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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:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
Version / remarks:
2002
Qualifier:
according to guideline
Guideline:
other: OECD: Guideline 106, Adsorption/Desorption
Version / remarks:
2001
GLP compliance:
yes (incl. QA statement)
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
other: Silt loam; soil identification: Hoefchen am Hohenseh plot 4011
% Clay:
24
% Silt:
54
% Sand:
22
% Org. C:
1.1
pH:
5.9
CEC:
12.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.1
Soil no.:
#2
Soil type:
other: Sandy loam; soil identification: Wellesbourne
% Clay:
16
% Silt:
12
% Sand:
72
% Org. C:
0.8
pH:
6.3
CEC:
9.3 meq/100 g soil d.w.
Bulk density (g/cm³):
1.31
Soil no.:
#3
Soil type:
other: Clay loam; soil identification: Mas du Coq
% Clay:
30
% Silt:
50
% Sand:
20
% Org. C:
0.8
pH:
7.7
CEC:
11.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.19
Soil no.:
#4
Soil type:
other: Sandy loam; soil identification: Vilobi d'Onyar
% Clay:
14
% Silt:
32
% Sand:
54
% Org. C:
0.8
pH:
6.2
CEC:
8 meq/100 g soil d.w.
Bulk density (g/cm³):
1.33
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- Geographic location: Soils were taken from agricultural used areas in northern and southern Europe and cover representative soil types with a representative range of physicochemical properties. The selected soils are well-known from field dissipation as well as from soil metabolism studies.
- Collection procedures: The soils were sampled freshly from the field.
- Storage conditions: Information on collection and storage of the soils is provided in the attached background material “1 Attached background material_M-405885-01-1_3458300 OECD 307_106.pdf”

PROPERTIES OF THE SOILS (in addition to defined fields)
- pH: The pH values of the soils Hoefchen am Hohenseh plot 4011, Wellesbourne, Mas du Coq and Vilobi d’Onyar in aqueous 0.01 M CaCl2 solution were 5.7, 6.1, 7.7, and 6.1, respectively.
- Organic carbon content: The organic carbon contents were 1.1%, 0.8%, 0.8% and 0.8% and the clay contents were 24%, 16%, 30% and 14% (USDA), respectively.

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.:
#1
Initial conc.:
20 other: µg/100g soil
Based on:
test mat.
Soil No.:
#2
Initial conc.:
20 other: µg/100g soil
Based on:
test mat.
Soil No.:
#3
Initial conc.:
20 other: µg/100g soil
Based on:
test mat.
Soil No.:
#4
Initial conc.:
20 other: µg/100g soil
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Soil No.:
#1
Temp.:
20 °C
Humidity:
55% of maximum water holding capacity
Microbial biomass:
341 mg micrbial carbon per kg of soil dry weight
Soil No.:
#2
Temp.:
20 °C
Humidity:
55% of maximum water holding capacity
Microbial biomass:
176 mg micrbial carbon per kg of soil dry weight
Soil No.:
#3
Temp.:
20 °C
Humidity:
55% of maximum water holding capacity
Microbial biomass:
129 mg micrbial carbon per kg of soil dry weight
Soil No.:
#4
Temp.:
20 °C
Humidity:
55% of maximum water holding capacity
Microbial biomass:
290mg micrbial carbon per kg of soil dry weight
Details on experimental conditions:
EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): Prior to the start of the test, the soils were successively sieved to a particle size of ≤ 2 mm and stored at ambient temperature in the laboratory for a maximum of 25 days until pre-incubation.
- Test apparatus (Type/material/volume): The incubation systems were static systems and consisted of Erlenmeyer flasks (300 mL) with 100 g soil (DM) for each sampling interval.
- Details of traps for CO2 and organic volatile, if any: After application, the flasks were closed with trap attachments, which were easily permeable for oxygen. The traps contained soda lime for absorption of CO2 and a polyurethane foam plug for adsorption of volatile organic compounds.
- Other: Four spare samples per soil were incubated as well as samples for the determination of biomass.

Test material application
- Volume of test solution used/treatment: Clothianidin was applied at a rate of 20 µg a.s./ 100 g soil

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: The soil moisture was determined by drying aliquots of the soils at 105 °C using a balance for humidity determination (Mettler Toledo HB43). Water (VE) was added to each soil aliquot in a way that the final moisture was 55% of the maximum water holding capacity (WHCmax). Aliquots of the soils, each corresponding to 100 g dry weight, were filled into 300-mL Erlenmeyer flasks.
- Continuous darkness: Yes
- Other: Samples were incubated in the dark at 20 ± 2 °C, under aerobic conditions and at 55% of the maximum water holding capacity.

SAMPLING DETAILS
- Sampling intervals: Samples were taken 0, 1, 3, 9, 21, 28, 35, 49, 63, 77, 98 and 120 days after application. At each sampling interval, two samples per soil were removed from the climatic chamber and processed.
- Sampling method for soil samples: At the processing dates, the vessels of each soil system treated with active substance were completely sacrificed. Directly after sampling, the soils were extracted within one day. After processing, the extracts were deep frozen until analysis.

Soil No.:
#1
% Total extractable:
> 37.7 - < 99
% Non extractable:
> 30.8 - < 31.5
% CO2:
29.3
% Other volatiles:
< 0.3
% Recovery:
98.1
Remarks on result:
other:
Remarks:
Soil identification: Hoefchen am Hohenseh plot 4011
Soil No.:
#2
% Total extractable:
61.8
% Non extractable:
20.2
% CO2:
16.2
% Other volatiles:
< 0.3
% Recovery:
98.5
Remarks on result:
other:
Remarks:
Soil identification: Wellesbourne
Soil No.:
#3
% Total extractable:
71.2
% Non extractable:
18.1
% CO2:
9.4
% Other volatiles:
< 0.3
% Recovery:
99
Remarks on result:
other:
Remarks:
Soil identification: Mas du Coq
Soil No.:
#4
% Total extractable:
63.6
% Non extractable:
19.8
% CO2:
15.9
% Other volatiles:
< 0.3
% Recovery:
99.6
Remarks on result:
other:
Remarks:
Soil identification: Vilobi d'Onyar
Parent/product:
parent
Soil No.:
#1
% Degr.:
29.3
Parameter:
radiochem. meas.
Remarks:
Amount of formed 14CO2 at the end of the study period
Sampling time:
120 d
Parent/product:
parent
Soil No.:
#2
% Degr.:
16.2
Parameter:
radiochem. meas.
Remarks:
Amount of formed 14CO2 at the end of the study period
Sampling time:
120 d
Parent/product:
parent
Soil No.:
#3
% Degr.:
9.4
Parameter:
radiochem. meas.
Remarks:
Amount of formed 14CO2 at the end of the study period
Sampling time:
120 d
Parent/product:
parent
Soil No.:
#4
% Degr.:
15.9
Parameter:
radiochem. meas.
Remarks:
Amount of formed 14CO2 at the end of the study period
Sampling time:
120 d
Soil No.:
#1
DT50:
9.7 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Soil identification: Hoefchen am Hohenseh plot 4011
Soil No.:
#1
DT50:
32.3 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Soil identification: Hoefchen am Hohenseh plot 4011; Calculated DT50 based on results at 20 °C
Soil No.:
#2
DT50:
86.9 d
Type:
other: First order multi compartment model (FOMC)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Soil identification: Wellesbourne
Soil No.:
#2
DT50:
184.5 d
Type:
other: First order multi compartment model (FOMC)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Soil identification: Wellesbourne; Calculated DT50 based on results at 20 °C
Soil No.:
#3
DT50:
174.6 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Soil identification: Mas du Coq
Soil No.:
#3
DT50:
370.7 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Soil identification: Mas du Coq; Calculated DT50 based on results at 20 °C
Soil No.:
#4
DT50:
122 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Soil identification: Vilobi d'Onyar
Soil No.:
#4
DT50:
259 d
Type:
other: Double first order parallel kinetics (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Soil identification: Vilobi d'Onyar; Claculated DT50 based on results at 20 °C
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
No.:
#5
No.:
#6
No.:
#7
Details on transformation products:
- Besides carbon dioxide six degradation products were detected and identified in the course of the incubation:
TZNG (FHW0107C), formed at maximum amounts of 1.0 to 3.0% of the applied amount of test substance in the four soils;
MNG (FHW0107F), formed at maximum amounts of 4.5 to 6.8% of the applied amount of test substance in the four soils;
TZMU (FHW0107E), formed at maximum amounts of 2.2 to 10.6% of the applied amount of test substance in the four soils;
TMG (FHW0107G), formed at maximum amounts of 0.3 to 0.8% of the applied amount of test substance in the four soils;
NTG (FHW0107H), formed at maximum amounts of 2.1 to 3.5% of the applied amount of test substance in the four soils;
TZFA (BCS-CQ81511), formed at maximum amounts of 0.7 to 6.7% of the applied amount of test substance in the four soils.
Evaporation of parent compound:
no
Remarks:
No significant radioactivity was detected in the polyurethane foams for adsoption of volatile organic compounds (<0.3 %).
Volatile metabolites:
no
Remarks:
No significant radioactivity was detected in the polyurethane foams for adsoption of volatile organic compounds (<0.3 %).
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes. The test conditions outlined in the study protocol were maintained throughout the study. The material balances ranged from 96.7% up to 104.2% of the applied amount of radioactivity (means of two replicates).

EXTRACTABLE RESIDUES
- % of applied amount at end of study period: Extractable 14C-residues decreased from 99.0%, 102.0%, 101.0%, and 100.9% of the applied amount at DAT-0 to 37.7%, 61.8%, 71.2% and 63.6% of the applied RA at the end of the study in soils Hoefchen am Hohenseh plot 4011, Wellesbourne, Mas du Coq and Vilobi d’Onyar, respectively.
- The test item Clothianidin degraded moderately fast. Its amount in the extracts decreased from 96.9-99.8% on DAT-0 to 21.5 – 60.8% of AR after incubation for 120 days. The calculated half-lives were in the range of 9.7 to 174.6 days (geometric mean: 65.1 days).

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: The non-extractable residues at DAT-0 varied from 2.2% – 3.0% of AR and were generated during the 24h lasting desorption step.
- % of applied amount at end of study period: At study termination they increased to 30.8%, 20.2%, 18.1%, and 19.8% of AR in soils Hoefchen am Hohenseh plot 4011, Wellesbourne, Mas du Coq and Vilobi d’Onyar, respectively. The formation of bound residues increased with the overall metabolism of test compound. They were separated into humin, humic acid and fulvic acid fractions for the last sampling interval.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: At the end of the study at DAT-120, evolved 14CO2 accounted for 29.3%, 16.2%, 9.4%, and 15.9% of the applied RA in soils Hoefchen am Hohenseh plot 4011, Wellesbourne, Mas du Coq and Vilobi d’Onyar, respectively.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Only once a very small amount of volatile organic compounds was measured in the polyurethane foam (Replicate A, DAT-120, 0.3% of AR).

TRANSFORMATION PRODUCTS
- Besides carbon dioxide six degradation products were detected and identified in the course of the incubation:
TZNG (FHW0107C), formed at maximum amounts of 1.0 to 3.0% of the applied amount of test substance in the four soils;
MNG (FHW0107F), formed at maximum amounts of 4.5 to 6.8% of the applied amount of test substance in the four soils;
TZMU (FHW0107E), formed at maximum amounts of 2.2 to 10.6% of the applied amount of test substance in the four soils;
TMG (FHW0107G), formed at maximum amounts of 0.3 to 0.8% of the applied amount of test substance in the four soils;
NTG (FHW0107H), formed at maximum amounts of 2.1 to 3.5% of the applied amount of test substance in the four soils;
TZFA (BCS-CQ81511), formed at maximum amounts of 0.7 to 6.7% of the applied amount of test substance in the four soils.

Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
06 Jul 1998 - 31 Jul 2000
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
other: EC Commission Directive 95/36/EC amending Council Directive 91/414/EEC Annexes I + II, Fate and Behaviour in the Environment
Version / remarks:
1995
Qualifier:
according to guideline
Guideline:
other: US EPA: Pesticide Assessment Guidelines, Subdivision N Chemistry: Environmental Fate § 162-1, Aerobic soil metabolism studies
Version / remarks:
1982
Qualifier:
according to guideline
Guideline:
other: Society of Environmental Toxicology and Chemistry (SETAC-Europe): Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides
Version / remarks:
1995
GLP compliance:
yes (incl. QA statement)
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
other: DIN 19682
Soil no.:
#1
Soil type:
other: Silt loam; soil identification: Crosby
% Clay:
23.5
% Silt:
60.9
% Sand:
15.6
% Org. C:
1.37
pH:
6.74
CEC:
15 meq/100 g soil d.w.
% Moisture content:
19.85
Soil no.:
#2
Soil type:
other: Loam; soil identification: Elder
% Clay:
11.7
% Silt:
41.3
% Sand:
47
% Org. C:
1.41
pH:
6.67
CEC:
18 meq/100 g soil d.w.
% Moisture content:
16.91
Soil no.:
#3
Soil type:
other: loamy sand; soil identification: Fuguay
% Clay:
3
% Silt:
22.6
% Sand:
74.4
% Org. C:
0.35
pH:
6.67
CEC:
5 meq/100 g soil d.w.
% Moisture content:
9.6
Soil no.:
#4
Soil type:
other: Loamy sand; soil identification: Quincy
% Org. C:
0.4
pH:
6.8
CEC:
6.08 meq/100 g soil d.w.
Bulk density (g/cm³):
1.57
% Moisture content:
6.08
Soil no.:
#5
Soil type:
other: Sand; soil identification: Sparta
% Clay:
0.9
% Silt:
7.1
% Sand:
92
% Org. C:
0.73
pH:
6.22
CEC:
6 meq/100 g soil d.w.
% Moisture content:
5.36
Soil no.:
#6
Soil type:
other: Silt loam; soil identification: Susan
% Clay:
27.4
% Silt:
58.3
% Sand:
14.3
% Org. C:
3.27
pH:
6.66
CEC:
30 meq/100 g soil d.w.
% Moisture content:
30.58
Parent/product:
parent
Soil No.:
#1
% Degr.:
16.9
Parameter:
radiochem. meas.
Sampling time:
379 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Parent/product:
parent
Soil No.:
#2
% Degr.:
2.5
Parameter:
radiochem. meas.
Sampling time:
181 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Parent/product:
parent
Soil No.:
#3
% Degr.:
2.1
Parameter:
radiochem. meas.
Sampling time:
181 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Parent/product:
parent
Soil No.:
#4
% Degr.:
7
Parameter:
radiochem. meas.
Sampling time:
181 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Parent/product:
parent
Soil No.:
#5
% Degr.:
5.2
Parameter:
radiochem. meas.
Sampling time:
181 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Parent/product:
parent
Soil No.:
#6
% Degr.:
3.4
Parameter:
radiochem. meas.
Sampling time:
181 d
Remarks on result:
other:
Remarks:
14CO2 formation at 20 °C.
Soil No.:
#1
DT50:
541 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Soil No.:
#1
DT50:
1 148.5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20 °C
Soil No.:
#2
DT50:
1 328 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Soil No.:
#2
DT50:
2 819.3 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20 °C
Soil No.:
#4
DT50:
549 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Soil No.:
#4
DT50:
1 165.5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20 °C
Soil No.:
#5
DT50:
533 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Soil No.:
#5
DT50:
1 131.6 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20 °C
Soil No.:
#6
DT50:
808 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Soil No.:
#6
DT50:
1 715.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 based on results at 20 °C
Conclusions:
The aerobic degradation and metabolism of the test substance were investigated in six freshly sampled US soils using one radioactive label at an application rate according to the highest recommended annual use rate for apples and tomatoes.
The soil samples were incubated in the dark at 20 °C for 181 and 379 days at 75% of the 1/3 bar moisture. A number of 7 respectively 11 individual experiments (depending on the soil) was set up for processing after defined time intervals.
Total recoveries of applied radioactivity ranged from 87.1% to 105.0%. The amount of extracted radioactivity showed a tendency to decrease with time due to an increase of the amount of bound residues and due to mineralisation to CO2. Radioactivity detected in the extracted soil, representing the amount of bound residues, increased towards the end of the study with a maximum of 11.7% in one of the six soils.
A total number of two metabolites was detected in the soil extracts. No metabolite has been classified as major metabolite since the maximum level at which a single metabolite occurred was 1.8% of applied radioactivity in an extract of one soil.
The breakdown of the test substance proposedly proceeded via two routes with carbon dioxide as final degradation product accounting for up to 16.9% of the applied radioactivity.
DT-50 values for the degradation of the active ingredient determined for the individual soils ranged from 533 to 1328 days. For one of the six soils a half-life could not be calculated with statistical significance.
Endpoint:
biodegradation in soil: simulation testing
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
15 Jul 2013 - 12 Sep 2014
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)
GLP compliance:
yes (incl. QA statement)
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic/anaerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
other: Loamy, mixed, mesic Typic Argudalf
% Clay:
19
% Silt:
65
% Sand:
16
% Org. C:
1.9
pH:
6.5
CEC:
11 meq/100 g soil d.w.
Bulk density (g/cm³):
1.02
% Moisture content:
29.1
Parent/product:
parent
Soil No.:
#1
% Degr.:
7.8
Parameter:
radiochem. meas.
Sampling time:
14 d
Remarks on result:
other:
Remarks:
14CO2 formation of the test substance label [guanidine-14C]clothianidin during the aerobic incubation phase.
Parent/product:
parent
Soil No.:
#1
% Degr.:
10.7
Parameter:
radiochem. meas.
Sampling time:
14 d
Remarks on result:
other:
Remarks:
14CO2 formation of the test substance label [thiazolyl-2-14C]clothianidin during the aerobic incubation phase.
Parent/product:
parent
Soil No.:
#1
% Degr.:
< 0.1
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other:
Remarks:
14CO2 formation of the test substance label [guanidine-14C]clothianidin during the anaerobic incubation phase.
Parent/product:
parent
Soil No.:
#1
% Degr.:
< 0.1
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other:
Remarks:
14CO2 formation of the test substance label [thiazolyl-2-14C]clothianidin during the anaerobic incubation phase.
Soil No.:
#1
DT50:
31.6 d
Type:
other: double first order in parallel (DFOP)
Temp.:
20.2 °C
Remarks on result:
other:
Remarks:
DT50 of the test substance label [guanidine-14C]clothianidin
Soil No.:
#1
DT50:
68.3 d
Type:
other: double first order in parallel (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 of the test substance label [guanidine-14C]clothianidin based on results at 20.2 °C
Soil No.:
#1
DT50:
24.8 d
Type:
other: double first order in parallel (DFOP)
Temp.:
20.2 °C
Remarks on result:
other:
Remarks:
DT50 of the test substance label [thiazolyl-2-14C]clothianidin
Soil No.:
#1
DT50:
53.6 d
Type:
other: double first order in parallel (DFOP)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 of the test substance label [thiazolyl-2-14C]clothianidin based on results at 20.2 °C
Conclusions:
The route and rate of degradation of [guanidine-14C]clothianidin and [thiazolyl-2-14C]clothianidin were studied in one soil under anaerobic conditions for 120 days, after an aerobic incubation phase of 14 days, in the dark in the laboratory at 20.2 °C (total study duration of 134 days).Both compounds only differ in their 14C-labelling position.
The study followed the OECD Guideline for the Testing of Chemicals No. 307 and was conducted in compliance with the OECD Principles of Good Laboratory Practice.
The test was performed in static systems consisting of Erlenmeyer flasks each containing 100 g soil (dry weight equivalents). For the aerobic incubation phase the flasks were equipped with traps (permeable for oxygen) for the collection of carbon dioxide and volatile organic compounds. For the anaerobic incubation phase, the traps were replaced by gas sampling bags for the collection of volatiles.
Duplicate samples were processed and analyzed 0 and 14 days after treatment (DAT) during the aerobic incubation phase and at DAT-14, -17, -21, -27, -43, -77, -107 and -134 of the anaerobic incubation phase. The sampling intervals of the anaerobic incubation phase correspond to 0, 3, 7, 13, 29, 63, 93 and 120 days after soil flooding (DASF).
The amounts of test item and degradation products in soil extracts and water were determined by liquid scintillation counting (LSC) and by HPLC/radiodetection analysis. The amounts of volatiles and non-extractable residues were determined by LSC and combustion/LSC, respectively. Test item and degradation products were identified by HPLC-MS(/MS) including accurate mass determination and/or by co-chromatography with reference items.
Mean material balances were 98.1% AR for the guanidine-label (range from 92.9 to 102.4% AR) and 100.5% AR for the thiazolyl-label (range from 97.6 to 104.7% AR).
The amount of carbon dioxide formed during the aerobic incubation phase (mean value of DAT-14 and DASF-0) was 7.8% AR (guanidine-label) and 10.7% AR (thiazolyl-label). The amount of carbon dioxide formed during the anaerobic incubation phase was ≤ 0.1% AR for both labels. Formation of volatile organic compounds (VOC) during the aerobic and anaerobic incubation phases was insignificant as demonstrated by values of ≤ 0.1% AR at all sampling intervals for both labels.
Non-extractable residues (NER) increased during the aerobic incubation phase from DAT-0 to DAT-14 from 3.2 to 10.8% AR for the guanidine-label and from 3.7 to 11.5% AR for the thiazolyl-label. During the following anaerobic incubation phase, NER further increased until DASF-120 to 38.6 and 37.1% AR for guanidine-label and thiazolyl-label, respectively.
Besides the formation of carbon dioxide, three degradation products were identified with the following maximum occurrences: TZMU with 9.2% AR (anaerobic, DASF-120) and 5.2% AR (aerobic, DAT-14) for the thiazolyl-label, TZFA with 18.8% AR (anaerobic, DASF-29, thiazolyl-label) and 10.2% AR (aerobic, DAT-14, guanidine-label), TMG with 22.5% AR (anaerobic, DASF-63) for the guanidine-label. For the aerobic incubation phase the amount of TMG was < LOD for both labels.
The half-life of clothianidin after flooding under anaerobic conditions was between 24.8 and 31.6 days for both labels.

Description of key information

DT50 = 9.7 to 1328 days (32.9 - 2819 days, recalculated to 12 °C), 9.4 – 29.3% mineralisation after 120 to 379 days, aerobic conditions

DT50 = 24.8 to 31.6 days (53.6 – 68.3 days, recalculated to 12 °C), ≤ 0.1% mineralisation after 120 days, anaerobic conditions

Key value for chemical safety assessment

Half-life in soil:
371 d
at the temperature of:
12 °C

Additional information

Three reports are available for the degradation of the substance in the soil compartment. The data gathered from a laboratory investigation according to GLP and OECD Test Guideline No. 307 (2002) demonstrated that the DT50 of (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine in four tested soils ranged from 9.7 to 174.6 days at 20°C (33 to 371 days, recalculated to 12 °C) under aerobic conditions. At the end of the study at DAT-120, evolved 14CO2 accounted for 29.3%, 16.2%, 9.4%, and 15.9% of the applied RA in the four tested soils.

Another study according to GLP and OECD Test Guideline No. 307 reported (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine was well degraded in soil under anaerobic conditions in the dark in the laboratory following an aerobic incubation phase. The calculated best fit half-lives were between 24.8 and 31.6 days (53.6 to 68.3 days, recalculated to 12 °C) for both labels in the tested soil. Formation of carbon dioxide was significant (7.8 to 10.7% AR) during the aerobic incubation phase (14 days) and was ≤ 0.1% AR during the anaerobic incubation phase (120 days). Formation of non-extractable residues (NER) was up to 38.6% AR at study end, which is an indication for biotic degradation of the test substance.

The results of a third study, following GLP and EU Council Directive 91/414 EEC as amended by Commission Directive 95/36/EC and US EPA Pesticide Assessment Guidelines, Subdivision N, Chemistry, Environmental Fate § 162-1 (1982), reported that degradation the half-life of (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine under aerobic conditions in six soils ranged from 541 to 1328 days at 20 °C (1149 to 2819 days, recalculated to 12 °C). The final degradation product carbon dioxide was detected at levels up to 16.9% after an incubation time of 379 days in a silt loam soil. The amounts of bound residues increased with incubation time but did not exceed 11.7% as found in another silt loam soil.

For the sake of completeness three more results are available.

The first study followed the FOCUS guidance document (2006, 2011) on estimating persistence and degradation kinetics from environmental fate studies on pesticides in EU registration and calculated the half-life of the test substance in three soil and by using four different models. The calculated half-life at 20 °C of the test substance ranged from 176 to >1000 days (374 to >1000 days, recalculated to 12 °C).

Two GLP studies performed lysimeter tests to assess the degradation and translocation of (E)-1-(2-chloro-1,3-thiazol-5-ylmethyl)-3-methyl-2-nitroguanidine into the subsoil. Over a period of 3 years the leaching behavior of the test substance was investigated in a total number of three lysimeters under practice-relevant field conditions. At the end of the testing period the amount of total radioactive residues (TRR) in soil was 59.3%, 43.5% and 46.1%, respectively, of the applied radioactivity. During the entire study only 0.3%, 1.1% and 1.3%, respectively, of the applied radioactivity were found in the leachates. The losses of radioactivity during the study were attributed to mineralisation of the active ingredient and amounted to 37.3%, 56.5% and 53.9%, respectively.