1-[(4-chlorophenyl)methyl]-1-cyclopentyl-3-phenylurea

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

1997-11-05 to 1998-06-02

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

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:

March 1995

Qualifier:

according to guideline

Guideline:

other: Official Journal of the European Communities No. L 172, 95/36/EC, Placing of the Plant Protection Products on the Market,

Version / remarks:

July 14, 1995

Qualifier:

according to guideline

Guideline:

other: Regulation Implementation Environmental Registration Criteria Pesticides (NL), Draft 30. Appendix 1, Section 1

Version / remarks:

Sep. 1994

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Remarks:

Specific radioactivity: 6.12 MBq/mg or 165.5 µCi/mg

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

1998

Soil no.:

#1

Soil type:

loam

% Clay:

16.9

% Silt:

49.5

% Sand:

33.6

% Org. C:

1.98

CEC:

15 meq/100 g soil d.w.

% Moisture content:

51.86

Soil no.:

#2

Soil type:

sandy loam

% Clay:

7.9

% Silt:

26.4

% Sand:

65.7

% Org. C:

1.12

CEC:

10 meq/100 g soil d.w.

% Moisture content:

34.3

Soil no.:

#3

Soil type:

Silt

% Clay:

10.2

% Silt:

81.3

% Sand:

8.5

% Org. C:

2.62

CEC:

15 meq/100 g soil d.w.

% Moisture content:

63.1

Soil no.:

#4

Soil type:

sandy loam

% Clay:

5

% Silt:

22.6

% Sand:

72.4

% Org. C:

1.8

CEC:

8 meq/100 g soil d.w.

% Moisture content:

34.42

Details on soil characteristics:

Soil #1: Nisse
Soil #2: Howe
Soil #3: Höfchen
Soil#4: Laacher hof

Four agricultural soils were used for testing, i.e. loam, obtained from Nisse (The Netherlands), sandy loam obtained from Howe (Indiana, USA), silt obtained from Höfchen (Germany) and a sandy loam, obtained from Laacher hof, Monheim, Germany. The soils from Höfchen and Laacher hof were freshly collected from the respective field plot and the soils from Nisse and Howe were collected from a large stock that was kept under natural conditions. For all soils, except Höfchen, it could be verified that there was no treatment with any pesticide in the previous five years. The characterisation of the soils is given in Table 1.

The soils were air-dried and sieved (2 mm) prior to use. After addition of demineralised water to adjust the moisture content to 40% of the MWHC of the corresponding soil, approximately 100 g dry weight soil was transferred to each test container (300 ml Erlenmeyer flasks, closed with cotton wool), followed by an acclimatisation period of approximately 4 days (at 20°C, in the dark).

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.:

3.37 mg/kg soil d.w.

Soil No.:

#2

Initial conc.:

3.37 mg/kg soil d.w.

Soil No.:

#3

Initial conc.:

3.37 mg/kg soil d.w.

Soil No.:

#4

Initial conc.:

3.37 mg/kg soil d.w.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20°C

Microbial biomass:

Biomass (mg C/kg dw):
At start: 1218
After 120 days: 179.5

Soil No.:

#2

Temp.:

20°C

Microbial biomass:

Biomass (mg C/kg dw):
At start: 412
After 120 days: 51.5

Soil No.:

#3

Temp.:

20°C

Microbial biomass:

Biomass (mg C/kg dw):
At start: 1315
After 120 days: 411

Soil No.:

#4

Temp.:

20°C

Microbial biomass:

Biomass (mg C/kg dw):
At start: 594
After 120 days: 75

Details on experimental conditions:

A treatment solution was prepared in acetonitrile; after acclimatisation of the soil, aliquots of this solution were applied to the soil surface in every Erlenmeyer flask. Subsequently, the acetonitrile was allowed to evaporate for 45 minutes. The application rate was 3.37 mg/kg dw which corresponds with approximately 2500 g/ha. After adjusting the soil moisture content to 50% of the MWHC, vessels were closed with a trap attachment for collecting volatiles and incubated under aerobic conditions, in the dark, at 20 ± 1°C for 120 days. The trap attachment was permeable for oxygen, but allowed to adsorb for 14CO2 (in soda lime) and other possible volatile metabolites (in a polyurethane plug). Prior to dosing, after application of half of the test vessels and at the end of dosing, samples of each treatment solution equal to the applied volume were diluted in acetonitrile and radio-assayed by LSC. Radiochemical purities of the treatment solution were determined by analysing the dilutions with TLC and HPLC.

Soil No.:

#1

DT50:

139 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Non-normalised modelling

Soil No.:

#1

DT50:

295 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#2

DT50:

167 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Non-normalised modelling

Soil No.:

#2

DT50:

329 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#3

DT50:

118 d

Type:

other: DFOP

Temp.:

20 °C

Remarks on result:

other: Non-normalised modelling

Soil No.:

#3

DT50:

251 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#4

DT50:

188 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Non-normalised modelling

Soil No.:

#4

DT50:

372 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Transformation products:

yes

Details on transformation products:

One metabolite was identified by co-chromatography as N-[(4-chlorophenyl)- methyl]-N-cyclopentylamide (= THS 3995 = M16 = Pencycuron-PB-Amine). This metabolite was evaluated as the sum of two peak zones. The highest percentage of Pencycuron-PB-Amine (M16) formed was 18.4% a.r. (in Nisse soil, after 120 days). According to the authors, tests in which Pencycuron-PB- Amine was isolated via HPLC and co-chromatographed using HPLC and TLC, have shown that it is eluted either as salt or as an undissociated molecule. There is no reference to test reports of these tests and it is not clear whether these tests were part of the present study. This observation was made within the study, documented in the GLP raw data. Furthermore, four minor metabolites were detected (RT 12’, RT 15’-16’, RT 18’-19’ and RT 20’), which were not identified.

Details on results:

In Tables 2- 5, the recoveries of radioactivity are given for the four tested soils.

After 120 days, the portion of 14CO2 recovered from the soda lime varied between 4.7 and 17.8% a.r. and the portion of not-extracted radioactivity varied between 11.2 and 17.3% a.r. Based on specific radioactivity and radiochemical purity of the test substance in the application solution, the applied amount of Pencycuron was calculated to be 3.46 mg/kg dry soil. By HPLC analysis of soil extracts, the identity of Pencycuron was confirmed.

By TLC analysis, similar results were obtained, although the determined portion of Pencycuron was slightly higher and the determined portion of Pencycuron-PB-Amine (M16) was slightly lower. Furthermore one minor metabolite (THS 2860, = M03 in zone F in Tables 7, 11, 12 and 13) was identified as N-[(4-chlorophenyl)-methyl]-N-cyclopentyl-urea (M03). As HPLC analysis was regarded as a better separation method, the HPLC results were used for final evaluation and calculations. The results from TLC analysis were used for confirmation of the metabolites.

Unidentified metabolite fraction RT20 occurred in Howe soil at >5% AR at two consecutive timepoints, when HPLC analysis was used. When TLC analysis was used however, no unidentified metabolite fraction was found at levels >5% AR. Unidentified metabolite fraction RT20 also occurred in Laacher Hof soil at >5% AR at two consecutive timepoints (day 63 and 84), when HPLC analysis was used. When TLC analysis was used, an unidentified metabolite fraction D was detected in Laacher Hof soil at >5% AR at the same two consecutive timepoints (day 63 and 84). RT20 and D may represent the same compound, and the notifier should addres the relevance of this compound.The level of unidentified metabolite fraction RT12 increased at study termination in Howe soil, when HPLC analysis was used. When TLC analysis was used however, no unidentified metabolite fraction showed a clear trend of increasing towards study end. Therefore fraction RT12 needs no further consideration.

In Tables 6 – 13, the results of the HPLC and TLC analysis of the soil extracts are given.

Table 2. Recoveries of radioactivity for Nisse soil (means of duplicates expressed as % a.r.)

Incubation time (days)		0	7	14	21	35	63	84	120
Volatiles	Soda lime		1.6	2.5	3.4	4.9	6.8	9.4	10.7
	PU foam		< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1	< 0.1
	Subtotal		1.6	2.5	3.4	4.9	6.8	9.4	10.7
Extracted soil	Acetonitrile fraction Dichloromethane fraction Subtotal	88.9   0.4^1 89.2	82.6   7.3   89.9	81.5   8.4   89.9	81.4   8.3   89.7	78.8   7.7   86.5	75.2   7.7   82.9	72.6   7.5   80.0	67.3   8.2   75.5
Not	Soil	2.5	4.2	3.8	4.6	5.8	7.1	7.8	9.7
extracted
	Filter	1.6	1.7	1.4	1.6	1.3	1.4	1.3	1.5
	Subtotal	4.1	6.0	5.2	6.2	7.1	8.5	9.2	11.2
Total		93.3	97.4	97.6	99.3	98.5	98.2	98.6	97.3
SD		0.1	1.0	1.0	0.7	0.1	1.1	1.1	0.5

¹The first extract was added to the acetonitrile extract

 

Table 3. Recoveries of radioactivity for Howe soil (expressed as % a.r.)

Incubation time (days)		0	7	14	21	35	63	84	120
Volatiles	Soda lime PU foam Subtotal	Not examined							4.7 < 0.1 4.7
Extracted soil	Acetonitrile fraction Dichloromethane fraction Subtotal	89.3   0.5^1 89.7	80.0   6.7   86.7	79.5   7.2   86.7	82.0   7.2   89.1	81.0   6.1   87.1	77.5   6.9   84.4	74.5   6.9   81.5	68.7   7.0   75.7
Not	Soil	2.3	4.9	5.0	5.1	7.9	7.7	11.6	15.9
extracted
	Filter	2.0	2.4	1.6	1.6	1.5	1.4	1.4	1.4
	Subtotal	4.3	7.2	6.7	6.7	9.4	9.1	13.0	17.3
Total		94.0	94.0	93.3	95.9	96.5	93.6	94.5	97.7

¹The first extract was added to the acetonitrile extract

 

Table 4. Recoveries of radioactivity for Höfchen soil (expressed as % a.r.)

Incubation time (days)		0	7	14	21	35	63	84	120
Volatiles	Soda lime PU foam Subtotal	Not examined							17.8 < 0.1 17.8
Extracted soil	Acetonitrile fraction Dichloromethane fraction Subtotal	89.7   0.8^1 90.5	75.7   8.9   84.6	78.5   9.5   88.0	77.0   9.3   86.3	75.9   8.6   84.5	70.9   8.6   79.5	68.0   8.5   76.5	59.7   8.4   68.1
Not	Soil	3.3	4.4	3.8	4.6	5.8	10.0	8.8	10.2
extracted
	Filter	1.7	1.7	1.5	1.3	1.4	1.2	1.4	1.2
	Subtotal	5.0	6.0	5.3	5.9	7.2	11.2	10.2	11.5
Total		95.5	90.7	93.3	92.2	91.7	90.7	86.7	97.4

¹The first extract was added to the acetonitrile extract

 

Table 5. Recoveries of radioactivity for Laacher hof soil (expressed as % a.r.)

Incubation time (days)		0	7	14	21	35	63	84	120
Volatiles	Soda lime PU foam Subtotal	Not examined							10.7 < 0.1 10.7
Extracted soil	Acetonitrile fraction Dichloromethane fraction Subtotal	89.4   0.7^1 90.0	81.1   7.6   88.7	81.8   9.2   91.0	81.5   9.4   90.9	80.5   9.0   89.5	79.2   8.8   88.1	77.4   9.3   86.7	65.1   7.7   72.8
Not	Soil	2.0	3.3	3.2	3.9	5.1	7.0	7.9	12.2
extracted
	Filter	1.8	2.7	2.1	1.7	1.9	1.5	1.4	1.3
	Subtotal	3.8	6.0	5.3	5.6	7.0	8.5	9.3	13.5
Total		93.9	94.7	96.3	96.5	96.6	96.6	96.1	97.0

¹The first extract was added to the acetonitrile extract

 

Table 6. Proportions (expressed as % a.r.) of radioactive components in Nisse soil after application of [Methylene-¹⁴C]Pencycuron, determined by HPLC

Incubation time (d)	Extracted radioact.	[Methylene-^14C] Pencycuron	THS            3995 (M16)	RT 12’	RT 15’-16’	RT          18’- 19’	RT 20’
0	89.2	85.9	2.9	n.d.	n.d.	n.d.	n.d.
7	89.9	85.4	3.1	n.d.	0.2	0.1	1.1
14	89.9	81.4	4.7	< 0.1	0.8	1.0	1.9
21	89.7	78.2	6.3	n.d.	2.2	0.5	2.5
35	86.5	73.9	8.3	n.d.	1.8	n.d.	2.4
63	82.9	65.0	12.4	n.d.	1.4	0.6	3.4
84	80.0	59.3	13.9	n.d.	2.9	0.6	3.3
120	75.5	49.8	18.4	n.d.	2.2	1.0	4.0

 

Table 7. Proportions (expressed as % a.r.) of radioactive components in Nisse soil after application of [Methylene-¹⁴C]Pencycuron, determined by TLC

Incubation time (d)	Extracted radioact.	Origin	[Methylene 14C] Pencycuron	THS 3995 (M16)	C	D	E	F	G	Diffuse radioact.
0	89.2	0.4	86.1	1.4	n.d.	n.d.	n.d.	n.d.	n.d.	1.3
7	89.9	0.6	86.0	1.1	n.d.	n.d.	n.d.	n.d.	n.d.	2.1
14	89.9	0.7	84.9	2.1	n.d.	n.d.	n.d.	n.d.	n.d.	2.1
21	89.7	1.1	82.6	3.4	n.d.	n.d.	n.d.	0.1	n.d.	2.4
35	86.5	0.9	77.5	4.9	n.d.	n.d.	n.d.	1.1	n.d.	2.1
63	82.9	0.9	71.4	6.7	n.d.	n.d.	n.d.	1.4	0.4	2.0
84	80.0	1.0	66.8	8.8	n.d.	n.d.	n.d.	1.4	0.5	1.5
120	75.5	1.1	62.1	10.1	n.d.	n.d.	n.d.	0.2	0.8	1.1

 

Table 8. Proportions (expressed as % a.r.) of radioactive components in Howe soil after application of [Methylene-¹⁴C]Pencycuron, determined by HPLC

Incubation	Extracted	[Methylene-^14C]	THS	RT 12’	RT 15’-16’	RT 18’-19’	RT 20’
time (d)	radioact.	Pencycuron	3995
			(M16)
0	89.7	87.0	2.2	n.d.	n.d.	n.d.	n.d.
7	86.7	83.3	1.7	n.d.	0.4	n.d.	1.3
14	86.7	80.6	2.2	n.d.	0.7	1.2	2.0
21	89.1	83.9	0.2	0.8	0.2	0.4	3.7
35	87.1	81.1	0.1	0.2	n.d.	n.d.	5.7
63	84.4	75.2	0.3	0.2	0.2	n.d.	8.6
84	81.5	66.4	9.7	1.6	0.3	0.3	3.2
120	75.7	48.9	15.5	4.3	1.3	0.9	4.8

 

Table 9. Proportions (expressed as % a.r.) of radioactive components in Howe soil after application of [Methylene-¹⁴C]Pencycuron, determined by TLC

Incubation time (d)	Extracted radioact.	Origin	[Methylene-^14C] Pencycuron	THS 3995 (M16)	C	D	F	G	Diffuse radioact.
0	89.7	0.3	86.7	1.5	n.d.	n.d.	n.d.	n.d.	1.2
7	86.7	0.7	83.5	0.7	n.d.	n.d.	n.d.	n.d.	1.8
14	86.7	0.7	83.5	0.9	n.d.	0.2	n.d.	n.d.	1.4
21	89.1	1.0	85.4	0.6	n.d.	0.2	n.d.	n.d.	1.9
35	87.1	0.7	81.2	< 0.1	1.0	3.0	n.d.	n.d.	1.1
63	84.4	0.7	76.2	1.0	0.9	4.3	n.d.	n.d.	1.3
84	81.5	0.9	73.2	5.2	1.0	n.d.	0.1	0.1	1.1
120	75.7	0.9	62.8	7.6	2.6	n.d.	0.1	0.7	0.9

 

Table 10. Proportions (expressed as % a.r.) of radioactive components in Höfchen soil after application of [Methylene-¹⁴C]Pencycuron, determined by HPLC

Incubation time (d)	Extracted radioact.	[Methylene-^14C] Pencycuron	THS 3995 (M16)	RT 12’	RT 15’-16’	RT 18’-19’	RT 20’
0	90.5	86.4	3.3	n.d.	n.d.	n.d.	n.d.
7	84.6	78.8	2.7	n.d.	0.3	1.3	1.5
14	88.0	78.2	4.5	0.3	1.9	1.3	1.8
21	86.3	75.1	5.9	n.d.	2.5	0.6	2.2
35	84.5	70.9	8.5	n.d.	2.4	n.d.	2.7
63	79.5	59.5	12.0	n.d.	3.7	0.8	3.5
84	76.5	54.7	12.8	n.d.	3.8	1.0	4.2
120	68.1	44.0	15.5	n.d.	3.6	1.4	3.6

 

Table 11. Proportions (expressed as % a.r.) of radioactive components in Höfchen soil after application of [Methylene-¹⁴C]Pencycuron, determined by TLC

Incubation time (d)	Extracted radioact.	Origin	[Methylene-^14C] Pencycuron	THS              3995 (M16)	C	D	F	G	Diffuse radioact.
0	90.5	0.2	87.8	1.5	n.d.	n.d.	n.d.	n.d.	0.9
7	84.6	0.8	81.3	0.9	n.d.	n.d.	n.d.	n.d.	1.6
14	88.0	0.6	83.4	2.1	n.d.	n.d.	n.d.	n.d.	1.9
21	86.3	1.1	79.5	3.4	n.d.	n.d.	0.1	n.d.	2.2
35	84.5	0.9	75.9	5.0	n.d.	n.d.	1.0	n.d.	1.6
63	79.5	1.0	67.7	6.7	1.0	n.d.	1.4	0.7	1.1
84	76.5	1.2	64.1	7.9	1.0	n.d.	0.9	0.8	0.6
120	68.1	1.1	55.5	8.5	1.6	n.d.	0.2	1.0	0.2

 

Table 12. Proportions (expressed as % a.r.) of radioactive components in Laacher hof soil after application of [Methylene-¹⁴C]Pencycuron, determined by HPLC

Incubation	Extracted	[Methylene-^14C]	THS	RT 12’	RT 15’-16’	RT 18’-19’	RT 20’
time (d)	radioact.	Pencycuron	3995
			(M16)
0	90.0	86.7	2.6	n.d.	n.d.	n.d.	n.d.
7	88.7	81.7	3.2	n.d.	1.1	1.5	1.2
14	91.0	82.9	3.5	1.1	0.8	1.3	1.3
21	90.9	81.2	5.0	1.6	0.6	1.2	1.2
35	89.5	79.4	6.9	2.0	0.7	n.d.	0.6
63	88.1	76.0	0.4	4.4	n.d.	n.d.	7.3
84	86.7	72.6	0.3	3.8	0.2	n.d.	9.9
120	72.8	49.3	15.1	1.5	2.6	0.3	4.0

 

Table 13. Proportions (expressed as % a.r.) of radioactive components in Laacher hof soil after application of [Methylene-¹⁴C]Pencycuron, determined by TLC

Incubation time (d)	Extracted radioact.	Origin	[Methylene-^14C] Pencycuron	THS 3995 (M16)	C	D	E	F	Diffuse radioact.
0	90.0	0.3	86.5	1.6	n.d.	n.d.	n.d.	n.d.	1.6
7	88.7	1.0	84.7	1.1	n.d.	n.d.	n.d.	n.d.	2.1
14	91.0	0.8	86.0	2.0	n.d.	n.d.	n.d.	n.d.	2.2
21	90.9	1.3	84.1	2.7	1.2	n.d.	n.d.	n.d.	1.6
35	89.5	0.9	81.8	3.3	2.0	n.d.	n.d.	n.d.	1.5
63	88.1	0.6	77.8	0.3	n.d.	5.7	2.3	n.d.	1.4
84	86.7	0.7	74.9	0.1	2.4	7.2	n.d.	n.d.	1.5
120	72.8	0.7	63.3	6.6	0.4	n.d.	n.d.	0.2	1.7

A modelling study to estimate degradation rates of pencycuron and the metabolite pencycuron-PB-amine for persistence and modelling from the results of the above study was submitted. Table 14 summarises the kinetics (recalculated by the RMS).

Table 14. Optimisation results for estimation of half-lives of pencycuron in soils Nisse, Howe, Hoffchen am Hohenseh and Laacherhof (cf. study 1 of this section) (recalculated by the RMS)

compound	soil	model	r^2	visual fit^(A)	X^2 (err)	model selected
						Persistence	Modelling (non-normalised)
Pency- curon	Nisse	SFO	0.983	4	1.88		kp = 0.00497688; M0 = 89.0581 DT50 = 139 d
		FOMC	0.991	4	1.48
		DFOP	1.00	5	0.30	g = 0.0705991; k1 = 0.195269; k2 = 0.00452292; M0 = 92.9236 DT50 = 121 d DT90 = 477 d
Pency- curon	Howe	SFO	0.895	3	4.29	kp = 0.00415435; M0 = 90.4673 DT50 = 167 d DT90 = 554 d	kp = 0.00415435; M0 = 90.4673 DT50 = 167 d
		FOMC	0.895	3	4.58
		DFOP	Not performed
Pency- curon	Hoffchen	SFO	0.949	3	3.89		kp = 0.00586823; M0 = 87.1824 DT50 = 118 d
		FOMC	0.962	3	3.59
		DFOP	0.996	4	1.20	g = 0.118301; k1 =0.983007; k2 =0.00517193; M0 =94.665 DT50 = 99.1 d DT90 = 410 d
Pency- curon	Laacherhof	SFO	0.830	3	5.07	kp = 0.003683; M0= 89.3653 DT50 = 188 d DT90 = 625 d	kp = 0.003683; M0= 89.3653 DT50 = 188 d
		FOMC	No fit could be obtained
		DFOP	Not performed

(A) Scale of 1 tot 5, where 1 = poor, 2 = fairly poor, 3 = fair, 4 = fairly good, 5 = good.

Conclusions:

The data gathered in the current laboratory study show the aerobic degradation of [methylene-14C]pencycuron in four different soils. In each of the four tested soils the disappearance of 50% of applied rate was reached within the incubation period of 120 days at 20 °C in the dark and at a soil moisture of about 50% of WHCmax.. The degradation proceeds via one main route to N-[(4-chlorophenyl)-methyl]-N-cyclopentylamine. At least further three minor metabolites were detected in the extracts of the four soils. The ultimate degradation product in the different soils was carbon dioxide which accounted for about 5% to 18% of the applied radioactivity after 120 days.

The bound residues resulting from [14C]pencycuron degradation slightly increased in all four soils as the incubation period progressed. After 120 days the not-extracted (bound) residues ranged from 11% to 17% of applied RA. The complete material balance found at all individual sampling intervals indicated that no relevant amount of RA dissipated from the systems during the entire testing period.

The resulting DT50 values (e.g. of best fit plots) were well comparable and ranged from 99 to 161 days in the different soils. Therefore, the test substance is regarded as moderately degradable in soil. Due to the known limitations of laboratory test systems (e.g. decline of active microbial biomass during the incubation period) the disappearance times reported here do not necessarily reflect the situation in a natural environment.

Executive summary:

Aliquots of 346 ug of test substance were applied to 100 g DS of soil each. The rate was oriented according to 2,500 g ai/hectare recommended maximum i.e. for protection of plant potatoes. The soil portions were held at a moisture of <50% of maximum water holding capacity and were incubated dark at 20°C under aerobic conditions in biometer flasks. The sampling intervals were 2 hrs, 7, 14, 21, 35, 63, 84 and 120 days post treatment of the soils. The final evaluation of study was performed by HPLC analysis of the organic extracts of soil. TLC was used as confirmatory method, only.

The complete material balances found (if that was tested) demonstrate that no relevant amount of radioactivity dissipated from the systems during the entire incubation period. The bound residues resulting from [14C]pencycuron degradation slightly increased in all four soils as the incubation period progressed. Finally, they ranged from 11 % to 17% of applied RA after 120 days.

The parent compound was thoroughly degraded to CO2 which accounted for 4.7% to 17.8% of the applied radioactivity after 120 days. In each of the four tested soils the disappearance of 50% of applied rate was reached within the incubation period of 120 days.

The resulting DT50 values (e.g. of the best fit plots) were well comparable and
ranged from 99 to 161 days in the different soils. Therefore, the test substance is regarded as moderately degradable in soil. Due to the known limitations of laboratory test systems the disappearance times reported here do not necessarily reflect the situation in a natural environment.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

calculation (if not (Q)SAR)

Adequacy of study:

key study

Study period:

2009-03-12

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: FOCUS

Version / remarks:

2005

GLP compliance:

not specified

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

2009

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: The biotransformation of radiolabelled Pencycuron was studied by Hellpointner [1998a] in the three European soils Nisse, Höfchen and Laacherhof and the US soil Howe.

The biotransformation of radiolabelled [methylene-2-14C]- and [phenyl- UL-14C]Pencycuron (= label #1 and label #2) was studied by Heinemann [2008] in the four European soils Laacher Hof AXXa, Dollendorf, Laacher Hof AIIIa and Hoefchen am Hohenseh 4a.

- Storage conditions: 120 days under aerobic conditions in the dark, at 20 °C. Soil moisture was adjusted to 50-55% of maximum water holding capacity.

In a third study, the biotransformation of radiolabelled Pencycuron-PB-amine was studied by Hellpointner [1998b] in the three European soils BBA 2.1, BBA 2.2 and Laacherhof for 100 days under aerobic conditions in the dark, at 20 °C. Soil moisture was adjusted to 45 % of maximum water holding capacity. In all studies, duplicate samples were analyzed for each soil at each sampling interval.

Details on experimental conditions:

For all residues used for the kinetic evaluation, the following procedure was applied. Any non-detect (n.d.) directly before or after a value ¿ n.d. was set to 0.5 LOD (limit of detection). A LOD of 0.5 % applied radioactivity (AR) was adopted following Heinemann [2008].

For metabolites of the compound incubated, the day zero value (days after treatment DAT = 0) was set to zero if the next value ¿ n.d. Additionally, the original experimental day zero value of the metabolite was added to the day zero value of the parent. The reason for this modification is that exactly at the time of application only parent can occur.

The remaining n.d. values were excluded from the analysis.

In the soil BBA 2.1 of the degradation study on Pencycuron-PB-amine [Hellpointner, 1998b] the microbial activity was much lower than in the other soils, and it decreased additionally by more than 50 % during the experimental period (Table 8). Therefore the soil BBA 2.1 was not considered for the kinetic evaluation.

Key result

Soil No.:

#1

DT50:

256.9 d

Type:

other: DFOP

Temp.:

12 °C

Remarks on result:

other: Calculated for 12°C (persistence) - Pencycuron in Nisse Soil

Key result

Soil No.:

#2

DT50:

354.5 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Calculated for 12°C (persistence) - Pencycuron in Howe Soil

Key result

Soil No.:

#3

DT50:

210.4 d

Type:

other: DFOP

Temp.:

12 °C

Remarks on result:

other: Calculated for 12°C (persistence) - Pencycuron in Hoffchen Soil

Key result

Soil No.:

#4

DT50:

399.1 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Calculated for 12°C (persistence) - Pencycuron in Laacherhof Soil

Transformation products:

not specified

Details on results:

MODEL SELECTION
PENCYCURON
Excellent to acceptable fits were obtained for the parent in all studies using the SFO (simple first order) model (Table 1, Table 2). The chi-squared error ranged from 0.7 % to 6.6 % which can be qualified as excellent values and are well below the recommended benchmark value of chi-squared of 15 %. All fits represented well the time course of the measured values without any indication of systematic deviations from SFO. All kinetic parameters were highly significant. Thus all 12 fits were accepted.

PENCYCURON-PB-AMINE
For Pencycuron-PB-amine, there are two parent studies available, i.e. 2 × 4 soil systems, and one study where it was directly incubated in three soils. One soil from the latter study was discarded due to the overall very low microbial activity.

For the elder parent study of Hellpointner [1998a], excellent visual fits were obtained for two soils (Nisse and Höfchen) and the SFO model with low chi-squared errors (< 10 %) and highly significant degradation rates (Table 1). The two other soils failed due to the large scatter of the data accompanied by poor significance of the degradation rates. Inspection of the fits shows that Pencycuron-PB-amine in this study is generally increasing till the end of the study. However, this does not indicate that there is no degradation. The fits were all performed as simultaneous fits of parent degradation, metabolite formation and metabolite degradation.

For the newer parent study of Heinemann [2008], acceptable visual fits were obtained for three soils and the SFO model with low to moderate chi-squared errors (< 23 %) and highly significant degradation rates (Table 2). The soil Dollendorf failed the visual assessment due to the irregular course of the data points (increase-decline-increase) where the overall level of the residues was rather low (about 4 % AR).

For the study of Hellpointner [1998b] where Pencycuron-PB-amine was incubated, an excellent visual fit was obtained for the soil BBA 2.2 and the SFO model with low chi2 error (Table 3).

For the soil Laacherhof the SFO fit was regarded visually not acceptable because the measurements indicate a bi-phasic behaviour. Using the FOMC kinetic model led to a visually and statistically clearly improved fit.

PENCYCURON-KETONE
The metabolite Pencycuron-ketone was analysed in the parent study of Heinemann [2008] via both labels, i.e. in 2 × 4 soil systems. All fits were visually acceptable or excellent using the SFO model. The chi-squared errors were mostly low (< 16 %) with the exception of Laacher Hof AIIIa (label #1, Chi-squared = 54 %) and Hoefchen am Hohenseh 4a (label #1, Chi-squared = 22 %). In these cases the higher chi2 errors were caused by single outliers. It was surprising that even some of the best fits did not produce significant degradation rates. Thus only four valid DT50 were obtained with a T-probability smaller or equal 0.1.

In three cases (Laacher Hof AXXa and Dollendorf, both label #1 and Hoefchen am Hohenseh 4a, label #2) the T-probability is greater than 0.05 in which case a justification should be given based on the fit or weight of evidence from other studies [FOCUS, 2005].

In case of Hoefchen am Hohenseh 4a there is a clear decline of the data where the overall level of the residues was rather low (about 3 % AR).

In case of Dollendorf there is also a clear decline of the data and an excellent visual fit even at a residue level of about 1 – 2 % AR.

In case of Laacher Hof AXXa there is no clear decline. Whereas a decline is sufficient to indicate degradation for a metabolite, it is not a necessary condition. This is illustrated in Figure 2 where the measured and fitted residues are compared to the residues without degradation. The residues without degradation were calculated using the parameters of the fit with the exception of the metabolite degradation rate which was set to zero. Both curves deviate by about 13 % AR which is more than double of the maximum residue value (5.6 % AR). The comparison demonstrates that significant degradation must have been occurred to produce this result. Moreover, in 3 soils and both labels a clear decline of Pencycuron-ketone is observed.

PENCYCURON-PHENYL-CYCLOPENTYL-UREA
Pencycuron-phenyl-cyclopentyl-urea was analysed in the study of Heinemann [2008] for label #2 only. There the maximum occurrence was about 1 % AR for three soils and about 7 % for the soil Laacher Hof AXXa. Employing the SFO model, the low residues inevitably led to high chi-squared errors from roughly 30 % up to more than 50 %, and non-significant degradation rates for three soils. In case of Laacher Hof AXXa the residues were higher and the fit was better in terms of the chi-squared error and the degradation rate was significant. However the fit was unable to describe the measured data in the first 40 days and was thus qualified as not acceptable. Thus no kinetic evaluation was possible for Pencycuron-phenyl-cyclopentyl-urea and neither a formation fraction nor a half-life could be determined. Following FOCUS [2005] it is recommended to use a formation fraction of 1 as conservative estimate for modelling purposes.


KINETIC PARAMETERS
For the model chosen the degradation parameters shown in Table 4 were obtained for Pencycuron. Generally arithmetic mean values of the two labels in the study of Heinemann [2008] were used to calculate the geometric mean and the median. This is considered to provide appropriate weights for the results, i.e. every soil has the same weight.

For the model chosen the degradation parameters shown in Table 5 were obtained for Pencycuron-PB-amine and in Table 6 for Pencycuron-ketone. No kinetic parameters could be determined for Pencycuron-phenyl-cyclopentyl-urea.

Table 1: Scaled error chi², visual assessment (VA) and significance of degradation rate (T-prob) for the soils studied by Hellpointner [1998a]. Kinetic evaluations accepted in bold.

Soil	Compound	Model	Chi^2 (%)	VA*	T-prob
	Pencycuron
Nisse		SFO	0.7	+	<0.001
Howe		SFO	4.1	o	<0.001
Höfchen		SFO	2.4	+	<0.001
Laacherhof		SFO	4.8	o	<0.001
Pencycuron-PB-amine
Nisse	SFO		8.2	+	0.002
Howe	SFO		71.8	--	0.500
Höfchen	SFO		5.6	+	0.020
Laacherhof	SFO		81.8	--	0.500

*Visual assessment: + excellent, ¿ acceptable, -- not acceptable

 

Table 2: Scaled error chi², visual assessment (VA) and significance of degradation rate (T-prob) for the soils studied by Heinemann [2008]. Kinetic evaluations accepted in bold.

Soil	Label	Model	Chi^2 (%)	VA*	T-prob
Pencycuron
Laacher Hof AIIIa	#1/#2	SFO/SFO	4.2 / 5.6	+/+	<0.001 / <0.001
Laacher Hof AXXa	#1/#2	SFO/SFO	6.6 / 6.6	o/o	<0.001 / <0.001
Dollendorf	#1/#2	SFO/SFO	2.9 / 2.6	+/+	<0.001 / <0.001
Hoefchen am H. 4a	#1/#2	SFO/SFO	5.5 / 3.7	+/+	<0.001 / <0.001
Pencycuron-ketone
Laacher Hof AIIIa	#1/#2	SFO/SFO	53.5 / 11.4	¿/¿	0.135 / 0.216
Laacher Hof AXXa	#1/#2	SFO/SFO	15.7 / 15.3	o/o	0.087 / 0.003
Dollendorf	#1/#2	SFO/SFO	10.1 / 7.5	+/+	0.105 / 0.241
Hoefchen am H. 4a	#1/#2	SFO/SFO	21.8 / 9.5	+/o	0.122 / 0.063
Pencycuron-PB-amine
Laacher Hof AIIIa	#1	SFO	16.1	o	0.023
Laacher Hof AXXa	#1	SFO	8.8	o	0.021
Dollendorf	#1	SFO	21.6	--	0.008
Hoefchen am H. 4a	#1	SFO	22.3	o	0.004
Pencycuron-phenyl- cyclopentyl-urea
Laacher Hof AIIIa	#2	SFO	55.2	--	0.361
Laacher Hof AXXa	#2	SFO	27.6	--	0.015
Dollendorf	#2	SFO	31.3	o	0.319
Hoefchen am H. 4a	#2	SFO	50.5	o	0.226

*Visual assessment: + excellent, ¿ acceptable, -- not acceptable

 

Table 3: Scaled error chi², visual assessment (VA) and significance of degradation rate (T-prob) for the soils studied by Hellpointner [1998b]. Kinetic evaluations accepted in bold. Soil BBA 2.1 was discarded from analysis because of insufficient microbial activity.

Soil	Compound	Model	Chi^2 (%)	VA*	T-prob
Pencycuron-PB-amine
BBA 2.2	SFO		8.0	+	<0.001
Laacherhof	SFO		14.2	--	<0.001
Laacherhof	FOMC		3.7	+	<0.001^a / 0.001^b

*Visual assessment: + excellent, ¿ acceptable, -- not acceptable, ^aα, ^bβ

 

Table 4: Optimised degradation parameters of Pencycuron (Parent in MatLab output). Values in bold are used to calculate geometric mean and median.

Soil	Model	Label	k (days^-1)	DT50SFO (days)
Nisse	SFO	n.a.	0.0048	144.4
Howe	SFO	n.a.	0.0039	177.7
Höfchen	SFO	n.a.	0.0056	123.8
Laacherhof	SFO	n.a.	0.0035	198.0
Laacher Hof AIIIa	SFO	#1	0.0167	41.5
Laacher Hof AIIIa	SFO	#2	0.0161	43.1
Laacher Hof AIIIa mean	SFO	n.a.	0.0164	42.3
Laacher Hof AXXa	SFO	#1	0.0133	52.1
Laacher Hof AXXa	SFO	#2	0.0129	53.7
Laacher Hof AXXa mean	SFO	n.a.	0.0131	52.9
Dollendorf	SFO	#1	0.0111	62.4
Dollendorf	SFO	#2	0.0109	63.6
Dollendorf mean	SFO	n.a.	0.0110	63.0
Hoefchen am H. 4a	SFO	#1	0.0105	66.0
Hoefchen am H. 4a	SFO	#2	0.0121	57.3
Hoefchen am H. 4a mean	SFO	n.a.	0.0113	61.6
Geometric mean			0.0075	92.7
Median			0.0083	93.4
n.a. not applicable

 

Table 5: Optimised degradation parameters of Pencycuron-PB-amine (B1 in MatLab output)

Soil	Model	k (days^-1)	DT50SFO (days)	fParent B1
Nisse	SFO	0.0070	99.0	0.709
Höfchen	SFO	0.0104	66.6	0.671
Laacher Hof AIIIa, #1	SFO	0.0662	10.5	0.367
Laacher Hof AXXa, #1	SFO	0.0101	68.6	0.414
Hoefchen am H. 4a, #1	SFO	0.0456	15.2	0.699
BBA 2.2	SFO	0.0242	28.6	n.a.
Laacherhof	FOMC	1.17^a/4.57^b	8.5*	n.a.
Arithmetic mean				0.572
Geometric mean			29.1
Median			28.6

n.a. not applicable, *back-calculated from DT90_FOMC, ^aα, ^bβ

 

Table 6: Optimised degradation parameters of Pencycuron-ketone (A1 in MatLab output). Values in bold are used to calculate the means.

Soil	Model	Label	k (days-1)     DT50SFO    fParent A1                       (days)
Laacher Hof AXXa	SFO	#1	0.0232	29.9	0.244
Laacher Hof AXXa	SFO	#2	0.0357	19.4	0.472
Laacher Hof AXXa mean	SFO	n.a.	0.0295	24.6	0.358
Dollendorf	SFO	#1	0.1557	4.5	0.355
Hoefchen am H. 4a	SFO	#2	0.0541	12.8	0.266
Arithmetic mean Geometric mean			0.0628	11.2	0.326
n.a. not applicable

 

The DT50 values were re-calculated by the RMS:

 

Table 6: Optimisation results for estimation of half-lives of pencycuron in soils Nisse, Howe, Hoffchen am Hohenseh and Laacherhof 

compound	soil	model	r2	visual fit(A)	x2 (err)	model selected
						persistence
Pencycuron	Nisse	SFO	0.983	4	1.88
		FOMC	0.991	4	1.48
		DFOP	1.00	5	0.30	g = 0.0705991; k1 = 0.195269; k2 = 0.00452292; M0 = 92.9236 DT50 = 121 d DT90 = 477 d
Pencycuron	Howe	SFO	0.895	3	4.29	kp = 0.00415435; M0 = 90.4673 DT50 = 167 d DT90 = 554 d
		FOMC	0.895	3	4.58
		DFOP	Not performed
Pencycuron	Hoffchen	SFO	0.949	3	3.89
		FOMC	0.962	3	3.59
		DFOP	0.996	4	1.20	g = 0.118301; k1 = 0.983007; k2 = 0.00517193; M0 = 94.665 DT50 = 99.1 d DT90 = 410 d
Pencycuron	Laacherhof	SFO	0.830	3	5.07	kp = 0.003683; M0 = 89.3653 DT50 = 188 d DT90 = 625 d
		FOMC	No fit could be obtained
		DFOP	Not performed

(A) Scale of 1 tot 5, where 1 = poor, 2 = fairly poor, 3 = fair, 4 = fairly good, 5 = good

 

Table 7: Normalisation of modelling DT₅₀ values of pencycuron for soil moisture^(A)

study	Soil	Texture	MHWC  (% w/w)	B = teta (%w/w)	C = teta ref (% w/w)		B/C		fmoisture	DT50 measured (d)	DT50 (d) normalised to pF 2
1	nisse	loam	51.86	25.93	25		1.04		1.00	139	139
1	howe	sandy loam	34.3	17.15	19		0.90		0.93	167	155
1	hoffchen	silt	63.1	31.55	27		1.17		1.00	118	118
1	Laacherhof	sandy loam	34.42	17.21	19		0.91		0.93	188	175
4	Laacherhof AXXa	sandy loam	n.r.	25.4	19		1.34		1	53.5	53.5
4	Dollendorf II	clay loam	n.r.	41.1	28		1.47		1	63.3	63.3
4	Laacherhof AIIIa	sandy loam	n.r.	28.2	19		1.48		1	42.5	42.5
4	Hoffchen	loam	n.r.	33.5	25		1.34		1	62.8	62.8

(A) Calculated according to section 2.4.2 of "Generic Guidance for Focus Groundwater scenarios, version 1.1, april 2002", by the FOCUS Groundwater Scenarios Workgroup.

 

Table 8: Optimisation results for estimation of modeling half-lives of pencycuron in four soils (2 labels per soil) from study 4 of this section

compound	soil	label	model	r2	visual fit(A)	x2 (err)	Modeling endpoints
Pencycuron	Laacher hof AXXa	M-label	SFO	0.976	4	5.8	DT50 = 53.2 d
		P-label	SFO	0.971	3	6.6	DT50 = 53.7 d
		mean					DT50 = 53.5 d
Pencycuron	Dollendorf II	M-label	SFO	0.996	5	2.0	DT50 = 62.8 d
		P-label	SFO	0.993	5	2.3	DT50 = 63.7 d
		mean					DT50 = 63.3 d
Pencycuron	Laacher- hof AIIIa	M-label	SFO	0.992	5	3.4	DT50 = 42.2 d
		P-label	SFO	0.986	4	5.6	DT50 = 42.8 d
		mean					DT50 = 42.5 d
Pencycuron	Hoffchen am Hohen seh 4a	M-label	SFO	0.967	4	4.8	DT50 = 67.8 d
		P-label	SFO	0.991	4	3.3	DT50 = 57.7 d
		mean					DT50 = 62.8 d

(A) Scale of 1 tot 5, where 1 = poor, 2 = fairly poor, 3 = fair, 4 = fairly good, 5 = good.

 

Conclusions:

Re-analysis of the results for pencycuron from Hellpointner, 1998 gave persistence DT50 values of pencycuron in 4 soils of 99.1-188 days, and persistence DT90 values of 410-625 days. SFO (M0 free, all data, no weighting) gave a statistically and visually acceptable fit for all data sets. The non-normalised SFO DT50 values of pencycuron for modelling were 118-188 days.
The non-normalised SFO DT50 values of pencycuron for modelling obtained from Heinemann, 2008 were 42.5-63.3 days.
The DT50 for modelling normalised to pF=2 was in the range 42.5-150 days, at 20°C (8 soils).

Executive summary:

A modelling study was undertaken to estimate the modelling endpoints for pencycuron and metabolites from residue data obtained during the aerobic soil degradation studies.

Calculations were based on the individual replicate measurements and the time zero values for pencycuron were corrected for radioactivity present as metabolites and non-extractable residues. Where modelling was performed on data from a study with pencycuron in order to estimate modelling endpoints for pencycuron-PB-amine, simultaneous fitting for parent and metabolite was carried out. The optimisation was based on visual assessment of the fit and the residuals plot, and the following statistical goodness of fit measures: chi squared (error) as recommended by FOCUS Kinetics and p-value to evaluate the confidence of the estimated degradation rate constants.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

2008-04-30 to 2008-11-25

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: Commission Directive 95/36/EC amending Council Directive91/414/EEC (Annexes I and II, Fate and Behavior in the Environment)

Version / remarks:

1995

Qualifier:

according to guideline

Guideline:

other: SETAC Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides

Version / remarks:

1995

Qualifier:

according to guideline

Guideline:

other: EPA Pesticide Assessment Guidelines, Subdivision N, Environmental Fate § 162-1, Aerobic Soil metabolism Studies

Version / remarks:

1982

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

USDA (US Department of Agriculture)

Year:

2008

Soil no.:

#1

Soil type:

sandy loam

% Clay:

11

% Silt:

18

% Sand:

71

% Org. C:

1.5

CEC:

7.7 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

clay loam

% Clay:

39

% Silt:

34

% Sand:

27

% Org. C:

3.8

CEC:

19.1 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

sandy loam

% Clay:

16

% Silt:

27

% Sand:

57

% Org. C:

1.5

CEC:

8.9 meq/100 g soil d.w.

Soil no.:

#4

Soil type:

loam

% Clay:

21

% Silt:

50

% Sand:

29

% Org. C:

1.2

CEC:

12 meq/100 g soil d.w.

Details on soil characteristics:

Soil A/#1: Laacher Hof AXXa
Soil B/#2: Dollendorf II
Soil C/#3: Laacher Hof AIIIa
Soil D/#4: Hoefchen am Hohenseh 4a

The test soils (properties see Table 1) were collected from a site untreated with pesticides during the previous 5 years

SOIL COLLECTION AND STORAGE
- Geographic location: Germany
- Pesticide use history at the collection site: From a site untreated with pesticides during the previous 5 years.
- Collection procedures: Sample taken with shovel and placed in plastic bag
- Sampling depth (cm): 0-20 cm
- Storage conditions:
Laacher Hof & AXXa Dollendorf II: After arrival at the test facility, the soil was sieved through a 1 cm sieve and dried at room temperature in a fume hood. The next day the soil was sieved through a 5 mm sieve and an aliquot was finally sieved through a 2 mm sieve. Then the soil was stored for two weeks at about 4°C in climate chamber until pre-incubation.

Laacher Hof AIIIa: After arrival at the test facility, the soil was sieved through a 1 cm sieve and dried at room temperature in a fume hood. The same day the soil was sieved through a 5 mm and subsequently through a 2 mm sieve. Then the soil was stored at about 4°C in a climate chamber until preincubation.

Hoefchen am Hohenseh 4a: After arrival at the test facility, the soil was sieved through a 1 cm sieve and dried at room temperature in a fume hood. The next day the soil was sieved through a 5 mm sieve and an aliquot was finally sieved through a 2 mm sieve. Then the soil was stored at about 4°C in climate chamber until preincubation.
- Storage length: Sampling to application: 12 to 13 days before application
- Soil preparation (e.g., 2 mm sieved; air dried etc.): Sieved (2 mm)

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.:

1.33 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#2

Initial conc.:

1.33 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#3

Initial conc.:

1.33 mg/kg soil d.w.

Based on:

test mat.

Soil No.:

#4

Initial conc.:

1.33 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

Soil No.:

#1

Temp.:

20°C

Soil No.:

#2

Temp.:

20°C

Soil No.:

#3

Temp.:

20°C

Soil No.:

#4

Temp.:

20°C

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil preincubation conditions (duration, temperature if applicable): Following field collection and sieving (2 mm), they were stored aerobically at the test facility for about two weeks at 4°C.
- Soil condition: Fresh
- Soil (g/replicate): 100 g/replicate
- No. of replication treatments: Duplicate samples for each sampling interval and each label
- Test apparatus (Type/material/volume): 300-mL Erlenmeyer flasks
- Details of traps for CO2 and organic volatile, if any: The traps were loaded with soda lime and polyurethane foam. The system was open to air.
- Identity and concentration of co-solvent: Water/methanol (1/1, v/v) including < 10 % acetonitrile due to insolubility of the test item.

Test material application
- Volume of test solution used/treatment: 400 µL/100 g soil (DM)
- Application method (e.g. applied on surface, homogeneous mixing etc.): Applied dropwise onto 100 g soil (DM) using an adjustable pipette.
- Is the co-solvent evaporated: No

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: Re-weighing and addition of lost water
- Continuous darkness: Yes

SAMPLING DETAILS
- Sampling intervals: 0, 7, 14, 28, 49, 63, 77, 91, 104, and 120 days post-application
- Method of collection of CO2 and volatile organic compounds: Soda lime for absorption of 14CO2 and polyurethane foam for volatile organic compounds
- Sampling intervals/times for:
> Moisture content: 0, 7, 14, 28, 49, 63, 77 and 91 days post application

Soil No.:

#1

DT50:

53.5 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Modelling (normalised)

Soil No.:

#2

DT50:

63.3 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Modelling (normalised)

Soil No.:

#3

DT50:

42.5 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Modelling (normalised)

Soil No.:

#4

DT50:

62.8 d

Type:

other: SFO

Temp.:

20 °C

Remarks on result:

other: Modelling (normalised)

Soil No.:

#1

DT50:

114 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#2

DT50:

134 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#3

DT50:

90.2 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Soil No.:

#4

DT50:

133 d

Type:

other: SFO

Temp.:

12 °C

Remarks on result:

other: Modelling value calculated for 12°C

Transformation products:

yes

Details on results:

TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Major metabolites (>10% or 2X >5%) were Pencycuron-PB-amine (max 16.3% AR on day 120), pencycuron-phenyl-cyclopentyl-urea (max 6.6% AR on day 91) and pencycuron-ketone (max 7.9% AR on day 77).
- Range of maximum concentrations in % of the applied amount at end of study period:
on the - the and -th day of incubation, respectively. At the end of the study period, the corresponding concentrations were - and -- % of the applied amount, respectively.

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: Another two minor metabolites below 5% of the AR were found, Pencycurondesphenyl and Pencycuron-descyclopentyl. Pencycuron-desphenyl was detected in label #1 in amounts of up to 4.5% of the AR (soil AA, label #1, DAT-63/DAT-91) and Pencycuron-descyclopentyl was detected in both labels in amounts of up to 2.8% of the AR (soil AX, label #2, DAT-91).

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT: The mean of sum of unknown extracted radioactivity did not exceed 5.5% of the AR.

EXTRACTABLE RESIDUES
Extractable 14C-residues decreased from 101.0, 97.9, 101.1, and 95.4% AR at DAT-0 to 47.6, 33.2, 25.2, and 42.3% AR at study end at DAT-120 in soils AX, DD, AA, and HH (all label #1), respectively, and from 102.0, 96.7, 102.5, and 98.8% AR at DAT-0 to 45.5, 28.6, 19.0, and 28.7% AR at study end at DAT-120 in soils AX, DD, AA, and HH (all label #2), respectively.

NON-EXTRACTABLE RESIDUES
The formation of bound residues increased with the overall metabolism of Pencycuron. Non-extractable 14C-residues increased from 0.8 to 4.4% of the AR at DAT-0 to 14.5 to 46.6% of the AR at the end of the study termination

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: The maximum amount of 14CO2 was 46.3% AR at the end of the study (Laacher Hof AIIIa, label #1, DAT-120; Appendix 9). No volatile organic compounds were detected at any sampling interval.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: No radioactivity was detected in organic volatile traps (mean 0.0% AR at all times).

Microbial activity of the test soil was confirmed at the start and at the end of aerobic incubation by determining the microbial biomass using the substrate induced respiration method. At the start of the test, microbial activity was >1% of organic C. The reduction observed in the course of the test is considered to be normal for soils kept under these conditions.

Results for extraction, distribution and identification of radioactivity are given in Table B.8.1.1.1.4b-e (M- label) and Table B.8.1.1.1.4f-i (P-label). Mass balances ranged between 90 and 104%, except for day 63, M-label, soil C and D (86-89%). The low mass balances in these two cases are most probably due to aberrant values for bound residues, possibly due to problems with combustion analysis. The results for extracts generated on these days are considered to be valid. No radioactivity was detected in organic volatile traps (mean 0.0% AR at all times). CO₂ was evolved from the soil in large amounts to a maximum of 31-46% AR (M-label) and 22-32% AR (P-label) on day 120. PES reached maximum values of 15-26% AR (M-label) and 35-47% AR (P-label) on day 120. Extractability on day 0 was excellent showing that pencycuron was recovered from treated soils using the extraction procedure employed. Pencycuron degraded to 13-29% AR within 120 days. Pencycuron-PB-amine was the only metabolite found at >10% AR (max 16.3% AR on day 120). Metabolites detected at >5% AR during at least two successive samplings were pencycuron-phenyl-cyclopentyl-urea (max 6.6% AR on day 91) and pencycuron-ketone (max 7.9% AR on day 77). Pencycuron-desphenyl and pencycuron-descyclopentyl were detected but at levels <5% AR. The levels of unidentified fractions were always: ≤2.7% AR.

 

Degradation rates

A separate report was submitted with estimations of the modelling endpoints for parent pencycuron and the degradation endpoints for major metabolites (Hammel, 2009). This report presented an estimation of the DT50 (persistence) values of the parent compound according to the “Guidance document on estimating persistence and degradation kinetics from Environmental Fate studies on pesticides in EU registration” (SANCO/10058/2005 version 2.0). Calculations were based on the individual replicate measurements and employed the model KinGUI v1.1 (SFO = single first-order, FOMC = first-order multi-compartment, DFOP = Double-First-Order in Parallel Mode). The conceptual model of SFO, FOMC and DFOP assumes that parent pencycuron is converted into a sink (degradation products, PES) with a flow F1. The flows are mathematically described by the equations given in the Guidance Documents for the various models.

SFO and FOMC were run first (M0 free, all data, no weighting). FOMC gave a comparable or better fit than SFO for all data sets. Therefore DFOP was run unmodified. The optimisation results are shown in Table B.8.1.1.1.4j, and the optimised fitting parameters for the best fit model in Table B.8.1.1.1.4k. The reported persistence endpoints were obtained from a biphasic model, and the estimated DT90 persistence value was not reached within the experimental period.

The author of the report took the time zero values for pencycuron to represent the actual measured values. This is not in agreement with the recommendations by FOCUS, which state that also the radioactivity in day 0 PES samples and that for metabolites should be added to the day 0 values for the parent substance. However, in all data sets except soil B (M-label), soil D (M-label) and soil B (P-label), parent compound represented 97.0-101.3% AR, and renewed calculations with adjusted day 0 values are presumed to have an insignificant effect on the endpoints. In order to investigate the magnitude of the effect of adjusting the day 0 values of pencyuron for PES and metabolites, the DT50 values were recalculated by the RMS for soil B (M-label), as in this soil the difference between the actual measured values (93.6-96.5% AR) and the total recovered radioactivity (99.3-101.9% AR) was highest of all soils. During recalculation of this data set, the time zero values for pencycuron were taken to represent total recovered radioactivity. The calculations by the reviewer were performed with ModelMaker v 4.0 software. For SFO, FOMC and DFOP, respectively: the reported x² (err) was 2.0, 1.8 and 1.3, the reported DT50 was 62.8, 60.5 and 60.2 days, and the reported DT90 209, 245 and 211 days; the recalculated x² (err) was 3.8, 3.1 and 1.4, the recalculated DT50 was 60.6, 54.9 and 55.8 days, and the recalculated DT90 201, 297 and 207 days. Recalculation for this data set gave essentially the same results: all three models gave an acceptable fit, DFOP gave the best fit, and there were no substantial differences between the reported and the recalculated DT50 and DT90 values. The fit obtained by the author of the report was slightly better, and the DT50 and DT90 values slightly higher, hence worst case.                                               

 

The RMS has recalcuted the half-lives of pencycuron in four soils, summaried in Table 12 taken from the DAR.

Table 12: Optimisation results for estimation of modeling half-lives of pencycuron in four soils (2 labels per soil) from study 4 of this section (recalculated by the RMS)

compound	soil	label			model	r2	visual fit(A)	2 (err)	Modeling endpoints
Pency- curon	Laacher- hof AXXa	M-label			SFO	0.976	4	5.8	DT50 = 53.2 d
		P-label			SFO	0.971	3	6.6	DT50 = 53.7 d
		mean							DT50 = 53.5 d
Pency- curon	Dollendorf II	M-label			SFO	0.996	5	2.0	DT50 = 62.8 d
		P-label			SFO	0.993	5	2.3	DT50 = 63.7 d
		mean							DT50 = 63.3 d
Pency- curon	Laacher- hof AIIIa		M-label		SFO	0.992	5	3.4	DT50 = 42.2 d
			P-label		SFO	0.986	4	5.6	DT50 = 42.8 d
		mean							DT50 = 42.5 d
Pency- curon	Hoffchen am Hohen seh 4a	M-label			SFO	0.967	4	4.8	DT50 = 67.8 d
		P-label			SFO	0.991	4	3.3	DT50 = 57.7 d
		mean							DT50 = 62.8 d

recalculated by the RMS

Conclusions:

In four soils treated with [methylene-14C]Pencycuron or [phenyl-U-14C]Pencycuron and incubated under aerobic conditions at 20°C and 55% MWHC in the dark, CO2 was evolved to 31-46% AR (M-label) and 22-32% AR (P-label), PES reached maximum values of 15-26% AR (M-label) and 35-47% AR (P-label) on day 120, pencycuron degraded to 13-29% AR within 120 days. Major metabolites (>10% or 2X >5%) were Pencycuron-PB-amine (max 16.3% AR on day 120), pencycuron-phenyl-cyclopentyl-urea (max 6.6% AR on day 91) and pencycuron-ketone (max 7.9% AR on day 77). DT50 (persistence, 20°C) of pencycuron was 36.4-60.1 days, DT90 (persistence, 20°C) 159-239 days.

Description of key information

Laboratory studies were carried out on the aerobic degradation of pencycuron in eight soils and the metabolites detected at >10% AR or at 2 successive times >5% AR were pencycuron-PB-amine (max. 45.0% AR on day 100), pencycuron-phenyl-cyclopentyl-urea (max 6.6% AR on day 91) and pencycuron-ketone (max 9.9% AR on day 84).

Aerobic metabolism of pencycuron proceeds due to hydrolysis and microbial processes. The ultimate breakdown products are CO₂ and non-extractable residues.

The normalised modelling DT50 values for the 8 soils were converted to 12°C to give the following DT50 values (in days at 12°C), 295 (Nisse), 329 (Howe), 251 (Hofchen), 372 (Laacherhof), 114 (Laacherhof AXXa), 134 (Dollendorf II), 90.2 (Laacherhof AIIIa) and 133 (Hoffchen). This gave a median value of 192 days at 12°C.

In the table below all available studies are listed. For some studies only the results are presented since they are not considered relevant due to the reasons given under “Assessment”. All available studies have been evaluated within the scope of Plant Protection Regulation.

Test Type	Result	Assessment	Reference
Aerobic soil degradation study following OECD 307 (2002) and SETAC guidelines using 4 soils and 2 radiolabels.	Normalised SFO DT50 values of pencycuron for modelling obtained were 42.5-63.3 days (at 20°C). This equates to 90.2-134 days (at 12°C).	Key study using 4 soils and 2 radiolabels	Heinemann (2008b)
Kinetic assessment of aerobic laboratory soil degradation carried out in line with Focus guidelines	DT50 (days): Pencycuron: Geometric mean: 89.2. Median: 90.7 (both at 20°C); Values were recalculated in the DAR.	Key study	Hammel (2009)
Aerobic soil degradation study to SETAC 1995 using 4 soils	Normalised SFO DT50 values of pencycuron for modelling were 118-175 days (at 20°C). This equates to 251-372 days at 12°C.	Supporting study, the DT50 values were recalculated in the DAR	Hellpointner (1998)
Aerobic soil degradation study to BBA guidelines.	No reliable DT50 was obtained for pencycuron. The report was finalised in 2003, whilst the experimental phase was conducted in 1993.	Acceptable study- but no DT50 obtained for pencycuron	Hellpointner  (2003a)
Aerobic soil degradation study to SETAC and BBA guidelines.	No reliable DT50 was obtained for pencycuron.	Acceptable study- but no DT50 obtained for pencycuron	Hellpointner (1998)
Field dissipation study carried out to BBA Guidelines at 4 sites in Germany.	Persistence DT50 endpoints of 35.9 to 68.2 days	Valid field study in DAR	Pogany (1986)
Field dissipation study carried out in France and Italy.	Persistence DT50 endpoints of 31.7 to 43.7 days	Valid field study in DAR	Sommer (2000)
Field dissipation study at sites in Germany (2), France and GB.	Persistence DT50 endpoints of 10.6 to 64.9 days	Valid field study in DAR	Sommer D and Schramel O (2000)
Modelling results from field studies	Modelling geomean of 35.9 days (and median of 38.3 days) obtained from n=10 normalised data	Valid kinetic assessment of field studies	Hammel & Kahl (2009)

 

Key value for chemical safety assessment

Half-life in soil:

192 d

at the temperature of:

12 °C