Methomyl

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Guidelines concerning the inclusion of active substances in Annex I to EEC Council Directive 91/414/EEC as amended by Commission Directive 95/36/EC

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Specific details on test material used for the study:

Test substance Name: [1-14C]Methomyl
Lot#: 555
Radiochemical purity: >95%
Specific activity: 42.96 µCi/mg

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

loam

% Clay:

10

% Silt:

46.8

% Sand:

43.2

% Org. C:

0.9

pH:

5.1

CEC:

4.44 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

sandy loam

% Clay:

10

% Silt:

32.8

% Sand:

57.2

% Org. C:

0.7

pH:

7.8

CEC:

6.48 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

sandy loam

% Clay:

6

% Silt:

24.8

% Sand:

69.2

% Org. C:

2.1

pH:

6.4

CEC:

10.67 meq/100 g soil d.w.

Soil No.:

#1

Duration:

30 d

Soil No.:

#2

Duration:

30 d

Soil No.:

#3

Duration:

21 d

Soil No.:

#1

Initial conc.:

3.6 mg/kg soil d.w.

Soil No.:

#2

Initial conc.:

3.6 mg/kg soil d.w.

Soil No.:

#3

Initial conc.:

3.6 mg/kg soil d.w.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 31 mg C/kg of soil; Final sampling time: 110 mg C/kg of soil

Soil No.:

#2

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 206 mg C/kg of soil; Final sampling time: 189 mg C/kg of soil

Soil No.:

#3

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 183 mg C/kg of soil; Final sampling time: 392 mg C/kg of soil

Soil No.:

#2

Temp.:

10°C

Microbial biomass:

Initial: 215 mg C/kg of soil; Final sampling time: 230 mg C/kg of soil

Soil No.:

#3

Remarks on result:

other: Recovery of radioactivity from Speyer 2.2 soil after application of 14C-test substance was is in range of 87 to 95%.

Soil No.:

#1

Remarks on result:

other: Recovery of radioactivity from Mattapex soil after application of 14C-test substance was is in range of 85.4 to 99.8%.

Soil No.:

#2

Remarks on result:

other: Recovery of radioactivity from Nambsheim soil after application of 14C-test substance at 20°C was is in range of 90.1 to 95.9%.

Soil No.:

#2

Remarks on result:

other: Recovery of radioactivity from Nambsheim soil after application of 14C-test substance at 10°C was is in range of 92.1 to 96.6%.

Key result

Soil No.:

#1

% Degr.:

83.3

Parameter:

radiochem. meas.

Sampling time:

30 d

Remarks on result:

other: Mattapex soil at 20°C

Key result

Soil No.:

#3

% Degr.:

88

Parameter:

radiochem. meas.

Sampling time:

21 d

Remarks on result:

other: Speyer 2.2 at 20°C

Key result

Soil No.:

#2

% Degr.:

86.4

Parameter:

radiochem. meas.

Sampling time:

30 d

Remarks on result:

other: Nambsheim soil at 20°C

Key result

Soil No.:

#2

% Degr.:

56.1

Parameter:

radiochem. meas.

Sampling time:

30 d

Remarks on result:

other: Nambsheim soil at 10°C

Key result

Soil No.:

#1

DT50:

8 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: Rate constant was 0.0878; R2 value was 0.9905

Key result

Soil No.:

#3

DT50:

4 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: rate constant was 0.0878; R2 value was 0.9957

Key result

Soil No.:

#2

DT50:

6 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: Rate constant was 0.1074/d, R2 value was 0.9923

Key result

Soil No.:

#2

DT50:

23 d

Type:

(pseudo-)first order (= half-life)

Temp.:

10 °C

Remarks on result:

other: Rate constant was 0.0307, R2 value was 0.9953

Transformation products:

yes

Remarks:

The major products of test substance degradation in aerobic soil were CO2 and unextractable bound residues.

Volatile metabolites:

yes

Remarks:

Volatile radioactivity increased to 51.3% AR in Speyer 2.2 soil after 21 days, to 51.1% AR in Mattapex soil after 30 days, to 61.0% AR in Nambsheim soil at 20°C after 30 days and to 32.7% in Nambsheim soil at 10°C after 30 days.

Residues:

yes

Remarks:

Unextractable bound residues at 20°C are up to 31.0% applied radioactivity in Speyer 2.2 soil after 21 days, 32.2% applied radioactivity in Mattapex soil after 30 days and 25.2% applied radioactivity in Nambsheim soil after 30 days (all mean values).

Conclusions:

In aerobic soil at 20°C, test substance was rapidly degraded with DT50 values of 4 days (Speyer 2.2 soil), 8 days (Mattapex soil) and 6 days (Nambsheim soil). DT90 values were 14 days (Speyer 2.2 soil), 26 days (Mattapex soil) and 21 days (Nambsheim soil). At 10°C, test substance degraded in Nambsheim soil with a DT50 of 23 days and a DT90 of 75 days. The ratio of degradation rates in Nambsheim soil (20°C:10°C) was 3.5:1.

Executive summary:

This study was conducted as part of a programme to determine the environmental fate of test substance and to provide data to support the inclusion of test substance as an active substance in Annex I to EEC Council Directive 91/414/EEC, as amended by Commission Directive 95/36/EC. The rate of degradation of test susbtance was studied in three agricultural aerobic soils (Nambsheim, Speyer 2.2 and Mattapex). Soils were treated with¹⁴C-labelled test substance at a rate of 3.6 mg/kg dry weight. This was equivalent to an agricultural use rate of 2.7 kg ai/ha assuming a uniform incorporation in the top 5 cm of soil and a soil bulk density of 1.5 g/cm³. Treated soil samples were incubated in the dark at 20±2°C for up to 21 (Speyer 2.2 soil) or 30 days (Mattapex and Nambsheim soils). Additionally, treated samples of Nambsheim soil were also incubated in the dark at 10±2°C, for up to 30 days. At various time intervals, soil samples were exhaustively extracted with aqueous/organic solvents and the total amount of extractable test substance and its degradation products were separated and quantified by chromatography. Radiolabelled volatile degradates, including CO2,were trapped and quantified using an air flow-through system. Unextractable¹⁴C residues were quantified.

Overall, material balances were satisfactory. Of the 70 samples analyzed in the study, values of at least 90% applied radioactivity (AR) were obtained in all except nine cases, and those values below 90% AR tended to be from samples that had been incubated longer and from samples in which test substance had been extensively degraded. However, mean material balances were all greater than 85% AR. There was at least one sample in every replicate pair with a total recovery of at least 90% AR.

The degradation behaviour was well described assuming first-order degradation kinetics (all r2 values were greater than 0.99). In aerobic soil at 20°C, test substance was rapidly degraded with DT50 values of 4 days (Speyer 2.2 soil), 8 days (Mattapex soil) and 6 days (Nambsheim soil). DT90 values were 14 days (Speyer 2.2 soil), 26 days (Mattapex soil) and 21 days (Nambsheim soil). At 10°C, test substance degraded in Nambsheim soil with a DT50 of 23 days and a DT90 of 75 days. The ratio of degradation rates in Nambsheim soil (20°C:10°C) was 3.5:1. Extractable degradation products of test substance in aerobic soil werequantitatively minor. None exceeded 10% applied radioactivity. These included the oxime (S-methyl N-(hydroxy)thioacetimidate) and three other, unidentified,more polar products. The maximum mean proportion of the applied radioactivity that the oxime represented at any one time was 2.5%. By far the major products of test substance degradation in aerobic soil were CO2 and unextractable bound residues. At 20°C,¹⁴CO2 represented up to 51.3% applied radioactivity in Speyer 2.2 soil after 21 days, 51.1% applied radioactivity in Mattapex soil after 30 days and 61.0% applied radioactivity in Nambsheim soil after 30 days. Unextractable bound residues at 20°C represented up to 31.0% applied radioactivity in Speyer 2.2 soil after 21 days, 32.2% applied radioactivity in Mattapex soil after 30 days and 25.2% applied radioactivity in Nambsheim soil after 30 days (all mean values).

Reference 2

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

supporting 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)

Deviations:

no

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:

Test susbtance Name: [14C]methomyl
Lot#: 83346-1-8-1
Radiochemical purity: 98.3%
Specific activity: 42 µCi/mg

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

9

% Silt:

37

% Sand:

54

% Org. C:

0.53

pH:

7.8

CEC:

3 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

sandy loam

% Clay:

11

% Silt:

30

% Sand:

59

% Org. C:

1.8

pH:

7.5

CEC:

9.5 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

silt loam

% Clay:

11

% Silt:

59

% Sand:

30

% Org. C:

5.1

pH:

5.5

CEC:

21.3 meq/100 g soil d.w.

Soil No.:

#1

Duration:

38 d

Soil No.:

#2

Duration:

38 d

Soil No.:

#3

Duration:

38 d

Soil No.:

#1

Initial conc.:

0.4 other: µg/g Soil d.w

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 337.7 µg/g dry soil; Final sampling interval: 252.2 µg/g dry soil

Soil No.:

#2

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 674.6 µg/g dry soil; Final sampling interval: 528.4 µg/g dry soil

Soil No.:

#3

Temp.:

20 ± 2°C

Microbial biomass:

Initial: 721.1 µg/g dry soil; Final sampling interval: 715.0 µg/g dry soil

Soil No.:

#1

% Recovery:

98.1

Remarks on result:

other: Sandy loam (Porterville) soil treated with test substance (expressed as % applied radioactivity) has recovery in range of 91.5 to 101.6%.

Soil No.:

#2

% Recovery:

96.6

Remarks on result:

other: Sandy loam (Nambsheim) soil treated with test substance (expressed as % applied radioactivity) has recovery in range of 94.1 to 101.2%.

Soil No.:

#3

% Recovery:

98

Remarks on result:

other: Silt loam (LRA-E1) soil treated with test substance (expressed as % applied radioactivity) has recover in range of 96.7 to 101.5%.

Key result

Soil No.:

#1

DT50:

11.6 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: R² value is 0.9844

Key result

Soil No.:

#2

DT50:

2.06 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: R² value is 0.9969

Key result

Soil No.:

#3

DT50:

6.18 d

Type:

(pseudo-)first order (= half-life)

Temp.:

20 °C

Remarks on result:

other: R² value is 0.9935

Volatile metabolites:

yes

Remarks:

14CO2

Residues:

yes

Remarks:

Given under "Any other information on results incl. tables".

Table 1: Extractability of Residues:

Soil	Sandy Loam (Porterville)	Sandy Loam (Nambsheim)	Silt Loam (LRA-E1)
Maximum Radioactivity extracted at 0 timepoint	101.0% AR	101.2% AR	100.4 AR
Maximum Radioactivity extracted at Day 38 timepoint	8.7% AR	5.1% AR	4.6% AR
Maximum Non-Extractable Residues, (Timepoint)	30.6% AR (Day 38)	33.8% AR (Day 10)	41.0% AR (Day 14)

Conclusions:

- The DT50 value for sandy loam (Porterville), sandy loam (Nambsheim) and silt loam (LRA-E1) was 11.6, 2.06 and 6.18 days. DT90 values for sandy loam (Porterville), sandy loam (Nambsheim) and silt loam (LRA-E1) was 38.4, 6.85 and 20.5 days respectively with X² 5.28, 4.87 and 4.52.

Executive summary:

The study was conducted according to guideline OECD 304 and EPA 835.4100 to evaluate the rate of degradation of [14C]test substance in three soils. The soils used were Porterville (sandy loam, 0.53% OC, pH 7.8), Nambsheim (sandy loam, 1.8% OC, pH 7.5), and LRA-E1 (silt loam, 5.1% OC, pH 5.5).

The test system was acclimatized for up to 11 days prior to treatment. [14C]test substance labelled in the 1-14C position was used. The test substance was applied to the soil at a nominal rate of 0.4 μg/g dry soil weight, correspondent to a 400 g a.i./ha application rate assuming 10 cm incorporation and 1.0 g/cm³ soil density. Treated vessels were incubated for up to 38 days under aerobic conditions in the dark at 20 ± 2°C at pF 2 moisture.

The test systems consisted of polypropylene Nalgene® bottles connected to flow-through systems for each soil. Test flasks were connected to traps for the collection of CO2 and non-specific volatile organic compounds. Samples were analyzed immediately following test substance application (Day 0) and after 1, 2, 4, 7, 10, 14, 30, and 38 days of aerobic incubation.

Soil samples were extracted three times with 50:50 methanol:water. Extractable soil radioactivity was quantified by LSC and the radioactive components were quantified by reversed phase HPLC with on-line radiodetection. Non-extractable 14C-residues were quantified by combustion analysis.

The material balance was quantitative for all samples and was in the range 91.5 to 102.9% applied radioactivity (% AR).

The extractable radioactivity was quantitative at time 0 in all soils (>99.5%). All three soils showed similar degradation, with the sandy loam (Nambsheim) soil displaying the most extensive degradation.

In the sandy loam (Nambsheim) soil, extractable radioactivity decreased progressively with study duration to 5.1% AR by the final timepoint, while non-extractable residue increased to 33.8% AR by Day 10. The amount of 14CO2 increased over the study duration, reaching a maximum of 65.6% AR. Volatile organics traps were analyzed at termination with no activity present.

In the sandy loam (Porterville) soil, extractable radioactivity decreased progressively with study duration to 8.7% AR by the final timepoint, while non-extractable residue increased to 30.6% AR by termination. The amount of 14CO2 increased over the study duration, reaching a maximum of 58.5% AR. Volatile organics traps were analyzed at termination with no activity present.

In the silt loam (LRA-E1) soil, extractable radioactivity decreased progressively with study duration to 4.6% AR by the final timepoint, while non-extractable residue increased to 41.0% AR by Day 14. The amount of 14CO2 increased over the study duration, reaching a maximum of 55.2% AR. Volatile organics traps were analyzed at termination with no activity present.

Degradation in all soils proceeded primarily via microbial degradation through mineralization. No major metabolites (>10% AR) were observed, though IN-X1177 did reach 6.5% AR in the sandy loam (Porterville) soil at Day 14 before decreasing to below 1% AR over the remainder of the study. Multiple minor metabolites were observed in the polar region of the chromatographic method, but no single metabolite reached >10% AR. The maximum percentage of each metabolites observed and expressed as % AR of IN-X1177 in sandy loam (Porterville), sandy loam (Nambsheim) and silt loam (LRA-E1) was 6.5 (Day 14), 2.5 (Day 2) and 1.9 (Day 2 and 4) respectively.

Test substance and metabolite IN-X1177 were initially assigned by comparison of the HPLC retention times with respective reference standards. The identity of unchanged test substance was then confirmed by LC/MS analysis.

The percentage of test substance was plotted against time for each soil type and the degradation rate (DT50 and DT90) determined using SFO kinetics. The DT50 value for sandy loam (Porterville), sandy loam (Nambsheim) and silt loam (LRA-E1) was 11.6, 2.06 and 6.18 days respectively. DT90 values for sandy loam (Porterville), sandy loam (Nambsheim) and silt loam (LRA-E1) was 38.4, 6.85 and 20.5 days respectively with X² 5.28, 4.87 and 4.52.

Test substance degrades to multiple components by a variety of processes primarily via microbial degradation to mineralization. Test substance would be expected to dissipate from the environment from aerobic soils

Reference 3

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Pesticide Assesment Guidelines Subdivision N, 162-1

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Specific details on test material used for the study:

Test substance name: [1-14C]Methomyl
Lot#: 1800-056
Radiochemical purity: >97%
Specific activity: 28.3 µCi/mg

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

other: Ohio State University Soil Characterization

Soil no.:

#1

Soil type:

loam

% Clay:

13.4

% Silt:

41.7

% Sand:

44.9

% Org. C:

0.93

pH:

7.8

CEC:

56.3 meq/100 g soil d.w.

Soil No.:

#1

Duration:

3 mo

Soil No.:

#1

Initial conc.:

4.1 ppm

Parameter followed for biodegradation estimation:

CO2 evolution

radiochem. meas.

Soil No.:

#1

Temp.:

25 ± 1°C

Soil No.:

#1

% Recovery:

97.3

St. dev.:

3.1

Remarks on result:

other: Recovery of applied radioactivity

Key result

Soil No.:

#1

% Degr.:

97.7

Parameter:

radiochem. meas.

Sampling time:

3 mo

Remarks on result:

other: The % of applied radioactivity present as test substance decreased from 99% for Day 0 to 1.3% after 3 months of aerobic incubation.

Key result

Soil No.:

#1

DT50:

11 d

Type:

other: First order

Temp.:

25 °C

Remarks on result:

other: Test substance is rapidly metabolized.

Transformation products:

yes

Remarks:

14CO2

Volatile metabolites:

no

Remarks:

Essentially no volatile organic radioactivity (<0.1%).

Residues:

yes

Remarks:

The unextractable radioactivity (bound) increased with time for 1st month, then declined to 14% at 3 months.

Conclusions:

Half-life: ~11 days (aerobic)

Executive summary:

The study was conducted according to guideline EPA 162 -1 to evaluate the aerobic metabolism of test substance in Madera, California Soil. Microbially active loam soil (pH 7.8, organic matter 0.9 percent), was treated with [1-14C]-labelled test substance at a concentration of 4.1 ppm. This treatment rate was equivalent to approximately 8 pounds’ active ingredient per acre or approximately 2.2 times the maximum label rate. Deionized water was added to each soil sample to maintain 75 percent field moisture capacity. The soils were incubated in the dark at 25 ± 1°C. Duplicate soil samples were harvested immediately after dosing and after aging aerobically 1, 2, 4, 8, 14, and 21 days, and 1, 2, and 3 months.

[1-14C]-labelled test substance was rapidly metabolized in this soil with a half-life of approximately 11 days. The major metabolic product was 14CO2 with over 75 percent of the radiolabel mineralized during the three-month study period. Extractable metabolites included minor amounts of methomyl oxime (methyl-N-hydroxythioacetimidate, MHTA) and two polar products, all of which were individually 3.3 percent or less of the applied radioactivity at any time during the study. Unextractable radioactivity (bound) increased with time for the first month, constituting 24 percent of the applied radioactivity at 1 month, then declined to 14 percent at 3 months. The majority of the unextractable radioactivity was associated with the soil organic matter and was further fractionated into the soluble and insoluble humin and fulvic acid fractions.

Reference 4

Endpoint:

biodegradation in soil, other

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Pesticide Assesment Guidelines Subdivision N, 162-2

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Specific details on test material used for the study:

Test substance Name: [1-14C]Methomyl
Lot#: 1800-056
Radiochemical purity: >97%
Specific activity: 28.3 µCi/mg

Radiolabelling:

yes

Oxygen conditions:

anaerobic

Soil classification:

other: Ohio state university soil characterization Laboratory, Columbus, Ohio

Soil no.:

#1

Soil type:

loam

% Clay:

13.4

% Silt:

41.7

% Sand:

44.9

% Org. C:

0.93

pH:

7.8

CEC:

56.3 meq/100 g soil d.w.

Soil No.:

#1

Duration:

60 d

Initial conc.:

4.1 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

25±1°C

Soil No.:

#1

Remarks on result:

other: In static phase, the material balance was 70 to 83% during anaerobic phase.

Soil No.:

#1

Remarks on result:

other: In dynamic system, the radioactive material balance was 85 to 89% during the anaerobic phase.

Key result

Soil No.:

#1

% Degr.:

96.6

Parameter:

radiochem. meas.

Sampling time:

60 d

Remarks on result:

other: Static phase

Key result

Soil No.:

#1

% Degr.:

94.3

Parameter:

radiochem. meas.

Sampling time:

60 d

Remarks on result:

other: Dynamic phase

Key result

Soil No.:

#1

DT50:

14 d

Type:

other: First order

Temp.:

25 °C

Remarks on result:

other: Test substance was rapidly metabolized under anaerobic conditions.

Transformation products:

yes

Remarks:

14CO2

Volatile metabolites:

yes

Remarks:

Volatile organic metabolites trapped in the ethylene glycol or dry ice/methanol traps accounted for 4.4 percent of applied radioactivity with significant amounts only observed during the anaerobic phase.

Residues:

yes

Remarks:

Unextractable radioactivity (bound) increased to 30.3% at Day 7 anaerobic sampling point and decreased to 24.4% at 60-day final anaerobic point.

Material balance during the anaerobic phase of the study ranged from 70 to 83% of the applied radioactivity. The low material balance appeared to be related to a failure to completely trap volatile radioactivity. To address this concern, a second set of soil samples were incubated anaerobically under slightly modified experimental conditions (dynamic nitrogen flow system, rather than a static nitrogen atmosphere). The results of the dynamic anaerobic experiments demonstrated that 14CO2 was not completely trapped in the initial experiment. Material balance during this dynamic anaerobic phase of the study was 85 to 89%, with a total of 52.9% of the applied radioactivity accounted for as 14CO2. The evolution of volatile metabolites (3.9%) was similar to static incubation (4.4%).

Conclusions:

Half-life: ~14 days (anaerobic)

Executive summary:

The study was conducted according to guideline EPA 162-2 to evaluate the anaerobic metabolism of [1-14C]-labelled test substance in Madera, California Soil. Microbially active loam soil (pH 7.8, organic matter 0.9%), was treated with [1-14C]-labelled test substance at a concentration of 4.1 ppm. This treatment rate was equivalent to approximately 8 pounds active ingredient per acre or approximately 2.2 times the maximum label rate. Deionized water was added to each soil sample to maintain soil moisture at 75% field moisture capacity. The soils were first incubated aerobically for 14 days and then converted to anaerobic conditions for 60 days. The soil samples were kept in the dark at 25 ± 1°C during both aerobic and anaerobic incubation periods. Duplicate soil samples were harvested at 7, 14, 30 and 60 days after the soils were converted to anaerobic conditions

[1-14C]-labelled test substance was rapidly metabolized in this soil with a half- life of approximately 11 days under aerobic conditions and approximately 14 days under anaerobic conditions. The major metabolic product was 14CO2 with days under anaerobic conditions. approximately 35% of the radiolabel mineralized to CO2 during the two-and-a-half-month period. Extractable metabolites included minor amounts of methomyl oxime (S-methyl-N-hydroxythioacetimidate, MHTA) and two polar products, all of which were individually 2.8% or less of the applied radioactivity at the final anaerobic (60 days) sampling point. Unextractable radioactivity (bound) increased to 30.3% at the Day 7 anaerobic sampling point and declined to 24.4% at the Day 60 (final) anaerobic sampling point. The majority of the unextractable radioactivity was associated with the soil organic matter and was further fractionated into the soluble and insoluble humin and fulvic acid fractions.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
aerobic metabolism	Madera, California Soil for up to 3 months	DT50 = 11 days	EPA 162 -1	1
anaerobic metabolism	Madera, California Soil for up to 2 months	DT50 = 14 days	EPA 162-2	1
aerobic metabolism	Porterville (sandy loam), Nambsheim (sandy loam), and LRA-E1 (silt loam) for up to 38 days	DT50 = 11.6, 2.06 and 6.18 days, respectively	OECD 304 EPA 835.4100	1
aerobic metabolism	Speyer 2.2 soil, Mattapex soil and Nambsheim soil up to 30 days	DT50 = 4, 8 and 6 days, respectively	Guidelines concerning the inclusion of active substances in Annex I to EEC Council Directive 91/414/EEC as amended by Commission Directive 95/36/EC	1

Key value for chemical safety assessment

Half-life in soil:

11.6 d