodegradation on Day 28 = 90 %
Results with reference substance:
- Theoretical oxygen demand (ThOD) = 0.8 mg/mg
- % biodegradation on Day 7: > 60 %
- % biodegradation on Day 14 = 78 %

Table 5.2.1/1: Dissolved oxygen concentrations (mg/L) in the closed bottles

 

Time (days)

Oxygen concentration (mg/L)

Ocs

Ot

Oc

Oa

0

9.1

9.1

9.1

9.1

 

9.1

9.1

9.1

9.1

Mean (M)

9.1

9.1

9.1

9.1

7

8.4

4.6

8.6

5.0

 

8.6

4.3

8.6

5.0

Mean (M)

8.5

4.5

8.6

5.0

14

8.2

3.1

8.3

4.0

 

8.2

3.5

8.3

4.2

Mean (M)

8.2

3.3

8.3

4.1

21

8.0

3.2

 

 

 

8.0

2.8

 

 

Mean (M)

8.0

3.0

 

 

28

8.0

2.9

 

 

 

7.9

2.6

 

 

Mean (M)

8.0

2.8

 

 

Ocs: River water with nutrients and silica gel but without test material

Ot: River water with nutrients, test material (2.0 mg/L), and silica gel

Oc: River water with nutrients

Oa: River water with nutrients and sodium acetate (6.7 mg/L)

 

Table 5.2.1/2: Oxygen consumption (mg/L) and the percentages biodegradation of the test substance, nerol (BOD/ThOD) and sodium acetate (BOD/ThOD) in the Closed Bottle test

 

Time (days)

Oxygen consumption (mg/L)

Biodegradation (%)

Test substance

Sodium acetate

Test substance

Sodium acetate

0

0.0

0.0

0

0

7

4.0

3.6

69

67

14

4.9

4.2

84

78

21

5.0

 

86

 

28

5.2

 

90

 

Validity criteria fulfilled:
yes
Remarks:
endogenous respiration at Day 28 was 1.1 mg/L; differences of the replicate values at Day 28 were < 20%; degradation in reference material was 78 % at Day 14; O2 concentration during the test was > 0.5 mg/L
Interpretation of results:
readily biodegradable
Conclusions:
Under the test conditions, nerol was readily biodegradable.
Executive summary:

In a ready biodegradation study performed according to OECD Guideline 301 D and GLP, nerol was tested at concentrations of 2 mg/L and the inoculum was river water (near to a domestic wastewater treatment plant, 3 km upstream). The degradation of the test material was assessed by the determination of the oxygen consumption. The test treatments, inoculum blank, and reference (sodium acetate) were measured in duplicates.

At 2 mg/L test concentration, greater than 10 % degradation was reached by Day 2 and greater than 60 % biodegradation was reached by Day 7. Thus, the test material met the 14 day window requirement for ready biodegradability. On Day 28, the biodegradation was 90 %.

 

The reference material, sodium acetate, reached greater than 60 % biodegradation on Day 7. Nerol was considered to be non-toxic to micro-organisms as inhibition of the endogenous respiration of the inoculum was not detected during the test. Hence, it met the validity criteria for reference material and toxicity control. The endogenous respiration at Day 28 was 1.1 mg/L and oxygen concentration during the test was greater than 0.5 mg/L.

 

Therefore, nerol was readily biodegradable.

Description of key information

The substance is readily biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

One reliable study is available for the substance. The biodegradability of the substance was studied according to OECD TG No. 301D and GLP.

Nerol was tested at a concentration of 2 mg/L. The inoculum was a river water, near to a domestic wastewater treatment plant (3 km upstream). Degradation was assessed by measurement of oxygen consumption.

The pass level for ready biodegradability was reached in the required time window within the 28-d period of the test: 90% biodegradation on Day 28. This result can be used as key value for chemical safety assessment.