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Biodegradation in water and sediment: simulation tests

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Reference
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
other: GLP Guideline Study
Qualifier:
according to guideline
Guideline:
other: Commission Directive 95/36/EC Amending Council Directive 91/414/EEC (Annexes I and II, Fate and Behaviour in the Environment), July 1995
Qualifier:
according to guideline
Guideline:
other: SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, March 1995
GLP compliance:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of sediment:
Aqueous sediments were collected from the River Erft approx. 500 m before flow into the Rhine river, and from Hönniger Weiher Pond, which is an artificial dammed pond.
The supernatant water was allowed to settle and then was separated by decanting. Plants and stones were removed and the sediment was sieved through 2 mm. After settling the remaining water was decanted, the sediment was mixed and the dry weight was determined.
Refer to Table 1 for sediment characteristics
Duration of test (contact time):
120 d
Initial conc.:
7 mg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Details on study design:
TEST CONDITIONS
120 days of incubation at 19.9 ± 0.8 °C in the dark.

TEST SYSTEM
The test system consist of a vessel of 10.5 cm diameter wit a magnetic stirrer and a trap for volatile compounds including 14CO2.
In this system the stagnant sediment is covered by a water layer in slow motion. The rippling surface of the water guarantees oxygen uptake. The air in the vessel has the same oxygen concentration as at the atmosphere.
130 mL of the aqueous sediments corresponding to 1.5 cm height in the vessels were weighted. The respective water was filtered through a 0.2 mm sieve and 390 mL were added to each incubation vessel. The total volume water plus sediment was 520 mL for both systems. The ratio water/sediment was 3:1. The total volume of water in each vessel was 495 mL (River Erft) and 489 mL (Hönniger Weiher).

TEST SOLUTION
For the preparation of the application solution: 133 mg non labelled Diuron and 1.872 µL of radioactive stock solution (7 MBq) were transferred into a 20 mL flask and filled with acetonitrile, to produce a radioactivity of 0.052 MBq/mg.
Application of test solution: An aliquot of 513 µL of the test solution containing 3.46 mg [14C]Diuron was applied to each system. The resulting actual concentration of Diuron was about 7mg Diuron/L water.

SAMPLING
Samples were taken at 0, 7 14, 28, 55, 91 and 120 days. At each sampling data two batches per water-sediment system were completely processed. Before taking off the trap attachment, volatile compounds were purged into the trap by pressurization. Redox potential, oxygen content and pH were determined before processing.

STATISTICAL METHODS:
SFO
FOMC
Test performance:
The mean recovery of the applied radioactivity (AR) in the individual vessels ranged from 91.7% to 103.4% (River Erft; mean 97.5%) and 98.5% to 103.3 (Hönniger Weiher, mean 100.8%). From the mean values, it is demonstrated that no relevant amount of radioactivity was lost from the systems during the testing period. (Refer also to Table 3)
% Degr.:
100
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other: River Erft: Degradation from water body to which parent compound was applied
% Degr.:
90
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other: Hönniger Weiher: Degradation from water body to which parent compound was applied
Compartment:
water
DT50:
4.2 d
Remarks on result:
other: Hönniger Weiher
Compartment:
entire system
DT50:
232 d
Remarks on result:
other: Hönniger Weiher
Compartment:
water
DT50:
8.8 d
Remarks on result:
other: River Erft
Compartment:
entire system
DT50:
48 d
Remarks on result:
other: River Erft
Compartment:
water
DT50:
8.9 d
Temp.:
12 °C
Remarks on result:
other: Hönniger Weiher
Compartment:
entire system
DT50:
492.5 d
Temp.:
12 °C
Remarks on result:
other: Hönniger Weiher
Compartment:
water
DT50:
18.7 d
Temp.:
12 °C
Remarks on result:
other: River Erft
Compartment:
entire system
DT50:
101.9 d
Temp.:
12 °C
Remarks on result:
other: River Erft
Transformation products:
yes
No.:
#1
No.:
#2
Volatile metabolites:
no
Details on results:
TEST ITEM:
Diuron was quickly eliminated from the water body, either by translocation into the sediment or by degradation The calculated DT50 values of Diuron for the supernatant water phase in both systems were 4.2 and 8.8 days, respectively for the Hönniger and River Erft. At study termination (120 days) no parent compound was detected in the water of River Erft and only 10 % in the water of the pond.
Despite having applied the parent compound into the water, the radioactivity portion found in the submerged sediments after 2 hours was about 9 to 11 % (River Erft and Hönniger Weiher) of applied RA. This indicates a rapid partitioning of Diuron into the sediments.
The maximum portion of Diuron in the sediment of River Erft was found after 28 days (about 74 % of applied RA). Then the residues of Diuron in the submerged sediment (expressed as % of applied RA) continually decreased to 10 % at day 120. The Erft sediment showed a high potential for degrading the test substance Diuron.
This also can be concluded from the high content of 14CO2 (30 % of applied radioactivity after 120 days) found in this water-sediment system.
The portion of Diuron found in the sediment of Hönniger Weiher after 7 days was about 58 % of applied radioactivity and remained unchanged at this level until the end of the study.
Considering the total system, Diuron will be thoroughly degraded in aquatic environment. The rate of mineralization in the system Hönniger Weiher was 2% and in the Erft system was 30 %.

METABOLITES/DEGRADATION PRODUCTS: (refer also to Tables 4a and 4b)
Two metabolites (mCPDMU and DCPMU) were found in the supernatant water of Hönniger Weiher. mCPDMU was found with a maximum residue of about 7 % of applied amount (55 days after incubation), then decreasing to 2 % at study termination. DCPMU was measured in traces only. In the water of River Erft no mCPDMU and no DCPMU could be detected.
In the sediment of River Erft the metabolite DCPMU could be measured with a maximum concentration of ca. 4 % of applied amount (day 91, decreasing). No mCPDMU (< 0.2 %) was observed in this sediment. In the sediment of Hönniger Weiher the residue of DCPMU was 0.3 % of applied amount (day 14) and increased to ca. 4 % at termination of the study. The metabolite mCPDMU was measured with 9 % of applied radioactivity after 55 days and decreased to 3 % at study termination.
Considering the total system, the main degradation product in the river Erft was DCPMU (max. 4%, mainly in the organic part). This metabolite occurred in Hönniger system at 4% too (mainly in the sediment). The metabolite m-CPDMU was found only in the Hönniger system, with a maximum of 15.2%.
No 3,4 –DCA was found (< 0.2 % AR).
The portion of bound residues ranged from about 4 – 5 % (day 7) to 17.5 %- 45.9 % of applied radioactivity at day 120

DEGRADATION RATE: (Refer also to Table 5)
The calculated DT50 values (degradation) of Diuron for the supernatant water phase in both systems were 4.2 and 8.8 days, respectively for the Hönniger and River Erft.
Based on the results it can be concluded that Diuron is eliminated of the system via degradation. The DT50 values (degradation) for the whole system were 48 and 232 days respectively for the River Erft and Hönniger Weiher.

Table 3 Material balances

% Applied radioactivity

System

Time

[days]

Sediment

Water

Volatiles

Recovery

 

Non extracted

Extracted

Total

 

CO2

VOC in PU*

 

River Erft

0

0.90

8.54

9.44

90.58

Not detected

Not detected

100.01

7

4.21

51.13

55.34

43.53

0.17

< 0.01

99.03

14

10.01

58.69

68.73

31.62

0.68

< 0.01

101.04

28

10.11

75.00

85.11

17.63

0.68

< 0.01

103.42

55

33.83

50.87

84.70

5.79

4.34

0.04

94.87

91

44.24

24.27

68.51

0.84

22.28

0.04

91.67

120

45.92

15.63

62.10

0.68

29.70

0.04

91.97

 

Mean

97.51

Hömmiger Weiher

0

1.19

9.90

11.09

92.17

Not detected

Not detected

103.25

7

5.04

57.51

62.55

38.02

0.14

< 0.01

100.71

14

8.00

62.12

70.12

29.91

0.61

0.02

100.65

28

9.87

64.22

74.09

25.77

1.33

< 0.01

101.20

55

14.66

61.84

76.50

21.92

1.56

0.01

99.99

91

14.70

67.57

82.27

14.67

1.56

< 0.01

98.51

120

17.48

68.64

86.12

13.42

2.05

< 0.01

101.60

 

Mean

100.84

*             Volatile organic compounds in polyurethane plug

 

Table 4a Distribution of radioactivity in the water phase

Incubation system

Molecule

Incubation day

0

7

14

28

55

91

120

River Erft

Diuron

m-CPDMU

DCPMU

Others

Total

90.3

n.d.

n.d.

n.d.

90.6

43.2

n.d.

n.d.

n.d.

43.5

29.9

n.d.

n.d.

n.d.

31.6

17.3

n.d.

n.d.

n.d.

17.6

3.3

n.d.

n.d.

n.d.

5.8

0.2

n.d.

n.d.

0.1.

0.8

n.d.

n.d.

n.d.

n.d.

0.7

Hönniger Weiher

Diuron

m-CPDMU

DCPMU

Others

Total

92.0

n.d.

n.d.

n.d.

92.2

38.0

n.d.

n.d.

n.d.

38.0

28.1

0.1

n.d.

n.d.

29.9

23.0

1.5

0.2

n.d.

25.8

14.5

6.7

n.d.

n.d.

21.9

13.5

0.6

0.3

n.d.

14.7

10.3

2.3

0.4

n.d.

13.4

n.d.         not detected (> 0.2%)

Table 4b Distribution of radioactivity in the sediment phase

 

Incubation system

Molecule

Incubation day

0

7

14

28

55

91

120

River Erft

Diuron

m-CPDMU

DCPMU

Others

Total

8.2

n.d.

n.d.

n.d.

8.5

50.9

n.d.

n.d.

n.d.

51.1

57.9

n.d

0.4

n.d.

58.7

73.5

n.d

0.9

n.d.

75.0

47.3

n.d.

2.2

0.2

50.9

18.8

n.d.

4.4

n.d.

24.3

10.2

n.d.

3.5

0.5

15.6

Hönniger Weiher

Diuron

m-CPDMU

DCPMU

Others

Total

9.7

n.d.

n.d.

n.d.

9.9

57.5

n.d.

n.d.

n.d.

57.5

60.1

n.d.

0.3

1.6

62.1

57.7

5.0

1.1

n.d.

64.2

50.7

8.5

1.3

1.0

61.8

64.0

1.4

2.1

0.1.

67.6

60.2

3.1

3.7

0.6

68.6

n.d.         not detected (> 0.2%)

Table 5 Summary of quantification of Diuron and metabolites in Total water-sediment systems

 

Time

 

[%] of AR in the total water-sediment system of River Erft

 

Diuron

m-CPDMU

DCPMU

CO2

2 h

98.5

n.d.

n.d.

n.m.

7 d

94.1

n.d.

n.d.

0.1

14 d

87.7

n.d.

0.4

0.7

28 d

90.7

n.d.

0.9

0.6

55 d

50.6

n.d.

2.2

4.3

91 d

19.0

n.d.

4.4

22.3

120 d

10.2

n.d.

3.5

30.3

n.d.         not detected

n.m.        not measured

 

 

Time

 

[%] of AR in the total water-sediment system of Hönniger-Weiher

 

Diuron

m-CPDMU

DCPMU

CO2

2 h

101.7

n.d.

n.d.

n.m.

7 d

95.5

n.d.

n.d.

0.1

14 d

88.2

0.1

0.3

0.6

28 d

80.7

6.5

1.3

1.3

55 d

65.2

15.2

1.3

1.5

91 d

77.5

2.0

2.4

1.5

120 d

70.4

5.4

4.1

2.0

n.d.         not detected

n.m.        not measured

 

Executive summary:

A GLP Guideline study is available for this test substance using aqueous sediments collected from the River Erft (approx. 500 m before flow into the Rhine river), and from Hönniger Weiher Pond (an artificial dammed pond). Diuron was quickly eliminated from the water body, either by translocation into the sediment or by degradation. The calculated DT50values of Diuron for the supernatant water phase in both systems were 4 and 9 days, respectively for the Hönniger Weiher and River Erft. The radioactivity portion found in the sediments after 2 hours was about 9 to 11% of applied radioactivity indicating a rapid partitioning of Diuron into the sediments. Considering the total system, Diuron will be thoroughly degraded in the aquatic environment. The maximum rate of mineralization in the system Hönniger Weiher was 2% and in the system River Erft 30% (equivalent to CO2production). The DT50values for Diuron in the total systems were 48 and 232 days for River Erft or Hönniger Weiher, respectively. The only metabolite exceeding 10% of applied RA was identified as mCPDMU found in the Hönniger Weiher system with a maximum of 15.2% of AR 55 days after application

Description of key information

Diuron has to be regarded as a well dissipating compound from the water phase of water/sediment systems. Degradation from the sediment phase is slower but field conditions are likely to increase degradation rates further.

Key value for chemical safety assessment

Additional information

The dissipation from the water phase and the kinetics of metabolic breakdown of [phenyl-UL-14C]Diuron were studied in two water/sediment systems; the River Erft (approx. 500 m before flow into the Rhine river), and the Hönniger Weiher Pond (an artificial dammed pond).Diuron was quickly eliminated from the water body, either by translocation into the sediment or by degradation. The calculated DT50values of Diuron for the supernatant water phase in both systems were 4 and 9 days (9 and 19 days recalculated to 12 °C), respectively for the Hönniger Weiher and River Erft. The DT50values for Diuron in the total systems were 48 and 232 days (102 and 493 days recalculated to 12 °C) for River Erft or Hönniger Weiher, respectively. The metabolic results demonstrate the existence of two degradation pathways: In the one way demethylation to DCPMU (System River Erft and Hönniger Weiher) and in the other way dechlorination to m-CPDMU (Hönniger Weiher). The water/sediment systems tested showed differences in the metabolism of Diuron which may be explained by differences in the microbial status. Additional biological activities (plants) and light exposure will raise the degradation rates under field conditions (Sneikus, 2001).