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Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: screening tests
Type of information:
experimental study
Adequacy of study:
key study
Study period:
02 March 2007 to 15 May 2007
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
The study was conducted in accordance with international guidelines in a GLP laboratory. All relevant validity criteria were met.
Qualifier:
according to
Guideline:
OECD Guideline 306 (Biodegradability in Seawater)
Version / remarks:
1992
Deviations:
no
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: marine
Details on inoculum:
Seawater was collected from the Burnham-on-Crouch estuary at high water. The Crouch estuary has no industrial and no river inputs. Suspended solids were removed from the raw seawater using a hydro-clone and settlement.Date of collection: 04 April 2007Storage conditions prior to test: Dark, ambient temperatureSalinity at start of test: 31 pptTemperature at start of test: 21.8 °CPre-treatment: Settled, decanted
Duration of test (contact time):
28 d
Initial conc.:
3.04 mg/L
Based on:
ThOD
Parameter followed for biodegradation estimation:
O2 consumption
Details on study design:
Replicate standard BOD bottles were filled with the test concentration, prepared by addition of a sample stock solution to dilution water. A series of test bottles was prepared with dilution water only for the determination of "blank losses". To check the integrity of the test procedure, a readily biodegradable reference material, sodium acetate, was also tested.Initial dissolved oxygen concentrations were measured using a dissolved oxygen meter. The bottles were then incubated in the dark at 20 +/- 1 °C for the test duration. Further measurements of dissolved oxygen concentration were made on bottles removed after 8, 14, 21 and 28 days.
Reference substance:
acetic acid, sodium salt
Remarks:
reported as "sodium acetate"
Preliminary study:
Not applicable
Test performance:
The guideline requires that a the reference material degrades by at least 60 % of it's ThOD, and that the blank dissolved oxygen loss should not exceed 30 % of the initial oxygen concentration. Both of these criteria were satisfied for this test; a maximum value of 79 % was achieved for the reference material and the blank dissolved oxygen loss was 15.9 %.
Key result
Parameter:
% degradation (O2 consumption)
Value:
65
Sampling time:
8 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
73
Sampling time:
14 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
66
Sampling time:
21 d
Key result
Parameter:
% degradation (O2 consumption)
Value:
64
Sampling time:
28 d
Details on results:
The calculated ThOD of the test item was 819 mg O2/g.

Table 1. Dissolved oxygen measurements and calculated BOD values for the test substance and reference material

 

Incubation period (days)

0

8

14

21

28

Incubator temperature (°C)

20.0

21.0

22.0

21.5

21.0

Average blank DO (mg/L)

6.74

6.19

6.46

5.94

5.67

Replicate

1

1

2

1

2

1

2

3

1

2

3

Test substance – DO (mg/L)

6.74

4.56

4.59

4.58

4.52

4.23

4.35

4.33

4.11

4.02

4.07

Test substance – BOD (mg O2/g)

-

536

526

586

605

563

523

530

513

543

526

Reference material – DO (mg/L)

6.77

3.63

3.63

3.25

3.32

3.12

3.06

2.95

2.62

2.74

2.74

Reference material – BOD (mg O2/g)

-

515

515

624

610

567

579

600

612

588

588

Table 2. % Degradation for the test substance and reference substance

 

Incubation period (days)

8

14

21

28

Replicate

1

2

1

2

1

2

3

1

2

3

Test Substance (%)

65

64

71

74

69

64

65

63

66

64

Average Degradation (%)

65

73

66

64

Reference Material (%)

66

66

80

78

73

74

77

79

75

75

Average Degradation (%)

66

79

75

76

Validity criteria fulfilled:
yes
Interpretation of results:
readily biodegradable
Conclusions:
The test substance was determined to be radily biodegradable, achieving >60 % biodegradation within 8 days of study initiation and achieving a maximum biodegradation value of 73 % over a 28-day period.

Description of key information

Ready Biodegradability = Readily biodegradable, OECD 306, Drake (2007) - See Section 5.2.2.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

A study was performed in accordance with OECD Guideline 306 “Biodegradability in Seawater” (Section 5.2.2.) using the closed bottle method. The test item was added to the test vessels from a stock solution and the vessels were filled with seawater with added minerals, and closed ensuring that there was no air filled head space in the vessel. Test vessels containing seawater only (blanks), and vessels containing reference item were also prepared. Initial dissolved oxygen concentrations were measured and the test vessels were then stored in the dark at 20°C for the duration of the test. Further measurements of dissolved oxygen were made after 8, 14, 21 and 28 days.

Hexahydro-1,3,5-trimethyl-1,3,4-triazine achieved 65 % biodegradation by day 8 of the study and a maximum biodegradation of 73 % by day 14. The reference material and blanks were within guideline requirements during the test confirming the validity of the study.

Based on these results, hexahydro-1,3,5-trimethyl-1,3,4-triazine is considered to be equivalent to the category of “readily biodegradable” as described in OECD 301.