8-Chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Biodegradation in soil

Administrative data

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:

2018

Report date:

2018

Materials and methods

Test guideline

Test guideline 1

Qualifier:

according to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

Test guideline 2

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.4100 (Aerobic Soil Metabolism)

Deviations:

no

Test guideline 3

Qualifier:

according to guideline

Guideline:

other: JMAFF Guideline No. 12-Nousan-8147, 2-5-2 (2000)

Deviations:

no

Test guideline 4

Qualifier:

according to guideline

Guideline:

other: SETAC Document “Procedures for Assessing the Environmental Fate and Ecotoxicology in Pesticides” (March 1995)

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Test material

Test material information

1

Reference substance name:

8-chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Cas Number:

353258-35-2

Molecular formula:

C9H4ClF3N2O2

IUPAC Name:

8-chloro-6-(trifluoromethyl)imidazo[1,2-a]pyridine-2-carboxylic acid

Specific details on test material used for the study:

Substance name: [14C]-IN-QEK31
Lot #: 1572460
Specific activity: 69.12 µCi/mg
Radiochemical purity: 97.8%

Radiolabelling:

yes

Study design

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

2018

Soil properties

Soil properties 1

Soil no.:

#1

Soil type:

silty clay loam

% Clay:

33

% Silt:

52

% Sand:

15

% Org. C:

2.8

pH:

7

CEC:

20.9 meq/100 g soil d.w.

% Moisture content:

33.4

Soil properties 2

Soil no.:

#2

Soil type:

sandy loam

% Clay:

5

% Silt:

21

% Sand:

74

% Org. C:

1.4

pH:

5.3

CEC:

6.1 meq/100 g soil d.w.

% Moisture content:

17

Soil properties 3

Soil no.:

#3

Soil type:

sandy loam

% Clay:

11

% Silt:

28

% Sand:

61

% Org. C:

1.5

pH:

7.7

CEC:

9.5 meq/100 g soil d.w.

% Moisture content:

16.9

Soil properties 4

Soil no.:

#4

Soil type:

loam

% Clay:

9

% Silt:

46

% Sand:

45

% Org. C:

0.8

pH:

7.9

CEC:

10.8 meq/100 g soil d.w.

% Moisture content:

17.5

Soil properties 5

Soil no.:

#5

Soil type:

loamy sand

% Clay:

5

% Silt:

12

% Sand:

83

% Org. C:

1.5

pH:

6.4

CEC:

6.8 meq/100 g soil d.w.

% Moisture content:

12.2

Duration of test (contact time)

Duration of test (contact time) 1

Soil No.:

#1

Duration:

119 d

Duration of test (contact time) 2

Soil No.:

#2

Duration:

119 d

Duration of test (contact time) 3

Soil No.:

#3

Duration:

119 d

Duration of test (contact time) 4

Soil No.:

#4

Duration:

119 d

Duration of test (contact time) 5

Soil No.:

#5

Duration:

119 d

Initial test substance concentration

Initial test substance concentration 1

Soil No.:

#1

Initial conc.:

1 mg/kg soil d.w.

Based on:

act. ingr.

Initial test substance concentration 2

Soil No.:

#2

Initial conc.:

1 mg/kg soil d.w.

Based on:

act. ingr.

Initial test substance concentration 3

Soil No.:

#3

Initial conc.:

1 mg/kg soil d.w.

Based on:

act. ingr.

Initial test substance concentration 4

Soil No.:

#4

Initial conc.:

1 mg/kg soil d.w.

Based on:

act. ingr.

Initial test substance concentration 5

Soil No.:

#5

Initial conc.:

1 mg/kg soil d.w.

Based on:

act. ingr.

Parameter followed for biodegradation estimation:

radiochem. meas.

Experimental conditions

Experimental conditions 1

Soil No.:

#1

Temp.:

20 ± 2°C

Humidity:

Soil-moisture content: 41.7%

Microbial biomass:

Initiation (biomass as % organic carbon): 2.7%
Termination (biomass as % organic carbon): 1.8%

Experimental conditions 2

Soil No.:

#2

Temp.:

20 ± 2°C

Humidity:

Soil-moisture content: 20.6%

Microbial biomass:

Initiation (biomass as % organic carbon): 1.5%
Termination (biomass as % organic carbon): 1.4%

Experimental conditions 3

Soil No.:

#3

Temp.:

20 ± 2°C

Humidity:

Soil-moisture content: 20.8%

Microbial biomass:

Initiation (biomass as % organic carbon): 4.0%
Termination (biomass as % organic carbon): 2.6%

Experimental conditions 4

Soil No.:

#4

Temp.:

20 ± 2°C

Humidity:

Soil-moisture content: 33.4%

Microbial biomass:

Initiation (biomass as % organic carbon): 2.7%
Termination (biomass as % organic carbon): 2.0%

Experimental conditions 5

Soil No.:

#5

Temp.:

20 ± 2°C

Humidity:

Soil-moisture content: 10.3%

Microbial biomass:

Initiation (biomass as % organic carbon): 1.2%
Termination (biomass as % organic carbon): 2.5%

Results and discussion

Material (mass) balance

Material (mass) balance 1

Soil No.:

#1

Sampling day(s):

119 d

% Total extractable:

75.3

% Non extractable:

19.5

% CO2:

6.1

% Other volatiles:

4.5

% Recovery:

99.6

St. dev.:

6.1

Remarks on result:

other: Tama soil

Material (mass) balance 2

Soil No.:

#2

Sampling day(s):

119 d

% Total extractable:

48.1

% Non extractable:

19.5

% CO2:

19.3

% Other volatiles:

14.3

% Recovery:

94.8

St. dev.:

11

Remarks on result:

other: Sassafras soil

Material (mass) balance 3

Soil No.:

#3

Sampling day(s):

119 d

% Total extractable:

56.3

% Non extractable:

17.4

% CO2:

7.4

% Other volatiles:

23.4

% Recovery:

97.9

St. dev.:

11.8

Remarks on result:

other: Nambsheim soil

Material (mass) balance 4

Soil No.:

#4

Sampling day(s):

119 d

% Total extractable:

91.6

% Non extractable:

10.1

% CO2:

3.7

% Other volatiles:

0.9

% Recovery:

100

St. dev.:

10.8

Remarks on result:

other: Porterville soil

Material (mass) balance 5

Soil No.:

#5

Sampling day(s):

119 d

% Total extractable:

63.7

% Non extractable:

13.4

% CO2:

10.9

% Other volatiles:

15.1

% Recovery:

99.9

St. dev.:

5.5

Remarks on result:

other: Speyer 2.2 soil

Half-life / dissipation time of parent compound

Half-life / dissipation time of parent compound 1

Key result

Soil No.:

#1

DT50:

182 d

Type:

other: SFO kinetics

Temp.:

20 °C

Remarks on result:

other: Tama soil

Half-life / dissipation time of parent compound 2

Key result

Soil No.:

#2

DT50:

57.2 d

Type:

other: SFO kinetics

Temp.:

20 °C

Remarks on result:

other: Sassafras soil

Half-life / dissipation time of parent compound 3

Key result

Soil No.:

#3

DT50:

59.7 d

Type:

other: SFO kinetics

Temp.:

20 °C

Remarks on result:

other: Nambsheim soil

Half-life / dissipation time of parent compound 4

Key result

Soil No.:

#4

Remarks on result:

other: Porterville soil failed to display meaningful decline of parent past the 10 day sampling interval, therefore, DT50 was not calculated.

Half-life / dissipation time of parent compound 5

Key result

Soil No.:

#5

DT50:

99.1 d

Type:

other: SFO kinetics

Temp.:

20 °C

Remarks on result:

other: Speyer 2.2 soil

Transformation products:

yes

Identity of transformation products

No.:

#1

Reference

Reference substance name:

Unnamed

Volatile metabolites:

yes

Remarks:

CO2

Residues:

yes

Applicant's summary and conclusion

Conclusions:

Based on the
results of this study, IN-QEK31 would degrade to IN-VM862 which would volatilise or become incorporated in soil residues where it may be mineralised to CO2. IN-QEK31 would become less prone to movement with water in aerobic soils over time.

Executive summary:

The rate of degradation and time dependent sorption of [14C]-IN-QEK31 was studied in five aerobic soils in the dark under aerobic conditions at 20 ± 2°C for 119 days. The soils named as Tama, Sassafras, Nambsheim, Porterville (cajon) and Speyer 2.2 were collected from Stark County, Illinois, USA; Kent, Maryland, USA; Alsace, France; Tulare, California, USA and Hanhofen, Germany respectively. All soils were incubated under non sterile conditions. The Tama soil was classified (USDA Textural Class) as a Silty Clay Loam, Sassafras and Nambsheim as Sandy Loam, Porterville as a Loam and Speyer 2.2 as a Loamy Sand. The organic carbon content (Walkley-Black method) of the Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils was 2.8, 1.4, 1.5, 0.8 and 1.5%, respectively. The pH (in water) of the Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils was 7.0, 5.3, 7.7, 7.9 and 6.4, respectively. The soil systems were allowed to acclimatize for up to 13 days prior to test item application.

A radiolabelled form of the test item with 14C in the imidazo[1,2-a]pyridine-5,8a (IP) label was used as the test substance. The radiolabelled test item was applied to the soil at a nominal rate of 1.0 μg/g oven dry soil which corresponded to a 1000 g a.i./ha application assuming 10 cm incorporation and 1.0 g/cm3 soil density. Treated vessels were incubated for up to 119 days under aerobic conditions in the dark at 20 ± 2°C.

This study was conducted under GLP and in accordance with the OECD Guideline 307 (2002), US EPA Guidelines, OPPTS 835.4100-Aerobic Soil Metabolism.

The test systems consisted of glass incubation vessels (one set for each soil type) containing a sample of soil. The vessels were connected to air flow-through systems which are typical for soil degradation studies, with polyurethane plugs (PU plug) inserted into the necks of soil flasks and safety traps for retention of a volatile metabolite IN-VM862, in addition to ethanediol and sodium hydroxide traps for the collection of non-specific volatile organic compounds and 14CO2, respectively. Samples were analysed immediately following test item application (zero time) and after the following periods of aerobic incubation: 10, 20, 40, 60, 90 and 119 days.

Prior to soil extractions, an aged desorption step was carried out by extracting the soil samples with 0.01M CaCl2 (50 mL). Extraction was facilitated by shaking on and end-over-end shaker overnight. Phases were separated by centrifugation followed by decanting of the supernatant. Each soil sample was then extracted using a series of organic solvents as follows: acetonitrile: 2% formic acid (aq) (9:1 v/v); followed by acetonitrile: 2% formic acid (aq) (4:1 v/v); and then twice with acetonitrile: 2% formic acid (aq) (1:1 v/v), all at 50°C in an ultrasonic bath. Extractable soil radioactivity was quantified by LSC. The two polyurethane plugs (per sample) were replaced at each sampling interval and were extracted with 20 mL acetonitrile. Radioactivity extracted from polyurethane plugs was quantified by LSC. Non-extractable 14C-residues were quantified by combustion analysis. Each CaCl2 extract was analysed by reverse phase HPLC with online radiodetection. Organic extracts for each sample were combined prior to analysis by reverse phase HPLC with fraction collection. PU plug extracts common for each timepoint were combined and analysed by reverse phase HPLC with fraction collection.

The material balance for all samples was quantitative with the exception of Sassafras Day 40 (replicate 1, 86% AR), Sassafras Day 90 [mean 87% AR] and Porterville Day 119 (replicate 2, 111% AR) samples. The amount of extractable residue declined gradually over the study period due to degradation of the applied material, IN-QEK31, and its partial incorporation into the soil organic matter. Non-extractable residue increased to nearly 20% in three of the five soils (Sassafras, Nambsheim and Speyer 2.2). The decreased extractability was clearly due to more extensive degradation of IN-QEK31 in these soils because a corresponding increased amount of 14CO2 and volatilised IN-VM862 from these soils was observed concomitantly over the duration of the study. Exact percentages of 19.3, 7.4, 10.9 % AR evolved as 14CO2 and 14.3, 23.4, 15.1 % AR captured as volatilised INVM862 in the Sassafras, Nambsheim and Speyer 2.2 soils, respectively, were noted at the final sampling interval.

The degradation of IN-QEK31 in all soils resulted in the formation of one major metabolite, IN-VM862, which was observed in the CaCl2 desorption extracts (quantities <4 % AR) as well as organic solvent extracts and PU plug extracts indicating that IN-VM862 had volatilised from the soil. The formation of INVM862 increased throughout the duration of the study in all 5 soils reaching mean maximum values of 21.5, 27.4, 48.8, 11.4 and 32.1% AR in the Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils at Day 119 (Tama Day 90), respectively.

IN-VM862 was tentatively identified initially by matching the HPLC retention time with the respective reference standard, and then confirmed by LC/MS analysis.

Tama and Porterville soils displayed lower non-extractable residue, as well as lower levels of 14CO2 and volatilised IN-VM862. Levels of 14CO2 and volatilised IN-VM862 observed in these soil reached a mean maximum of 6.1 and 3.7% for 14CO2 and 4.5 and 0.9% for IN-VM862 at the final sampling interval.

Non-extractable residues in all soils were characterised using organic matter fractionation. After extractions with NaOH solutions, the non-extractable residue of select samples from each soil type was fractionated into humin, fulvic acid and humic acid fractions. In four of the soils (Tama, Sassafras, Porterville and Speyer 2.2) the majority of the radioactivity was characterised as being associated with the humin and fulvic acid fractions of the soil organic matter, in nearly equal quantities, while the balance was found in the humic acid fractions. In the Nambsheim soil the majority of the radioactivity was characterised as being associated with the humin fraction (>64%) with the balance found in the humicand fulvic acid fractions.

The decline of IN-QEK31 was plotted against sampling intervals and the degradation rates (DT50 and DT90) determined using SFO kinetics. IN-QEK31 degrades under aerobic conditions in five soils examined in this study with a DT50 of 182, 57.2, 59.7 and 99.1 days and DT90 of 605, 190, 198 and 239 days in the Tama, Sassafras, Nambsheim and Speyer soils, respectively. Porterville degradation data did not display a consistent pattern and was therefore not modelled.

 

The desorption coefficient, Kd,des, of IN-QEK31 was calculated for each soil at each sampling interval based on the concentrations found in soil and in CaCl2 extracts. At zero time the mean Kd,des values for Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils were 2.50, 2.26, 0.86, 2.84 and 1.25, respectively. The corresponding Day 119 values were 5.67, 7.15, 2.61, 7.82 and 3.63 respectively.

 

The desorption coefficients were normalised to the organic matter and organic carbon contents for each soil to calculate the coefficients Kom,des and Koc,des, respectively. At zero time the mean Kom,des values for Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils were 51, 94, 34, 219 and 50, respectively. The corresponding Day 119 values were 116, 298, 105, 601 and 145, respectively. At zero time the mean Koc,des values for Tama, Sassafras, Nambsheim, Porterville and Speyer 2.2 soils were 89, 162, 57, 355 and 83, respectively. The corresponding Day 119 values were 202, 511, 174, 977 and 242, respectively.

These results demonstrate a clear increase in time dependent sorption for INQEK31 and hence a decreasing potential for mobility with time. Based on the results of this study, IN-QEK31 would degrade to IN-VM862 which would volatilise or become incorporated in soil residues where it may be mineralised to CO2. IN-QEK31 would become less prone to movement with water in aerobic soils over time.