Diquat dibromide

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

key study

Study period:

22 Apr 2010 to 26 Jan 2012

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:

draft document, January 2002

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: EPA Guideline Series OPPTS 835.2410 Photodegradation of Soil

Version / remarks:

October 2008

Deviations:

no

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Analytical monitoring:

yes

Analytical method:

liquid chromatography

high-performance liquid chromatography

mass spectrometry

other: Liquid scintillation counting (LSC) and Thin layer chromatography (TLC)

Details on sampling:

Soil vessels were sampled in duplicate from each soil type immediately after treatment (zero time) and at six other timepoints as shown in Table 1 in ’Any other information on materials and methods incl. tables’. After removal of samples from the incubation system, all vessels were extracted immediately.

Details on soil:

- The study was conducted using one soil, Gartenacker (loam). The soil was sampled to a maximum depth of 20 cm on 31 March 2010. The soil was sieved (2 mm mesh). Full details of the soil sampling date and the location of the soil sampling site are given in Table 2 in ‘Any other information on materials and methods incl. tables‘. After receipt at the test facility on 12 April 2010, the soil was thoroughly mixed with the minimum of air-drying and was stored in loosely tied plastic bags in an incubator routinely maintained at 4 ± 2 °C. Aliquots of the sieved soils were taken and air-dried for determination of physico-chemical characteristics. The main characteristics of the soils are summarised in Table 2 in ‘Any other information on materials and methods incl. tables‘. The microbial biomass of the bulk soils was determined by the fumigation-extraction method in accordance with BS7755: Section 4.4.2 (1997) and ISO 14240.2 (1997).
- Preparation of the test system: Prior to each dispensing, the moisture content of the stored soil was determined at Covance by drying a portion at ca 105°C. The wet : dry weight ratio was calculated and this allowed the dry weight equivalent of the dispensed soil to be calculated from the wet weight. Dry soil weight = wet soil weight / (wet : dry ratio). All calculations were based upon soil dry weight. For preparation of the dry soil layers, approximately 2 g (dry weight equivalent) of 2 mm sieved soil was mixed with reverse osmosis (RO) water before transferring to the pre-weighed metal trays and spreading to a uniform depth using a wet spatula. The soil was then allowed to air dry at ambient temperature prior to application of the test item. This gave layers measuring approximately 2 mm thick. The moist soils were prepared in essentially the same way except that, once air dried to a moisture content at or below pF2, these soil layers were then re-moistened, if necessary, to a moisture content of pF2 by addition of RO water prior to test item application. The exact weight of soil was recorded (ca 2 g dry weight equivalent) for each vessel and the layers were approximately 3 mm thick.

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

>= 300 - <= 800

Details on light source:

Suntest accelerated exposure machines were used as the light source. These instruments filter radiation from a xenon burner to remove light below 290 nm to give ultra-violet and visible light with a spectral distribution close to that of natural sunlight. The spectral properties and radiation intensity of the lamps were measured at the height of the soil surface at the position of each of the irradiated units. Measurements were made at 1 nm intervals before the irradiation period and after the final sampling interval using a spectroradiometer. The average intensity over the 300 to 400 nm range for the definitive tests was 24.31 Watts/m2, which, for continuous irradiation over 24 hours, is approximately equivalent to 0.97 US or UK summer days. No correction factor was required to convert days under the sun test to equivalent summer sunlight days at 30°, 40° and 50°N.

Details on test conditions:

TEST ITEM STOCK SOLUTION
- A [14C]-substance stock solution was available in acetonitrile (35%) and methanol (65%) with a concentration of 3.778 mg/mL (Stock solution 1). The concentration of substance ion in stock solution 1 was 2.02 mg/mL.

STANDARD REFERENCE COMPOUNDS
- Standard reference compounds were used for the identification of degradates by high performance liquid chromatography (HPLC).

TEST SYSTEM
- The study was conducted using one soil, Gartenacker (loam). The soil was sampled to a maximum depth of 20 cm on 31 March 2010. The soil was sieved (2 mm mesh). Full details of the soil sampling date and the location of the soil sampling site are given in Table 2 in ‘Any other information on materials and methods incl. tables’. After receipt at the test facility on 12 April 2010, the soil was thoroughly mixed with the minimum of air-drying and was stored in loosely tied plastic bags in an incubator routinely maintained at 4 ± 2 °C. Aliquots of the sieved soils were taken and air-dried for determination of physico-chemical characteristics. The main characteristics of the soils are summarised in Table 2 in ‘Any other information on materials and methods incl. tables‘. The microbial biomass of the bulk soils was determined by the fumigation-extraction method in accordance with BS7755: Section 4.4.2 (1997) and ISO 14240.2 (1997).
- Preparation of the test system: Prior to each dispensing, the moisture content of the stored soil was determined at the test facility by drying a portion at ca 105°C. The wet : dry weight ratio was calculated and this allowed the dry weight equivalent of the dispensed soil to be calculated from the wet weight. Dry soil weight = wet soil weight / (wet : dry ratio). All calculations were based upon soil dry weight. For preparation of the dry soil layers, approximately 2 g (dry weight equivalent) of 2 mm sieved soil was mixed with reverse osmosis (RO) water before transferring to the pre-weighed metal trays and spreading to a uniform depth using a wet spatula. The soil was then allowed to air dry at ambient temperature prior to application of the test item. This gave layers measuring approximately 2 mm thick. The moist soils were prepared in essentially the same way except that, once air dried to a moisture content at or below pF2, these soil layers were then re-moistened, if necessary, to a moisture content of pF2 by addition of RO water prior to test item application. The exact weight of soil was recorded (ca 2 g dry weight equivalent) for each vessel and the layers were approximately 3 mm thick.

DESCRIPTON OF THE PHOTOLYSIS APPARATUS
- Photolysis vessel: Vessels with side arms were used for this study in order to trap volatiles. Moist samples were incubated in individual vessels and dry samples were incubated in a communal vessel. Each vessel was individually covered with a quartz lid, which is suitable for general optical applications requiring good transmission in the near ultraviolet and visible range.
- Cooling tank: Treated samples in photolysis vessels were placed in a stainless steel tank, which was designed to enable cooling water to circulate through its base. In order to maintain the temperature of the vessels at ca 20 ± 2°C, they were placed in a cooling block that was cooled by internal circulation of cold water. To monitor the temperature of the solutions in the vessels, a thermocouple was placed in an untreated sample and positioned in the block alongside the treated samples. Temperature measurements were taken throughout the photolysis period.

PREPARATION OF APPLICATION SOLUTION
- An application solution containing [14C]-substance was prepared by transferring an aliquot (3.71 mL) of stock solution 1, to a vial and removing the solvent by evaporation under nitrogen. [14C]-Substance was then dissolved, with the aid of sonication, into solution by addition of HPLC grade water (10 mL). The solution (application solution 1) had a concentration of ca 1.32 mg/mL (0.71 mg/mL substance ion concentration) by LSC assay.

RADIOCHEMICAL PURITY
The radiochemical purity value of test item in the application solution was ≥ 95% by HPLC at the time of each use.

APPLICATION OF [14C]-SUBSTANCE
[14C]-Substance was applied to the soils dropwise in 94 µL of acetonitrile on two occasions. On the first occasion (24 May 2010) units A4-5 (0 DAT dry soils), A8-17 (dry light), B8-17 (dry dark), C4-17 (0 DAT moist soils and moist light) and D6-17 (moist dark) were treated and on the second occasion (28 June 2010) units A6-7 and B6-7 were treated. For the determination of the exact application rate and to check homogeneity, triplicate aliquots (90 or 94 µL) of the application solution was transferred to 25 mL volumetric flasks pre- and post-application (6 samples in total). The volume in each flask was made up to the mark with water and the solutions quantified by LSC. Each photolysis vessel was sealed using a quartz lid and the side arms were connected to traps containing 2M sodium hydroxide. The photolysis vessels were arranged inside the temperature controlled tanks and the tanks were placed directly under the xenon arc lamp in the Suntest Accelerated Exposure Instrument.

INCUBATION CONDITIONS
The irradiated units were continuously irradiated in one of three Suntest instruments for periods up to the equivalent of ca 30 days of summer sunlight at latitudes of 30 - 50ºNc and the dark control units were maintained in the dark for up to 30 days. The temperature of irradiated units was maintained at 20 ± 2°C, by circulating water through a cooling block in which the vessels were housed. The temperature was monitored in a control unit using a thermocouple. The dark controls were maintained in a temperature-controlled room. Air humidified by means of a trap containing RO water, was pulled by pumps over the soil in the incubation units. Moisture was maintained daily.

DARK CONTROL SAMPLES
Duplicate soil layers per timepoint were treated as above, placed in glass chambers connected to traps and maintained in a constant temperature room (at 20 ± 2ºC) for up to 30 days.

TRAPPING VOLATILE PRODUCTS
Volatile products were trapped using a flow-through system. The air was pulled through an inlet trap and through the incubation vessels. Any volatiles were trapped in the outlet solution. The inlet trap contained RO water to humidify the air going into the vessels.
The outlet trap consisted of one empty “security” trap and the second trap contained 2M sodium hydroxide. At each sampling interval the traps were removed for analysis. The weight of the trapping solution was determined and weighed aliquots taken for quantification by LSC.

CONFIRMATION OF CARBON DIOXIDE IN SODIUM HYDROXIDE TRAPS
The nature of the radioactivity trapped in the sodium hydroxide traps was investigated by addition of barium chloride solution. Analyses were performed on traps associated with a single unit from the 30 DAT timepoint for the irradiated moist soil incubation group. A saturated solution of barium chloride in water (8 mL) was added to a sub-sample (4 mL) of the pooled traps and mixed with the sample, allowed to stand for at least 1 hour, centrifuged (ca 2000 g) and the radioactivity in the supernatant determined by LSC. Any dissolved 14CO2 present precipitated as insoluble barium [14C]-carbonate during this process.

EXTRACTION OF SAMPLES
Each soil sample (complete vessels of treated soil) was extracted as described in Table 4 in ‘Any other information on materials and methods incl. tables’. The soil extracts and residue washes were quantified by LSC. Any unextracted radioactivity present in the soil residue was quantified by sample combustion and LSC. The mass balance for each soil sample was determined by summation of the radioactivity recovered in the soil extracts, residue wash, soil residue and sodium hydroxide traps.

WORK-UP OF EXTRACTS
Soil extracts were typically cleaned up and concentrated as described in Table 5 in ‘Any other information on materials and methods incl. tables’, prior to analysis by HPLC. All extracts were co-chromatographed with authenticated reference standards for component identification.

ISOLATION OF UNKNOWN SP-1
A sub-sample (ca 1 mL) of concentrated soil extract (C15, 23 DAT) was injected on to HPLC. Fractions of the HPLC eluate were collected in 20 second intervals. Each fraction was quantified by LSC and the fractions containing Unknown SP-1 were identified by retention time. The Unknown SP-1 fractions were pooled and the pooled sample concentrated under nitrogen. The Unknown SP-1 isolate was analysed by LSC and TLC (method 2).

Duration:

30 d

% Moisture:

39

Temp.:

20 °C

Initial conc. measured:

1 000 other: g ai/ha, registered test substance

Reference substance:

no

Dark controls:

yes

Remarks:

See details in 'Any other information on materials and methods incl tables'

Computational methods:

- Degradation rates: The percentage of applied radioactivity present as parent substance determined using HPLC was plotted against days of incubation and fitted to single first-order (SFO)kinetics using KinGUI version 1.1. The software calculated the degradation rates and associated parameters.

Preliminary study:

No preliminary test conducted.

Parameter:

not applicable

Key result

% Degr.:

42.7

Sampling time:

30 d

Test condition:

irradiated, moist conditions

Key result

% Degr.:

< 10

Sampling time:

30 d

Test condition:

irradiated, dry conditions

% Degr.:

< 10

Sampling time:

30 d

Test condition:

dark, moist conditions

% Degr.:

< 10

Sampling time:

30 d

Test condition:

dark, dry conditions

Key result

DT50:

236.8 d

Test condition:

Dissipation half life under light conditions and dry soil

Key result

DT50:

36.7 d

Test condition:

Dissipation half life under light conditions and moist soil

DT50:

857.461 d

Test condition:

Dissipation half life under dark conditions and dry soil

DT50:

> 10 001 d

Test condition:

Dissipation half life under dark conditions and moist soil

Transformation products:

yes

No.:

#1

No.:

#2

Details on results:

MICROBIAL BIOMASS
The results for the soil microbial biomass analysis undertaken prior to treatment are shown in Table 2 in ‘Any other information on materials and methods incl. tables’. The quantity of microbial biomass carbon constituted 2.5% of the soil organic carbon. This indicated the soil supported a viable microbial population and that the soil was suitable for use in this study.

APPLICATION RATE
The amount of radiochemical applied to each photolysis vessel was determined by LSC before and after application. The application solutions were shown to be homogenous during each application. The application rate for each test is shown in Table 1 ‘Any other information on results incl. tables’.

RADIOCHEMICAL PURITY
The radiochemical purity of substance in the application solution before and after each application, was ≥ 95%, which was considered adequate for the purposes of this study.

LIGHT INTENSITY MEASUREMENTS
Intensity measurements were taken at the beginning and end of each irradiation period. Measurements were taken at the positions of the soil trays and at the same height as the soil layers. An overall average intensity was calculated from measurements. The mean intensity values for each incubation condition (Table 2 in ‘Any other information on results incl. tables’) ranged 24.08 to 24.53 Watts/m2 (300 to 400 nm). No correction factor was required to convert days under the Suntest to equivalent summer sunlight days at 30°, 40° and 50°N.

TEMPERATURE RECORDS
The temperature of the irradiated vessels was recorded daily by means of a thermocouple inserted into a thin layer of untreated soil. All dark control samples were maintained in constant temperature rooms at 20 ± 2°C. The temperature was maintained mainly within the protocol limits of 20 ± 2°C.

MASS BALANCE
The total radioactivity recovered was calculated as the sum of radioactivity in the soil extracts, residue wash, soil residue on combustion and that trapped as 14CO2 in the 2M sodium hydroxide trap. These data are presented in Tables 3 to 6 in ‘Any other information on results incl. tables’.

SOIL EXTRACTS
The total extractability at 0 DAT was high (ranging from 98.9 to 100.4% AR) for all conditions. This remained high throughout the incubation period with 96.5 to 99.2% AR remaining after 30 DAT, with the exception of the irradiated moist soil samples where the extractability decreased slightly to 87.0% at 30 DAT.

UNEXTRACTED RADIOACTIVITY
In the light, levels of unextracted radioactivity increased to 1.6 and 3.1% AR at 30 DAT for dry and moist soils, respectively. In dark control samples ≤ 1% AR remained as unextracted radioactivity.

VOLATILE DEGRADATION PRODUCTS
In the light, levels of volatile radioactivity increased up to 0.8% AR at 8 DAT and 7.2% AR at 30 DAT for dry and moist soils, respectively. Levels of volatile radioactivity formed in the dark were ≤ 0.1%. Carbon dioxide was proven in sodium hydroxide traps by barium precipitation of the radioactivity from a sodium hydroxide trap following addition of barium chloride solution.

DEGRADATION OF SUBSTANCE AND IDENTIFICATION OF METABOLITES
HPLC was used for quantitative analyses of extracts. The levels of parent compound and metabolites (% of applied radioactivity) are shown in Tables 7 to 10 in ‘Any other information on results incl. tables’.
Degradation was more significant in the light moist soil samples with only a small degree of degradation occurring in the light dry and dark soil samples. Transformation product #1 was a major degradation product in moist light-irradiated samples.
Under irradiated conditions, substance was found to be stable on dry soil with 90.2% applied radioactivity present as parent compound by the 30 DAT timepoint. However, when moist soil was irradiated, levels of parent compound decreased from 99.4 to 57.3% applied radioactivity over the 30 days incubation period. Transformation product #1 was present as major photodegradation product in moist soil at ≥ 9.9% applied radioactivity at 30 DAT. Transformation product #2 was present in moist soil at 6% applied radioactivity at only one timepoint and in only one sample (23 DAT) and declined thereafter. An unknown peak, labelled Unknown SP-1 present at ≥ 5% applied radioactivity (maximum 5.4% AR), which appeared to run as one entity by HPLC was later found to be composed of two compounds by TLC. The maximum level of any single unknown component was 4.0% applied radioactivity.
Carbon dioxide was formed under the irradiated moist conditions at 7% applied radioactivity by 30 days.
The test substance was found to be stable in the control incubations which were performed in the dark using dry and moist soil conditions. The levels of the test substance remaining after 30 days was >95% applied radioactivity and only low levels of transformation product #2 (< 1% AR) were present in dark samples at 30 DAT.
A number of other minor unknown metabolites were observed in all conditions, each of which individually comprised ≤ 4% AR.

TLC ANALYSIS
Verification of metabolites by a second technique (TLC) was performed using reference standards. Parent and transformation product #2 were confirmed using TLC method 1. Transformation product #1 and Unknown SP-1 were assigned based on polarities of the compounds, order of HPLC elution and ratios from the HPLC analysis. A comparison of HPLC and TLC results is presented in Table 11 in ‘Any other information on results incl. tables’. Levels determined by the two analytical methods were comparable. The isolated Unknown SP-1 was analysed using TLC method 2.

LC-MS-MS CONFIRMATION AND IDENTIFICATION
The test substance and the degradation products #1 and #2 were confirmed by accurate mass measurements (< 3 ppm) in one or more of the three soil extracts supplied.

LC-MS-MS CONFIRMATION AND IDENTIFICATION
- The test substance (m/z 183): Full scan data and MS-MS data were obtained from a substance reference standard at a retention time of 13.9 minutes. A peak with m/z 183.0915 was also observed in sample C17 extract 3 at a retention time of 13.3 minutes in the MS trace corresponding to a peak in the radio trace of 13.6 minutes. Full scan ions of m/z 92.0493 correspond to the doubly charged substance species and m/z 184.0948 corresponds to singly charged radical cation and can be used to confirm the presence of substance samples. The fragmentation pattern was consistent with that observed for the substance standard. The test substance was also observed in samples A16 extract 3 (30 DAT dry light), B16 extract 3 (30 DAT dry dark) and D17 extract 3 (30 DAT moist dark).
Transformation product #1 was also observed in sample A16 extract 3 (30 DAT dry light).
- Transformation product #1: Full scan data and MS-MS data were obtained for a standard of this degradation product at a retention time of 6.9 minutes. A peak with m/z 149.0708 was observed in sample C17 extract 3 (30 DAT moist light) at a retention time of 6.7 minutes in the MS trace corresponding to a peak in the radio trace of 6.9 minutes. The fragmentation pattern was consistent with that observed for the transformation product #1 standard.
- Transformation product #2: Full scan data and MS-MS data were obtained for a standard of degradation product #2 at a retention time of 8.1 minutes. A peak with m/z 199.0864 was also observed in sample C17 extract 3 (30 DAT moist light) at a retention time of 7.9 minutes in the MS trace corresponding to a peak in the radio trace of 8.2 minutes. The fragmentation pattern was consistent with that observed for the transformation product #2 standard. Transformation product #2 was also observed in samples A16 extract 3 (30 DAT dry light), B16 extract 3 (30 DAT dry dark) and D17 extract 3 (30 DAT moist dark).

ROUTE OF DEGRADATION
Photodegradation under moist and irradiated conditions is proposed as the oxidation to transformation product #2 and degradation to transformation product #1. Under these conditions, further minor compounds were also present with no single entity occurring at levels above 4% applied radioactivity. Ultimately the parent compound and/or metabolites were assimilated into bound residue and were mineralised to carbon dioxide.

PHOTOLYTIC DEGT50 OF THE TESTS SUBSTANCE IN SOIL
The percent of applied radioactivity present as parent substance was plotted against days of continuous irradiation and fitted to single first-order kinetics using KinGUI version 1.1. summarised in Table 12 in ‘Any other information on results incl. tables’. DegT50 values applicable to Europe and North America (latitudes 30°, 40° and 50°) were 237 days and 37 days in dry and moist soil, respectively.

Table 1. Application Rates for [14C]-substance

Application	Measurement	Homogeneity Check			Application Rate
		MBq/mL application solution	Mean	% Coefficient of Variation	MBq per vessel	µg per vessel	Equivalent field application rate (g ai/ha)
Units A4,A5,A8 to A17, B8 toB17, C4 toC17 and D6 to D17	Pre-application	3.9019	3.8831	1.08	0.3650	125.2	996 (533 substance ion)
		3.9455
		3.9023
	Post-application	3.8556
		3.8654
		3.8279
Units A6 to A7, B6 to B7	Pre-application	3.8495	3.8751	0.58	0.3643	124.9	994 (532 substance ion)
		3.9140
		3.8695
	Post-application	3.8851
		3.8714
		3.8613

The field application rate calculation uses a surface area of the soil disc of 12.57 cm2 All values in terms of substance dibromide

 

Table 2. Light intensity Measurements

Incubation conditions	Initial Light Intensity			Final Light Intensity			Overall Mean Intensity (W/m2) 300-400 nm
	Mean W/m2 (300-400 nm)	SD	% CV	Mean W/m2 (300-400 nm)	SD	% CV
Dry soil	23.99	2.32	9.66	24.18	1.84	7.62	24.08
Moist soil	22.72	2.82	12.41	26.34	3.65	13.87	24.53

The resultant intensity is equivalent toca1 UK or US summer day.

 

Table 3. Distribution and Recovery of Radioactivity from Irradiated Dry Soil Samples Treated with [14C]-Substance Ion

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	A4	A5	A6	A7	A8	A9	A10	A11	A12	A13	A14	A15	A16	A17
Initial soil extract	97.4	100.3	99.1	100.4	95.9	98.3	97.1	97.8	96.3	94.4	96.3	94.7	97.0	96.0
Mean	98.9		99.8		97.1		97.5		95.4		95.5		96.5
Residue Wash	0.2	0.2	0.4	0.5	0.7	0.8	0.5	0.9	1.2	0.7	0.6	1.0	1.5	1.0
Mean	0.2		0.5		0.8		0.7		1.0		0.8		1.3
Unextracted	0.3	0.2	0.8	1.1	0.8	0.7	1.3	1.0	0.5	1.7	0.6	0.9	1.2	1.9
Mean	0.3		1.0		0.8		1.2		1.1		0.8		1.6
Total in soil	97.9	100.7	100.3	102.0	97.4	99.8	98.9	99.7	98.0	96.8	97.5	96.6	99.7	98.9
Mean	99.3		101.2		98.6		99.3		97.4		97.1		99.3
Total volatiles	NA	NA	0.2	0.2	0.8	0.8	0.3	0.3	0.2	0.2	0.2	0.2	0.2	0.2
Mean	NA		0.2		0.8		0.3		0.2		0.2		0.2
Mass Balance (%)	97.9	100.7	100.5	102.2	98.2	100.6	99.2	100.0	98.2	97.0	97.7	96.8	99.9	99.1
Mean	99.3		101.4		99.4		99.6		97.6		97.3		99.5

All values are expressed as a percent of applied radioactivity NA = Not Applicable

 

Table 4. Distribution and Recovery of Radioactivity from Dark Control Dry Soil Samples Treated with [14C]-Substance Ion

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	A4	A5	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15	B16	B17
Initial soil extract	97.4	100.3	98.6	101.5	99.4	98.6	99.4	100.0	96.4	98.3	98.8	99.1	97.2	99.2
Mean	98.9		100.1		99.0		99.7		97.4		99.0		98.2
Residue Wash	0.2	0.2	0.2	0.3	0.4	0.4	0.4	0.4	0.4	0.5	0.6	0.4	0.5	0.9
Mean	0.2		0.3		0.4		0.4		0.5		0.5		0.7
Unextracted	0.3	0.2	0.4	0.5	0.5	0.7	1.0	0.9	0.5	0.6	0.5	0.7	0.5	0.8
Mean	0.3		0.5		0.6		1.0		0.6		0.6		0.7
Total in soil	97.9	100.7	99.2	102.3	100.3	99.7	100.8	101.3	97.3	99.4	99.9	100.2	98.2	100.9
Mean	99.3		100.8		100.0		101.1		98.4		100.1		99.6
Total volatiles	NA	NA	ND	ND	0.1	0.1	ND	ND	ND	ND	ND	ND	ND	ND
Mean	NA		ND		0.1		ND		ND		ND		ND
Mass Balance (%)	97.9	100.7	99.2	102.3	100.4	99.8	100.8	101.3	97.3	99.4	99.9	100.2	98.2	100.9
Mean	99.3		100.8		100.1		101.1		98.4		100.1		99.6

All values are expressed as a percent of applied radioactivity ND = Not Detected (< 0.1%), NA = Not Applicable

 

Table 5. Distribution and Recovery of Radioactivity from Irradiated Moist Soil Samples Treated with [14C]-Substance Ion

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	C8	C5	C6	C7	C4	C9	C10	C11	C12	C13	C14	C15	C16	C17
Initial soil extract	100.8	100.0	96.2	96.4	94.5	95.3	94.0	90.7	92.2	89.6	85.0	85.5	84.7	89.2
Mean	100.4		96.3		94.9		92.4		90.9		85.3		87.0
Residue Wash	0.2	0.2	0.6	0.5	1.0	0.4	1.0	1.0	2.9	1.1	4.4	2.2	1.1	3.4
Mean	0.2		0.6		0.7		1.0		2.0		3.3		2.3
Unextracted	0.3	0.3	0.9	0.3	2.1	1.8	1.5	3.3	1.0	1.1	1.3	3.4	4.6	1.6
Mean	0.3		0.6		2.0		2.4		1.1		2.4		3.1
Total in soil	101.3	100.5	97.7	97.2	97.6	97.5	96.5	95.0	96.1	91.8	90.7	91.1	90.4	94.2
Mean	100.9		97.5		97.6		95.8		94.0		90.9		92.3
Total volatiles	NA	NA	1.0	0.9	2.4	2.7	4.1	2.5	5.0	3.7	6.2	7.4	7.6	6.8
Mean	NA		1.0		2.6		3.3		4.4		6.8		7.2
Mass Balance (%)	101.3	100.5	98.7	98.1	100.0	100.2	100.6	97.5	101.1	95.5	96.9	98.5	98.0	101.0
Mean	100.9		98.4		100.1		99.1		98.3		97.7		99.5

All values are expressed as a percent of applied radioactivity NA = Not Applicable

 

Table 6. Distribution and Recovery of Radioactivity from Dark Control Moist Soil Samples Treated with [14C]-Substance Ion

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	C8	C5	D6	D7	D8	D9	D10	D11	D12	D13	D14	D15	D16	D17
Initial soil extract	100.8	100.0	98.1	99.3	99.7	99.7	97.8	100.3	99.7	99.4	96.8	97.2	99.5	98.9
Mean	100.4		98.7		99.7		99.1		99.6		97.0		99.2
Residue Wash	0.2	0.2	0.2	0.2	0.4	0.4	0.5	0.5	0.7	0.6	1.0	0.4	0.6	0.3
Mean	0.2		0.2		0.4		0.5		0.7		0.7		0.5
Unextracted	0.3	0.3	0.2	0.4	0.8	0.7	0.8	0.9	0.6	0.9	0.6	0.9	0.5	1.2
Mean	0.3		0.3		0.8		0.9		0.8		0.8		0.9
Total in soil	101.3	100.5	98.5	99.9	100.9	100.8	99.1	101.7	101.0	100.9	98.4	98.5	100.6	100.4
Mean	100.9		99.2		100.9		100.4		101.0		98.5		100.5
Total volatiles	NA	NA	0.1	0.1	ND	ND	ND	ND	ND	ND	0.1	0.1	0.1	0.1
Mean	NA		0.1		ND		ND		ND		0.1		0.1
Mass Balance (%)	101.3	100.5	98.6	100.0	100.9	100.8	99.1	101.7	101.0	100.9	98.5	98.6	100.7	100.5
Mean	100.9		99.3		100.9		100.4		101.0		98.6		100.6

All values are expressed as a percent of applied radioactivity ND = Not Detected (< 0.1%), NA = Not Applicable

 

Table 7. Quantification of substance Ion and photodegradates: Dry soil.

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	A4	A5	A6	A7	A8	A9	A10	A11	A12	A13	A14	A15	A16	A17
Substance	96.4	96.7	98.1	99.4	92.4	96.7	94.5	94.3	92.4	89.8	93.7	88.2	88.4	92.0
Mean	96.5		98.7		94.5		94.4		91.1		91.0		90.2
Transformation product #1	ND	ND	ND	ND	0.5	0.7	0.5	0.6	0.7	0.6	0.5	1.2	1.7	ND
Mean	ND		ND		0.6		0.6		0.7		0.8		0.9
Transformation product #2	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	0.6	ND
Mean	ND		ND		ND		ND		ND		ND		0.3
Total Minor Unknowns*	ND	1.5	0.7	0.4	1.6	0.8	1.3	1.4	1.6	2.0	0.9	2.5	3.2	1.3
Mean	0.7		0.5		1.2		1.4		1.8		1.7		2.3
Unresolved Background	0.9	2.0	0.3	0.7	1.4	0.1	0.7	1.5	1.7	2.0	1.2	0.8	1.6	1.0
Mean	1.5		0.5		0.8		1.1		1.8		1.0		1.3
SPE Eluate (Unanalysed)	0.1	0.1	NA	NA	NA	NA	NA	NA	NA	NA	NA	2.0	1.4	1.7
Mean	0.1		NA		NA		NA		NA		1.0		1.6
Total analysed	97.4	100.3	99.1	100.4	95.9	98.3	97.1	97.8	96.3	94.4	96.3	94.7	97.0	96.0
Mean	98.8		99.7		97.1		97.5		95.3		95.5		96.5
Largest Unknown	NA	1.6	0.8	0.4	1.4	1.2	1.3	1.5	1.6	1.8	1.0	1.3	2.1	1.0

Note: all values quoted for each replicate are the mean of two injections except for Unknowns where the values are the maximum values found.

DAT = Days After Treatment,

ND = Not Detected (< 0.1%),

NA = Not applicable

* Mean values.

No single unknown was present > 5%

 

Table 8. Quantification of substance Ion and photodegradates: Dry soil Dark

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	A4	A5	B6	B7	B8	B9	B10	B11	B12	B13	B14	B15	B16	B17
Substance	96.4	96.7	98.1	101.0	97.8	96.0	98.3	98.5	94.6	96.8	96.6	97.5	93.3	97.1
Mean	96.5		99.6		96.9		98.4		95.7		97.1		95.2
Transformation product #1	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND	ND
Mean	ND		ND		ND		ND		ND		ND		ND
Transformation product #2	ND	ND	ND	ND	0.5	0.6	0.3	0.3	0.4	0.4	ND	0.5	1.2	0.5
Mean	ND		ND		0.5		0.3		0.4		0.2		0.9
Total Minor Unknowns*	ND	1.5	ND	0.4	0.8	1.5	0.8	1.0	0.8	0.6	ND	0.7	1.5	0.8
Mean	0.7		0.2		1.1		0.9		0.7		0.4		1.1
Unresolved Background	0.9	2.0	0.5	0.1	0.4	0.5	0.1	0.2	0.5	0.5	2.2	0.4	1.2	0.8
Mean	1.5		0.3		0.5		0.2		0.5		1.3		1.0
SPE Eluate (Unanalysed)	0.1	0.1	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA	NA
Mean	0.1		NA		NA		NA		NA		NA		NA
Total analysed	97.4	100.3	98.6	101.5	99.4	98.6	99.4	100.0	96.4	98.3	98.8	99.1	97.2	99.2
Mean	98.8		100.1		99.0		99.7		97.4		99.0		98.2
Largest Unknown	NA	1.6	NA	0.4	0.8	1.4	0.8	1.1	1.2	0.6	NA	0.9	1.6	1.1

Note: all values quoted for each replicate are the mean of two injections except for Unknowns where the values are the maximum values found.

DAT = Days After Treatment,

ND = Not Detected (< 0.1%),

NA = Not applicable

* Mean values.

No single unknown was present > 5%.

 

Table 9. Quantification of substance Ion and photodegradates: Moist soil.

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	C8	C5	C6	C7	C4	C9	C10	C11	C12	C13	C14	C15	C16	C17
Substance	99.2	99.5	87.8	79.8	86.0	84.6	87.4	63.5	71.1	81.5	44.5	67.0	53.9	60.7
Mean	99.4		83.8		85.3		75.4		76.3		55.7		57.3
Transformation product #1	ND	ND	1.9	ND	3.8	3.5	3.2	4.0	6.7	5.0	2.9	7.8	9.7	10.1
Mean	ND		0.9		3.6		3.6		5.8		5.3		9.9
Transformation product #2	ND	ND	ND	ND	0.5	0.5	0.3	ND	0.8	ND	11.1	0.8	1.0	0.7
Mean	ND		ND		0.5		0.2		0.4		6.0		0.8
Unk SP-1	ND	ND	1.8	5.7	2.4	2.6	1.8	6.9	5.8	1.2	6.4	3.9	4.8	6.0
Mean	ND		3.7		2.5		4.3		3.5		5.2		5.4
Total Minor Unknowns*	ND	ND	ND	9.0	0.2	0.9	0.6	11.5	2.9	0.8	12.5	1.9	4.0	4.1
Mean	ND		4.5		0.6		6.0		1.9		7.2		4.1
Unresolved Background	1.6	0.5	1.8	1.8	1.6	1.5	0.8	4.8	1.7	1.1	0.6	0.8	3.0	2.5
Mean	1.0		1.8		1.5		2.8		1.4		0.7		2.8
SPE Eluate (Unanalysed)	NA	NA	3.0	NA	NA	1.7	NA	NA	3.2	NA	6.9	3.4	8.3	5.1
Mean	ND		1.5		0.9		ND		1.6		5.2		6.7
Total analysed	100.8	100.0	96.2	96.4	94.5	95.3	94.0	90.7	92.2	89.6	85.0	85.5	84.7	89.2
Mean	100.4		96.3		94.9		92.4		90.9		85.2		87.0
Largest Unknown	NA	NA	NA	3.7	0.5	1.1	0.7	4.6	1.5	0.6	4.2	1.2	2.3	1.9

Note: all values quoted for each replicate are the mean of two injections except (with the exception of C7 and C11, where only single injection performed) for Unknowns where the values are the maximum values found.

DAT = Days After Treatment, ND = Not Detected (< 0.1%), NA = Not applicable

Unk SP-1 comprises of at least 2 entities, with any single component reaching a maximum level of 4.0 %AR.

* Mean values.

No single unknown was present > 5%

 

Table 10. Quantification of substance Ion and photodegradates: Moist soil dark

	% Applied Radioactivity
Timepoint (DAT)	0		4		8		12		17		23		30
Unit	C8	C5	D6	D7	D8	D9	D10	D11	D12	D13	D14	D15	D16	D17
Substance	99.2	99.5	96.2	93.5	98.2	97.3	96.8	99.1	96.5	98.0	95.8	95.9	98.4	97.6
Mean	99.4		94.9		97.8		98.0		97.3		95.9		98.0
Transformation product #2	ND	ND	ND	ND	ND	0.3	ND	0.2	0.6	0.2	0.3	0.3	0.2	0.4
Mean	ND		ND		0.1		0.1		0.4		0.3		0.3
Total Minor Unknowns*	ND	ND	1.1	2.0	1.1	1.6	0.7	0.7	1.0	1.0	0.5	0.5	0.4	0.5
Mean	ND		1.5		1.3		0.7		1.0		0.5		0.5
Unresolved Background	1.6	0.5	0.8	3.8	0.4	0.5	0.3	0.3	1.6	0.3	0.2	0.5	0.5	0.4
Mean	1.0		2.3		0.5		0.3		0.9		0.4		0.4
Total analysed	100.8	100.0	98.1	99.3	99.7	99.7	97.8	100.3	99.7	99.4	96.8	97.2	99.5	98.9
Mean	100.0		98.7		99.7		99.1		99.5		97.0		99.2
Largest Unknown	NA	NA	2.2	2.0	0.9	1.3	0.8	0.7	1.1	0.8	0.7	0.6	0.5	0.6

Note: all values quoted for each replicate are the mean of two injections (with the exception of D7, where only single injection performed) except for Unknowns where the values are the maximum valuesfound.

DAT = Days After Treatment, ND = Not Detected (<0.1%)

* Mean values.

No single unknown was present > 5%

 

Table 11. Comparison of HPLC and TLC results in selected extracts

Sample	Timepoint (DAT)	%AR Analysed	Technique	Substance	Transformation product #1	Transformation product #2	Unknown SP-1	Origin	Other Unknowns
A7	4	100.4	TLC	94.6	ND	ND	2.1	ND	ND
			HPLC	99.4	ND	ND	ND	NA	0.4
A17	30	94.3	TLC	86.5	ND	ND	2.6	ND	1.9
			HPLC	92.0	ND	ND	ND	NA	1.3
B7	4	101.5	TLC	98.7	ND	ND	1.3	ND	ND
			HPLC	101.0	ND	ND	ND	NA	0.4
B17	30	99.2	TLC	93.5	ND	1.1	2.0	ND	0.8
			HPLC	97.1	ND	0.5	ND	NA	0.8
C6	4	93.2	TLC	83.2	2.7	1.1	3.3	ND	1.1
			HPLC	87.8	1.9	ND	1.8	NA	ND
C17	30	84.1	TLC	53.5	10.2	2.9	8.9	ND	4.0
			HPLC	60.7	10.1	0.7	6.0	NA	4.1
D6	4	98.1	TLC	92.7	ND	ND	2.7	ND	ND
			HPLC	96.2	ND	ND	ND	NA	1.1
D17	30	98.9	TLC	94.6	ND	1.1	2.0	ND	0.4
			HPLC	97.6	ND	0.4	ND	NA	0.5

DAT = Days after treatment

%AR = percentage of applied radioactivity, based on single replicate from each sampling interval

ND = Not detected

NA = Not applicable

 

Table 12. Summary of DegT50 values: Degradation Kinetics (days)

Test System	DegT50	Chi2	R2	Prob > t
Light Dry	237	1.0515	0.6410	3 x 10-4
Dark Dry	857.461	0.9496	0.1943	0.0578
Light Moist	37	4.6634	0.7388	6.1 x 10-5
Dark Moist	>10001	1.1253	0.0089	0.3741

(1) Although there was a small amount of degradation in the dark, DegT50 values calculated could not be differentiated from zero using SFO kinetics, therefore no degradation thought to occur.

No correction factor was required to convert days into equivalent summer sunlight days for Europe or North America, latitudes 30, 40 and 50°N.

Validity criteria fulfilled:

not specified

Conclusions:

Photolytic DegT50 values were 237 and 37 days (equivalent summer days for Europe and North America at latitudes 30°, 40° and 50°N) in dry soil and in moist soil, respectively. No degradation was observed for dry and moist dark soils. The major photodegradation product was transformation product #1, present at 9.9% applied radioactivity in moist irradiated soil. Transformation product #2 was a transient metabolite and unknown SP-1, was determined by TLC to be composed of at least two entities with maximum levels of any single entity being ≤ 4.0%. Degradation involved oxidation of the molecule to yield transformation product #2 and #1.

Executive summary:

The photolysis of the test substance was investigated on both dry and moist soil surfaces of Gartenacker soil. [14C]-Substance (cation) was applied at a rate equivalent to 536 g ai/ha (equivalent to ca. 1000 g ai/ha test substance) to thin layers of either dry or moist soil in individual metal trays. Dry soil trays were housed in a communal chamber and moist soil trays in individual 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 ca. 20 ± 2°C and were irradiated with a mean light intensity of 24.31 W/m2, for periods up to the equivalent of ca. 30 days summer sunlight. In each test, duplicate samples were taken for analysis immediately after treatment and at six sampling intervals during irradiation. Dark control samples were also maintained at ca. 20 ± 2°C in the dark for the duration of the test and duplicate samples taken for analysis at each of the six sampling intervals. Volatile products were trapped, using a flow-through system, in 2M sodium hydroxide solution. Degradation rates were determined using single first-order kinetics. The mean mass balance ranged from 97.3 to 101.4% for the irradiated samples and from 98.4 to 101.1% for the dark controls.

 

Only slight degradation occurred in the light and dark dry soil samples. Two minor degradation products #1 and #2 were observed in the irradiated samples individually accounting up to 0.9% applied radioactivity.

Degradation was more significant in irradiated moist soil samples with only a small degree of degradation occurring in the dark soil samples. The major photolytic degradation product was transformation product #1 which reached a maximum of 9.9% AR after 30 days. Transformation product #1 was present at levels > 5% over three timepoints. Transformation product #2 was also detected and was present generally at levels < 1% applied radioactivity. A number of other minor degradation products were also detected. Unknown SP-1, which was present at a level between 5.2 and 5.4% after 30 days, was found to be composed of two components by TLC and the maximum level of any single component of Unknown SP-1 was 4.0% applied radioactivity.Volatile radioactivity, confirmed as CO2, resulted mainly from irradiation of moist soil under light conditions with levels of 14CO2 reaching 7.2% applied radioactivity by 30 DAT. The maximum levels of unextractable residues were observed under light and moist conditions and were present up to a level of 3.1% applied radioactivity after the 30 DAT incubation period.

The test substance was stable in the dark under both dry and moist conditions.

The rate of degradation was estimated using single first-order (SFO) kinetics. Under the experimental conditions, photolytic DegT50 values were 236.8 and 36.7 days (equivalent summer days for Europe and North America at latitudes 30°, 40° and 50°N) in dry soil and in moist soil respectively. No degradation occurred in the dark dry or moist controls. Photolytic DegT50 values were 237 and 37 days (equivalent summer days for Europe and North America at latitudes 30°, 40° and 50°N) in dry soil and in moist soil, respectively. No degradation in the dark controls was observed.

Description of key information

DT50 = 36.7 days, Moist soil, continuous irradiation for 30d, 30-50°N / Summer, OECD TG draft, Dixon 2012

DT50 = 236.8 days, Dry soil, continuous irradiation for 30d, 30-50°N / Summer, OECD TG draft, Dixon 2012

Key value for chemical safety assessment

Half-life in soil:

36.7 d

Additional information

The photolysis of the test substance was investigated on both dry and moist soil surfaces of Gartenacker soil. [14C]-Substance (cation) was applied at a rate equivalent to 536 g ai/ha (equivalent to ca. 1000 g ai/ha test substance) to thin layers of either dry or moist soil in individual metal trays. Dry soil trays were housed in a communal chamber and moist soil trays in individual 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 ca. 20 ± 2°C and were irradiated with a mean light intensity of 24.31 W/m2, for periods up to the equivalent of ca. 30 days summer sunlight. In each test, duplicate samples were taken for analysis immediately after treatment and at six sampling intervals during irradiation. Dark control samples were also maintained at ca. 20 ± 2°C in the dark for the duration of the test and duplicate samples taken for analysis at each of the six sampling intervals. Volatile products were trapped, using a flow-through system, in 2M sodium hydroxide solution. Degradation rates were determined using single first-order kinetics. The mean mass balance ranged from 97.3 to 101.4% for the irradiated samples and from 98.4 to 101.1% for the dark controls.

 

Only slight degradation occurred in the light and dark dry soil samples. Two minor degradation products #1 and #2 were observed in the irradiated samples individually accounting up to 0.9% applied radioactivity.

Degradation was more significant in irradiated moist soil samples with only a small degree of degradation occurring in the dark soil samples. The major photolytic degradation product was transformation product #1 which reached a maximum of 9.9% AR after 30 days. Transformation product #1 was present at levels > 5% over three timepoints. Transformation product #2 was also detected and was present generally at levels < 1% applied radioactivity. A number of other minor degradation products were also detected. Unknown SP-1, which was present at a level between 5.2 and 5.4% after 30 days, was found to be composed of two components by TLC and the maximum level of any single component of Unknown SP-1 was 4.0% applied radioactivity.Volatile radioactivity, confirmed as CO2, resulted mainly from irradiation of moist soil under light conditions with levels of 14CO2 reaching 7.2% applied radioactivity by 30 DAT. The maximum levels of unextractable residues were observed under light and moist conditions and were present up to a level of 3.1% applied radioactivity after the 30 DAT incubation period.

The test substance was stable in the dark under both dry and moist conditions.

The rate of degradation was estimated using single first-order (SFO) kinetics. Under the experimental conditions, photolytic DegT50 values were 236.8 and 36.7 days (equivalent summer days for Europe and North America at latitudes 30°, 40° and 50°N) in dry soil and in moist soil respectively. No degradation occurred in the dark dry or moist controls. Photolytic DegT50 values were 237 and 37 days (equivalent summer days for Europe and North America at latitudes 30°, 40° and 50°N) in dry soil and in moist soil, respectively. No degradation in the dark controls was observed.