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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:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
according to guideline
Guideline:
other: BBA Guideline Part IV, Section 4-1
Deviations:
no
GLP compliance:
no
Test type:
laboratory
Specific details on test material used for the study:
- Name of substance: Quinoline labeled 14C-quinoxyfen; phenyl and 2-quinoline labeled quinoxyfen
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
loamy sand
% Clay:
5
% Silt:
9
% Sand:
86
% Org. C:
3.9
pH:
6.1
CEC:
10 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy clay loam
% Clay:
25
% Silt:
21
% Sand:
54
% Org. C:
25.1
pH:
7.5
CEC:
44 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
clay loam
% Clay:
30
% Silt:
27
% Sand:
43
% Org. C:
3.71
pH:
7.8
CEC:
24 meq/100 g soil d.w.
Soil no.:
#4
Soil type:
sandy loam
% Clay:
11
% Silt:
10
% Sand:
79
% Org. C:
5.03
pH:
4.2
CEC:
15 meq/100 g soil d.w.
Soil no.:
#5
Soil type:
loamy sand
% Clay:
5
% Silt:
8
% Sand:
87
% Org. C:
2.8
pH:
5.6
CEC:
8.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.17
Soil no.:
#6
Soil type:
sandy clay loam
% Clay:
31
% Silt:
22
% Sand:
47
% Org. C:
3.4
pH:
7.4
CEC:
19.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.16
Soil no.:
#7
Soil type:
sandy loam
% Clay:
17
% Silt:
20
% Sand:
63
% Org. C:
1.7
pH:
7.6
CEC:
8.3 meq/100 g soil d.w.
Bulk density (g/cm³):
1.2
Soil no.:
#8
Soil type:
clay
% Clay:
47
% Silt:
20
% Sand:
33
% Org. C:
3
pH:
7.1
CEC:
20.8 meq/100 g soil d.w.
Bulk density (g/cm³):
1.18
Duration:
200 d
Duration:
124 d
Initial conc.:
250 g/ha d.w.
Based on:
act. ingr.
Remarks:
in the first study
Initial conc.:
15.4 other: µg of phenyl labeled test substance
Based on:
other: maximum single label application rate of 300 g a.i. per ha
Remarks:
in the second study
Initial conc.:
15.4 other: µg of 2-quinoline labeled test substance
Based on:
other: maximum single label application rate of 300 g a.i. per ha
Remarks:
in the second study
Parameter followed for biodegradation estimation:
radiochem. meas.
Temp.:
20°C
Key result
Soil No.:
#1
DT50:
207 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Speyer 2.2 (quinoline label)
Key result
Soil No.:
#2
DT50:
500 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Castle rising (quinoline label)
Key result
Soil No.:
#3
DT50:
328 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Marcham (quinoline label)
Key result
Soil No.:
#4
DT50:
560 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Wereham (quinoline label)
Key result
Soil No.:
#5
DT50:
421 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 2.2 (phenyl label)
Key result
Soil No.:
#5
DT50:
512 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 2.2 (2-quinoline label)
Key result
Soil No.:
#6
DT50:
209 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 2.4 (phenyl label)
Key result
Soil No.:
#6
DT50:
124 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 2.4 (2-quinoline label)
Key result
Soil No.:
#7
DT50:
296 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 5M (phenyl label)
Key result
Soil No.:
#7
DT50:
220 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 5M (2-quinoline label)
Key result
Soil No.:
#8
DT50:
210 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 6S (phenyl label)
Key result
Soil No.:
#8
DT50:
110 d
Type:
other: single first order
Temp.:
20 °C
Remarks on result:
other: Soil 6S (2-quinoline label)
Transformation products:
yes
Remarks:
2-oxo-quinoxyfen and DCHQ
Conclusions:
The normalized Lab DT50 values of the test substance range from to 110 to 560 days, with a geometric mean of 272 days
Executive summary:

As part of the environmental fate assessment of the test substance for EU registration and renewal, the route and rate of degradation in aerobic soil was investigated in two studies with 8 European soils. Two major metabolites were identified: 2-oxo-quinoxyfen and DCHQ. The aim of this study has been to re-calculate the kinetics parameters for the test substance according to FOCUS Degradation Kinetics to determine degradation parameters for test substance that are suitable inputs for environmental fate models.

SFO DT50 values for the test substance ranged from to 110 to 560 days, with a geometric mean of 272 days.

Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
test procedure in accordance with national standard methods with acceptable restrictions
Qualifier:
according to guideline
Guideline:
other: BBA Guideline Part IV, Section 4-1
Deviations:
no
GLP compliance:
yes
Test type:
laboratory
Specific details on test material used for the study:
- [14C]-XDE-795 labelled in position 2 of the quinoline ring
- Batch GHD-3058-19
- Purity: >99%
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
not specified
Soil no.:
#1
Soil type:
loamy sand
% Clay:
5
% Silt:
9
% Sand:
86
% Org. C:
3.9
pH:
6.1
CEC:
10 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy clay loam
% Clay:
25
% Silt:
21
% Sand:
54
% Org. C:
25.1
pH:
7.5
CEC:
44 meq/100 g soil d.w.
Soil no.:
#3
Soil type:
clay loam
% Clay:
30
% Silt:
27
% Sand:
43
% Org. C:
3.71
pH:
7.8
CEC:
24 meq/100 g soil d.w.
Soil no.:
#4
Soil type:
sandy loam
% Clay:
11
% Silt:
10
% Sand:
79
% Org. C:
5.03
pH:
4.2
CEC:
15 meq/100 g soil d.w.
Duration:
200 d
Initial conc.:
250 g/ha d.w.
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
radiochem. meas.
Temp.:
20°C
Microbial biomass:
441 µgC/g (Speyer 2.2), 2328 µgC/g (C. Rising), 379 µgC/g (Marcham), 27 µgC/g (Wereham)
Soil No.:
#1
% Recovery:
101.21
Remarks on result:
other: Speyer 2.2 soil (200 DAT)
Soil No.:
#2
% Recovery:
99.71
Remarks on result:
other: Castle rising soil (200 DAT)
Soil No.:
#3
% Recovery:
100.55
Remarks on result:
other: Marcham soil (200 DAT)
Soil No.:
#4
% Recovery:
101.73
Remarks on result:
other: Wereham soil (200 DAT)
Key result
Soil No.:
#1
DT50:
87 d
Type:
(pseudo-)first order (= half-life)
Temp.:
30 °C
Remarks on result:
other: 40% MHC (Speyer 2.2 soil)
Key result
Soil No.:
#1
DT50:
874 d
Type:
(pseudo-)first order (= half-life)
Temp.:
10 °C
Remarks on result:
other: 40% MHC (Speyer 2.2 soil)
Key result
Soil No.:
#1
DT50:
218 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: 40% MHC (Speyer 2.2 soil)
Remarks:
test substance: 4X application rate when compared to the field rate of 250 g a.i. per ha
Key result
Soil No.:
#1
DT50:
225 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: 40% MHC (Speyer 2.2 soil)
Remarks:
test substance: 1/4X application rate when compared to the field rate of 250 g a.i. per ha
Key result
Soil No.:
#2
DT50:
448 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: 60% MHC (Castle rising soil)
Key result
Soil No.:
#1
DT50:
224 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Speyer 2.2 soil (using data to 100 DAT)
Key result
Soil No.:
#2
DT50:
508 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Castle rising soil (using data to 100 DAT)
Key result
Soil No.:
#3
DT50:
299 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Marcham (using data to 100 DAT)
Key result
Soil No.:
#4
DT50:
465 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Wereham soil (using data to 100 DAT)
Transformation products:
yes
Remarks:
Met 1 (27% of applied at 200 days), Met 2 (up to 6% of applied at 100 days, co-chromatographed with DCHQ)
Conclusions:
DT50 (first order kinetics): 224 days or 7 months (Speyer 2.2)
DT50 (first order kinetics): 508 days or 17 months (Castle rising)
DT50 (first order kinetics): 299 days or 10 months (Marcham)
DT50 (first order kinetics): 465 days or 15 months (Wereham)
Executive summary:

The degradation of the test substance was investigated using one standard (Speyer 2.2) and three agricultural soils under aerobic conditions at 20°C, according to BBA Guideline Part IV, Section 4-1.

Portions of Speyer 2.2, Castle Rising, Marcham and Wereham soils at 40% MHC and contained in biometer flasks, were treated with quinoline-labelled [14C]-test substance at a rate equivalent to 250 g a.i. per ha, corresponding to a soil concentration of 0.33 ppm in the top 5 cm and assuming a bulk density of 1.5 g/cm³. The biometers, containing caustic trap solution in the side-flask, were then incubated in the dark at 20°C under aerobic conditions.

Samples from each soil were taken for analysis at intervals to 200 days after treatment. The trap solution was removed and assayed by LSC. The soil was extracted with solvents and the extracts analyzed by LSC, followed by HPLC to show the metabolite profile. The soil residue was subjected to a combustion technique to determine the amount of non-extractable residue and to show a radiochemical balance. The results are as follows.

A radiochemical balance (98-103%) was achieved for all samples. In the Speyer 2.2, Marcham, Wereham and Castle Rising soils test substance degraded with a DT50 (assuming first-order kinetics) of 7, 10, 15 and 17 months respectively. The corresponding DT90 values were 24, 33, 51 and 55 months.

The major degradation product from the Speyer 2.2, Marcham and Castle Rising soils was predominantly a single metabolite (Met 1; maximum 27% of applied at 200 days in Speyer 2.2 soil), together with non-extractable residue (up to 25%) and small amounts of CO2 (up to 2%). However, in the acidic Wereham soil with low biomass a different metabolite (Met 2) was observed, reaching a maximum of 6% of applied at 100 days. This matched 5,7-dichloro-4-hydroxyquinoline (DCHQ) by co-chromatography (HPLC). Met 1 was not found.

The effect of environmental factors on the degradation rate of test substance has also been investigated. The effect of soil moisture content was examined using Castle Rising soil at 60% MHC. Little or no difference was seen in either the rate of degradation or metabolite profile when compared to the results at 40% MHC. The effect of temperature was studied using Speyer 2.2 soil at 40% MHC where greatest degradation was found at 20°C (DT50 ca. 7 months). At 30°C the DT50 decreased to ca. 3 months, whilst at 10°C the DT50 was in excess of 2 years. The effect of soil concentration was investigated in Speyer 2.2 soil at 40% MHC at 20°C, using 4X and 1/4X application rates. The results showed no significant difference in the degradation of test substance at these high and low application rates. The major metabolite in all comparative work, as before, was Met 1, with a radiochemical balance (97-103%) found for all samples.

Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EPA OPPTS 835.4100 (Aerobic Soil Metabolism)
Deviations:
no
GLP compliance:
yes
Test type:
laboratory
Specific details on test material used for the study:
- Name of substance: DE-795-phenoxy-UL-14C
- Lot: YB1-4100780-062
- Purity: 98.9%

- Name of substance: DE-795-quinoline
- Lot: 54290-06-10
- Purity: 100%
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Year:
2012
Soil no.:
#1
Soil type:
loamy sand
% Clay:
5
% Silt:
8
% Sand:
87
% Org. C:
2.8
pH:
5.6
CEC:
8.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.17
Soil no.:
#2
Soil type:
sandy clay loam
% Clay:
31
% Silt:
22
% Sand:
47
% Org. C:
3.4
pH:
7.4
CEC:
19.1 meq/100 g soil d.w.
Bulk density (g/cm³):
1.16
Soil no.:
#3
Soil type:
sandy loam
% Clay:
17
% Silt:
20
% Sand:
63
% Org. C:
1.7
pH:
7.6
CEC:
8.3 meq/100 g soil d.w.
Bulk density (g/cm³):
1.2
Soil no.:
#4
Soil type:
clay
% Clay:
47
% Silt:
20
% Sand:
33
% Org. C:
3
pH:
7.1
CEC:
20.8 meq/100 g soil d.w.
Bulk density (g/cm³):
1.18
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: Germany
- Storage conditions: The bulk soil samples were stored in the dark in an incubator set at 4 ± 2°C, with free access to air
- Storage length: Until used
- Soil preparation: 2.0 mm sieved

PROPERTIES OF THE SOILS
- Moisture at 1/3 atm (%): Soil #1: 11.1; Soil #2: 23.2; Soil #3: 13.8; Soil #4: 26.4
Duration:
124 d
Initial conc.:
0.3 other: µg/g of soil
Based on:
act. ingr.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 ± 2°C
Microbial biomass:
253.1 µg/g (pre-application); 65.0 µg/g (after final time point)
Soil No.:
#2
Temp.:
20 ± 2°C
Microbial biomass:
252.2 µg/g (pre-application); 113.7 µg/g (after final time point)
Soil No.:
#3
Temp.:
20 ± 2°C
Microbial biomass:
69.8 µg/g (pre-application); 30.9 µg/g (after final time point)
Soil No.:
#4
Temp.:
20 ± 2°C
Microbial biomass:
217.8 µg/g (pre-application); 106.8 µg/g (after final time point)
Details on experimental conditions:
EXPERIMENTAL DESIGN
- Soil preincubation conditions: 29 days in the dark at 20 ± 2 °C under aerobic conditions
- Soil condition: Dry
- Soil (g/replicate): 50
- No. of replication treatments: 3
- Test apparatus (Type/material/volume): 4-oz. (ca. 125 mL) glass wide-mouth bottles. Soil was added to the test vessels to a total thickness of approximately 4 cm, 50.00 g dry weight.
- Details of traps for CO2 and organic volatile, if any: Immediately following treatment, traps were connected to samples for the collection of volatiles. Each soil set of 16 test vessels per label were equipped with a trapping system (train) consisting of ethylene glycol trap (100 mL) and two 1 N sodium hydroxide traps (100 mL each). Each set of traps was connected to a vacuum pump which pulled humidified air over the test system.

Test material application
- Volume of test solution used/treatment: 25 µL

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: The soil moisture of individual samples was monitored throughout the study approximately every two weeks by periodically removing samples from the environmental chamber and adjusting the sample back to its original weight with HPLC grade water as necessary.
- Continuous darkness: Yes

OXYGEN CONDITIONS
- Methods used to create the aerobic conditions: The test systems were maintained under aerobic conditions by drawing humidified air through the test system. Tygon® or similar tubing was used for all connectors.

SAMPLING DETAILS
- Sampling intervals: Two replicates from each soil type were analyzed immediately following treatment (Day 0). The remaining samples were maintained under aerobic conditions for approximately 124 days. Two replicates of each soil type were removed from the incubator for analysis at 7, 21, 46, 83, and 124 days after treatment (DAT). In addition, at 161 DAT two replicates of soil 2.2, dosed with 2-quinoline label, were removed.
- Sampling method for soil samples: The soils were transferred to separate 250 mL plastic centrifuge bottles. The soils were extracted three times with 50 mL of 90:10 acetonitrile:0.1 N HCl by agitating for 30 minutes on a wrist action shaker and then centrifuged to separate solids. The volume of each extract was recorded and the radioactivity determined in triplicate by LSC (1 mL). The extracts were pooled in their entirety, counted by LSC to confirm radioactivity and
then a subsample was removed. The subsample was concentrated to dryness under a stream of nitrogen, and then dissolved in 500 μL of acetonitrile and 1-2 mL of water. Throughout the study selected concentrated subsamples were counted by LSC to confirm recovery. The sample was then spiked with 10-20 μL of standard mix and analyzed by HPLC.
- Method of collection of CO2 and volatile organic compounds: Triplicate 1 mL aliquots from the ethylene glycol traps were taken at each sampling point to determine volatiles by LSC analyses. Triplicate 2 mL aliquots from the 1 N NaOH traps were taken at each sampling point to determine trapped 14CO2 by LSC analyses.
Soil No.:
#1
% Recovery:
96.6
Remarks on result:
other: soil 2.2 system (phenyl label)
Soil No.:
#1
% Recovery:
92.8
Remarks on result:
other: soil 2.2 system (2-quinoline label)
Soil No.:
#2
% Recovery:
96.7
Remarks on result:
other: soil 2.4 system (phenyl label)
Soil No.:
#2
% Recovery:
100
Remarks on result:
other: soil 2.4 system (2-quinoline label)
Soil No.:
#3
% Recovery:
99.9
Remarks on result:
other: soil 5M system (phenyl label)
Soil No.:
#3
% Recovery:
101.9
Remarks on result:
other: soil 5M system (2-quinoline label)
Soil No.:
#4
% Recovery:
99.1
Remarks on result:
other: soil 6S system (phenyl label)
Soil No.:
#4
% Recovery:
103.1
Remarks on result:
other: soil 6S system (2-quinoline label)
Key result
Soil No.:
#1
DT50:
181 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Average [14C] quinoxyfen in Soil 2.2
Remarks:
Kinetic evaluation excluding 124 and 161-DAT 2-quinoline data
Key result
Soil No.:
#1
DT50:
494 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Average [14C] quinoxyfen in Soil 2.2
Key result
Soil No.:
#2
DT50:
333 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Average [14C] quinoxyfen in Soil 2.4
Key result
Soil No.:
#3
DT50:
329 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Average [14C] quinoxyfen in Soil 5M
Key result
Soil No.:
#4
DT50:
355 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other: Average [14C] quinoxyfen in Soil 6S
Transformation products:
yes
Remarks:
2-oxo-quinoxyfen and DCHQ (which reached maximum levels at 83 or 124 DAT)
No.:
#1
No.:
#2
Details on transformation products:
- Under aerobic soil conditions, the test substance slowly degraded. The test substance primarily metabolized into two components, 2-oxo-quinoxyfen and DCHQ, which reached maximum levels at 83 or 124 DAT. Further degradation of 2-oxo-quinoxyfen and DCHQ occurred through mineralization to carbon dioxide and immobilization as soil-bound residue.
Volatile metabolites:
yes
Remarks:
Trace amounts of phenyl and 2-quinoline labeled radioactivity (≤0.1% AR) were present in the ethylene glycol volatile organic traps and remained low throughout the course of the study.
Details on results:
TEST CONDITIONS
- Aerobicity, temperature and other experimental conditions maintained throughout the study: Yes

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: For soil 2.2 the amount of extractable radioactivity generally slowly declined throughout the study ranging from 96.2% AR to 81.1% AR at 83 DAT.
For soil 2.4, the amount of extractable radioactivity slowly declined throughout the study from 101.5% AR to 81.0% AR.
For soil 5M, the amount of extractable radioactivity slowly declined throughout the study from 102.3% AR to 80.1% AR.
For soil 6S, the amount of extractable radioactivity slowly declined throughout the study from 102.6% AR to 82.2% AR.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: The volatile traps contained less than 0.1% AR
Conclusions:
DT50s in various soils ranged from 181-494. This study demonstrated that the test substance was stable under the aerobic soil conditions employed in this study. The test substance degraded slowly to form 2-oxo-quinoxyfen and DCHQ.
Executive summary:

The aerobic soil metabolism study for both the phenyl and 2-quinoline labeled test substance was conducted in a soil system under laboratory conditions. This study was conducted to understand the overall fate of test substance in the environment. The 14C test substances were applied to four different German soil systems. The study was conducted following the guideline, OPPTS 835.4100.

The first soil system, 2.2 (EFS 385) from Hanhofen, Germany, consisted of a loamy sand soil. The microbial activity of the soil prior to test substance application was 253.1 μg/g on a dry basis. The second soil system, 2.4 (EFS 386) from Leimersheim, Germany, consisted of a sandy clay loam. The microbial activity of the soil prior to test substance application was 252.2 μg/g on a dry basis. The third soil system, 5M (EFS 387) from Mechtersheim, Germany, consisted of a sandy loam soil. The microbial activity of the soil prior to test substance application was 69.8 μg/g on a dry basis. The fourth soil system, 6S (EFS 388) from Siebeldingen, Germany, consisted of a clay soil. The microbial activity of the soil prior to test substance application was 217.8 μg/g on a dry basis. The soil (50.00 g dry weight) was weighed into separate 125 mL glass jars, adjusted with water to approximately pF 2.5 and maintained under aerobic conditions in flow-through test systems to determine the rate and route of degradation of test substance in the dark at 20 ± 2 °C.

Each test sample was treated with either 14.9 μg of phenyl or 15.4 μg of 2-quinoline labeled [14C]test substance. The [14C]test substance was applied based on the maximum single label application rate of 300 g ai/ha. The actual amount of phenyl labeled [14C]test substance in the test vessels upon dosing (Day 0) as determined by liquid scintillation counting (LSC) was 0.30 μg/g, and 0.31 μg/g for the 2-quinoline labeled [14C]test substance. The incubation of treated test systems continued under aerobic conditions by continuously flowing air over the soil for 124 days. Each set of soils was equipped with its own trapping system consisting of a trap to collect organic volatiles (ethylene glycol) followed by two traps to collect carbon dioxide [1 N sodium hydroxide (NaOH)].

Duplicate soil samples from each label were assayed at 0, 7, 21, 46, 83 and 124 days after application of the test substance. In addition for Soil 2.2 the 2-quinoline label, two samples were assayed at 161 days after application. At each sampling interval the soil was transferred to a 250 mL centrifuge bottle and extracted with acetonitrile:0.1 N HCl (90:10, v:v) extraction solvent. The soil extracts were radioassayed and analyzed by HPLC to determine the amount of test substance and degradates present. Radioactivity in the post-extracted solids (PES) was quantified by combustion analysis. The 1 N NaOH and volatile organic traps for each time point were radioassayed by LSC typically on the day of their collection. In addition, all traps were radioassayed by LSC and replenished with fresh sodium hydroxide and ethylene glycol following each time point.

Following the final sampling time, the microbial activity was determined for each soil. Soil 2.2 was 65.0 μg/g, soil 2.4 was 113.7 μg/g, soil 5M was 30.9 μg/g, and soil 6S was 106.8 μg/g (dry basis).

For soil 2.2, at all sample points the mass balance of the applied radioactivity (based on the sum of the extracts, CO2, volatiles, and bound radioactivity) was between 90-102% applied radioactivity (AR) with the exception of one sample at 88.4% AR. The amount of extractable radioactivity generally slowly declined throughout the study ranging from 96.2% AR to 81.1% AR at 83 DAT. Throughout the course of the study the phenyl label CO2 traps increased, accumulating up to 3.5% AR at day 124 while no more than 0.1% AR was found in the CO2 traps for the 2-quinoline label. The volatile traps contained less than 0.1% AR. Degradation was to 2-oxo-quinoxyfen (maximum 16.8% AR at 83 DAT) and DCHQ (maximum 13.6% AR at 83 DAT).

For soil 2.4, the mass balance of the applied radioactivity (based on the sum of the extracts, CO2, volatiles, and bound radioactivity) was between 94.2% AR and 103.3% AR at all sampling points. The amount of extractable radioactivity slowly declined throughout the study from 101.5% AR to 81.0% AR. Throughout the course of the study the CO2 traps increased, accumulating up to 2.6% AR and 0.7% AR in the phenyl and 2-quinoline labels, respectively, while the volatile traps did not accumulate any radioactivity. Degradation was to 2-oxoquinoxyfen (maximum 9.9% AR at 83 DAT) and DCHQ (maximum 7.2% AR at 124 DAT).

For soil 5M, the mass balance of the applied radioactivity (based on the sum of the extracts, CO2, volatiles, and bound radioactivity) ranged between 94.7% and 103.8% AR at all sampling points. The amount of extractable radioactivity slowly declined throughout the study from 102.3% AR to 80.1% AR. Throughout the course of the study the CO2 traps increased, accumulating up to 3.7% AR and 0.8% AR in the phenyl and 2-quinoline labels, respectively, while the volatile traps did not accumulate any radioactivity. Degradation was to 2-oxo-quinoxyfen (maximum 6.2% AR at 124 DAT) and DCHQ (maximum 12.8% AR at 83 DAT).

For soil 6S, the mass balance of the applied radioactivity (based on the sum of the extracts, CO2, volatiles, and bound radioactivity) ranged between 97.1% and 104.0% AR at all sampling points. The amount of extractable radioactivity slowly declined throughout the study from 102.6% AR to 82.2% AR. Throughout the course of the study the CO2 traps increased, accumulating up to 4.1% AR and 1.4% AR in the phenyl and 2-quinoline labels, respectively, while the volatile traps did not accumulate radioactivity. Minor degradation was to 2-oxo-quinoxyfen (maximum 9.2% AR at 83 DAT) and DCHQ (maximum 9.3% AR at 124 DAT).

Soil extracts were typically analyzed by HPLC within 24 hours of sampling. Whenever immediate analysis was not possible samples were placed in storage at -20 °C. However, all samples were analyzed within 6 months of sampling. As a result no storage stability testing was required.

The DT50 and DT90 of test substance under aerobic soil conditions were estimated by fitting the data to a single first-order linear regression analysis using the data through 124 DAT. For soil system 2.2, data is presented through 124 DAT with and without 2-quinoline 124 DAT results.

Average [14C] quinoxyfen in Soil 2.2 (Kinetic evaluation excluding 124 and 161 -DAT 2-quinoline data): DT50: 181 days; DT90: 628 days; r²: 0.8426

Average [14C] quinoxyfen in Soil 2.2: DT50: 494 days; DT90: 1835 days; r²: 0.3883

Average [14C] quinoxyfen in Soil 2.4: DT50: 333 days; DT90: 1138 days; r²: 0.9564

Average [14C] quinoxyfen in Soil 5M: DT50: 329 days; DT90: 1095 days; r²: 0.8446

Average [14C] quinoxyfen in Soil 6S: DT50: 355 days; DT90: 1202 days; r²: 0.9601

Description of key information

DT50s of the test substance in soil ranged from 110 days to 17 months.

Key value for chemical safety assessment

Additional information