Propargite

Biodegradation in soil

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

6th August 2001 to 21st January 2003

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: Commission Directive 95/36/EC, July 14, 1995 amending Council Directive 91/41/EEC, Annex I, 7.1.1.2.1

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

silt loam

% Clay:

24.27

% Silt:

53.43

% Sand:

22.3

% Org. C:

1.02

pH:

5.71

CEC:

16.46

Soil no.:

#2

Soil type:

silty clay loam

% Clay:

34.52

% Silt:

49.96

% Sand:

15.52

% Org. C:

1.21

pH:

7.58

CEC:

15.82

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Senozan, Saint-Laurent-sur-Saône, France (silt loam); Recerca, Agricola, Spain (silty clay loam)
- Pesticide use history at the collection site: none for the last five years (silt loam); at the edge of a filed where normally no pesticide treatment occurs (silty clay loam)
- Sampling depth (cm): 0-30 cm top layer
- Soil preparation (e.g., 2 mm sieved; air dried etc.): air dried slightly at room temperature (silt loam); used as received (silty clay loam). All soils were sieved with a 2 mm mesh prior to study.

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture retention at 1/3 atm (%): 25.11 (silt loam); 27.39 (silty clay loam)
- MWC: adjusted to 36 to 42 %

Soil No.:

#1

Duration:

120 d

Soil No.:

#2

Duration:

120 d

Soil No.:

#1

Initial conc.:

3.52 ppm

Based on:

test mat.

Soil No.:

#2

Initial conc.:

3.47 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Soil No.:

#1

Temp.:

20 ± 2ºC

Soil No.:

#2

Temp.:

20 ± 2ºC

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil condition: air dried (silt loam); fresh (silty clay loam)
- Soil (g/replicate): 10 g (dry soil weight equivalent)
- Control conditions, if used: same as treated samples except no radioactive test material was applied.
- No. of replication controls, if used: 4
- No. of replication treatments: 20
- Test apparatus (Type/material/volume): 50 mL Oak Ridge Teflon® FEP Centrifuge tubes
- Details of traps for CO2 and organic volatile, if any: 40 mL glass vials with Teflon®-lined screw septum caps. Arranged in a series consisting of one blank trap, one ethylene glycol trap (to capture organic and neutral molecules) and two 1 N NaOH traps (to capture 14CO2) in that order. The first NaOH trap of samples not yet harvested was replenished by fresh solution at approximately 30 day intervals.
- Identity and concentration of co-solvent: methanol

Test material application
- Volume of test solution used/treatment: 34.2 µg [14C]-propargite to 10 g soil.
- Application method: added to the soil surface using a syringe and then each tube shaken to distribute the radioactivity.

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: two control flasks were weighed biweekly to monitor moisture loss. Moisture level in the treated samples was adjusted approximately every two weeks according to the level lost in the control flasks.
- Continuous darkness: yes

OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: continuously passing, via positive pressure, scrubbed and humidified air through each incubation tube and its trapping solutions at 2-5 mL/min.

SUPPLEMENTARY EXPERIMENTS:
- Four flasks, two per soil type, each containing approximately 200 g (dry weight equivalent) were set up for microbial biomass analysis. The samples were incubated at 20 ± 2 ºC under the same conditions as the treated samples. The soil in these flasks was treated with the solvent used to prepare the treatment solution but without the test material. At the end of the study, one of the samples was used to determine microbial biomass.

SAMPLING DETAILS
- Sampling intervals: 0, 3, 7, 14, 21, 29, 63, 92 and 120 days (silt loam); 0, 3, 7, 14, 22, 30, 59, 91 and 120 days (silty clay loam)
- Sampling method for soil samples: two replicates and associated traps were removed from the test system.
- Method of collection of CO2 and volatile organic compounds: ethylene glycol and NaOH traps
- Sampling intervals/times for:
> Moisture content: bi-weekly
> Sample storage before analysis: <-10 ºC( soil extracts and post-extracted solids); <7 ºC (trapping solutions)

Soil No.:

#1

% Recovery:

93

Remarks on result:

other: day 120 value

Soil No.:

#2

% Recovery:

94

Remarks on result:

other: day 120 value

Key result

Soil No.:

#1

DT50:

90.74 d

Type:

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

Remarks on result:

other: DT90 = 301.43 days; r2 = 0.978

Key result

Soil No.:

#2

DT50:

55.53 d

Type:

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

Remarks on result:

other: DT90 = 184.48 days; r2 = 0.994

Transformation products:

yes

No.:

#1

Details on transformation products:

- Figure attached: No
- Other: DT50 = 9.70 days; DT90 = 32.22 days; r2 = 0.994

Evaporation of parent compound:

not specified

Volatile metabolites:

not specified

Residues:

yes

Details on results:

TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: yes
- Anomalies or problems encountered (if yes): no

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount: 1.91 % on the 29th day of incubation and 10.43 % on the 30th day of incubation for silt loam and silty clay loam, respectively. At the end of the study period, the corresponding concentrations were 1.39 and 2.95 % of the applied amount, respectively.

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT:

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 98.3 % (silt loam); 97.37 % (silty clay loam)
- % of applied amount at end of study period: 46.69 % (silt loam); 26.12 % (silty clay loam)

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: 1.00 % (silt loam); 0.90 % (silty clay loam)
- % of applied amount at end of study period: 23.92 % (silt loam); 37.59 % (silty clay loam)

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 21.71 % (silt loam); 29.64 % (silty clay loam)

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: 0.09 % (silt loam); 0.15 % (silty clay loam)

Table 1: ¹⁴C distribution

Time (day)	Propargite	TBPC	UNK1 (run time = 4 min)	Bound residue	CO2	Volatile	Mass balance
Silt loam
0	97.30	0.38	n.d.	1.00	n.a.	n.a.	99.30
3	93.73	0.69	0.34	2.18	0.10	<LOD	95.64
7	87.53	1.62	0.89	3.54	0.40	0.01	94.86
14	85.82	1.58	1.93	7.09	1.25	<LOD	98.90
21	80.97	1.16	3.41	7.77	1.75	0.01	96.70
29	75.98	1.91	4.72	8.97	4.64	0.03	98.47
63	55.84	1.71	5.03	15.81	12.21	0.05	92.78
92	47.55	1.87	5.29	21.85	16.08	0.23	94.72
120	40.14	1.39	3.08	23.92	21.71	0.09	92.41
Silty clay loam
0	95.12	0.54	n.d.	0.90	n.a.	n.a.	98.27
3	93.32	3.13	n.d.	2.15	<LOD	<LOD	99.93
7	88.78	5.59	0.75	3.84	0.08	<LOD	100.21
14	74.80	8.53	1.85	6.26	0.24	<LOD	93.23
22	74.44	10.05	2.36	8.74	0.45	<LOD	98.04
30	66.62	10.43	3.59	8.17	1.15	<LOD	96.11
59	44.04	9.48	7.55	20.42	4.35	0.03	95.74
91	35.02	5.40	2.63	28.35	16.26	0.04	93.83
120	18.02	2.95	1.47	37.59	29.64	0.15	93.50

n.d. = not detected; n.a. = not analysed

The peak at 4 minutes is effectively the solvent front and hence is likely to be composed of a number of fractions. In addition, up to 11 unidentified peaks were observed from the incubations in the two soild be each always consisted of <3.38 % of applied radioactivity.

Table 2: ¹⁴C distribution into humic acid, fluvic acid and humin.

Sample	Fulvic acid	Humic acid	Humin
Silt loam
63	2.46	1.26	10.19
92	4.95	7.16	4.05
120	4.40	8.86	3.96
Silty clay loam
59	1.94	0.52	10.61
120	2.17	0.76	21.36

Conclusions:

Under the conditions of the test, in two European soils, propargite degraded to CO2 and bound residues, levels of which reached 21.71-29.64 % and 23.92-37.59 %, respectively, at the completion of the 210 day incubation period. The metabolite TBPC reached 10 % in one soil (after 22-30 days) and then declined; in the second soil a maximum level of only 2 % was reached. An unidentified polar peak (close to the solvent front) reached 5-8 % at approximately 60-90 days. The first-order DT50 for propargite incubated in silt loam and a silt clay loam soil at 20 ºC in darkness at 40-50 % of 33 kPa was 56-91 days and the DT90 was 184-301 days.

Executive summary:

The degradation rate of [¹⁴C]-propargite was studied in two European soils (a silt loam and a silty clay loam) at a moisture level of 40 to 50 % of field capacity at 1/3 bar. The study was conducted to a target concentration of 3.42 mg/kg (ppm) with actual concentrations measured at 3.52 and 3.47 mg/kg respectively. The incubation was conducted in the dark at 20 ± 2 ºC for 120 days.

Propargite represented a mean total of 97 % of the applied radioactivity at zero time in the soil-extractable residues in the silt loam. The presence of propargite in the soil-extractable residues declined over the course of the study representing 40 % at 120 days. At 120 days, the distribution of significant radioactivity was in the soil extractable residues, ¹⁴CO₂ and soil-bound residues representing 47, 22 and 24 % of the applied radioactivity respectively. The identity of residual propargite in the silt loam soil extracts was confirmed by HPLC cochromatography and mass spectrometry. The DT50 and DT90 values for propargite in silt loam were calculated to be 90.74 and 301.43 days, respectively. There were no degrades formed accounting for more than 10 % of the applied radioactivity at any time during the incubation period.

Propargite represented a mean total of 95 % of the applied radioactivity at zero time in the soil-extractable residues in the silty clay loam. The presence of propargite in the soil-extractable residues declined over the course of the study representing 18 % at 120 days. The major soil degradate detected in the silty clay loam was 2 -(4 -tert-butylphenoxy)cyclohexanol (TBPC) representing a mean maximum of 10 % at 30 days. At 120 days, the distribution of significant radioactivity was in the soil-extractable residues, ¹⁴CO₂ and soil-bound residues representing 26, 30 and 38 % of the applied radioactivity, respectively. The identities of residual propargite and TBPC in the silty clay loam soil extracts was confirmed by HPLC cochromatography and mass spectrometry. The DT50 and DT90 for propargite in silty clay loam was calculated to be 53.53 and 184.48 days respectively. The DT50 and DT90 for TBPC in silty clay loam was calculated to be 9.70 and 32.22 days, respectively.

Reference 2

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Not stated

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: USA EPA Guidelines, Subdivision N, Section 162-1

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

sandy clay loam

% Clay:

22

% Silt:

26.8

% Sand:

51.2

% Org. C:

1.7

pH:

6.9

CEC:

12.18

Bulk density (g/cm³):

1.128 - 1.331

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Fresno, California, USA

PROPERTIES OF THE SOILS (in addition to defined fields)
- Moisture at 1/3 atm: 16.92 %

Soil No.:

#1

Duration:

90 d

Soil No.:

#1

Initial conc.:

4.9 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Soil No.:

#1

Temp.:

25ºC

Details on experimental conditions:

1. EXPERIMENTAL DESIGN
- Soil (g/replicate): 25 g
- No. of replication treatments: 2
- Test apparatus (Type/material/volume): 250 mL Erlenmeyer flasks
- Details of traps for CO2 and organic volatile, if any: CO2 trapping towers with foam plugs. The evolved 14CO2 was trapped on the lower layer of ascarite contained in an 18cm cylindrical glass tower (see Figure 1). Weekly changing of the drierite was necessary to ensure dryness in the ascarite layer.
- Identity and concentration of co-solvent: acetone

Test material application
- Volume of test solution used/treatment: 123.4 µg in 59 µL acetone
- Application method (e.g. applied on surface, homogeneous mixing etc.): added to the soil and hand shaken

Any indication of the test material adsorbing to the walls of the test apparatus: no data

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: moisture lost was replaced once or twice per week as needed
- Continuous darkness: No

2. SAMPLING DETAILS
- Sampling intervals: 0, 2, 5, 7, 14, 29, 62 and 90 days
- Sampling method for soil samples: treated soil was extracted with acetone (70 mL; 1 hour) at room temperature, filtered and reextracted with acetone (50 mL; 1 hour). Extracts were combined and two 0.5 mL aliquots radioassayed by LSC. The extracts were characterised for HPLC/LSC using a gradient system.
- Method of collection of CO2 and volatile organic compounds: the appropriate flask and trapping tower were removed and the two layers of ascarite carefully transferred for analysis for 14CO2. The ascarite was transferred to the CO2 release apparatus. 40 mL concentrated HCl was injected through the septum at a controlled rate while passing nitrogen through the apparatus continuously. After the reaction was completed, indicated by the yellow colour of the ascarite, the apparatus was flushed with nitrogen for an additional 30 minutes, the CO2 traps were disconnected and the combustion cocktail was quantitated by LSC. Foam plugs were analysed by combustion analysis for 14C-volatiles.

Soil No.:

#1

% Recovery:

93.1

Key result

Soil No.:

#1

DT50:

39.5 d

Type:

not specified

Remarks on result:

other: r2 = 0.998

Transformation products:

no

Evaporation of parent compound:

no

Volatile metabolites:

no

Residues:

yes

Details on results:

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

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT: 4.7-12.4 %

EXTRACTABLE RESIDUES
- % of applied amount at end of study period: 31 %

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: 0.6 %
- % of applied amount at end of study period: 30.1 %

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 31.4 %

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: 0.2 %

Table 1: Total ¹⁴C distribution

Time (day)	Propargite	BGES	Bound residue	CO2	Volatiles	Mass balance
0	88.7	5.6	0.6	n.a.	n.a.	95.3
2	85.4	5.3	2.1	n.a.	<0.1	96.2
5	84.5	5.5	4.4	0.8	<0.1	99.0
7	81.0	5.7	6.5	1.5	<0.1	98.0
14	77.6	6.1	9.2	4.3	<0.1	100.4
29	55.9	5.3	18.2	8.0	0.2	93.0
62	34.8	4.9	21.9	22.9	0.2	87.6
90	24.3	4.3	30.1	31.4	0.2	93.1

Conclusions:

Under the conditions of the test, propargite degraded to CO2 and bound residues, reaching 31 and 30 %, respectively, at the completion of the 90 day incubation period. No other metabolites were identified during the study. The first-order DT50 for propargite incubated in sandy clay loam at 25 ºC in darkness was 39.5 days; from this value a DT90 of 131 days can be calculated.

Executive summary:

An aerobic soil metabolism study was conducted on sandy clay loam soil treated with [¹⁴C]Omite at 4.9 ppm and incubated in darkness at 25 ºC. Duplicate samples were analysed at 0, 2, 5, 7, 14, 29, 62 and 90 days after treatment. At 90 days, 31 % of the applied radioactivity was extractable from the soil. Omite was identified by HPLC as the major extractable residue representing 24 % of the applied radioactivity at 90 days. Combustion analysis indicated 30 % of the applied radioactivity as bound residue and 31 % of the applied radioactivity was identified as radioactive CO₂. The half-life of Omite under aerobic conditions was calculated by linear regression analysis to be 40 days.

Reference 3

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

19th July 1989 to 8th November 1989

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: BBA Richtlinie Teil IV, 4-1

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil no.:

#1

Soil type:

loamy sand

% Clay:

4.9

% Silt:

7.1

% Sand:

88

% Org. C:

2.55

pH:

6

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Soil preparation (e.g., 2 mm sieved; air dried etc.): 2mm sieved

Soil No.:

#1

Duration:

100 d

Soil No.:

#1

Initial conc.:

2.887 mg/kg soil d.w.

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Soil No.:

#1

Temp.:

22 ± 2ºC

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil condition: fresh
- Soil (g/replicate): fresh soil corresponding to 100g dry soil
- No. of replication treatments: 6
- Test apparatus (Type/material/volume): all-glass metabolism apparatus with open gas-flow system (see Figure 1).
- Details of traps for CO2 and organic volatile, if any: gas washing bottles each containing 50 mL 2 N sodium hydroxide/50 mL 2-methoxyethanol to absorb CO2 from soil respiration and 14CO2 from mineralisation of the test material.
- Identity and concentration of co-solvent: acetone/water (8:2 v/v)

Test material application
- Volume of test solution used/treatment: 1.4 mL from a solution containing 2.1 mg unlabelled test material diluted with labelled test material up to a volume of 20 mL
- Application method (e.g. applied on surface, homogeneous mixing etc.): applied dropwise to the soil and the soil mixed thoroughly

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

Experimental conditions (in addition to defined fields)
- Moisture maintenance method: controlled and adjusted weekly during the first month and thereafter every two weeks. The amount of water required to maintain moisture content was 0-1.2 g.
- Continuous darkness: no

OXYGEN CONDITIONS (delete elements as appropriate)
- Methods used to create the an/aerobic conditions: airflow of 40-60 mL/min

SAMPLING DETAILS
- Sampling intervals: sodium hydroxide and 2-methoxyethanil solutions were exchanged weekly during the first month and thereafter about every two weeks.
- Sampling method for soil samples: 0, 7, 14, 32, 64 and 100 days after treatment.

Soil No.:

#1

% Recovery:

102.14

St. dev.:

3.46

Key result

Soil No.:

#1

DT50:

53.3 d

Type:

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

Temp.:

22 °C

Key result

Soil No.:

#1

DT50:

177.1 d

Type:

other: (pseudo-)first order (= DT90)

Temp.:

22 °C

Key result

Soil No.:

#1

DT50:

44.9 d

Type:

other: 1.5-order kinetics (DT50)

Temp.:

22 °C

Key result

Soil No.:

#1

DT50:

234.2 d

Type:

other: 1.5-order kinetics (DT90)

Temp.:

22 °C

Transformation products:

yes

No.:

#1

Details on transformation products:

TLC-analysis of the extractables at days 32, 64 and 100 showed, besides the parent compound, two metabolites in very low concentrations. They appeared at day 32 at 1.4 and 1.1 % of the applied radioactivity but had declined to 0.5 and 0.7 %, respectively, by day 100.

Evaporation of parent compound:

not specified

Volatile metabolites:

yes

Residues:

yes

Details on results:

TEST CONDITIONS
- Aerobicity, moisture, temperature and other experimental conditions maintained throughout the study: no data

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: 1.4 % (M-2) and 1.1 % (M-3), both day 32.
- Range of maximum concentrations in % of the applied amount at end of study period: 0.5 % (M-2), 0.7 % (M-3)

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 107.7 %
- % of applied amount at end of study period: 28.9 %

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: 0.37 %
- % of applied amount at end of study period: 25.79 %

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 41.85 %

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: 0.05 %

Table 1: Total ¹⁴C distribution

Time (day)	Propargite	M-2	M-3	Bound residue	CO2	Volatile
0	107.7	0.0	0.0	0.37	n.d.	n.d.
7	94.2	0.0	0.0	4.83	4.14	0.01
14	86.9	0.0	0.0	7.60	4.78	0.01
32	65.1	1.4	1.1	14.33	20.57	0.02
64	43.9	0.8	0.6	21.87	33.18	0.03
100	28.9	0.5	0.7	25.79	41.85	0.05

n.d. = not detected

Conclusions:

Under the conditions of the test, the test material primarily degraded to CO2 and bound residues reaching 42 and 26 %, respectively, at the completion of the 100 day incubation. Two unidentified metabolites were found during the study but levels were <1.5 %. 28.9 % of the initially applied radioactivity was detected as the parent compound. The first-order DT50 for propargite incubated in loamy sand soil at 22 ºC in darkness was 53.3 days (DT90 177.1 days).

Executive summary:

14C-labelled propargite technical was investigated for 100 days in one German standard soil (loamy sand Speyer 2.2) incubated under aerobic conditions in the laboratory.

The half-life of the test material (DT50) in the soil was found to be 44.9 days (1.5-order kinetics) and 53.3 days (1.0-order kinetics). The DT90 value was found to be 234.2 days (1.5-order kinetics) and 177.1 days (1.0-order kinetics). The rate constant for the first kinetic order was determined by linear regression to be 0.013 (1/day). For the 1.5 kinetic order the corresponding rate constant was 0.0052 [(kg/mg)^0.5 · 1/day].

The best fit was obtained with the 1.5-order kinetics. The DT90 values reported are extrapolated values only and depend strongly on the model used. These DT90 values are not confirmed experimentally. Due to the high rate of mineralisation it can be expected that the actual DT90 value will occur rather as predicted by the first-order kinetic model.

Besides the parent compound, two other extractable metabolites (M2, M3, unknown) were found in very small amounts in the soil. They were detected only after 32 days when they showed a maximum i.e. 1.4 % (M2) and 1.1 % (M3) from the radioactivity applied and decreased on sampling day 64 and 100 to 0.5 % (M2) and 0.7 % (M3) of the radioactivity applied. By comparison, of the retardation factors (Rf) obtained in both the application solution and the extracts of the last sample intervals, it is apparent that M2 and M3 were already present in the application solution.

Up to 41.85 % of the radioactivity applied to the soil was converted to ¹⁴CO2 at the end of the incubation period, thus demonstrating the high mineralisation rate of the ¹⁴C-labelled molecule by soil microorganisms.

Non-extractable radioactivity ranged from 0.37 % (day 0) to 25.79 % (day 100) of the radioactivity applied. Total recoveries of radioactivity were on average 102.14 ± 3.46 %.

Reference 4

Endpoint:

biodegradation in soil: simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

26th April 1994 to 20th June 1995

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: US EPA Guidelines, Subdivision N, Section 162-1

Deviations:

no

Qualifier:

equivalent or similar to guideline

Guideline:

OECD Guideline 307 (Aerobic and Anaerobic Transformation in Soil)

Deviations:

no

GLP compliance:

yes

Test type:

laboratory

Radiolabelling:

yes

Oxygen conditions:

aerobic

Soil classification:

not specified

Soil no.:

#1

Soil type:

sandy loam

% Clay:

8

% Silt:

28

% Sand:

64

% Org. C:

2.32

pH:

6.6

Details on soil characteristics:

SOIL COLLECTION AND STORAGE
- Geographic location: Middlebury, Connecticut, USA
- Pesticide use history at the collection site: none for at least 3 years prior to collection
- Sampling depth: 0-8 inches

Soil No.:

#1

Duration:

365 d

Soil No.:

#1

Initial conc.:

ca. 5.8 ppm

Based on:

test mat.

Soil No.:

#1

Initial conc.:

ca. 24 ppm

Based on:

test mat.

Parameter followed for biodegradation estimation:

CO2 evolution

Soil No.:

#1

Temp.:

25 ± 1ºC

Details on experimental conditions:

EXPERIMENTAL DESIGN
- Soil condition: air dried/fresh
- Soil (g/replicate): 55.5 ± 0.1g fresh (equivalent to approximately 50 g soil dry weight)
- No. of replication controls, if used: two
- No. of replication treatments: 27 dosed at 5.8 ppm; four flasks dosed at 20 ppm
- Test apparatus (Type/material/volume): biometer flasks with side-arms
- Details of traps for CO2 and organic volatile, if any: 10 mL of 1 N potassium hydroxide in a standard vial.
- Identity and concentration of co-solvent: acetonitrile

Test material application
- Volume of test solution used/treatment: 45 µL for 5.8 ppm dose; 205 µL for 20 ppm dose
- Application method: applied on surface and soil mixed well once solvent had evaporated

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

Experimental conditions (in addition to defined fields)
- Continuous darkness: Yes

OXYGEN CONDITIONS
- Methods used to create the an/aerobic conditions: no

SAMPLING DETAILS
- Sampling intervals: 0, 3, 7, 14, 30, 59, 90, 120, 181, 269 and 365 days after treatment.
- Method of collection of CO2 and volatile organic compounds: vials containing potassium hydroxide were replaced every two weeks and duplicate 0.5 mL aliquots taken from the used traps.
- Other observations, if any: confirmation that the radioactivity trapped in the potassium hydroxide vials was 14CO2 was performed by adding approximately 0.5 mL of saturated barium chloride solution or barium hydroxide and 0.1 mL potassium carbonate to the potassium hydroxide solution and shaken by hand. The samples were centrifuged for approximately 3 minutes and the supernatant into a scintillation vial and 10 mL of Ready Value™ cocktail added. Water was added to the precipitate and the contents counted by LSC. Validation of 14CO2 was conducted on day 14, 28, 98, 168, 266 and 364 day samples.

Soil No.:

#1

% Recovery:

94.45

Remarks on result:

other: average recovery

Key result

Soil No.:

#1

DT50:

67.19 d

Type:

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

Remarks on result:

other: Based on results from days 0-59 of the study

Key result

Soil No.:

#1

DT50:

231.14 d

Type:

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

Remarks on result:

other: Based on results from days 59-365 of the study

Transformation products:

yes

No.:

#1

No.:

#3

No.:

#4

No.:

#8

Details on transformation products:

- Description of biotransformation pathway: Figure attached (see Figure 47 below)

Evaporation of parent compound:

no

Volatile metabolites:

no

Residues:

yes

Details on results:

MAJOR TRANSFORMATION PRODUCTS (see Figure 11)
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: 7.62 % on day 90 (Met-8); 1.98 % on day 14 (Met-3)
- Range of maximum concentrations in % of the applied amount at end of study period: 3.83 % (Met-8); 1.49 % (Met-3)

MINOR TRANSFORMATION PRODUCTS (see Figure 11)
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: 0.65 % on day 365 (Met-1); 0.28 % on day 14 (Met-2); 0.4 % on day 181 (Met-4); 0.33 % on day 181 (Met-5); 0.5 % on day 14 (Met-6); 0.44 % on day 269 (Met-7); 0.23 % on day 365 (Met-9)
- Range of maximum concentrations in % of the applied amount at end of study period: 0.65, 0.11, 0.27, 0.17, 0.31, 0.05 and 0.23 % on day 365 for Met-1, Met-2, Met-4, Met-5, Met-6, Met-7 and Met-9, respectively.

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 99.99 %
- % of applied amount at end of study period: 21.45 %

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: 0.11 %
- % of applied amount at end of study period: 32.96 %

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 31.96 %

Table 1: Total ¹⁴C distribution (see Figure 10)

Time (day)	Propargite	BGES (Met-1)	TBPC (Met-3)	TBPC-sulphate (Met-8)	Bound residue	CO2
0	99.99	n.d.	0.43	n.d.	0.11	n.a.
3	89.37	n.d.	1.66	n.d.	3.2	0.10
7	84.39	n.d.	1.45	n.d.	7.14	0.69
14	78.18	0.29	1.98	3.09	7.83	2.50
30	65.90	0.34	1.53	3.73	13.48	5.22
59	52.12	0.56	1.40	6.72	18.93	10.87
90	47.43	0.33	1.49	7.62	22.69	15.62
120	42.35	0.39	1.40	6.33	25.30	17.49
181	33.14	0.45	1.52	4.76	27.19	25.13
269	25.65	0.45	1.33	4.53	27.62	28.95
365	21.45	0.65	1.49	3.83	32.96	31.96

n.d. = not detected

n.a. = not analysed

After 120 days, the post-extracted soil contained 2.0, 5.99 and 8.02 % applied radioactivity in the humin fraction, fulvic acid fraction and humic acid fraction, respectively. After 365 days, the post-extracted soil contained 7.8, 4.34 and 14.05 % applied radioactivity in the humin fraction, fulvic acid fraction and humic acid fraction, respectively.

Conclusions:

Under the conditions of the test, propargite degraded primarily to CO2 and bound residues reaching 15.6 and 22.7 %, respectively, at day 90 and 32 and 33 %, respectively, at day 365. PTBP, TBPC and its sulphate derivative were identified during the study at levels <8 %. The DT50 and DT90 values for propargite incubated in loamy sand soil at 25 ºC in darkness were 168 and 559 days, respectively, over the full 365 day study duration but 67 and 223 days when re-calculated for the first 59 days (i.e. during the microbially active phase).

Executive summary:

14C-labelled Omite degraded moderately following treatment at approximately 6 ppm (µg/g parent compound equivalents) when incubated in a sandy loam soil under aerobic conditions. Samples were harvested at 0, 3, 7, 14, 30, 59, 90, 120, 181, 269 and 365 days after treatment. Because the dissipation curve was biphasic, a separate half-life was calculated for each phase. The estimated initial half-life based on the first 59 days (6 time points) of the study was approximately 67 days with a rate constant of k = 0.0103 per day. Thereafter (up to 365 days), the remainder of the applied material dissipated more slowly with a half-life of approximately 231 days (k = 0.003 per day). The half-life based on all 11 time points was estimated at approximately 168 days.

The samples were initially extracted with ethyl acetate followed by an extraction with acetonitrile:water (4:1) to extract any additional radioactive residues from the soil. The CH₃CN/H₂O fraction was partitioned with methylene chloride.

Organoextractables (CH₃COOC₂H₅ and CH₂Cl₂/CH₃CN) were routinely analysed by TLC with radiometric detection. Representative CH₃COOC₂H₅ and CH₂Cl₂/CH₃CN fractions were also analysed by HPLC to confirm TLC results. High dose (approximately 24 ppm treatments) samples were used for preparative isolation and separation of radioactive metabolites by TLC followed by HPLC purification. Each isolated and purified metabolite was compared with respective reference standards by HPLC as well as one-dimensional and/or two-dimensional TLC. LC/MS was used for the identification of certain unknown metabolites.

Initially, most of the applied radioactivity was extracted into the CH₃COOC₂H₅ fraction (100.42 % on day 0, 91.02 % on day 3) which gradually decreased to less than 25 % after the 365 day incubation period. The percentage of the applied radioactivity which was extracted into the CH₃CN/H₂O fraction ranged from 4.39 to 8.35 %. A majority of the radioactivity in the CH₃CN/H₂O was partitioned into the CH₂Cl₂/CH₃CN fraction (3.88 to 6.93 % of the applied radioactivity). The amount of remaining aqueous soluble residues was very low ranging from 0.27 to 1.63 % of the applied radioactivity. Radioactivity remaining in the PES slowly increased to 32.96 by day 365. Omite^® was also gradually mineralised to form ¹⁴CO₂. Up to 31.96 % of the total applied radioactivity was converted to ¹⁴CO₂ by day 365. The overall ¹⁴C recovery was excellent (>90 %) throughout the entire study.

At least nine metabolites (Met-1 to Met-9) were observed with the major metabolite being Met-8. This metabolite, first detected on day 14 at the level of 3.09 % of applied radioactivity, increased to its maximum level of 7.62 % of applied radioactivity by day 90 and then decreased gradually to 3.83 % by day 365. It was identified by LC-MS as a sulfate derivative of p-tertiarybutylphenoxycyclohexanol (TBPC) which was the other major metabolite (Met-3) detected in the extractable fractions. TBPC was first detected on day 0 (0.43 % of applied radioactivity). The level of TBPC reached 1.98 % of applied radioactivity by day 14 and remained between 1.33 and 1.53 % thereafter. The remaining seven metabolites were detected in the extractable fractions throughout the study. Met-1 (0.29-0.65 % of the applied radioactivity), Met-3 (0.43-1.98 % of the applied radioactivity) and Met-4 (0.27-0.50 % of the applied radioactivity) were isolated by preparative TLC.

The HPLC analysis of the TLC region (Band C) of Met-2 showed that it consisted of at least five components including cis and trans-p-tertiarybutylphenoxy cyclohexanol (TBPC), Omite^® and two unknown metabolites. The LC/MS analysis of the unknown metabolites suggested that they may be structural isomers of the parent compound. Co-chromatography of Met-1 showed that this substance was the dimeric degradation product of Omite^®. Co-chromatography of Met-4 showed that this substance was p-tertiarybutyl phenol (PTBP). LC/MS analysis suggested that Met-5 was a derivative of Omite^® in which one of the methyl groups at the tertiary butyl position is oxidised to an acid. The remaining metabolites were considered to be less significant with none exceeding 0.5 % of the total soil residue.

Soil-bound residues, increasing gradually as the study progressed, reached 32.96 % of the applied dose by day 365. Day 120 and day 365 post-extraction solids (PES i.e. 25.30 and 32.96 % of the applied radioactivity, respectively) were subjected to acid treatment consisting of an initial extraction in acetonitrile:water (4:1) containing 1 % HCl followed by acid hydrolysis in refluxing 0.25 N HCl. The procedures released a minor amount of radioactivity (13.84 and 22.91 % of the radioactivity in PES for day 120 and 6.39 and 14.13 % of the radioactivity in PES for day 365) into the aqueous media. The majority of the CH₃CN/acidic water fraction could be extracted with an organic solvent (EtOAc-2 fraction). TLC analysis of this fraction showed the presence of Met-8 and Omite® as major components, in addition to Met-1 to Met-5 and Met-7. Approximately half of the radioactivity in the hydrolysate-1 fraction after 0.25 N HCl hydrolysis was extractable with ethyl acetate (EtOAc-3 fraction). TLC analysis of this EtOAc-3 fraction showed the presence of Omite^® and metabolites Met-1 and Met-3 to Met-8. Bound residue characterisation of the remaining acid-released bound residues in the day 120 and day 365 PES samples using various techniques yielded 5.99 and 4.34 % of the total radioactivity as fulvic acid, 8.02 and 14.05 % as humic acid and 2.00 and 7.80 % as humins, respectively.

Description of key information

The mean half-life of propargite was determined to be 61.6 days from a number of aerobic studies performed in line with guidelines (Directive 95/36/EC; EPA Guidelines, Subdivision N, Section 162-1; BBA Richtlinie Teil IV, 4-1) considered to be equivalent or similar to OECD 307.

The half-life of propargite was determined to be 64.4 days in an anaerobic study performed in line with EPA Guidelines, Subdivision N, Section 162-2.

Key value for chemical safety assessment

Half-life in soil:

61.6 d

Additional information

The rate of aerobic soil degradation of propargite was investigated in five soils (silt loam, loamy sand, sandy loam, sandy clay loam and silty clay loam) at 20-25 ºC in the dark. Respective DT50 (and DT90) values were 90.74 (301.43), 55.53 (184.48), 39.5 (131), 53.3 (177.1) and 168 (559) days were reported. However, the last value was obtained from a study of extended duration (365 days) in which the kinetics appeared to be biphasic, probably due to a loss of microbial viability in the latter phase of the study. When the first-order degradation rate was re-calculated for the first 59 days of the study (i.e. during the microbially active phase), DT50 and DT90 values of 67.2 and 223 days, respectively, were calculated. These values are more consistent with DT50/90 values reported for the other four laboratory soils and with data obtained in field dissipation trials. Therefore, the mean DT50 was calculated to be 61.6 days with the mean DT90 to be 203.4 days. There was no evidence of soil conditions affecting the rate of degradation.