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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Remarks:
The test substance 1,3-Diisopropylnaphthalene (1,3-DIPN; CAS-No.: 57122-16-4) represents one constituent (isomer) of the registered substance bis(isopropyl)naphthalene (DIPN, CAS-No.: 38640-62-9).
Adequacy of study:
weight of evidence
Study period:
18 Mar 2019 - 20 Feb 2020
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: guideline study
Remarks:
Based on volatility of the test item biodegradability in surface water cannot be finally assessed under OECD 309 test conditions. However, the results contribute to the persistence assessment of DIPN within a weight of evidence approach.
Qualifier:
according to
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Version / remarks:
2004
GLP compliance:
yes (incl. certificate)
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on source and properties of surface water:
Details on collection:
- Location: Aalkistensee, a natural aerobic surface water source (75433 Maulbronn, Germany, 48°59’37.439’’N, 8°45’25.714’’E)
- Sampling procedure: Water was sampled from the top 5 to 10 cm of the natural resource and transported in polyethylene containers to the laboratory.
- Date of sampling: 23 Jul 2019
- Prior to use, coarse particles were removed by filtration through a filter with 100 µm mesh size.

Characteristics of the water at time of collection:
- Temperature [°C]: 24.9°C
- pH at time of collection: 7.97
- Redox potential [mv]: 250
- Oxygen concentration [mg/l]: 8.6

Characteristics of the water at study start:
- pH at time of collection: 8.44
- Total Organic Carbon (TOC) [mg/L]: 8.9
- Dissolved Organic Carbon (DOC) [mg/L]: 8.7
- Total nitrogen [mg/L]: 50
- Total phosphorus [mg/L]: <0.02
- Total ammonium [mg/L]: 59
- Total nitrite [mg/L]: 22
- Total nitrate [mg/L]: 0.65
- Dissolved Orthophosphate [mg/L]: <0.01
- Biological Oxygen Demand (BOD) [mg/L O2]: 6.7
Duration of test (contact time):
63 d
Initial conc.:
10.2 µg/L
Based on:
test mat.
Initial conc.:
51.3 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
test mat. analysis
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 1000 mL all-glass metabolism flasks
- Composition of medium: natural freshwater
- Test temperature: 12°C (11.9 – 13.3 °C)
- pH: 7.5-8.4
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Each vessel was equipped with an open trap system, a stack containing different layers of adsorbing materials.
- The organic volatiles were trapped by polyurethane foam as adsorbent.
- The carbon dioxide was trapped by a soda lime layer.
- Number of culture flasks/concentration: 20 (14/conc. were analysed; 6 flask reserve)
- Sterile samples: 6
- Reference samples with sodium bezoate: 8
- Blank controls with solvent: 2
- Method used to create aerobic conditions: slightly constant orbital movement and constant air flow

SAMPLING
- Sampling frequency: 0, 2, 7, 14, 21, 33 and 63 days
- Sampling sterile control: 19 days
- Sampling reference substance: 0 and 10 days
- pH and oxygen measurement: once a week

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION CONTROL AND BLANK SYSTEM
- Sterile control: treated with 51.3 μg/L [14C] test item
- References: treated with 10 μg/L [14C] sodium benzoate and additional the highest amount of solvent
- Blanks: treated with the highest amount of solvent
Reference substance:
benzoic acid, sodium salt
Compartment:
natural water: freshwater
Remarks on result:
other: 91-107% Recovery
Remarks:
Sum of evaporated test item and test item in the whater phase.
% Degr.:
0
Parameter:
CO2 evolution
Sampling time:
63 d
Compartment:
natural water: freshwater
DT50:
>= 1.43 - <= 1.58 d
Type:
other: Best fit model for the kinetic analysis: Double first order in parallel kinetic model (DFOP) for the lower concentration (10.2 µg/L) and first order multi compartment kinetic model (FOMC) for the higher concentration (51.3 µg/L)
Temp.:
12 °C
Remarks on result:
other: only dissipation from water phase (DisT50) caused by volatility / no biodegradation occured
Transformation products:
no
Evaporation of parent compound:
yes
Remarks:
traped with PU foam
Volatile metabolites:
no
Residues:
no
Details on results:
The majority of radioactivity was found in the toluene extract after extraction of the water phase. The radioactivity extractable from the water phase dosed with the low concentration accounted for 92.2 % at the test start and 2.9 % AR at the test end. For the high concentration the extractable radioactivity amounted to 90.3 % AR after dosing and 2.9 % AR after 63 days of incubation. The radioactivity remaining in the water phase did not exceed 3.0 % AR for both concentrations throughout the study.
The radioactivity extracted from the water phase was analysed by GC-MS for [14C]1,3-DIPN. Results confirmed the data obtained by LSC measurement. Thus, the radioactivity found in the extract consisted of the [14C]1,3-DIPN only.
The organic volatiles have been analysed by GC-MS as well. And it was confirmed that the trapped radioactivity consisted of [14C]1,3-DIPN, only.
No degradation products were detected in the course of the study.
Results with reference substance:
The test system was validated with the reference substance sodium benzoate. After 10 days 88.4 % AR of the reference item was mineralised. Thus, the system was biologically active.

Distribution of the radioactivity between test water, carbon dioxide and organic volatiles in % of the applied radioactivity (AR) for the test concentration of 10.2 µg/L:

Sampling interval [days]

0

2

7

14

21

33

63

 

% AR

Toluene phase*

92.9

34.6

11.3

5.1

4.1

3.1

2.6

91.5

36.9

8.7

5.0

4.1

3.0

3.2

mean

92.2

35.7

10.0

5.1

4.1

3.0

2.9

Water phase

0.6

1.9

2.1

1.5

1.4

1.4

1.4

1.0

2.8

1.6

1.5

1.4

1.5

1.8

mean

0.8

2.4

1.9

1.5

1.4

1.5

1.6

Water + Toleuene

(= Total Water)

93.5

36.5

13.4

6.6

5.5

4.5

4.0

92.5

39.7

10.3

6.5

5.5

4.5

5.0

mean

93.0

38.1

11.9

6.6

5.5

4.5

4.5

Carbon dioxide
(Soda Limes)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

mean

0

0

0

0

0

0

0

Organic volatiles*

n.a.

61.4

79.9

97.3

95.0

86.1

102.9

n.a.

64.3

90.4

94.5

95.0

88.8

103.0

mean

n.a.

62.8

85.2

95.9

95.0

87.4

102.9

Recovery

93.5

97.9

93.4

103.9

100.6

90.6

107.0

92.5

104.0

100.8

101.1

100.5

93.3

107.9

mean

93.0

100.9

97.1

102.5

100.5

91.9

107.4

Distribution of the radioactivity between test water, carbon dioxide and organic volatiles in % of the applied radioactivity (AR) for the test concentration of 51.3 µg/L:

Sampling interval [days]

0

2

7

14

21

33

63

 

% AR

Toluene phase*

91.7

45.3

11.9

7.0

5.9

3.9

3.0

88.9

34.7

21.2

6.3

5.2

4.4

2.9

mean

90.3

40.0

16.6

6.6

5.5

4.1

2.9

Water phase

0.6

3.7

2.5

1.3

1.6

1.6

1.2

1.1

2.4

2.6

1.3

1.4

1.9

1.4

mean

0.8

3.0

2.6

1.3

1.5

1.8

1.3

Water + Toleuene

(= Total Water)

92.3

49.0

14.4

8.3

7.5

5.5

4.2

90.0

37.1

23.8

7.6

6.6

6.3

4.3

mean

91.1

43.0

19.2

7.9

7.0

5.9

4.3

Carbon dioxide
(Soda Limes)

0

0

0

0

0

0

0

0

0

0

0

0

0

0

mean

0

0

0

0

0

0

0

Organic volatiles*

n.a.

39.1

84.9

84.1

90.9

87.0

99.3

n.a.

52.0

72.3

86.5

90.7

88.6

102.8

mean

n.a.

45.6

78.6

85.3

90.8

87.8

101.0

Recovery

92.3

88.1

99.3

92.4

98.3

92.5

103.4

90.0

89.1

96.1

94.1

97.3

94.9

107.0

mean

91.2

88.6

97.7

93.3

97.8

93.7

105.2

For further details on results please see attached study report.

Validity criteria fulfilled:
yes
Conclusions:
Organic volatiles increased during incubation to maximum amounts of 102.9 % AR (low concentration) and 101.0 % AR (high concentration). The dissipation time of 1,3-DIPN from water phase was short (DisT50 < 2 days). Therefore, it can be concluded that 1,3-DIPN is rapidly evaporating from the water phase into the atmosphere. Since no CO2 was observed and no metabolites were detected the test substance can be considered as stable under the OECD 309 test conditions.
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Remarks:
The test substance 1,4-Diisopropylnaphthalene (1,4-DIPN; CAS-No.: 24157-79-7) represents one constituent (isomer) of the registered substance bis(isopropyl)naphthalene (DIPN, CAS-No.: 38640-62-9).
Adequacy of study:
weight of evidence
Study period:
17 Feb 2020 - 02 Jul 2020
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: guideline study
Remarks:
Based on volatility of the test item biodegradability in surface water cannot be finally assessed under OECD 309 test conditions. However, the results contribute to the persistence assessment of DIPN within a weight of evidence approach.
Qualifier:
according to
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Version / remarks:
2004
GLP compliance:
yes (incl. certificate)
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
natural water: freshwater
Details on source and properties of surface water:
Details on collection:
- Location: Aalkistensee, a natural aerobic surface water source (75433 Maulbronn, Germany, 48°59’37.439’’N, 8°45’25.714’’E)
- Sampling procedure: Water was sampled from the top 5 to 10 cm of the natural resource and transported in polyethylene containers to the laboratory.
- Date of sampling: 03 Mar 2020
- Prior to use, coarse particles were removed by filtration through a filter with 100 µm mesh size.

Characteristics of the water at time of collection:
- Temperature [°C]: 7.4°C
- pH at time of collection: 7.74
- Redox potential [mv]: 204
- Oxygen concentration [mg/l]: 9.22 - 9.44

Characteristics of the water at study start:
- pH at time of collection: 7.83
- Total Organic Carbon (TOC) [mg/L]: 9.6
- Dissolved Organic Carbon (DOC) [mg/L]: 8.6
- Total nitrogen [mg/L]: 3.3
- Total phosphorus [mg/L]: <0.02
- Total ammonium [mg/L]: 1.0
- Total nitrite [mg/L]: 0.06
- Total nitrate [mg/L]: 6.7
- Dissolved Orthophosphate [mg/L]: 0.03
- Biological Oxygen Demand (BOD) [mg/L O2]: 3.3
Duration of test (contact time):
61 d
Initial conc.:
10.5 µg/L
Based on:
test mat.
Initial conc.:
53.7 µg/L
Based on:
test mat.
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
test mat. analysis
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: 1000 mL all-glass metabolism flasks
- Composition of medium: natural freshwater
- Test temperature: 12°C (11.3 – 13.4 °C)
- pH: 7.8-8.6
- pH adjusted: no
- Continuous darkness: yes

TEST SYSTEM
- Each vessel was equipped with an open trap system, a stack containing different layers of adsorbing materials.
- The organic volatiles were trapped by polyurethane foam as adsorbent.
- The carbon dioxide was trapped by a soda lime layer.
- Number of culture flasks/concentration: 20 (14/conc. were analysed; 6 flask reserve)
- Sterile samples: 6
- Reference samples with sodium bezoate: 8
- Blank controls with solvent: 2
- Method used to create aerobic conditions: slightly constant orbital movement and constant air flow

SAMPLING
- Sampling frequency: 0, 2, 7, 14, 21, 30 and 61 days
- Sampling sterile control: 14 days
- Sampling reference substance: 0 and 7 days
- pH and oxygen measurement: once a week

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION CONTROL AND BLANK SYSTEM
- Sterile control: treated with 53.7 μg/L [14C] test item
- References: treated with 26.3 μg/L [14C] sodium benzoate and additional the highest amount of solvent
- Blanks: treated with the highest amount of solvent
Reference substance:
benzoic acid, sodium salt
Compartment:
natural water: freshwater
Remarks on result:
other: 83.5-103.3% Recovery
Remarks:
Sum of evaporated test item and test item in the whater phase.
% Degr.:
0.1
Parameter:
CO2 evolution
Sampling time:
61 d
Compartment:
natural water: freshwater
DT50:
>= 1.46 - <= 1.79 h
Type:
other: First order multi compartment kinetic model (FOMC)
Temp.:
12 °C
Remarks on result:
other: only dissipation from water phase (DisT50) caused by volatility / no biodegradation occured
Transformation products:
no
Evaporation of parent compound:
yes
Remarks:
traped with PU foam
Volatile metabolites:
no
Residues:
no
Details on results:
The majority of radioactivity was found in the toluene extract after extraction of the water phase. The radioactivity extractable from the water phase dosed with the low concentration accounted for 101.2 % at the test start and 5.2 % AR at the test end. For the high concentration the extractable radioactivity amounted to 101.1 % AR after dosing and 1.3 % AR after 61 days of incubation. The radioactivity remaining in the water phase did not exceed 3.3 % AR for both concentrations throughout the study.
The radioactivity extracted from the water phase was analysed by GC-MS for [14C]1,4-DIPN. Results confirmed the data obtained by LSC measurement. Thus, the radioactivity found in the extract consisted of the [14C]1,4-DIPN only.
The organic volatiles have been analysed by GC-MS as well. And it was confirmed that the trapped radioactivity consisted of [14C]1,4-DIPN, only.
No degradation products were detected in the course of the study.
Results with reference substance:
The test system was validated with the reference substance sodium benzoate. After 7 days 69.1 % AR of the reference item was mineralised. Thus, the system was biologically active.

Distribution of the radioactivity between test water, carbon dioxide and organic volatiles in % of the applied radioactivity (AR) for the test concentration of 10.5 µg/L:

Sampling interval [days]

0

2

7

14

21

30

61

 

% AR

Toluene phase*

102.8

42.6

18.3

10.8

7.2

9.8

4.8

99.6

43.7

27.2

10.3

7.5

9.2

5.6

mean

101.2

43.2

22.8

10.6

7.4

9.5

5.2

Water phase

1.5

3.0

1.8

2.0

2.2

3.2

1.9

2.1

3.0

2.6

2.7

2.5

3.1

2.1

mean

1.8

3.0

2.2

2.4

2.3

3.1

2.0

Water + Toluene

(= Total Water)

104.3

45.6

20.1

12.9

9.4

13.0

6.6

101.7

46.7

29.8

13.0

10.0

12.2

7.7

mean

103.0

46.2

25.0

12.9

9.7

12.6

7.2

Carbon dioxide
(Soda Limes)

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.0

0.1

mean

0.0

0.0

0.0

0.0

0.0

0.0

0.1

Organic volatiles

n.a.

45.8

71.9

72.2

86.9

70.2

76.2

n.a.

39.1

62.6

83.3

67.4

81.7

79.1

mean

n.a.

42.4

67.2

77.8

77.1

76.0

77.7

Recovery

104.3

91.4

92.0

85.1

96.2

83.2

82.8

101.7

85.8

92.5

96.2

77.3

93.9

86.9

mean

103.0

88.6

92.2

90.7

86.8

88.6

84.9

Distribution of the radioactivity between test water, carbon dioxide and organic volatiles in % of the applied radioactivity (AR) for the test concentration of 53.7 µg/L:

Sampling interval [days]

0

2

7

14

21

30

61

 

% AR

Toluene phase*

100.5

44.5

26.3

10.0

3.6

7.7

1.6

101.7

47.1

26.4

8.8

7.4

7.2

1.0

mean

101.1

45.8

26.3

9.4

7.4

7.4

1.3

Water phase

1.6

3.6

3.5

3.6

1.1

2.6

1.8

2.7

2.5

3.1

2.8

2.7

2.4

1.2

mean

2.2

3.0

3.3

3.2

2.7

2.5

1.5

Water + Toluene

(= Total Water)

102.1

48.0

29.8

13.6

4.7

10.3

3.4

104.5

49.6

29.5

11.7

10.2

9.6

2.2

mean

103.3

48.8

29.6

12.6

10.2

9.9

2.8

Carbon dioxide
(Soda Limes)

0.0

0.0

0.0

0.0

0.0

0.0

0.1

0.0

0.0

0.0

0.0

0.0

0.0

0.2

mean

0.0

0.0

0.0

0.0

0.0

0.0

0.1

Organic volatiles

n.a.

43.6

60.1

66.9

22.4

81.4

80.1

n.a.

40.1

59.4

78.6

86.5

88.8

63.2

mean

n.a.

41.8

59.8

72.7

86.5

85.1

71.6

Recovery

102.1

91.6

89.9

80.4

27.1*

91.7

83.5

104.5

89.6

88.9

90.3

96.7

98.4

65.6*

mean

103.3

90.6

89.4

85.3

96.7

95.0

83.5

For further details on results please see attached study report.

Validity criteria fulfilled:
yes
Conclusions:
Organic volatiles increased during incubation to maximum amounts of 77.8 % AR (low concentration) and 86.5 % AR (high concentration). The dissipation time of 1,4-DIPN from water phase was short (DisT50 < 2 hours). Therefore, it can be concluded that 1,4-DIPN is rapidly evaporating from the water phase into the atmosphere. Since only a negligible amount of CO2 formed and no metabolites were detected the test substance can be considered as stable under the OECD 309 test conditions.
Endpoint:
biodegradation in water: sediment simulation testing
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:
other:
Transformation products:
no
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
(Q)SAR
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
results derived from a valid (Q)SAR model and falling into its applicability domain, with adequate and reliable documentation / justification
Justification for type of information:
1. SOFTWARE
Vega version 1.1.4

2. MODEL (incl. version number)
Persistence in sediment Model version 1.0.0

3. SMILES OR OTHER IDENTIFIERS USED AS INPUT FOR THE MODEL
See “Test material information”

4. SCIENTIFIC VALIDITY OF THE (Q)SAR MODEL
See attached information on the model provided by the developer. Further information on the OECD criteria as outlined by the applicant is provided below under "Any other information of materials and methods incl. tables"

5. APPLICABILITY DOMAIN
See attached information and information as provided in "Any other information on results incl. tables".

6. ADEQUACY OF THE RESULT
See assessment of adequacy as outlined in the "Overall remarks, attachments" section.
Qualifier:
according to
Guideline:
other: REACH Guidance on QSARs R.6
Principles of method if other than guideline:
- Software tool(s) used including version: Vega v1.1.4
- Model(s) used: Persistence in sediment Model version 1.0.0

Full reference and details of the used formulas can be found in:
A. Manganaro, F. Pizzo, A. Lombardo, A. Pogliaghi, E. Benfenati, “Predicting persistence in the sediment compartment with a new automatic software based on the k-Nearest Neighbor (k-NN) algorithm”, Chemosphere (2015), accepted paper.
Gouin, T., Cousins, I., Mackay, D., “Comparison of two methods for obtaining degradation halflives”, Chemosphere 56, 2004, 531-535
Gramatica, P., Papa, E., “Screening and ranking of POPs for Global Half-Life: QSAR approaches for prioritization based on molecular structure”, Environ. Sci. Technol. 41, 2007, 2833-9.

- Model description: see field 'Justification for non-standard information', 'Attached justification' and 'any other information on Material and methods'
- Justification of QSAR prediction: see field 'Justification for type of information', 'Attached justification' and/or 'overall remarks'
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
aerobic
Remarks on result:
other: DIPN was predicted to be P/vP
Transformation products:
not specified

For detailed information on the results please refer to the attached report.

Validity criteria fulfilled:
not applicable

Description of key information

Bis(isopropyl)naphthalene (DIPN) is an isomeric mixture, which consist of seven isomers (1,3-, 1,4-, 1,5-, 1,6-, 2,6- and 2,7-DIPN). Biodegradation potential differs between the isomers.

The isomers 1,3-DIPN and 1,4-DIPN which were less degradable on screening test level were also stable in surface water simulation tests according to OECD 309 (Eurofins, 2020). However, based on volatility the dissipation time from water phase was very short. The determined DisT50 values were below 2 days indicating a rapid evaporation from the water phase, which means that the results of the OECD 309 studies are not sufficient for a final persistence assessment. Therefore, QSAR estimates for the degradation in the compartments sediment and soil considered additional in a weight of evidence approach. For degradation in sediment the QSAR prediction is persistent (P) and/or very persistent (vP). Based on study results and QSAR estimates, it can be assumed that bis(isopropyl)naphthalene (CAS 38640-62-9) contains persistent and/or very persistent isomers. Therefore, the isomeric mixture bis(isopropyl)naphthalene (CAS 38640-62-9) needs to be assessed as potentially persistent (P) and/or very persistent (vP). No substantial new findings can be expected from further simulation tests with DIPN isomers. Therefore, further testing is not intended.

Key value for chemical safety assessment

Additional information

Bis(isopropyl)naphthalene (DIPN) is an isomeric mixture, which consist of seven isomers (1,3-, 1,4-, 1,5-, 1,6-, 2,6- and 2,7-DIPN). Aerobic mineralization in surface water was investigated for the isomers 1,3-DIPN (CAS 57122-16-4) and 1,4-DIPN (CAS 24157-79-7), which turned out in biodegradation screening tests to be less biodegradable than the other isomers of the mixture. Additionally persistence in sediment and soil was estimated by reliable QSAR calculation. Study results on aerobic mineralisation of the isomers 1,3-DIPN and 1,4 -DIPN together with QSAR results on degradation of DIPN in sediment and soil were used in a weight of evidence approach for the persistence assessment of the registered DIPN isomeric mixture (CAS 38640-62-9).

Aerobic mineraliation in surface water (simulation tests according to OECD 309 with the isomers 1,3 -DIPN and 1,4 -DIPN)

The surface water studies were conducted according to OECD 309 guideline under aerobic conditions with natural water and at a temperature of 12°C. Carbon 14 ring-labelled 1,3-DIPN and 1,4-DIPN was used as test item. The tests were performed with two different application rates for each isomer in a static system using 1000 mL all-glass metabolism flasks. Each vessel was equipped with an open trap system. The organic volatiles were trapped by polyurethane foam as adsorbent. The carbon dioxide was trapped by a soda lime layer.

The incubation period after treatment was 61 days for the test with 1,4-DIPN and 63 days for the test with 1,3-DIPN. In both tests duplicate samples were taken for analysis at 7 time points after application. The water phase was extracted with toluene immediately after sampling. The radioactivity in the toluene phase and in the water phase was quantified by liquid scintillation counting. Furthermore, the PU foam, used as trap for organic volatiles, was extracted with acetone. The organic extracts (toluene and acetone) were analyzed by GC-MS to confirm the results obtained by characterization of radioactivity.

The radioactivity in the water phase decreased in the course of the study from application to the end of the test duration from 103.0 – 103.3 % AR to 2.8 - 7.2 % AR for 1,4-DIPN and from 91.2 – 93.0 % AR to 4.3 - 4.5 % AR for 1,3-DIPN. Conversely the organic volatiles increased during incubation to maximum amounts of 77.8 - 86.5 % AR for 1,4-DIPN and 101.0 – 102.9 % AR for 1,3-DIPN. The resulting dissipation times (DisT50 values) from water phase were below 2 days. Therefore, it can be concluded that both isomers rapidly evaporate from the water phase. Since only a negligible amount of CO2 (0 – 0.1% AR) was formed during the test and no metabolites occurred both isomers can be considered as stable under the OECD 309 test condition.

QSAR predictions for DIPN degradation in sediment

For the prediction of the persistence of DIPN in sediment/water systems the VEGA 1.1.4 “Persistence sediment model” (IRFMN) 1.0.0 was used. DIPN falls within the applicability of the model and the performance of the model on similar molecules is good. The prediction is persistent (P) and/or very persistent (vP). The QSAR estimate is considered to be valid and is used as information within a weight of evidence approach for the persistency assessment of the substance.