Reaction mass of 3-(difluoromethyl)-1-methyl-N-[(1RS,4SR,9RS)-1,2,3,4-tetrahydro-9-isopropyl-1,4-methanonaphthalen-5-yl]pyrazole-4-carboxamide and of 3-(difluoromethyl)-1-methyl-N-[(1RS,4SR,9SR)-1,2,3,4-tetrahydro-9-isopropyl-1,4-methanonaphthalen-5-yl]pyrazole-4-carboxamide; isopyrazam

Phototransformation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

21 Jul 2006 to 13 Oct 2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline draft (Phototransformation of Chemicals on Soil Surfaces)

Version / remarks:

January 2002

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

Version / remarks:

October 18, 1982

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

liquid chromatography

high-performance liquid chromatography

mass spectrometry

other:

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 295 - <= 800

Duration:

21 d

% Moisture:

44.1

Temp.:

20 °C

Initial conc. measured:

133 g/ha d.w.

Reference substance:

yes

Dark controls:

yes

% Degr.:

27.6

Sampling time:

21

DT50:

>= 64.7 - <= 67.8 d

Test condition:

Continuous irradiation

Remarks on result:

other: Days Summer sunlight at 30-50 ˚N

DT50:

861.1 h

Test condition:

Continuous Irradiation

Transformation products:

not specified

Results of the distribution of radioactivity in the soil are presented in Table 3 and characterisation in Table 4.

No major metabolites were identified. Differences in radioactivity balance between the soil extracts and the extracted test item were accounted for by up to 13 separate minor fractions, none of which represented >3% AR at any time. A maximum of 8.9% AR was recovered in NaOH traps. An investigation by barium carbonate precipitation followed by regeneration of 14CO2 by addition of HCl and trapping of 14CO2 by ethanolamine indicated that 5.9% AR was due to CO2. As the recovery of 14CO2 from this procedure was considered rather low, the study authors repeated the procedure twice, however, the low recovery was confirmed. The authors concluded that other volatile gases, accounting for approximately 3% AR, must have also been trapped in the NaOH solutions. The study author calculated the SFO DT50 using ModelManager v1.1 as 36 experimental days (861.1 hours) under continuous irradiation (i.e. extrapolated beyond study duration). This was equated to DT50 of 64.7 – 67.8 days at 30 – 50ºN.

Table 3. Mass balance and distribution of radioactivity in dry soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-phenyl]-labelled test item

DAT	Replicate	% of Applied Radioactivity			Total	Mean
		% Extracted	% in NaOH Trap	% Unextracted
0	A	107.0	0.0	0.6	107.6	106.8
	B	105.5	0.0	0.5	106.0
3	A	103.3	1.6	2.1	107.0	107.8
	B	104.7	1.7	2.1	108.5
7	A	102.2	2.8	2.9	107.9	105.6
	B	97.1	3.3	2.8	103.2
10	A	94.4	4.9	3.4	102.7	100.9
	B	91.9	3.7	3.5	99.1
14	A	80.0	3.5	3.0	86.5	93.1
	B	89.3	6.5	3.9	99.7
21	A	83.5	9.8	4.1	97.4	97.9
	B	85.5	8.8	4.0	98.3
Dark Control 21	A	102.4	NA	0.8	103.2	104.3
	B	104.6	NA	0.8	105.4

Table 4. Characterisation of extracted radioactivity in dry soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-phenyl]-labelled test item

DAT	% test item
0	104.7
3	98.3
7	90.0
10	83.1
14	76.4
21	72.4
Dark Control 21	102.0

 

Validity criteria fulfilled:

not specified

Conclusions:

In a phototransformation in soil study performed in accordance with a draft OECD test guideline and EPA 161-3, the half-life of the test substance was determined to be 65 - 68 days under summer sunlight (latitudes of 30, 40 and 50°N).

Executive summary:

The photolysis of 14C-phenyl-labelled test item was investigated on dry soil surfaces in accordance with a draft OECD test guideline and EPA 161-3. The study was in compliance with GLP. In a previous study using 14-pyrazolyl-labelled test item, the photolysis was studied in both dry and moist soil layers. In this study, no significant degradation was observed in the moist soil test, therefore it was not considered necessary to repeat this with the 14C-phenyl-labelled test item. The 14C-labelled test item was applied, at rates equivalent to ca. 133 - 136 g/ha, to thin layers (≤1 mm thickness) of soil in individual photolysis vessels. The treated soils were continuously irradiated using light from a xenon arc lamp. The emitted light was filtered to give a spectral distribution close to that of natural sunlight. The samples were maintained at 20 ± 2˚C and were irradiated for periods up to the equivalent of > 30 days summer sunlight. Duplicate samples were taken for analysis at up to 6 intervals. During irradiation, volatile products were trapped, using a sealed system, in a 2M sodium hydroxide solution. Two 'dark control' samples were also prepared and maintained at ca. 20°C for the duration of the irradiation.
The mass balance from the irradiated samples (mean of duplicate samples) ranged from 93.1 - 106.8 % of applied radioactivity. Trapped volatiles accounted for a maximum of 9.8 %. Of this, 5.9% was characterised as 14CO2, whilst the remainder (3.9% of applied radioactivity was possibly due to one or more other small, volatile compounds. Levels of unextracted radioactivity remained low (< 5 % of initial radioactivity). Degradation of test item during the irradiation period was significant, such that the parent compound represented 72.4 % of applied radioactivity after 21 days of continuous irradiation. The remainder of the radioactivity in the extract consisted of up to 13 minor components, none of which represented > 3% of applied radioactivity at the end of the irradiation period. No significant degradation was apparent in the 'dark controls' indicating that the degradation in irradiated samples was due to photodegradation only. Degradation of the test item on dry soil layers followed first-order kinetics. The estimated DT50 was 65 - 68 days of summer sunlight at latitudes of 30 - 50°N. As observed in a previous 14C - pyrazolyl - labelled test item soil photolysis study, degradation was assumed to involve cleavage of the molecule between the two ring systems to yield a large number of transient degradates containing the phenyl moiety of the molecule, which then underwent ring opening to yield volatile degradates, including 14CO2, to a maximum of 9.8% of the applied radioactivity.

Reference 2

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

10 Feb 2006 to 19 Oct 2006

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

OECD Guideline draft (Phototransformation of Chemicals on Soil Surfaces)

Version / remarks:

January 2002

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-3 (Photodegradation Studies on Soil)

Version / remarks:

October 18, 1982

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

liquid chromatography

high-performance liquid chromatography

mass spectrometry

other:

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 295 - <= 800

Relative light intensity:

>= 35.68 - <= 37.2

Duration:

30 d

% Moisture:

23.4

Temp.:

20 °C

Initial conc. measured:

139.5 g/ha d.w.

Duration:

30 d

% Moisture:

23.4

Temp.:

20 °C

Initial conc. measured:

131.5 g/ha d.w.

Reference substance:

no

Dark controls:

yes

% Degr.:

6.2

Sampling time:

21 d

Test condition:

Irradiated

Remarks on result:

other: Moist soil - Direct

% Degr.:

31.7

Sampling time:

21 d

Test condition:

Irradiated

Remarks on result:

other: Dry soil - Direct

DT50:

>= 68.2 - <= 71.6 d

Test condition:

Continuous irradiation

Remarks on result:

other: Summer Sunlight at 30-50°N - Dry Soil Layers

DT50:

1 006.9 h

Test condition:

Continuous Irradiation

Remarks on result:

other: Dry Soil Layers

Transformation products:

not specified

Remarks:

M8, M9

An overview of the results is provided in Table 2 - Table 5 below.

- Mass balance: In the dry soil test, the mass balance from the irradiated samples (mean of duplicate samples) ranged from 97.7 - 106.0 % of applied radioactivity. The mean recovery from dark control samples was 103.2 %. Levels of unextracted residue remained low (< 5 % of initial radioactivity). In the moist soil test, the mass balance from the irradiated samples (mean of duplicate samples) ranged from 101.9 - 110.3 % of initial radioactivity. The mean recovery from dark control samples was 102.6 %. Levels of unextracted residue remained low (generally < 7 % of initial radioactivity).

- Volatile degradation products: Low levels of radioactivity were evolved as volatile products, which were trapped in sodium hydroxide. The volatile radioactivity evolved reached a maximum of 2.9 % of initial radioactivity for the dry soil test and < 1 % for the moist soil test. This radioactivity was assumed to be due to 14CO2. As no radioactivity was unaccounted for in the dry soil test, no analysis was conducted on the "ORBO" traps.

- Radioactive residues in soil extracts (Dry soil test): Degradation of the test substance during the irradiation period was significant, such that the parent compound represented 68.3 % of applied radioactivity after 21 days of continuous irradiation. Two discrete degradates were observed, namely M8 (which reached a maximum level of 5.4 % of applied radioactivity after 21 days) and M9 (which reached a maximum level of 8.0 % of applied radioactivity after 2 1 days). The remainder of the radioactivity in the extract consisted of 2 minor components (neither of which represented > 5 % of the applied radioactivity) and areas of "streaked" radioactivity which did not contain any discrete components.

- Radioactive residues in soil extracts (Moist soil test): No significant degradation was observed in the moist soils layers, with the test substance still representing 93.8 % of applied radioactivity after 21 days of continuous irradiation. Low levels of M8 were observed (reaching a maximum of 1.6 % of applied radioactivity after 21 days). No degradates were observed which represented > 5 % of the applied radioactivity.

It is considered that the relatively low amount of degradation of the test substance in moist soil may have been due to more even distribution of the substance through the soil, protecting a significant amount of the residue from photolysis, this being exaggerated with the regular re-wetting of the soil through the study. The SFO DT50 was calculated using the ModelManager v1.1 as 42 experimental days (1006.9 hours) for dry soil under continuous irradiation (i.e. extrapolated beyond study duration). This was equated to DT50 of 68.2 – 71.6 days at 30 – 50ºN. Whilst not conducted according to FOCUS Kinetics principles. The ratio of syn:anti isomer of the test substance isomers was measured at the beginning and end of the irradiation periods in both dry and moist soil tests. The ratio was essentially unchanged over the course of the 21 day study duration.

Table 2. Mass balance and distribution of radioactivity in dry soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-pyrazole] labelled test item

DAT	Replicate	% of Applied Radioactivity			Total	Mean
		% Extracted	% CO2	% Unextracted
0	A	102.1	0.0	0.6	102.7	102.9
	B	102.4	0.0	0.6	103.0
3	A	105.9	0.1	1.4	107.4	106.0
	B	102.6	0.1	1.8	104.5
7	A	102.6	0.5	2.3	105.4	102.7
	B	96.3	0.9	2.7	99.9
10	A	97.3	1.0	2.7	101.0	101.1
	B	96.7	1.6	2.8	101.1
14	A	99.1	0.9	2.7	102.7	102.6
	B	97.7	1.2	3.6	102.5
21	A	91.2	2.9	3.6	97.7	97.7 (a)
	B	113.1 (a)	2.1	4.2	119.4 (a)
Dark Control 21	A	102.6	0.0	0.6	103.2	103.2 (a)
	B	80.4 (a)	0.0	1.8	82.2 (a)

During transfer, some of the Dark Control Rep B extract was erroneously mixed with the 21 DAT Rep B Extract (hence the discrepancy between the recoveries). These samples were not, therefore, included in the mean.

Table 3 Characterisation of extracted radioactivity in dry soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-pyrazole] labelled test item

DAT	Replicate	% Test item	Mean	% M9	Mean	% M8	Mean
0	A	102.1	102.3	0.0	0.0	0.0	0.0
	B	102.4		0.0		0.0
3	A	105.9	102.7	0.0	0.5	0.0	0.7
	B	99.5		1.0		1.3
7	A	96.6	92.6	0.9	1.6	3.0	3.3
	B	88.5		2.3		3.5
10	A	86.8	84.8	2.2	3.0	3.5	4.0
	B	82.7		3.7		4.4
14	A	91.7	89.4	2.3	2.9	3.7	4.0
	B	87.7		3.5		4.2
21	A	68.3	68.3(a)	8.0	8.0	5.4	5.4
	B	104.1(a)		3.8(a)		5.3(a)
Dark Control 21	A	102.6	102.6(a)	0.0	0.0	0.0	0.0
	B	80.4(a)		NA		NA

(a) During transfer, some of the Dark Control Rep B extract was erroneously mixed with the 21 DAT Rep B Extract (hence the discrepancy between the recoveries). These samples were not, therefore, included in the mean.

Table 4. Mass balance and distribution of radioactivity in moist soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-pyrazole] labelled test item

DAT	Replicate	% of Applied Radioactivity			Total	Mean
		% Extracted	% CO2	% Unextracted
0	A	99.7	0.0	16.4	116.1	110.3
	B	98.2	0.0	6.3	104.5
3	A	103.0	0.1	2.8	105.9	105.2
	B	100.6	0.1	3.7	104.4
7	A	102.7	0.0	3.1	105.8	105.4
	B	101.6	0.1	3.3	105.0
10	A	99.9	0.1	2.9	102.9	103.6
	B	99.5	0.4	4.3	104.2
14	A	97.1	0.1	3.5	100.7	103.3
	B	99.5	0.6	5.7	105.8
21	A	96.4	0.5	3.8	100.7	101.9
	B	97.1	0.7	5.2	103.0
Dark Controls	A	102.1	0.0	2.2	104.3	102.6
	B	99.0	0.0	1.8	100.8

Table 5. Characterisation of extracted radioactivity in moist soil photolysis Gartenacker soil - individual replicates (values as % AR), [14C-pyrazole] labelled test item

DAT	Replicate	% test item	Mean	% M8	Mean
0	A	99.7	99.0	0.0	0.0
	B	98.2		0.0
3	A	103.0	101.8	0.0	0.0
	B	100.6		0.0
7	A	102.7	102.2	0.0	0.0
	B	101.6		0.0
10	A	99.9	99.7	0.0	0.0
	B	99.5		0.0
14	A	95.6	96.4	1.5	1.4
	B	97.1		1.2
21	A	93.6	93.8	1.0	1.6
	B	93.9		2.1
Dark Control	A	102.1	100.6	0.0	0.0
	B	99.0		0.0

 

Validity criteria fulfilled:

not specified

Conclusions:

In a soil photolysis study conducted according to a draft OECD test guideline and EPA 161-3, the DT50 of the test substance was estimated to be 68 - 72 days of summer sunlight using SFO.

Executive summary:

A soil photolysis study was conducted according to a draft OECD test guideline and EPA 161-3. The study was in compliance with GLP. The photolysis of the test item was investigated on both dry and moist soil surfaces. The 14C-labelled test item was applied at rates equivalent to ca. 131 - 142 g/ha, to thin layers (≤ 1 mm for dry soil ; ≤ 2 mm for moist soil) of soil in individual photolysis vessels. The treated soils were continuously irradiated using light from a xenon arc lamp. The emitted light was filtered to give a spectral distribution close to that of natural sunlight. The samples were maintained at 20 ± 2˚C and were irradiated for periods up to the equivalent of ca 30 days summer sunlight. In each test, duplicate samples were taken for analysis at up to 6 intervals during irradiation. During irradiation, volatile products were trapped, using a sealed system, in a 2M sodium hydroxide solution. Two 'dark control' samples were also prepared and maintained at ca. 20°C for the duration of the irradiation.

In the dry soil test, the mass balance from the irradiated samples (mean of duplicate samples) ranged from 97.7 - 106.0 % of applied radioactivity. Trapped volatiles (14CO2) accounted for a maximum of 2.9 % and levels of unextracted radioactivity remained low (< 5 % of initial radioactivity). At the end of the irradiation period, the 14C-labelled test item represented 68.3 % of the applied radioactivity. Two discrete degradates were formed, namely M8 (representing a maximum of 5.4% of the applied radioactivity) and M9 (representing a maximum of 8.0 % of the applied radioactivity). No other component represented greater than 5 % of applied radioactivity. No significant degradation was apparent in the 'dark controls' indicating that the degradation in irradiated samples was due to photodegradation only. The ratio of the syn and anti isomers remained unchanged throughout the irradiation, indicating that no isomer-specific degradation had occurred.
Degradation of test item on dry soil layers followed first order kinetics. The estimated DT50 was 68 - 72 days of summer sunlight at latitudes of 30 - 50°N. In the moist soil test, the mass balance from the irradiated samples (mean of duplicate samples) ranged from 101.9 - 110.3 % of applied radioactivity. Trapped volatiles (14CO2)accounted for a maximum of < 1 % and levels of unextracted radioactivity remained low (generally < 7 % of initial radioactivity). In contrast to the dry soil test, no significant degradation was observed in the moist soil test.

Degradation involved cleavage of the molecule between the two ring systems to yield the carboxylic acid and amide derivatives of the pyrazole ring, which represented maximum levels of 5.4% and 8.0 of applied radioactivity, respectively. Low levels of mineralization were observed (< 3 %). No significant degradation was observed in the moist soil layers. It is likely that the chemical was distributed evenly through the soil layer on moistening after application, protecting a significant proportion from the effects of irradiation. The regular re-moistening of the layers would then further promote this effect.

Description of key information

DT50 = 68 - 72 days of summer sunlight latitudes of 30 - 50°N, dry soil, continuous irradiation, Xenon arc lamp, 14C-pyrazole-labelled substance, OECD draft guideline and EPA 161 -3, Hand and Khawaja 2006

DT50 = 65 – 68 days of summer sunlight latitudes of 30 - 50°N, continuous irradiation, Xenon arc lamp, 14C-phenyl-labelled substance, OECD draft guideline and EPA 161 -3, Hand and Khawaka 2007

Additional information

Two studies on photodegradation in soil (EPA 161-3 and OECD draft guideline) are available. In the first study (Hand and Khawaja 2006), both dry and moist Gartenacker soil (loam) were exposed to the 14C-pyrazole-labelled test substance at an approximate rate of 131 - 142 g/ha. The treated soils were continuously irradiated using light from a xenon arc lamp. The emitted light was filtered to give a spectral distribution close to that of natural sunlight. The samples were maintained at 20 ± 2°C and were irradiated for periods up to the equivalent of ca. 30 days summer sunlight. Degradation of the test substance on dry soil layers followed first order kinetics. The estimated DT50 was 68 - 72 days of summer sunlight at latitudes of 30 - 50°N. In contrast to the dry soil test, no significant degradation was observed in the moist soil test. In the second study (Hand and Khawaja 2007), dry Gartenacker soil (loam) was exposed to the 14C-phyenyl labelled substance at an approximate rate of 133 - 136 g/ha. The treated soils were continuously irradiated using light from a xenon arc lamp. The emitted light was filtered to give a spectral distribution close to that of natural sunlight. The samples were maintained at 20 ± 2°C and were irradiated for periods up to the equivalent of > 30 days summer sunlight. Degradation of the test substance on dry soil layers followed first order kinetics. The estimated DT50 was 65 - 68 days of summer sunlight at latitudes of 30 - 50°N.