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Environmental fate & pathways

Biodegradation in soil

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Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
2012
Report Date:
2012

Materials and methods

Test guidelineopen allclose all
Qualifier:
according to
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Deviations:
no
Qualifier:
according to
Guideline:
other: U.S. EPA Pesticide Assessment Guidelines Subdivision N, Series 162-1
Deviations:
no
Qualifier:
according to
Guideline:
other: Society for Environmental Toxicology and Chemistry-Europe (Procedures for Assessing the Environmental Fate and Ecotoxicology in Pesticides)
Deviations:
no
GLP compliance:
yes
Test type:
laboratory

Test material

Reference
Name:
Unnamed
Type:
Constituent
Test material form:
solid
Details on test material:
Purity: Not reported
Radiolabelling:
yes
Remarks:
Phenyl and Triazinel label

Study design

Oxygen conditions:
aerobic/anaerobic
Soil classification:
USDA (US Department of Agriculture)
Year:
2007
Soil propertiesopen allclose all
Soil no.:
#1
Soil type:
silty clay
% Clay:
43
% Silt:
57
% Sand:
0
% Org. C:
2.03
pH:
7.7
CEC:
16.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Soil no.:
#2
Soil type:
silty clay loam
% Clay:
41
% Silt:
59
% Sand:
0
% Org. C:
1.6
pH:
7.7
CEC:
17.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Soil no.:
#3
Soil type:
loam
% Clay:
25
% Silt:
46
% Sand:
29
% Org. C:
1.1
pH:
7.9
CEC:
1.03 meq/100 g soil d.w.
Bulk density (g/cm³):
1.2
Soil no.:
#4
Soil type:
loam
% Clay:
13
% Silt:
38
% Sand:
49
% Org. C:
1.6
pH:
7.5
CEC:
7.7 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Soil no.:
#5
Soil type:
sandy loam
% Clay:
11
% Silt:
20
% Sand:
69
% Org. C:
1.7
pH:
6.8
CEC:
7.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Duration of test (contact time)open allclose all
Soil No.:
#1
Duration:
120 d
Soil No.:
#2
Duration:
120 d
Soil No.:
#3
Duration:
120 d
Soil No.:
#4
Duration:
120 d
Soil No.:
#5
Duration:
120 d
Initial test substance concentration
Initial conc.:
0.4 mg/kg soil d.w.
Based on:
act. ingr.
Remarks:
For all soil types
Parameter followed for biodegradation estimation:
radiochem. meas.
Experimental conditionsopen allclose all
Soil No.:
#1
Temp.:
20 ± 2°C
Microbial biomass:
Initial: 40.6 mg C/100 g soil; at day 120: 16.9 mg C/100 g soil
Soil No.:
#2
Temp.:
20 ± 2°C
Microbial biomass:
Initial: 36.2 mg C/100 g soil; at day 120: 12.1 mg C/100 g soil
Soil No.:
#3
Temp.:
20 ± 2°C
Microbial biomass:
Initial: 18.7 mg C/100 g soil; at day 120: 9.4 mg C/100 g soil
Soil No.:
#4
Temp.:
20 ± 2°C
Microbial biomass:
Initial: 34.9 mg C/100 g soil; at day 120: 16.2 mg C/100 g soil
Soil No.:
#5
Temp.:
20 ± 2°C
Microbial biomass:
Initial: 19.3 mg C/100 g soil; at day 120: 8.0 mg C/100 g soil

Results and discussion

Material (mass) balanceopen allclose all
Soil No.:
#1
% Recovery:
14.19
Remarks on result:
other: Phenyl label
Soil No.:
#2
% Recovery:
28.26
Remarks on result:
other: Phenyl lablel
Soil No.:
#3
% Recovery:
7.54
Remarks on result:
other: Phenyl lablel
Soil No.:
#4
% Recovery:
9.71
Remarks on result:
other: Phenyl lablel
Soil No.:
#5
% Recovery:
16.2
Remarks on result:
other: Phenyl lablel
Soil No.:
#1
% Recovery:
14.81
Remarks on result:
other: Triazine label
Soil No.:
#2
% Recovery:
31.57
Remarks on result:
other: Triazine label
Soil No.:
#3
% Recovery:
17.66
Remarks on result:
other: Triazine label
Soil No.:
#4
% Recovery:
8.71
Remarks on result:
other: Triazine label
Soil No.:
#5
% Recovery:
15.08
Remarks on result:
other: Triazine label
Half-life / dissipation time of parent compoundopen allclose all
Key result
Soil No.:
#1
Half-life:
29.9 d
Type:
other: FOMC
Temp.:
20 °C
Key result
Soil No.:
#2
Half-life:
57.4 d
Type:
other: DFOP
Temp.:
20 °C
Key result
Soil No.:
#3
Half-life:
29.6 d
Type:
other: DFOP
Temp.:
20 °C
Key result
Soil No.:
#4
Half-life:
22.6 d
Type:
other: DFOP
Temp.:
20 °C
Key result
Soil No.:
#5
Half-life:
26.9 d
Type:
other: DFOP
Temp.:
20 °C
Transformation products:
yes
Remarks:
Nine transformation products that exceeded 5% of the applied radioacitivty at two sequential time points were observed in the study: IN-D5803, IN-A8768, IN-N7469, IN-N7468, IN-RXR81, IN-D5119, IN-B9161, IN-D7556, and IN-A9795.
Evaporation of parent compound:
no
Volatile metabolites:
yes
Remarks:
CO2

Any other information on results incl. tables

Mass balance was calculated as the percent of applied radioactivity (% AR) as presented in the table below. The extractability of DPX-A7881 decreased while the non-extractable residues (NER) increased as the study progressed. Non-extractable residues reached a peak at Day 120 for all systems ranging from 10.83-22.93%.

Volatile organics were produced in significant levels. For systems dosed with [phenyl-14C] DPX-A7881, the amount of 14CO2 evolved ranged from 25.47-51.59% AR whereas 14CO2 evolved from the triazine systems ranged from 0.96-11.92% AR. The amounts of CaCl2 and organic extractable and mineralized radioactivity in each system for Day 120 samples are summarized in the following table.

Soil
(texture)

A7881 Label

Extractable with CaCl2 at Day 120 (%AR)

Extractable with Organic Solvents at Day 120
(%AR)

NER at Day 120
(%AR)

Evolved 14CO2 at Day 120
(%AR)

Overall Mean Mass Balance (%AR)

Lleida
(Silty Clay)

Phenyl

2.7

14.67

22.7

51.59

96.89± 5.11

Triazine

7.6

62.41

22.93

1.37

98.48±1.74

Tama
(Silty Clay )

Phenyl

5.92

50.45

14.88

25.47

100.14±2.91

Triazine

2.55

76.34

18.68

0.96

98.90±1.19

Gross-Umstadt (Loam)

Phenyl

15.82

20.03

17.99

46.33

99.61±1.69

Triazine

24.51

55.21

13.28

8.17

100.52±2.40

Nambsheim(Loam)

Phenyl

30.17

27.84

13.37

34.23

100.99±3.42

Triazine

25.07

47.51

12.79

11.92

100.01±1.87

Sassafras
No. 16 (Sandy Loam)

Phenyl

8.05

19.47

19.46

35.42

93.48±7.74

Triazine

21.51

62.32

10.83

3.05

99.73±0.95

A summary of the amount of test substance and major and minor transformation products at the termination time point and the maximum amount reached for each is presented in the following tables.

Nine transformation products that exceeded 5% of the applied radioacitivty at two sequential time points were observed in the study: IN-D5803, IN-A8768, IN-N7469, IN-N7468, IN-RXR81, IN-D5119, IN-B9161, IN-D7556, and IN-A9795.

% AR Observed on Day 120, Phenyl Label

Component

Lleida

Tama

Gross-Umstadt

Nambsheim

Sassafras No. 16

Test substance

14.19

28.26

7.54

9.71

16.2

IN‑A8768

ND

15.42

21.6

36.63

11.3

IN‑N7469

ND

NA

2.51

2.30

ND

IN‑N7468

1.75

1.31

ND

ND

ND

IN‑RXR81

ND

ND

< 5.0

3.01

< 5.0

IN‑D5803

NA

ND

NA

2.89

ND

IN‑D5119

1.44

ND

2.22

1.48

ND

ND = Not detected, NA = Not applicable, metabolite was not found in this test system. IN-RXR81 is shown as < 5.0 since it was not reported independently, but reported in the sum of “Other” metabolites that accounted for < 5 % A.R

% AR Observed on Day 120, Triazine Label

Component

Lleida

Tama

Gross-Umstadt

Nambsheim

Sassafras No. 16

Test substance

14.81

31.57

17.66

8.71

15.08

IN‑A8768

ND

7.90

3.51

3.50

9.52

IN‑N7469

3.63

NA

8.25

20.06

5.77

IN‑N7468

1.02

2.11

2.09

ND

1.79

IN‑RXR81

ND

ND

< 5.0

6.14

< 5.0

IN‑B9161

43.81

11.87

27.59

18.72

23.35

IN‑D7556

6.74

21.75

11.68

9.06

25.90

IN‑A9795

ND

ND

1.36

4.70

0.00

ND = Not detected, NA = Not applicable, metabolite was not found in this test system. IN-RXR81 is shown as < 5.0 since it was not reported independently, but reported in the sum of “Other” metabolites that accounted for < 5 % A.R

Maximum % AR, Phenyl Label

Component

Lleida

Tama

Gross-Umstadt

Nambsheim

Sassafras No. 16

Test substance

93.70 (Day 0)

89.85 (Day 0)

95.06 (Day 0)

97.47 (Day 0)

95.12 (Day 0)

IN‑A8768

4.99 (Day 13)

15.42 (Day 120)

28.48 (Day 90)

33.63 (Day 120)

13.84 (Day 64)

IN‑N7469

1.05 (Day 64)

ND

2.96 (Day 41)

6.51 (Day 64)

1.49 (Day 41)

IN‑N7468

3.57 (Day 41)

3.67 (Day 13)

3.8 (Day 41)

7.04 (Day 13)

5.14 (Day 20)

IN‑RXR81

*

*

*

4.83 (Day 64)

*

IN‑D5803

NA

8.02 (Day 90)

1.94

2.88 (Day 90)

0.93 (Day 14)

IN‑D5119

3.34 (Day 41)

2.56 (20)

2.74 (Day 13)

5.24 (Day 90)

5.95 (Day 41)

ND = Not detected, NA = Not applicable, metabolite was not found in this test system, * = exact quantification of IN-RXR81 is not available for every sampling point, but in all instances the metabolite accounted for < 5 % A.R.

Maximum % AR, Triazine Label

Component

Lleida

Tama

Gross-Umstadt

Nambsheim

Sassafras No. 16

Test substance

92.54 (Day 0)

94.73 (Day 0)

94.82 (Day 0)

98.00 (Day 0)

94.51 (Day 0)

IN‑A8768

4.95 (Day 7)

9.86 (Day 90)

22.77 (Day 90)

22.46 (Day 64)

23.17 (Day 64)

IN‑N7469

4.64 (Day 90)

ND

8.25 (Day 120)

20.06 (Day 120)

5.77 (Day120)

IN‑N7468

7.55 (Day 41)

11.43 (Day 41)

6.38 (Day 20)

7.66 (Day 64)

12.28 (Day 41)

IN‑RXR81

*

*

*

9.15 (Day 90)

*

IN‑B9161

59.01 (Day 90)

14.37 (Day 64)

27.59 (Day 120)

18.72 (Day 120)

25.61 (Day 90)

IN‑D7556

7.66 (Day 90)

21.75 (Day 120)

11.68 (Day 120)

9.06 (Day 120)

25.90 (Day 120)

IN‑A9795

2.28 (Day 20)

7.04 (Day 41)

9.04 (Day 41)

4.7 (Day 120

12.13 (Day 41)

ND = Not detected, NA = Not applicable, metabolite was not found in this test system, * = exact quantification of IN-RXR81 is not available for every sampling point, but in all instances the metabolite accounted for < 5 % A.R.

Soil

Model

DT50

DT90

chi² error

Lleida

FOMC

29.9

153.7

3

0.987

Tama

DFOP

57.4

320.4

4

0.975

Gross-Umstadt

DFOP

29.6

118.7

3

0.985

Nambsheim

DFOP

22.6

111.2

3

0.986

Sassafras
No. 16

DFOP

26.9

145.8

5

0.979

The r² value reported in this table was calculated using the formula for model efficiency in the FOCUS (2006) guidance.

A summary of the desorption coefficient results at zero time and Day 64 are summarized for each soil type in the following table:

Soil Name

at Zero Time

At (Day 64)

Change in Kd, des From Day 0

Kd des

Kom des

Koc des

Kd des

Kom des

Koc des

PH-Lleida

0.52

14.83

25.57

7.35

210

362

14.2

PH-Tama

2.72

82.29

142

48.53

1471

2535

17.9

PH-Gross-Umstadt

0.33

17.22

29.53

3.32

175

302

10.2

PH-Nambsheim

0.34

12.31

21.22

3.70

132

228

10.7

PH-Sassafras No. 16

1.12

38.69

66.70

6.14

212

365

5.5

TR-Lleida

0.51

14.65

25.26

9.14

261

450

17.6

TR-Tama

2.62

79.26

137

100

3044

5248

38.4

TR-Gross-Umstadt

0.37

19.44

33.52

3.77

198

342

10.2

TR-Nambsheim

0.36

12.87

22.18

2.33

83.36

144

6.5

TR-Sassafras No. 16

1.07

37.00

63.80

7.19

248

427

6.7

* (Day 64) was chosen as Kd des values generally decreased for Day 90 and 120 due to an artifact that was caused by very low concentrations of DPX A7881 in the soil.

Applicant's summary and conclusion

Conclusions:
The test substance would extensively degrade to a number of metabolite products and become less prone to movement with soil water in aerobic soils.
Executive summary:

The rate of degradation and sorption of carbon-14 labeled test substance was studied in five soils according to U.S. EPA, Pesticide Assessment Guidelines, Subdivision N, 162-1 and, OECD Guideline 307, and in compliance with the GLP standards of the United States Environmental Protection Agency. The five soils were either sandy loam, loam, or silty clay, differing significantly in their sand and clay content.

The study was conducted at 20 ± 2°C in the dark for 120 days. The moisture content of the soils was maintained between 40 and 60% MWHC (close to 75% water holding capacity at 0.33 bar). The test substance used was labeled separately in two portions, the triazine and the phenyl group. The test substance was radiolabelled at stable positions and allowed detection of all significant degradation products. The test substance was applied to each soil at a nominal rate of 0.4 µg/g soil.

Nine transformation products that exceeded 5% of the applied radioacitivty at two sequential time points were observed in the study: IN-D5803, IN-A8768, IN-N7469, IN-N7468, IN-RXR81, IN-D5119, IN-B9161, IN-D7556, and IN-A9795.

The %AR for the test substance observed on Day 120 for the phenyl label ranged from 7.54 to 28.26 and from 8.71 to 31.57 for the triazine label. There were higher %AR of IN-A8768 for the phenyl label and higher amounts of %AR of IN-N7469 for the triazine label. Low levels of %AR of IN-D5803 and IN-D5119 were found for the phenyl systems and IN-A9795 for the triazine system. For the triazine system, IN-B9161 ranged from 11.87-43.81 %AR and D7556 ranged from 6.74 to 25.90 %AR. The levels of IN-RXR81 exceeded 5%AR in more than two sampling points for the triazine label in the Nambsheim soil. The chromatograms in the study records were reviewed for occurrences of this metabolite in the other four soils as well. The review revealed that IN-RXR81 never exceeded 5%AR in the Lleida, Tama, Gross-Umstadt or Sassafras soils.

The DT50 and DT90 of the test substance were calculated using the simple first-order (SFO), first-order multi-compartment (FOMC), Hockey Stick (HS), and Double First Order Parallel (DFOP) models using Model Maker for Focus Kinetics (Focus 2006). The multi-compartment models provided best fit to the observed data across all soils. The residual values were more randomly distributed and the chi² error value was lower compared to the other models.

The desorption coefficient, Kd, des, of [14C]-test substance was calculated for each soil and label at each sampling interval using the amount of test substance extracted in CaCl2 and the soil concentration. Kom, des and Koc, des are calculated from the Walkley-Black method. The Kd des in the fourth column represents the highest Kd established throughout the study. Beyond the day in parentheses no further increase was observed. The concentration of parent test substance was so low in the soil phase that the decreasing Kd des represents an artifact. No Kd des was calculated when test substance had completely degraded.

The sorption of [14C]-test substance increased over time and subsequently its potential for mobility decreased.

Based on the results of this study, The test substance would extensively degrade to a number of metabolite products, including CO2, and become less prone to movement with soil water in aerobic soils.