diethyl 1-(2,4-dichlorophenyl)-5-methyl-4,5-dihydro-1H-pyrazole-3,5-dicarboxylate

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil

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:

other: BBA Part IV, 4-1 and USEPA (=EPA) § 162-1

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil no.:

#1

Soil type:

sandy loam

% Clay:

5.7

% Silt:

8.9

% Sand:

85.4

% Org. C:

5.01

pH:

5

CEC:

9 meq/100 g soil d.w.

Bulk density (g/cm³):

1.33

Soil no.:

#2

Soil type:

loamy sand

% Clay:

11.6

% Silt:

31.6

% Sand:

56.8

% Org. C:

1.79

pH:

6.1

CEC:

6.6 meq/100 g soil d.w.

Bulk density (g/cm³):

1.14

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: The soils were sampled from the upper horizon of test fields
Source of the soils:
- LS 2.2: standard soil 2.2 of the Landwirtschaftliche Untersuchungs- und Forschungsanstalt, 67346 Speyer, Obere Langgasse 40, FRG
- SL V: agricultural test field of the Hoechst AG, 65926 Frankfurt, near Gate South, FRG

- Soil preparation: The soils were sieved through a 2 mm sieve and adjusted to 40 % of the maximum water holding capacity which corresponded to approximately 75 % of the field capacity.

Soil No.:

#1

Duration:

152 d

Soil No.:

#2

Duration:

152 d

Soil No.:

#1

Initial conc.:

0.132 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

0.132 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20

Microbial biomass:

16.9

Soil No.:

#2

Temp.:

20

Microbial biomass:

19

Details on experimental conditions:

2. EXPERIMENTAL DESIGN
- Soil preincubation conditions: To maintain the biological activity chickweed (Stellaria media) was planted into the soils. The plants were grown under artificial sunlight with 14/10 hours light/dark phases. The soils were irrigated with desaltinated water when necessary.


Test material application
- Application method:
The radiolabelled test substance was dissolved in ethanol (concentration: approx. 450 µg/mL) . About 540 µL of this solution were transferred
to a 25 mL volumetric flask and made up to the mark with a mixture of water and ethanol (9/1, v/v) resulting in the application
mixture. 700 µL of the application mixture were added to each 50 g soil sample. Consequently the applied radioactivity amounted to 739 649 dpm which corresponded to 6.579 µg test substance per soil sample.

This laboratory application rate (132 mg/kg; appr.99 g/ha) exceeded the maximum field rate by 9.7 %.
- Test apparatus (Type/material/volume): 200mL Erlenmayer flasks with ground joints

5. SAMPLING DETAILS
- Sampling intervals: Duplicate samples per soil were taken for analysis at 0, 2, 9, 16, 33, 65, 97 and 152 days after application

Soil No.:

#1

DT50:

12 d

Type:

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

Temp.:

ca. 20 - 25 °C

Soil No.:

#2

DT50:

7 d

Type:

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

Temp.:

ca. 20 - 25 °C

Soil No.:

#1

DT50:

29 d

Type:

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

Temp.:

ca. 20 - 25 °C

Remarks on result:

other: DT90

Soil No.:

#2

DT50:

22 d

Type:

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

Temp.:

ca. 20 - 25 °C

Remarks on result:

other: DT90

Transformation products:

yes

No.:

#1

No.:

#2

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Findings:

The overall mean recoveries of radioactivity ranged from approx. 93% to 102% for soil LS 2.2 and from approx. 88% to 106% for soil SLV. For both soils, lower recoveries were observed at the last sampling interval in soil LS 2.2 (approx. 73%) and at the last two sampling intervals in soil SLV (approx. 78% each).

In both soils, the extractable radioactivity declined from 101.3% (soil LS 2.2) and 96.8% (soil SLV) of applied dose by day 0 to values of 51.8% and 54.1%, respectively, by the end of the study, day 152. In parallel, non-extractable residues increased from 0.8% (LS 2.2) / 3.2% (SLV) by day 0 to 30.4% / 23.4% by day 152. The formation of non-extractable residues was accompanied by the formation of¹⁴C-carbon dioxide accounting for 0.9% of applied radioactivity in both soils at the end of the incubation.

Starting with the parent molecule, the hydrolysis of the ester group at the 3-position of the heterocycle was the initial step of degradation to result in the formation of the monoester mefenpyr-ethyl AE F113225 as a major metabolite at peak values of 33.3% (soil LS 2.2, day 9) and 42.6% (soil SLV, day 2) of the applied dose within the first two weeks after application. AE F113225 rapidly disappeared to values of less than 5% within the first 30 days of incubation. In parallel, the pyrazole carboxylic acid AE F094270 was formed at maximum levels of 65.1% of applied radiolabel at day 97 (soil LS 2.2) and 67.5% at days 33 and 65 (soil SLV). The process of formation of AE F094270 required at least two metabolic steps of conversion: hydrolysis of the remaining ester group of AE F113225 and, formally, a combined decarboxylation/elimination step of carbonic acid in the heterocycle to result in an aromatisation to the substituted pyrazole in AE F094270. The further decomposition to form non-extractable residues and carbon dioxide proceeds presumably via an attack at the dichlorophenyl ring, for example, by hydroxylation as described for 2,4-D or diclofop-methyl, Aizawa, 1989[1]or, at the pyrazole ring system by oxidation of the 5-methyl group, as published for pyrazolynate, Domsch, 1992[2].

In addition, two further minor metabolites were observed in a range between 0.8% to 5.6 % of applied radiolabel in soil SLV at the first three sampling intervals (days 0, 2 and 9) only. Due to their low occurrence, no further identification was carried out.

 

Conclusion:

The parent compound mefenpyr-diethyl showed a fast decomposition via ester hydrolysis to the monoester metabolite mefenpyr-ethyl, AE F113225, as the initial and major step in the route of degradation. A combined decarboxylation/elimination process in the heterocyclic ring system resulted in the formation the pyrazole carboxylic acid AE F094270 as a second major product of degradation of mefenpyr-diethyl. The metabolic pathway in soil along with additional structures found in abiotic degradation

[1]Aizawa, H., Metabolic Maps of Pesticides, Academic Press, Inc.; San Diego, California, Volume 1, 1982, and Volume 2, 1989.

[2]Domsch, K.H., Pestizide im Boden, VCH Weinheim, New York, Basel, Cambridge, 1992.

Reference 2

Endpoint:

biodegradation in soil

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 (=EPA) 162-1 and 162-2

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic/anaerobic

Soil classification:

DIN 19863 (Deutsche Industrie-Norm)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

11.3

% Silt:

31.4

% Sand:

57.4

% Org. C:

1.55

pH:

5.8

CEC:

6.9 meq/100 g soil d.w.

Bulk density (g/cm³):

1.26

Soil No.:

#1

Initial conc.:

ca. 0.1 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20 °C

Microbial biomass:

19.9

Details on transformation products:

- Formation and decline of each transformation product during test:
The major conversion products were again AE F113225 and AE F094270 under both, aerobic and anaerobic conditions. Whereas AE F113225 steadily decreased from 47% at the beginning to 20% at the end of the anaerobic phase, no decrease was observed for AE F094270 in the course of the study. As a minor metabolite, AE F109453 was observed at peak values of  5% of total applied dose during the anaerobic phase of the study

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

Results with reference substance:

As reference material unlabelled Hoe 107892 was used.

Findings:

The overall mean recoveries of radioactivity ranged from approx. 96% to 98% for the aerobic ageing period and from approx. 97% to 100% for samples of the anaerobic phase of the study.

For theaerobic samples, the extractable portion of radioactivity declined from 97.4% of applied dose by day 0 to values of 89.7% by day 3. Non-extractable residues increased from 0.7% by day 0 to 6.3% by day 3. Volatile components accounted for 0.2% of applied radioactivity by day 3.

For theanaerobic samples, the extractable portion of radioactivity declined from 53.2% of applied dose by day 0 (= day 13 after application) to values of 46.1% by day 60 (= day 73 after application). Non-extractable residues increased from 8.3% by day 0 to 16.1% by day 60. Volatile components accounted for 0.7% of applied radioactivity by day 60.

After three days of aerobic ageing the profile of residues consisted of 34.7% of applied dose for parent compound AE F107982, 39.1% for mefenpyr-ethyl AE F113225 and 15.8% for the pyrazole carboxylic acid AE F094270.

In anaerobic samples, the profile of residues changed from 18.0% (AE F107892), 46.7% (AE F113225) and 19.7% (AE F094270) by day 0 (= day 13 after application) to 8.7% (AE F107892), 19.5% (AE F113225), 34.9% (AE F094270) by day 60. In addition, the dicarboxylic acid AE F109453 was present in a range from 2.1% by day 0 to 4.9% by day 60.

 

Conclusion:

There was no significant deviation in the route of degradation under anaerobic conditions when compared with the results from aerobic studies. As observed in the predominant number of cases for this study type,¹⁴C-carbon dioxide was not virtually formed and the formation of non-extractable residues was low.

The formation of the dicarboxylic acid AE F109453 was observed as a minor metabolite below 5% of applied radiolabel in the course of the study.

Results:

 Pattern of degradation of AE F107892 in sandy loam SLV at 20 °C under anaerobic conditions after a 3-day aerobic ageing phase
(% of total applied radioactivity)

Day	Extractable Residues identified as				^14CO2	Non-Extractable Residues	Total
	AE F107892	AE F113225	AE F109453	AE F094270
aerobic
0	97.4	-	-	-	-	0.7	98.1
3	34.7	39.1	-	15.8	-	6.3	95.9
anaerobic
0	18.0	46.7	2.1	19.7	-	8.3	94.8
15	12.0	41.2	3.8	25.3	0.1	12.5	94.9
30	11.3	27.9	4.0	26.5	0.2	17.4	87.3
60	8.7	19.5	4.9	34.9	0.3	16.1	84.4

 

Disappearance times of AE F107892 in soil under anaerobic conditions at 20 C

Soil	DT50 [days]
Sandyloam SL	46.5

Calculation based on first order kinetics and one compartment approach with an EXCEL software spreadsheet.

 

 Apparent Disappearance times of AE F113225 in soil under anaerobic conditions at 20 C

Soil	DT50 APP [days]
Sandyloam SL	47.6

Calculation based on first order kinetics and one compartment approach with an EXCEL software spreadsheet.

 

Reference 3

Endpoint:

biodegradation in soil

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: BBA Part IV, 4-1

GLP compliance:

yes

Test type:

field trial

Oxygen conditions:

aerobic

Soil classification:

DIN 19863 (Deutsche Industrie-Norm)

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location:
Two locations: “Pruefstelle Nord” at Stelle 21435 and “Pruefstelle Sued” at Gersthofen, Germany.

Soil No.:

#1

Initial conc.:

90 g/ha d.w.

Based on:

other: AE F107892

Soil No.:

#2

Initial conc.:

90 g/ha d.w.

Based on:

other: AE F107892

Parameter followed for biodegradation estimation:

test mat. analysis

Details on experimental conditions:

SAMPLING DETAILS
- Sampling intervals: Soil cores were taken after 0, 7, 14, 28 (31), 54 (61), 91 and 153 days after treatment (deviations for Gersthofen in brackets). The soil cores were sampled from depths of 0 to 10 cm, 10 to 20 cm and 20 to 40 cm in the field.

Transformation products:

yes

Residues:

yes

Findings:

The results are expressed as concentrations of the given component per kg soil.

The parent compound AE F107892 and the metabolite mefenpyr-ethyl AE F113225 showed their highest concentrations immediately after application in the top 10 cm of the soil (parent compound: 0.0289 mg/kg; AE F113225: 0.0324 mg/kg). Both compounds disappeared completely to concentrations below the LOD within 14 or 28 days after treatment. The pyrazole carboxylic acid AE F094270 is formed at a later stage in the metabolic pathway in principle. However, the peak concentration of 0.0247 mg/kg soil for AE F094270 was already detected by day 0 (Gersthofen) for the spring application.

The disappearance times for AE F107892, AE F113225 and AE F094270 were calculated on the basis of a first order kinetics and a one compartment approach

Dissipation of AE F107892 and its metabolites AE F113225 and AE F094270
in a loamy sand (location Stelle) and a sandy loam (location Gersthofen) under field conditions following spring application¹

Location Stelle
Day	Residues detected as
	AE F107892	AE F113225	AE F094270
0	0.0289	0.0183	-
7	0.0093	0.0077	-
14	-	0.0094	-
28	-	-	-
54	-	-	-
91	-	-	-
153	n.d.	n.d.	n.d.
Location Gersthofen
Day	Residues detected as
	AE F107892	AE F113225	AE F094270
0	-	0.0324	0.0247
7	-	-^2	0.0164
14	-	0.0061	0.0169
31	-	-	0.0110
61	-	-	-
91	-	-	-
153	n.d.	n.d.	n.d.

¹:(mg component detected per kg soil for the top 10 cm)

²: outlier

-: belowlimits of detection (LOD). LODwas 0.005 mg/kg soil each for AE F107892 and AE F113225. LOD for AE F094270: 0.007 mg/kg soil

N.D.: not determined

 

Results:

Location / Soil	Disappearance Times for
	AE F107892		AE F113225		AE F094270
	DT50 [days]		DT50 [days]		DT50 [days]
Stelle / loamy sand	4.0		10.6		-
Gersthofen / sandy loam	-		11.3		22.8

 

Reference 4

Endpoint:

biodegradation in soil

Type of information:

experimental study

Adequacy of study:

other information

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: BBA Part IV, 4-1

GLP compliance:

yes

Test type:

field trial

Oxygen conditions:

aerobic

Soil classification:

DIN 19863 (Deutsche Industrie-Norm)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

18

% Silt:

36.9

% Sand:

45.1

% Org. C:

1.5

pH:

7.1

CEC:

14.6 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

other: Sandy silty loam

% Clay:

14.8

% Silt:

48

% Sand:

37.2

% Org. C:

1.1

pH:

5.7

CEC:

8.5 meq/100 g soil d.w.

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: “Pruefstelle Nord” at Bornheim and “Versuchsfeld Schwanheim” at Frankfurt-Schwanheim, Germany.

Soil No.:

#1

Duration:

587 d

Soil No.:

#2

Duration:

615 d

Parameter followed for biodegradation estimation:

test mat. analysis

Details on experimental conditions:

EXPERIMENTAL DESIGN
Test material application
- Application method: Essential application data
The test substance was applied once at the recommended use rate of 1.2 L/ha
= 1.26 kg/ha, equivalent to 82.5 g/ha fenoxaprop-P-ethyl and 90 g/ha active
ingredient Hoe 107892 (nominal).

Application:
The test plots were ploughed before application and prepared fine-crumbly.
The test substance was applied with a plot sprayer (van der Weij) equipped
with a 2 m spray boom in one Trial and a field sprayer with TJ80015 flat
fan nozzles in the other Trial as used under conditions of normal agricultural
practice. The water output was approx. 300 L/ha.

SAMPLING DETAILS
- Sampling intervals: Soil cores were taken after 0, 7 (7), 14 (14), 28, 56 (64), 101 (117), 159 (181), 222 (244), 322 (330), 481 (495) and 587 (615) days after treatment (sampling intervals for location Schwanheim in brackets). The soil cores were sampled from depths of 0 to 10 cm, 10 to 20 cm and 20 to 40 cm in the field.

Transformation products:

yes

Residues:

yes

The results from the regression calculations (DT50 and DT90) are summarised in the following table. The regression calculations have been conducted separately for Hoe 113225 and Hoe 094270 and refer to a soil column of 10 cm.

Location / Soil	Disappearance Times for
	AE F107892		AE F113225		AE F094270
	DT50 [days]		DT50 [days]		DT50 [days]
Bornheim / sandy loam	-		6.4		44.2
Schwanheim / sandy silty loam	-		19.4		79.1

The disappearance times for AE F107892, AE F113225 and AE F094270 were calculated on the basis of a simple first order kinetics according to the approach by Timme et al..

The parent compound AE F107892 and the metabolite AE F113225 showed their highest concentrations immediately after application in the top 10 cm of the soil (parent: 0.0133 mg/kg; AE F113225: 0.0464 mg/kg). Both compounds disappeared completely to concentrations below the LOD within 14 or 28 days after treatment.

The pyrazole carboxylic acid AE F094270 occurred at a later stage in metabolism in principle, thus a prolonged period of time is required for the formation of the peak concentration in soil. In particular, this was true when the overall metabolism in soil was slowed down in autumn. The highest concentrations of 0.0948 mg/kg soil and 0.0250 mg/kg soil for AE F094270 were observed at both test sites by day 7. The higher persistence accompanied by limited adsorption to soil may indicate a potential for mobility of the pyrazole carboxylic acid AE F094270 into deeper soil layers. However, AE F094270 was only detected at one of the autumn application sites (Bornheim) in soil below the top 10 cm. The maximum concentrations were 0.024 mg/kg soil for the 10 to 20 cm soil layer and a value of 0.009 mg/kg soil in the zone between 20 and 40 cm, both by day 56 after application. The pyrazole carboxylic acid AE F094270 was not detected beyond the LOD at sampling intervals later than day 56 after application.

Reference 5

Endpoint:

biodegradation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

17 Jun 1991 - 08 Oct 1992

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: BBA Part IV, 4-1 and US EPA (=EPA) § 161-1

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

DIN 19863 (Deutsche Industrie-Norm)

Soil no.:

#1

Soil type:

silt loam

% Clay:

19.3

% Silt:

73.8

% Sand:

6.9

% Org. C:

1.66

pH:

6.1

CEC:

10 meq/100 g soil d.w.

Bulk density (g/cm³):

1.13

Soil no.:

#2

Soil type:

loamy sand

% Clay:

8.2

% Silt:

10.5

% Sand:

81.3

% Org. C:

1.53

pH:

7.1

CEC:

5.5 meq/100 g soil d.w.

Bulk density (g/cm³):

1.31

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
Test soils:
Two soils were used:
- silt loam (SLH)
origin: agricultural area of Hoechst AC near D-65795 Hattersheim,
Germany
- loamy sand (LSN),
origin: agricultural area at Birkenheide, Rhineland Palatinate, Germany,
sampled by LLFA, Abt. Phytomedizin, D-67435 Neustadt/WeinstraBe



Differend maximum water holding capacity and temperatures:
Soil, MWHC*, Temp:
SLH, 40 %, 20°C
LSN, 40 %, 20°C
SLH, 60 %, 20°C
SLH, 40 %, 10°C
SLH, 40 %, 20°C, sterile

Soil No.:

#1

Duration:

150 d

Soil No.:

#2

Duration:

360 d

Soil No.:

#1

Initial conc.:

0.132 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

0.132 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20± 2

Microbial biomass:

47.8

Soil No.:

#2

Temp.:

20 ± 2 (10±2)

Microbial biomass:

49.1

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil preincubation conditions: The soils were freshly sampled from the plough horizon of the fields and acclimatised for a period of about 1 - 2 weeks.
- Soil: 50 g dry weight
- Test apparatus : 200 ml Erlenmeyer flasks with ground joints
- Details of traps for CO2 and organic volatile, if any: Erlenmeyer flasks were closed with absorption devices consisting of loosely filled 15 cm glass tubes with a fitting ground joint. The tubes contained different layers of glass wool, granular soda lime (source e.g. Riedel-de Haen, order no. 31474) and glass wool coated with paraffin in a stratification permeable to air.
- Identity and concentration of co-solvent: The radiolabelled test substance was dissolved in water/ethanol.


Test material application
- Application method: The radiolabelled test substance was dissolved in ethanol (concentration: approx. 400 µg/mL). About 4 ml of this solution were transferred to a 50 ml volumetric flask and made up to the mark with a mixture of water and ethanol (1/1, v/v) resulting in the application mixture (concentration: approx. 32 µg/ml).

Any indication of the test material adsorbing to the walls of the test apparatus: No


SAMPLING DETAILS
- Sampling intervals: For the standard incubation conditions (40% moisture, 20°C), duplicate samples per soil were taken for analysis at 0, 2, 4, 8, 16, 32, 64, 100, 150 and 360 days after application. With the exception of day 360, the same time points apply for samples of soil SLH incubated at 60% moisture and 20°C. Analysis of sterilised samples of soil SLH (40% moisture, 20°C) was carried out after 0, 2, 4, 8, 32, 64 and 100 days of incubation. Finally, samples incubated at 40% moisture and 10°C were analysed by days 0, 8, 64, 100 and 150 after application.

Transformation products:

yes

Details on transformation products:

- Description of biotransformation pathway:
A first metabolite Hoe 113225 (1-(2,4-dichlorophenyl)-5-ethoxycarbonyl-5-rnethyl-2-pyrazoline-3-carboxylic acid) was formed within a few days by hydrolysis of one of the two carboxylic ester groups, reaching a maximum portion of 31 - 43 % of the applied radioactivity (Day 4). This metabolite appeared to degrade with a half-life of about 2 weeks at 20°C and 3 weeks at 10°C.
A second degradation product Hoe 109453 (1-(2,4-dichlorophenyl)-5-methyl-2-pyrazoline-
3,5-dicarboxylic acid) formed by hydrolysis of the second ester group seemed to be very unstable because it could only be detected at the lower temperature (10°C) to a very small portion (3 %).
A further product Hoe 094270 (1-(2,4-dichlorophenyl)-5-methyl-2-pyrazole-3-carboxylic acid) represented the main portion of the total residues with longer incubation. This compound, which rose to 54 - 72 % of the applied radioactivity, was formed by decarboxylation and aromatization of the heterocyclic ring. As already observed in a previous study on the same subject, the portion of Hoe 094270 decreased until the end of the study (360 days). The half-lives were estimated between 100 and 200 days at 20°C.

Up to three additional unknown metabolites with medium to low polarity could also be detected, though two of them in insignificant portions (< 3 %). One of them with a HPLC retention similar to that of Hoe 114952 appeared with a maximum percentage of 11.5 % in soil SLH (40 % MWHC, 20°C) 4 days after application. It was never more detectable after Day 8.
After a first increase until Day 150, the non-extractable residues decreased again in soil SLH until the end of incubation at 20°C (to 51 %, 40 % MWHC, Day 360 ). In soil LSN, only a continual increase could be registered (to 50 %, 40 % MWHC, Day 360). A similar course has been observed in soil SLH at the higher moisture content (to 65 %, 60 % MWHC, Day 150) and at the lower temperature (to 39 %, 40 % MWHC, 10°C, Day 150)
The mineralization rose to a maximum of 19 % of the applied radioactivity in soil SLH (40 % MWHC, 20°C, Day 360) and to 8 % in soil LSN (40 % MWHC, 20°C, Day 360), indicating that the disappearance of Hoe 107892 and its intermediate soil metabolites is resulting in an actual and complete degradation.
Summing up, the soil degradation of Hoe 107892 can be characterized as rapid disappearance of the parent compound accompanied by the formation of the metabolite Hoe 094270 and nonextractable, bound residues and a significant mineralization.

Evaporation of parent compound:

yes

Volatile metabolites:

yes

Residues:

yes

When first order kinetics were used to try the 50 % disappearance times (DT-50)

for Mefenpyr-diethyl resulted in the following values:

Soil, MWHC*, Temp.	DT-50 (days)		squared correlation coefficient r2
SLH, 40 %, 20°C	60		0.158
LSN, 40 %, 20°C	49		0.226
SLH, 60 %, 20°C	8		0.819
SLH, 40 %, 10°C	38		0.763
SLH, 40 %, 20°C, sterile	no degradation

* MWHC = maximum water holding capacity

The approximation and consequently the DT values fitted very poorly as indicated by the low

values of the quality criterion r2 due to a extremely rapid degradation down to <L 10 % of the

applied amount within 1 - 2 weeks at 20°C followed by a second phase with a lower rate. Even

at 10°C only 21 % of the parent compound were detectable 8 days after application. Therefore

visual estimation of the half-lives in the degradation graphs describes the fate of Hoe 107892 in

the soil more realistically than the formal first order approximation.

Thus, the half-life of degradation is in a range of 1 - 3 days at 20°C and less than one week at

10°C. Degradation was not observed under sterile conditions.

Findings:

Soils SLH and LSN, incubation at 40% moisture and 20°C:

The overall mean recoveries of radioactivity ranged from approx. 90% to 95% for soil SLH and from approx. 95% to 102% for soil LSN. For both soils, lower recoveries were observed at the last sampling interval, day 360 (soil SLH: approx. 83%, soil LSN: approx. 88%).The extractable portion of radioactivity declined from 91.8% (soil SLH) and 99.1% (soil LSN) of applied dose by day 0 to values of 12.1% and 32.6%, respectively, by the end of the study, day 360. In parallel, non-extractable residues increased from 2.7% (SLH) / 2.5% (LSN) by day 0 to 51.3% / 47.6% by day 360. The formation of¹⁴C-carbon dioxide accounted for 19.3% (soil SLH) and 8.0% (soil LSN) of applied radioactivity at the end of the incubation.

 

Soil SLH, incubation at 60% moisture and 20°C:

The overall mean recoveries of radioactivity ranged from approx. 90% to 95% with exceptions of lower recoveries at days 64 (86%) and day 150 (89%).The extractable portion of radioactivity declined from 86.9% of applied dose by day 0 to 17.1% by the end of incubation, day 150. Non-extractable residues had increased from 5.8% by day 0 to 64.8% by day 150.¹⁴C-carbon dioxide accounted for 7.4% of applied radioactivity at the end of the incubation period.

 

Soil SLH, incubation at 40% moisture and 10°C:

The overall mean recoveries of radioactivity ranged from approx. 92% to 99%.The extractable portion of radioactivity declined from 91.8% of applied dose by day 0 to 57.7% by the end of incubation, day 150. Non-extractable residues had increased from 2.7% by day 0 to 38.6% by day 150.¹⁴C-carbon dioxide accounted for 2.3% of applied radioactivity at the end of the incubation period.

 

 

Soil SLH, sterilised samples, incubation at 40% moisture and 20°C:

The overall mean recoveries of radioactivity ranged from approx. 93% to 102%.The extractable portion of radioactivity declined from 101.6% of applied dose by day 0 to 95.8% by the end of incubation, day 100. Non-extractable residues had increased from 2.8% by day 0 to 3.9% by day 100. There was no formation of¹⁴C-carbon dioxide in the course of the incubation period.

 

Description of key information

The substance is not persistent in soil. It is concluded that long-term concentrations of residues in soil will be very low and accumulation will not occur.

Key value for chemical safety assessment

Half-life in soil:

12 d

at the temperature of:

20 °C

Additional information

The route of degradation of radio-labelled test substance in aerobic soil was followed in two standard soils at standard conditions of 20°- 25°C and 40% mwrc for 152 days (guidelines BBA Part IV, 4-1 and USEPA (=EPA) § 162-1). The test substance was decomposed in a first degradation step by ester hydrolysis resulting in the formation of a monoester metabolite. The monoester metabolite was further degraded to a second major metabolite. This second metabolite was further decomposed to non-extractable residues and CO2. The measured proportion of non-extractable-residues was 30 % of the applied amount at the end of the experiment. The proportion of formed CO2 was 1% at the end of the 5 month test period. The determined DT50 of the partent substance in sandy loam was 12 days. In loamy sand a half-life of 7 days was reported.

The results of the key study are supported by two additional studies investigating the degradation of the parent substance in soil. Investigations in sterilized soil confirmed the biotic nature of transformation of the test substance in aerobic soil. A significant deviation between the route of degradation at anaerobic conditions and the degradation at aerobic conditions was not observed.

A prolonged half-life of the substance at anaerobic conditions was determined. The delayed degradation at anaerobic conditions is a result of general significantly lower microbial activity and processes in anaerobic testing.

The results of field dissipation studies (1994a and 1994b) conducted with formulated substance indicate that the predominant portion of parent substance and its metabolites are subject to degradation in the top layers of soil. These include aerobic conditions, in particular following an intended use in cereal crops. A significant entry of residues into anaerobic compartments of the environment is therefore rather unlikely.

On the basis of these predictions and by taking into account the results from soil dissipation tests in the field it is concluded that long-term concentrations in soil will be very low and accumulation will not occur.