2-tetradecyloxirane, reaction products with boric acid

Biodegradation in soil

Link to relevant study record(s)

Reference

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

05 July 2019 to 07 February 2020

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:

April 2002

Deviations:

yes

Remarks:

with no impact on results or integrity of the study (see below)

GLP compliance:

yes (incl. QA statement)

Test type:

laboratory

Radiolabelling:

no

Oxygen conditions:

aerobic/anaerobic

Soil classification:

USDA (US Department of Agriculture)

Soil no.:

#1

Soil type:

sandy loam

% Clay:

15

% Silt:

18

% Sand:

67

% Org. C:

2.9

pH:

6.1

CEC:

13 meq/100 g soil d.w.

Soil no.:

#2

Soil type:

silty clay loam

% Clay:

23

% Silt:

57

% Sand:

20

% Org. C:

3.9

pH:

5.8

CEC:

19.8 meq/100 g soil d.w.

Soil no.:

#3

Soil type:

clay

% Clay:

41

% Silt:

28

% Sand:

31

% Org. C:

3.7

pH:

7.7

CEC:

24.4 meq/100 g soil d.w.

Soil no.:

#4

Soil type:

loamy sand

% Clay:

>= 7 - <= 9

% Silt:

>= 7 - <= 9

% Sand:

>= 82 - <= 86

% Org. C:

>= 1 - <= 1.26

pH:

5.9

CEC:

>= 5.4 - <= 8.5 meq/100 g soil d.w.

Details on soil characteristics:

TEST SOILS
- Four different soils were used in the study.
- Each soil had previously been passed through a 2 mm sieve.
- Calke, Brierlow, South Witham and Ingleby soils (aerobic test) were received on 18 July 2019. The soils were stored at + 4 °C for a maximum of 69 days prior to incubation.
- Ingleby soil (anaerobic test) was received on 13 November 2019. The soil was stored at + 4 °C for a maximum of 12 days prior to incubation.

Soil No.:

#1

Duration:

146 h

Soil No.:

#2

Duration:

146 h

Soil No.:

#3

Duration:

146 h

Soil No.:

#4

Duration:

>= 169 - <= 336 h

Soil No.:

#1

Initial conc.:

10 mg/kg soil d.w.

Based on:

test mat.

Remarks:

Calke (sandy loam) under aerobic conditions

Soil No.:

#2

Initial conc.:

10 mg/kg soil d.w.

Based on:

test mat.

Remarks:

Brierlow (silt clay loam) under aerobic conditions

Soil No.:

#3

Initial conc.:

10 mg/kg soil d.w.

Based on:

test mat.

Remarks:

South Witham (clay) under aerobic conditions

Soil No.:

#4

Initial conc.:

10 mg/kg soil d.w.

Based on:

test mat.

Remarks:

Ingleby (loamy sand) under aerobic and anaerobic conditions

Parameter followed for biodegradation estimation:

test mat. analysis

Soil No.:

#1

Temp.:

20 ± 2°C

Humidity:

Moisture tension of pF 2

Microbial biomass:

4.34 % (aerobic incubation start); 3.93 % (end of aerobic incubation)

Soil No.:

#2

Temp.:

20 ± 2°C

Humidity:

Moisture tension of pF 2

Microbial biomass:

2.62 % (aerobic incubation start); 2.15 % (end of aerobic incubation)

Soil No.:

#3

Temp.:

20 ± 2°C

Humidity:

Moisture tension of pF 2

Microbial biomass:

5.43 % (aerobic incubation start); 4.63 % (end of aerobic incubation)

Soil No.:

#4

Temp.:

20 ± 2°C

Humidity:

Moisture tension of pF 2

Microbial biomass:

4.33 % (aerobic incubation start); 3.24 % (end of aerobic incubation)

Soil No.:

#4

Temp.:

20 ± 2°C

Humidity:

not applicable

Microbial biomass:

Anaerobic bacteria (end of anaerobic incubation) 2.31E+04; Anaerobic bacteria spores (end of anaerobic incubation) 1.35E+04

Details on experimental conditions:

STUDY DESIGN – AEROBIC TEST
- The rate of degradation of the test item was studied in four soils incubated at 20 ± 2 °C under aerobic conditions in the laboratory. Samples of soil (50 g dry weight equivalent) were acclimatised under aerobic conditions prior to application of the test item at a nominal application rate of 10 mg/kg soil, dry weight.
- For the preliminary experiment, single soil samples from each soil type were taken for analysis immediately after test substance application and at 1 and 7 days after treatment in order to determine appropriate sampling occasions for the main experiment. The results indicated that the test item had degraded to < 10 % of T0 in each soil type after 7 days. Consequently, sampling occasions for the main experiment were set based on these results.
- For the main experiment, duplicate soil samples from each soil type were taken for analysis immediately after test item application and at intervals of up to 146 hours after treatment for Calke, Brierlow and South Witham soils and up to 169 hours after treatment for Ingleby soil. All samples were extracted and analysed using the validated analytical methodology.

PREPARATION AND ACCLIMATISATION OF TEST VESSELS FOR RATE OF DEGRADATION DETERMINATION – AEROBIC TEST
- Portions of sieved soil (50 g, dry weight equivalent) were added to glass bottles, the depth of soil in each bottle was between 1-5 cm.
- Eighteen vessels of each soil type were set up for the purposes of treatment with the test item.
- Purified water was added to each soil sample to bring the water content of the soil to that at pF 2 and the total weight of vessel + soil + water was recorded.
- Each vessel was loosely stoppered with a cotton wool plug and maintained in darkness at 20 ± 2°C in a temperature-controlled environment for 13 days prior to test item application.

PREPARATION AND ACCLIMATISATION OF TEST VESSELS FOR MICROBIOLOGICAL ACTIVITY MEASUREMENT – AEROBIC TEST
- Five vessels of each soil type were prepared in glass bottles of 1000 mL capacity and contained 500 g soil on a dry weight basis.
- Purified water was added to each soil sample to bring the water content of the soil to that at pF 2 and the total weight of vessel + soil + water was recorded.
- Each vessel was loosely stoppered with a cotton wool plug and maintained in darkness at 20 ± 2°C in a temperature-controlled environment.
- These samples covered the maximum duration period of the aerobic test.

APPLICATION OF THE TEST ITEM – AEROBIC TEST
- An aliquot (250 μL) of the 2 mg/mL soil fortification solution was applied to the surface of the soil (50 g) in each test vessel resulting in a nominal application rate equivalent to 10 mg/kg.
- The vessels were lightly shaken in order to disperse the test item as evenly as possible.
- The samples for microbiology activity measurement were not treated with the test item but two vessels were treated with the same amount (on a v/w basis) of solvent that was used to treat the aerobic test vessels.

INCUBATION AND MAINTENANCE OF THE TEST SOILS AFTER TEST ITEM APPLICATION – AEROBIC TEST
- The vessels of treated soil were maintained in darkness at 20 ± 2 °C in a temperature controlled environment without significant deviation. The temperature was monitored throughout the incubation period.
- Test vessels were weighed at approximately two-weekly intervals and water added if necessary to maintain the moisture content to that at a moisture tension of pF 2. At regular intervals (nominally weekly), the cotton wool plug was removed from each vessel for a minimum of 30 seconds to allow air replenishment (this may coincide with the soil moisture adjustments as described above).

SAMPLING INTERVALS – AEROBIC TEST
- Duplicate vessels of each soil type were taken at zero-time, 8, 16, 24, 40, 48, 72 and 146 hours after test item application for Calke, Brierlow and South Witham soils.
- Duplicate vessels were taken at zero-time, 8, 16, 24, 40, 48, 72 and 169 hours after test item application for Ingleby soil.

SAMPLE ANALYSIS – AEROBIC TEST
- The soil samples were analysed with one chromatographic analysis per sample.
- Samples were analysed in batches together with an untreated test soil sample (control) and untreated test soil sample fortified with the test item which acted as a procedural recovery sample to ensure the validity of the method on the day of analysis.

MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – AEROBIC TEST
- The microbiological activity of soils was measured prior to the start and at the end of incubation for each soil type.
- Microbiological activity of the soils was estimated by measurement of microbial biomass by the substrate-induced respiration method (Soil Quality – Determination of Soil Microbial Biomass, Part 1 (ISO 14240-1:1997 (E)).

STUDY DESIGN – ANAEROBIC TEST
- The rate of degradation of the test item was studied in one soil, Ingleby soil, under anaerobic conditions in the laboratory.
- Samples of soil (50 g dry weight equivalent) were acclimatised under aerobic conditions and a moisture content equivalent to pF 2 prior to the application of the test item at a nominal application rate of 10 mg/kg soil, dry weight.
- After 60 hours (DT50) under aerobic conditions, the soil in each vessel (apart from T0 samples) was flooded with high purity degassed water (100 mL) to a depth of approximately 3cm.
- The vessels were purged with nitrogen, then sealed and maintained under anaerobic conditions in the dark at 20 °C ± 2 °C.
- Duplicate samples were taken at zero-time (soil samples only), before vessels were flooded. Duplicate samples were taken after flooding at intervals up to 336 hours. The soil and water
samples were analysed separately.
- All samples were extracted and analysed using the validated analytical methodology.
- Two vessels of soil were set up for measurements of redox potential, pH and oxygen content. These vessels were not treated with the test substance but were flooded at the same time as the test vessels.

PREPARATION AND ACCLIMATISATION OF TEST VESSELS FOR RATE OF DEGRADATION DETERMINATION – ANAEROBIC TEST
- Portions of sieved soil (50 g, dry weight equivalent) were added to glass bottles, the depth of soil in each bottle was between 1-5 cm.
- Eighteen vessels were set up for the purposes of treatment with the test item. Purified water was added to each sample to bring the water content of the soil to that at pF 2 and the total weight of vessel + soil + water was recorded.
- Each vessel was loosely stoppered with a cotton wool plug and maintained in darkness at approximately 20 ± 2 °C in a temperature-controlled environment for 11 days prior to test item application.

PREPARATION AND ACCLIMATISATION OF TEST VESSELS FOR MICROBIOLOGICAL ACTIVITY MEASUREMENT – ANAEROBIC TEST
- Four vessels of soil were prepared in glass bottles of 500 mL capacity and contained 100 g soil on a dry weight basis. These were prepared and maintained as per the test vessels.
APPLICATION OF THE TEST ITEM – ANAEROBIC TEST
- An aliquot (250 μL) of the 2 mg/mL soil fortification solution was applied to the surface of the soil (50 g) in each test vessel resulting in a nominal application rate equivalent to 10 mg/kg. The vessels were lightly shaken in order to disperse the test item as evenly as possible.
- The samples for microbiology activity measurement were not treated with the test item but two vessels were treated with the same amount (on a v/w basis) of solvent that was used to treat the anaerobic test vessels.

INCUBATION AND MAINTENANCE OF THE TEST SOILS AFTER TEST ITEM APPLICATION – ANAEROBIC TEST
- The vessels of treated soil were maintained in darkness at 20 ± 2 °C in a temperature controlled environment without significant deviation.
- The temperature was monitored throughout the incubation period. On one occasion the day’s lowest temperature was recorded as 17 °C for 5 minutes. This deviation was deemed to have no significant effect on the study conduct.

SAMPLING INTERVALS – ANAEROBIC TEST
- Duplicate vessels were taken at zero-time (pre-flood) and then 7, 24, 48, 72, 96, 192 and 336 hours post flooding.

SAMPLE ANALYSIS – ANAEROBIC TEST
- The overlying water of the flooded soil sample was decanted off and the soil and water samples were analysed separately, with one chromatographic analysis per sample.
- Samples were analysed in batches together with an untreated test soil/water sample (control) and an untreated test soil/water sample fortified with the test item which acted as a procedural recovery sample to ensure the validity of the method on the day of analysis.

MEASUREMENT OF WATER AND SOIL REDOX POTENTIAL, WATER pH AND OXYGEN CONTENT – ANAEROBIC TEST
- Redox potential in water and soil and pH and dissolved oxygen in water was measured regularly in either the vessels set up this purpose or for each test vessel before analysis.

MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – ANAEROBIC TEST
- The soil microbiological activity, as total viable counts, was measured at the end of the anaerobic phase.
- Microbiological activity was estimated by measurement of total counts of anaerobic bacteria and anaerobic bacterial spores in slurry of soil combined with the overlying water.

Soil No.:

#1

DT50:

25 h

Type:

other: single first order (SFO) model

Temp.:

20 °C

Remarks on result:

other: Calke (sandy loam) under aerobic conditions

Soil No.:

#2

DT50:

28.5 h

Type:

other: single first order (SFO) model

Temp.:

20 °C

Remarks on result:

other: Brierlow (silt clay loam) under aerobic conditions

Soil No.:

#3

DT50:

24.9 h

Type:

other: single first order (SFO) model

Temp.:

20 °C

Remarks on result:

other: South Witham (clay) under aerobic conditions

Soil No.:

#4

DT50:

59.6 h

Type:

other: single first order (SFO) model

Temp.:

20 °C

Remarks on result:

other: Ingleby (loamy sand) under aerobic conditions

Soil No.:

#4

DT50:

13 h

Type:

other: first order multi compartment (FOMC) model

Temp.:

20 °C

Remarks on result:

other: Ingleby (loamy sand) under anaerobic conditions

Transformation products:

yes

No.:

#1

No.:

#2

Details on transformation products:

Refer to the document 'Expert opinion on degradation pathways of EC 701-392-2' attached to this robust study summary.

Details on results:

DEGRADATION OF TEST ITEM – AEROBIC TEST
- For the preliminary experiment, single soil samples from each soil type were taken for analysis immediately after test substance application and at 1 and 7 days after treatment in order to determine appropriate sampling occasions for the main experiment. The results indicated that the test item had degraded to < 10 % of T0 in each soil type after 7 days.
- For the main experiment, duplicate soil samples from each soil type were taken for analysis immediately after test item application and at 8, 16, 24, 40, 48, 72, and 146 hours after treatment in Calke, Brierlow and South Witham soils and at 8, 16, 24, 40, 48, 72, and 169 hours after treatment in Ingleby soil. The concentrations of test item in soil were summarised in Tables 5 to 8 of the full study report. Example chromatograms of rate of degradation soil sample extracts were presented in Figures 11, 12, 15, 16, 19, 20, 23 and 24 of the full study report. The decline information is summarised below:
(a) Calke (sandy loam): the mean test item detected declined from 9.10 mg/kg at zero-time to (b) Brierlow (silt clay loam): the mean test item detected declined from 8.63 mg/kg at zero-time to (c) South Witham (clay): the mean test item detected declined from 9.05 mg/kg at zero-time to (d) Ingleby (loamy sand): the mean test item detected declined from 10.2 mg/kg at zero-time to - The DT50 and DT90 values for Calke, Brierlow, South Witham and Ingleby soil were calculated on the results obtained using Single First Order (SFO) kinetic models as described in Annex 4 of the full study report. The results were presented in Table 13 of the full study report and are summarised below.

PROCEDURAL RECOVERIES – AEROBIC TEST
- Rate of degradation samples were analysed in suitably sized batches together with an untreated sample (control) and an untreated sample fortified with the test item, which acted as a procedural recovery sample to ensure the validity of the method on the day of analysis. Batch analysis performed and the associated procedural recovery results were presented in Tables 9 to 12 of the full study report.
- The mean procedural recovery results obtained for each batch of sample analysis were within the acceptable range of 70 to 110%, demonstrating the methodology to be working within its requirements. Example chromatograms of control (untreated) samples and procedural recovery samples were presented in Figures 9, 10, 13, 14, 17, 18, 21 and 22 of the full study report.

MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – AEROBIC TEST
- The microbiological analysis results were presented in Annex 3 of the full study report and are
summarised in the table below.

DEGRADATION OF TEST ITEM – ANAEROBIC TEST
- Duplicate soil samples were taken at zero-time (soil samples only) before flooding. Duplicate soil samples were taken at 7, 24, 48, 72, 96, 192, and 336 hours after flooding. The soil and water samples were analysed separately. The concentrations of test item in soil and water were summarised in Tables 15 to 16 of the full study report. Example chromatograms of rate of degradation sample extracts were presented in Figures 29 to 33 of the full study report. The decline information is summarised as Ingleby (loamy sand): the mean test item detected declined from 4.08 mg/kg (pre-flood) to - The DT50 and DT90 values were calculated on the results obtained using First Order Multi
Compartment (FOMC) kinetic models as described in Annex 4 of the full study report. The results were presented in Table 19 of the full study report and are summarised in the table below.

PROCEDURAL RECOVERIES – ANAEROBIC TEST
- Rate of degradation samples were analysed in suitably sized batches together with an untreated sample (control) and an untreated sample fortified with the test item, which acted as a procedural recovery sample to ensure the validity of the method on the day of analysis. Batch analysis performed and the associated procedural recovery results were presented in Tables 17 and 18 of the full study report.
- The mean procedural recovery results obtained for each batch of sample analysis were within the acceptable range of 70 to 110%, demonstrating the methodology to be working within its requirements. Example chromatograms of control (untreated) samples and procedural recovery samples were presented in Figures 25, 26, 27 and 28 of the full study report.

MEASUREMENT OF WATER AND SOIL REDOX POTENTIAL, WATER pH AND OXYGEN CONTENT – ANAEROBIC TEST
- The results of measurements of water and soil redox potential, water pH and oxygen content are presented in Annex 5 of the full study report.
- During the anaerobic incubation period, oxygen levels in the water ranged from 5 % saturation down to 1 % saturation. The mean redox potential in the soil was 400.4 mV after flooding and 122.5 mV at the end of the test. The mean redox potential in the water was 271.6 mV after flood and 210.7 mV at the end of the test.

MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – ANAEROBIC TEST
- The microbiological analysis results were presented in Annex 3 of the full study report and are summarised in the table below.

VALIDATION OF ANALYTICAL METHODOLOGY – CALIBRATION (LINEARITY)
- The response of the LC-MS/MS system to the test item was shown to give a quadratic response over the range of concentrations 0.05 μg/mL to 1 μg/mL (soil analysis) and 0.025 μg/mL to 1 μg/mL (water analysis)
- Typical calibration data were presented in Figures 1 and 2 of the full study report.
- Typical chromatograms of the calibration standards were presented in Figures 3 to 8 of the full study report.

VALIDATION OF ANALYTICAL METHODOLOGY – LIMIT OF DETECTION (LOD)
- The LOD of the method is defined as the value of the lowest calibration standard giving rise to a measureable chromatographic response.
- The LOD of the analytical system was confirmed as 0.05 μg/mL (equivalent to 0.1 mg/kg in soil) and 0.025 μg/mL (equivalent to 0.005μg/mL in water).

VALIDATION OF ANALYTICAL METHODOLOGY – ACCURACY AND PRECISION
- The analytical method was validated at 0.5 and 10 mg/kg in soil. The mean recoveries for the analytical method validation were within the acceptable range of 70 to 110 %, demonstrating accuracy (recovery) of the method. The relative standard deviation (RSD) obtained at each fortification level was within the acceptable range of ≤ 20 %, demonstrating precision of the method.
- The validation data were presented in Tables 1 to 4 of the full study report and precision data obtained are summarised in the table below.
- The analytical method was validated at 0.025 and 2.5 μg/mL in water. The mean recoveries for the analytical method validation were within the acceptable range of 70 to 110 %, demonstrating accuracy (recovery) of the method. The relative standard deviation (RSD) obtained at each fortification level was within the acceptable range of ≤ 20 %, demonstrating precision of the method.
- The validation data was presented in Table 14 of the full study report and the accuracy and precision data obtained are summarised in the table below.

VALIDATION OF ANALYTICAL METHODOLOGY – LIMIT OF QUANTIFICATION (LOQ)
- The LOQ of the method is defined as the lowest fortification level at which acceptable recovery data are obtained.
- The validation of the methodology for the determination of test item demonstrated that it can be accurately determined at a LOQ of 0.5 mg/kg in soil and 0.025 μg/mL in water.

VALIDATION OF ANALYTICAL METHODOLOGY – SPECIFICITY
- No significant interferences (greater than the equivalent of 30% of the LOQ) were found when the method was applied to control samples, thus assuring the specificity of the method.

VALIDATION OF ANALYTICAL METHODOLOGY – SAMPLE FINAL EXTRACT STABILITY
- The sample final extract stability samples indicated that the test item was stable in the final extracts of the four soil types for a period of at least 7 days when stored at approximately
-20 °C.
- The sample final extract stability samples indicated that the test item was stable in the final extracts of water for a period of at least 8 days when stored at approximately -20 °C.
- The results of the sample final extract stability test were presented in Tables 20 to 21 of the full study report.

VALIDATION OF ANALYTICAL METHODOLOGY – ANALYTICAL STANDARD SOLUTIONS STORAGE STABILITY
- The analytical standard solutions storage stability test indicated that a 2 mg/mL stock solution was stable in acetone for a period of at least 31 days when stored at approximately +4 °C in the dark.
- The analytical standard solutions storage stability test indicated that a 100 μg/mL calibration fortifying solution was stable in methanol for a period of at least 16 days when stored at approximately +4 °C in the dark. The stability data was summarized in Table 23 of the full study report.
- The analytical standard solutions storage stability test indicated that a 100 μg/mL calibration fortifying solution was stable in acetonitile for a period of at least 14 days when stored at approximately +4 °C in the dark. The stability data was summarized in Table 24 of the full study report.

RESULTS FROM SINGLE FIRST ORDER (SFO) KINETIC MODELS – AEROBIC TEST

Soil	Soil type (USDA classification)	DT50 (hours)	DT90 (hours)
Calke	Sandy loam	25.0	82.9
Brierlow	Silt clay loam	28.5	94.7
South Witham	Clay	24.9	82.6
Ingleby	Loamy sand	59.6	198

 

RESULTS OF MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – AEROBIC TEST

Sampling occasion	Units	Calke	Brierlow	South Witham	Ingleby
Prior to start of incubation	mg C/kg soil	1260	1021	2008	433
Prior to start of incubation	% organic carbon	4.34	2.62	5.43	4.33
End of incubation	mg C/kg soil	1141	837	1712	324
End of incubation	% organic carbon	3.93	2.15	4.63	3.24
End of incubation *	mg C/kg soil	1525	1206	3321	568
End of incubation *	% organic carbon	5.26	3.09	8.98	5.68
* Vessel treated with solvent at start of incubation (as per test vessels)
% organic carbon = microbial biomass

 

RESULTS FROM FIRST ORDER MULTI COMPARTMENT KINETIC MODELS – ANAEROBIC TEST

Soil	Soil type (USDA classification)	DT50 (hours)	DT90 (hours)
Ingleby	Loamy sand	13.0	981

 

RESULTS OF MEASUREMENT OF SOIL MICROBIOLOGICAL ACTIVITY – ANAEROBIC TEST

Sampling occasion	Organism	Ingleby corrected count
End of incubation	Anaerobic bacteria	2.31E+04
End of incubation	Anaerobic bacteria spores	1.35E+04
End of incubation *	Anaerobic bacteria	4.25E+04
End of incubation *	Anaerobic bacteria spores	1.25E+04
* Vessel treated with solvent at start of incubation (as per test vessels)

 

VALIDATION OF ANALYTICAL METHODOLOGY – SUMMARY OF PRECISION DATA

Soil	Fortification level (mg/kg)	Number of replicates	Recovery range (%)	Mean recovery (%)	Relative standard deviation (%)
Calke	0.5	5	69‑70	74	4.9
Calke	10	5	87‑100	94	5.3
Brierlow	0.5	5	73‑84	80	5.4
Brierlow	10	5	83‑92	87	5.3
South Witham	0.5	5	69‑83	74	7.8
South Witham	10	5	87‑102	94	7.2
Ingleby	0.5	5	72‑83	79	6.3
Ingleby	10	5	94‑104	100	4.4

 

VALIDATION OF ANALYTICAL METHODOLOGY – SUMMARY OF ACCURACY AND PRECISION DATA

Fortification level (µg/mL)	Number of replicates	Recovery range (%)	Mean recovery (%)	Relative standard deviation (%)
0.025	5	62‑85	75	11.0
2.5	5	94‑109	102	5.6

Conclusions:

Following incubation in four different soil types under aerobic conditions at 20 ± 2 °C and at a moisture content equivalent to that at pF 2, the test item degraded with DT50 values of 25.0 h (Calke; sandy loam), 28.5 h (Brierlow; silt clay loam), 24.9 h (South Witham; clay) and 59.6 h (Ingleby; loamy sand). The DT90 values determined under aerobic conditions were 82.9 h (Calke; sandy loam), 94.7 h (Brierlow; silt clay loam), 82.6 h (South Witham; clay) and 198 h (Ingleby; loamy sand). Following incubation in one soil type (Ingleby; loamy sand) under anaerobic conditions at 20 ± 2 °C the test item degraded with a DT50 value of 13 hours and a DT90 value of 981 hours.

Executive summary:

GUIDELINE

The study was performed in compliance with OECD Guidelines for the Testing of Chemicals 307: Aerobic and Anaerobic Transformation in Soil (April 2002).

 

METHODS

The rate of degradation (DT50, DT90) of the test material was studied in four soils incubated under aerobic conditions and one soil under anaerobic conditions in the laboratory.

 

For the rate of degradation tests under aerobic conditions, soil samples were set up and allowed to acclimatise before being treated with test item at a nominal application rate of 10 mg/kg (on a dry weight basis). The soil samples were incubated under aerobic conditions in the dark at approximately 20°C at a moisture content equivalent to pF 2. At each sampling occasion, the amounts of test item in the soil samples were determined using the validated analytical methodology. Duplicate soil samples from each soil type were taken for analysis immediately after test item application and at intervals of up to 146 hours after treatment in Calke, Brierlow and South Witham soil and up to 169 hours in Ingleby soil.

 

For the rate of degradation test under anaerobic conditions, soil samples were set up and allowed to acclimatise before being treated with test item at a nominal application rate of 10 mg/kg (on a dry weight basis), as per the aerobic test. The period of the aerobic phase was DT50 (60 hours). At the end of this period, the soil in each vessel (apart from the T0 samples) was flooded with high purity degassed water. Duplicate soil samples were taken for analysis at zero-time (soil samples only), before the vessels were flooded. Subsequent duplicate samples were taken for analysis (soil and water samples were analysed separately) at intervals of up to 336 hours post flooding.

 

The analytical method was validated at 0.5 and 10 mg/kg in soil. The analytical method comprised of an extraction with acidified methanol prior to quantitation using liquid chromatography with tandem mass spectrometric detection (LC-MS/MS).

The analytical method was validated at 0.025 μg/mL and 2.5 μg/mL in water (equivalent to 2.5 μg/100 mL and 250 μg/100 mL). The analytical method comprised of an extraction with acetonitrile, followed by the addition of a QuEChERS citrate extraction mix and subsequent shaking and centrifuge. The acetonitrile phase was transferred to an auto-sampler vial prior to quantitation using liquid chromatography with tandem mass spectrometric detection (LC-MS/MS).

 

RESULTS

The concentration of test item declined in each soil type during investigation of degradation under aerobic conditions. The decline information is summarised below:

(a) Calke (sandy loam):the mean test item detected declined from 9.10 mg/kg at zero-time to <LOQ (less than the limit of quantitation of 0.5 mg//kg) at 146 hours.

(b) Brierlow (silt clay loam):the mean test item detected declined from 8.63 mg/kg at zero-time to <LOQ (less than the limit of quantitation of 0.5 mg//kg) at 146 hours.

(c) South Witham (clay):the mean test item detected declined from 9.05 mg/kg at zero-time to <LOQ (less than the limit of quantitation of 0.5 mg//kg) at 146 hours.

(d) Ingleby (loamy sand):the mean test item detected declined from 10.2 mg/kg at zero-time to <LOQ (less than the limit of quantitation of 0.5 mg//kg) at 169 hours.

 

The DT50 and DT90 values for Calke, Brierlow, South Witham and Ingleby soil were calculated on the results obtained using Single First Order (SFO) kinetic models and values are shown in the table below:

Soil	Soil type (USDA classification)	DT50 (hours)	DT90 (hours)
Calke	Sandy loam	25.0	82.9
Brierlow	Silt clay loam	28.5	94.7
South Witham	Clay	24.9	82.6
Ingleby	Loamy sand	59.6	198

 

The concentration of test item declined during investigation of degradation under anaerobic conditions. The decline information is summarised asIngleby (loamy sand):the mean test item detected declined from 4.08 mg/kg (pre-flood) to <LOQ (less than the limit of quantitation of 0.5 mg//kg) at 336 hours (post-flood).

 

The DT50 and DT90 values for Ingleby soil were calculated on the results obtained using First Order Multi Compartment (FOMC) kinetic model and values are shown in the table below:

Soil	Soil type (USDA classification)	DT50 (hours)	DT90 (hours)
Ingleby	Loamy sand	13.0	981

 

The mean recoveries for the analytical method validation in soil were within the acceptable range of 70 to 110 %, demonstrating accuracy (recovery) of the method. The relative standard deviation (RSD) obtained at each fortification level was within the acceptable range of≤20 %, demonstrating precision of the method.

 

The mean recoveries for the analytical method validation in water were within the acceptable range of 70 to 110 %, demonstrating accuracy (recovery) of the method. The relative standard deviation (RSD) obtained at each fortification level was within the acceptable range of≤20 %, demonstrating precision of the method.

 

CONCLUSION

 

Following incubation in four different soil types under aerobic conditions at 20 ± 2 °C and at a moisture content equivalent to that at pF 2, the test item degraded with DT50 values of 25.0 h (Calke; sandy loam), 28.5 h (Brierlow; silt clay loam), 24.9 h (South Witham; clay) and 59.6 h (Ingleby; loamy sand). The DT90 values determined under aerobic conditions were 82.9 h (Calke; sandy loam), 94.7 h (Brierlow; silt clay loam), 82.6 h (South Witham; clay) and 198 h (Ingleby; loamy sand). Following incubation in one soil type (Ingleby; loamy sand) under anaerobic conditions at 20 ± 2 °C the test item degraded with a DT50 value of 13 hours and a DT90 value of 981 hours.

Key value for chemical safety assessment

Half-life in soil:

59.6

at the temperature of:

20 °C