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Environmental fate & pathways

Biodegradation in soil

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Reference
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:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
according to guideline
Guideline:
other: SETAC Procedures for assessing the Environmental Fate and Ecotoxicology of Pesticides, Section 1.1 (March 1995)
Deviations:
no
Qualifier:
according to guideline
Guideline:
other: EC Directive 95/36/EC, Active Substances, Sections 7.1.1 (July 1995)
Deviations:
no
GLP compliance:
yes
Test type:
laboratory
Specific details on test material used for the study:
(14C-phenyl)-haloxyfop-(R)-methyl ester
Lot # INV 1536
Purity: 97.9%
Specific activity: 18.3 mCi/mmol

(14C-pyridine)-haloxyfop-(R)-methyl ester
Lot # INV 1532
Purity: >99%
Specific activity: 28.1 mCi/mmol
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Remarks:
also classified by UK & BBA particle size distribution
Soil no.:
#1
Soil type:
sandy loam
% Clay:
15
% Silt:
8
% Sand:
77
% Org. C:
1.1
pH:
7.6
CEC:
18.5 other: mEq/100 g
Soil no.:
#2
Soil type:
sandy loam
% Clay:
7
% Silt:
16
% Sand:
77
% Org. C:
1.5
pH:
6.4
CEC:
8.2 other: mEq/100 g
Soil no.:
#3
Soil type:
sandy loam
% Clay:
15
% Silt:
2
% Sand:
83
% Org. C:
0.7
pH:
6.5
CEC:
6.2 other: mEq/100 g
Soil no.:
#4
Soil type:
sand
% Clay:
1
% Silt:
0
% Sand:
99
% Org. C:
0.1
pH:
6.4
CEC:
1 other: mEq/100 g
Details on soil characteristics:
SOIL COLLECTION AND STORAGE
- A sample of freshly collected Marcham sandy loam soil and three Borstel soil horizons (0-30, 30-60 and 60-100 cm) were supplied by the Sponsor
- Soil preparation: On arrival, the soils were thoroughly mixed and sieved (2 mm mesh), with the minimum of air drying.

Soil No.:
#1
Duration:
>= 120 - <= 268 d
Soil No.:
#2
Duration:
268 d
Soil No.:
#3
Duration:
268 d
Soil No.:
#4
Duration:
268 d
Soil No.:
#1
Initial conc.:
>= 5.33 - <= 5.37 other: µg
Based on:
other: mass applied to unit
Remarks:
Group A & B: 5.33 µg (14C-Phenyl labelled test substance) Group C & D: 5.37 µg (14C-Pyridine labelled test substance)
Soil No.:
#2
Initial conc.:
5.37 other: µg
Based on:
other: mass applied to unit
Remarks:
Group E: 14C-Pyridine labelled test substance
Soil No.:
#3
Initial conc.:
5.37 other: µg
Based on:
other: mass applied to unit
Remarks:
Group F: 14C-Pyridine labelled test substance
Soil No.:
#4
Initial conc.:
5.37 other: µg
Based on:
other: mass applied to unit
Remarks:
Group G: 14C-Pyridine labelled test substance
Parameter followed for biodegradation estimation:
CO2 evolution
radiochem. meas.
Soil No.:
#1
Temp.:
20±2°C in Group A, B & C; 10±2°C in Group D
Humidity:
40% moisture
Microbial biomass:
234 µg C/g
Soil No.:
#2
Temp.:
20±2°C
Humidity:
40% moisture
Microbial biomass:
234 µg C/g
Soil No.:
#3
Temp.:
20±2°C
Humidity:
40% moisture
Microbial biomass:
234 µg C/g
Soil No.:
#4
Temp.:
20±2°C
Humidity:
40% moisture
Microbial biomass:
234 µg C/g
Details on experimental conditions:
EXPERIMENTAL DESIGN
- Soil preincubation conditions: Prior to use, soils were stored in the dark, in an incubator routinely maintained at 4 ± 2°C, in loosely tied plastic. Soils were stored for less than three months prior to dispensing into the test units.
- Soil condition: Fresh soil for all the groups except group B (sterile soil)
- Soil (g/replicate): 50 g dry weight equivalent
- Test apparatus: Erlenmeyer flasks
- Details of traps for CO2 and organic volatile: 5 traps: The first was empty as a security trap and the second and third contained ethanediol and 2% liquid paraffin in xylene to trap polar and non-polar organic volatiles respectively. The final two contained 2M sodium hydroxide solution to trap liberated carbon dioxide.

Test material application
- Volume of test solution used/treatment: The volume of radiolabeled test compound solution applied to each unit was between 34 and 59 µL, and the volume of non-radiolabelled test compound solution applied was 24 µL
- Application method: dispensed dropwise on the surface of the soil

Experimental conditions
- Moisture maintenance method: After test compound application, soil samples were incubated in a constant temperature room at 20 ± 2°C (or in a laboratory incubator at 10 ± 2°C for incubation group D samples).
- Continuous darkness: Yes

SAMPLING DETAILS
- Sampling intervals: Immediately after application and at intervals of 2, 7, 14, 30, 59, 90, and 120 days single units from each incubation group were removed for analysis. In addition, single units from groups C, D, E, F and G were removed for analysis at 181 and 268 days. Trap solutions were analysed when the units to which they were attached were removed for analysis, or were analysed and replenished with fresh reagents every 30 to 40 days.
- Extraction: Soil from each incubation unit was sequentially extracted with acetonitrile (2 x 100 mL) followed by 0.1M hydrochloric acid (2 x 100 mL), with liquid extracts separated by centrifugation. Radioactivity remaining unextracted was determined by combustion analysis. The acetonitrile and acid extracts were concentrated by rotary evaporation and solid phase extraction (SPE) respectively, before combining them for analysis by HPLC and TLC.
Unextracted soil residues were further extracted with methanol : water : 40% sodium hydroxide solution, 20:1:1 v/v/v (2 x 100 mL). The extracts were separated by centrifugation, neutralised and rotary evaporated to remove the methanol. The resulting concentrated extracts were diluted with water and acidified (ca. pH 1), prior to concentration by SPE and analysis by HPLC and TLC.
SPE concentration methods for the initial and further extracts produced a proportion of radioactivity not retained on the SPE cartridge. Where the combined level of radioactivity in these extracts exceeded 10% of the applied radioactivity the unretained SPE samples were combined and partitioned against ethyl acetate. The ethyl acetate fraction was separated and concentrated by rotary evaporation, prior to analysis by HPLC and TLC.
Key result
Soil No.:
#1
% Degr.:
94.4
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other: Group A
Key result
Soil No.:
#1
% Degr.:
93.5
Parameter:
radiochem. meas.
Sampling time:
120 d
Remarks on result:
other: Group B
Key result
Soil No.:
#1
% Degr.:
94.8
Parameter:
radiochem. meas.
Sampling time:
268 d
Remarks on result:
other: Group C
Key result
Soil No.:
#1
% Degr.:
93.1
Parameter:
radiochem. meas.
Sampling time:
268 d
Remarks on result:
other: Group D
Key result
Soil No.:
#2
% Degr.:
91.8
Parameter:
radiochem. meas.
Sampling time:
268 d
Remarks on result:
other: Group E
Key result
Soil No.:
#3
% Degr.:
94.1
Parameter:
radiochem. meas.
Sampling time:
268 d
Remarks on result:
other: Group F
Key result
Soil No.:
#4
% Degr.:
97.6
Parameter:
radiochem. meas.
Sampling time:
268 d
Remarks on result:
other: Group G
Key result
Soil No.:
#1
DT50:
0.6 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group A
Key result
Soil No.:
#1
DT50:
0.5 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group B
Key result
Soil No.:
#1
DT50:
0.5 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group C
Key result
Soil No.:
#1
DT50:
0.5 d
Type:
other: first order
Temp.:
10 °C
Remarks on result:
other: Group D
Key result
Soil No.:
#2
DT50:
0.5 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group E
Key result
Soil No.:
#3
DT50:
0.7 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group F
Key result
Soil No.:
#4
DT50:
0.6 d
Type:
other: first order
Temp.:
20 °C
Remarks on result:
other: Group G
Transformation products:
yes
No.:
#1
Details on transformation products:
Degradation of the test substance ester resulted initially in the formation of DE-535 acid and then subsequently to the formation of DE-535 phenol, DE-535 pyridinol and DE-535 pyridinone.
DE-535 acid was degraded rapidly (DT50= 5 to 36 days, DT90= 58 to 120 days) in fresh Marcham sandy loam and Borstel upper and middle soil horizons. A slower rate of degradation (DT50= 117 days, DT90= 390 days) was observed in the lower Borstel soil horizon and in sterile soil there was essentially no degradation.
Levels of DE-535 phenol did not exceed 10% of applied radioactivity in any soil at any sampling interval. DE-535 phenol degradation was rapid in fresh Marcham sandy loam and Borstel upper and middle soil horizons (DT50 = 15 to 45 days, DT90=53 to 131 days).
DE-535 pyridinol reached maximum concentrations between 22 and 37% of applied radioactivity in fresh Marcham sandy loam and Borstel soil horizons. The rate of degradation of DE-535 pyridinol in these soils was slow (DT50 = 129 to 508 days, DT90= 299 to 1615 days).
DE-535 pyridinone reached maximum concentrations between 7 and 17% of applied radioactivity in fresh Marcham sandy loam and the Borstel soil horizons. DE-535 pyridinone degradation in fresh Marcham sandy loam and Borstel upper soil horizon was slow (DT50= 205 to 246 days, DT90= 475 to 666 days).
Further degradation of DE-535 phenol, DE-535 pyridinol and DE-535 pyridinone resulted in the formation of soil bound residues (up to 48% of applied radioactivity) and carbon dioxide (up to 33% of applied radioactivity).
Volatile metabolites:
yes
Remarks:
Refer 'Any other information on results incl. tables'
Details on results:
TOTAL UNIDENTIFIED RADIOACTIVITY OF APPLIED AMOUNT: <1 to 3%

STERILE TREATMENTS
- Degradation of the test substance ester was rapid in sterile Marcham sandy loam soil incubated at 20°C. The total level of applied radioactivity present as DE-535-ME compound declined from 95% immediately after application, to 5% after 2 days and to 1% after 120 days incubation.
Degradation under sterile conditions again resulted in the formation of DE-535 acid, which increased to a maximum level of 85% of applied radioactivity after 30 days. The concentration of DE-535 acid remained high throughout the rest of the incubation period, with between 69 and 76% of applied radioactivity detected between 59 and 120 days. Further degradation of DE-535 acid was not observed, with the presence of DE-535 phenol and other degradates not exceeding 1% of applied radioactivity at any sampling interval.

Volatile metabolites:

In Group A, volatile products were detected exclusively in 2M sodium hydroxide traps and increased steadily throughout the incubation to a maximum of 33% of applied radioactivity after 120 days.

In Group B, the amount of applied radioactivity remaining unextracted accounted for the majority of the radioactive balance at each sampling interval, with radioactivity detected in all volatile traps remaining at <1% of applied throughout the incubation period.

In groups C and D, the total amount of applied radioactivity detected in the volatile traps increased gradually during the incubation period to 24% (20°C) and 6% (10°C) after 268 days. The majority of the volatile radioactivity was present in the 2M sodium hydroxide traps in each instance.

In groups E, F and G, over the same period the amount of applied radioactivity unextracted from the soil increased to between 22 and 30%, with volatile traps containing between 23 and 27% of applied radioactivity. The majority of the volatile radioactivity was present in the 2M sodium hydroxide traps, however the lower Borstel soil horizon (60-100 cm) contained a larger proportion (8%) in the organic traps compared to the other two horizons (1%).

Conclusions:
The test substance was degraded very rapidly in fresh and sterile soils under aerobic conditions at 10 and 20°C (DT50= <1 day, DT90= 1.5 to 2.4 days).
Executive summary:

The aerobic degradation of the 14C labelled-test substance was investigated to determine the effects of sterility in Marcham, UK sandy loam soil. The aerobic degradation of 14C-pyridine labelled-test substance was investigated to determine the effects of temperature under laboratory conditions again using Marcham sandy loam soil. Further studies were also conducted using 14C-pyridine labelled-test substance to determine the aerobic degradation rate in three horizons of a Borstel, German soil used for a previous lysimeter study.

In all experiments, the application rate was nominally 5.4 µg per 50 g soil, equivalent to a field application rate of 108 g/ha. The soils were maintained at 40% moisture holding capacity in the dark at the appropriate temperature regimes.

Liberated carbon dioxide was trapped and, at selected time points, samples of soil were extracted with acetonitrile and 0.1M hydrochloric acid. Radioactivity in extracts, trapping solutions and soil residues was determined by liquid scintillation counting. Extracts were analysed by HPLC to determine the proportion of the test substance and metabolites.

The test substance was degraded very rapidly in fresh and sterile soils under aerobic conditions at 10 and 20°C (DT50= <1 day, DT90= 1.5 to 2.4 days).

Degradation of the test substance ester resulted initially in the formation of DE-535 acid and then subsequently to the formation of DE-535 phenol, DE-535 pyridinol and DE-535 pyridinone.

DE-535 acid was degraded rapidly (DT50= 5 to 36 days, DT90= 58 to 120 days) in fresh Marcham sandy loam and Borstel upper and middle soil horizons. A slower rate of degradation (DT50= 117 days, DT90= 390 days) was observed in the lower Borstel soil horizon and in sterile soil there was essentially no degradation.

Levels of DE-535 phenol did not exceed 10% of applied radioactivity in any soil at any sampling interval. DE-535 phenol degradation was rapid in fresh Marcham sandy loam and Borstel upper and middle soil horizons (DT50 = 15 to 45 days, DT90=53 to 131 days).

DE-535 pyridinol reached maximum concentrations between 22 and 37% of applied radioactivity in fresh Marcham sandy loam and Borstel soil horizons. The rate of degradation of DE-535 pyridinol in these soils was slow (DT50 = 129 to 508 days, DT90= 299 to 1615 days).

DE-535 pyridinone reached maximum concentrations between 7 and 17% of applied radioactivity in fresh Marcham sandy loam and the Borstel soil horizons. DE-535 pyridinone degradation in fresh Marcham sandy loam and Borstel upper soil horizon was slow (DT50= 205 to 246 days, DT90= 475 to 666 days).

Further degradation of DE-535 phenol, DE-535 pyridinol and DE-535 pyridinone resulted in the formation of soil bound residues (up to 48% of applied radioactivity) and carbon dioxide (up to 33% of applied radioactivity).

Description of key information

Study Type

 Study Details Value  Guideline Reliability 
Aerobic metabolism   Marcham, UK sandy loam soil & Borstel, German soil  DT50= <1 day, DT90= 1.5 to 2.4 days). EU Council Directive 91/414/EEC, Annex II, point 7.1.1, as amended by Directive 95/36/EC,SETAC Procedures for assessing the Environmental Fate and Ecotoxicity of Pesticides Section 1.1

Key value for chemical safety assessment

Half-life in soil:
0.6 d

Additional information