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Biodegradation in soil

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Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
key study
Study period:
2000-08-21 - 2000-11-29 (experimental phase)
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: Commission Directive 95/36/EC amending Council Directive 91/414/EEC: Annex II:7.1 Fate and Behaviour in soil, 7.1.1.2 Rate of degradation
Qualifier:
according to guideline
Guideline:
other: Society of Environmental Toxicology and Chemistry (SETAC), 1995. Procedures for assessing the environmental fate and ecotoxicity of pesticides, ISBN 90-5607-002-9.
GLP compliance:
yes
Remarks:
except sediment characterisation carried out at AGROLAB AG, Switzerland
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Remarks:
in the dark
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
silt loam
% Clay:
11.36
% Silt:
50.46
% Sand:
38.18
% Org. C:
2.35
pH:
7.2
CEC:
15.7 meq/100 g soil d.w.
Bulk density (g/cm³):
0.95
Soil no.:
#2
Soil type:
sandy loam
% Clay:
6.5
% Silt:
22.1
% Sand:
71.5
% Org. C:
1
pH:
7.5
CEC:
6.2 meq/100 g soil d.w.
Bulk density (g/cm³):
1.26
Details on soil characteristics:
soil #1 (Gartenacker):
- Origin: Gartenacker, Les Barges, Vouvry, VS, Switzerland; soil classification given in report: loam/silt-loam)
- maximum water holding capacity (MWC; g water /100 g dry soil): 67.9
- microbial biomass (mg C / 100 g soil):
at start: 65.3
after 56 days (incubation): 55.9

soil #2 (Pappelacker):
- Origin: Pappelacker, Les Barges, Vouvry, VS, Switzerland
- maximum water holding capacity (MWC; g water /100 g dry soil): 44.1
- microbial biomass (mg C / 100 g soil):
at start: 29.4
after 56 days (incubation): 22.6

The soils have been freshly sampled (May 2000).

Soil preparation: Before use the soils were partially air-dried at room temperature and passed through a 2mm sieve. After treatment the moisture content was adjusted to 40% of the maximum water holding capacity.
Soil No.:
#1
Duration:
56 d
Soil No.:
#2
Duration:
56 d
Soil No.:
#1
Initial conc.:
0.1 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
0.1 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 °C
Humidity:
40 % maximum water holding capacity (MWC)
Microbial biomass:
at start: 65.3 mg C / 100 g soil; after 56 days (incubation): 55.9 mg C / 100 g soil
Soil No.:
#2
Temp.:
20 °C
Humidity:
40 % maximum water holding capacity (MWC)
Microbial biomass:
at start: 29.4 mg C / 100 g soil; after 56 days (incubation): 22.6 mg C / 100 g soil
Details on experimental conditions:
Apparatus:
Soil samples were incubated in 300 ml Erlenmeyer flasks equipped with a trapping system.
The samples were incubated under ventilation with moistened air (flow-rate: about 50 ml/min) in incubation chambers (open gas-flow system). The effluent air was passed through a trapping system consisting of two absorption bottles each containing 50 ml 2 N NaOH.

Sample Size:
75 g soil (dry weight) per treated system.
For each biomass determination 660 g soil (dry weight) were used. Prior to analysis the water content of the soil was determined. Thus, three flasks (1 litre Steilbrust) each with about 220 g soil were incubated for each biomass analysis. The samples received the equivalent amount of vehicle (acetone) as the treated samples.

Number of Samples:
Soil #1: Treated: 24 (including 4 reserve samples), Untreated Biomass: 3
Soil #2: Treated: 24 (including 4 reserve samples), Untreated Biomass: 3

Absorption Solutions:
The absorption solutions was be changed at the sampling days or in two weeks intervals.

Moisture Content:
The soil moisture was adjusted to 40 % of its maximum water holding capacity (MWC). The soil moisture was checked and adjusted, if necessary, every week during the first month and thereafter in intervals of about two weeks.

Incubation Temperature:
Soil samples were incubated in the dark at 20 ± 0.1 °C.
The temperature was continuously monitored during incubation.

Treatment: The test substance was added individually to the soil samples at a quantity corresponding to 0.1 mg/kg (based on soil dry weight). The test substance was added as acetone solution to the soil, whereby not more than 0.5 ml acetone / 100 g dry soil was used. After treatment the soil moisture content was adjusted to 40 % of its MWC. Then the incubation flasks were connected to the open air-flow system and incubated in climatic chambers at 20°C.

Sampling:
Soil: Soil samples were taken for work-up and analysis immediately after treatment (day 0) and 0.2, 1, 3, 7, 14, 28 and 56 days after application.
Absorption Solutions: The absorption solutions were exchanged at the sampling dates or in two-weeks intervals.
Microbial Biomass of Soils: The microbial biomass of each soil type was determined at the beginning and at the end of the study.

Sample Preparation and Extraction Procedure
Extraction of Soil Samples, at Room Temperature: The soils were extracted four times with acetone/buffer pH 4.65 (80/20, v/v; about 2 ml/g soil) or acetone/water (80/20, v/v, from day 14 on) under strong agitation (300 rpm) for 30 min. After each extraction step, the suspensions were centrifuged at 2000 rpm for 10 minutes at 20 °C and the radioactivity determined in the supernatants. Thereafter extracts were combined and concentrated under reduced pressure. Aliquots of the concentrates were directly analysed by HPLC and/or TLC.

Extraction of Soil Samples, Soxhlet Extraction: The extraction of soil samples was completed by Soxhlet extraction with acetone over 2-3 hours. Due to the low amount of radioactivity found in Soxhlet extracts (<0.5%) no further extraction was performed with samples from day 3 on.

Harsh Extractions: After Soxhlet extraction, soil samples of incubation day 56 were further submitted to harsh extractions:
a) First step: Extracted soil was air dried, pulverised and thereafter aliquots of 20 g suspended in about 180 ml acetonitrile / water (4/1, v/v) and refluxed at 80°C in a round bottomed flask for four hours under stirring. After centrifugation (2500 rpm, 10 min) the solvent was decanted, filtered through a fluted filter paper and the volume and radioactivity determined. Finally the remaining radioactivity in the soil was determined by combustion.
b) Second step: The second extraction step was performed by adding about 40 ml acetonitrile/0.1 N HCl (9/1, v/v) to 20g of the same soil sample and refluxing it again for two hours. After centrifugation, the solvent was decanted, filtered through a fluted filter paper and the volume and radioactivity determined.

Organic Matter Fractionation: The fractionation of soil organic matter was performed according to the procedure described in Stevenson, F.J. (1965) “Methods of Soil Analysis”, edited by Black, B.A.. et al., Am. Soc. Agron. Vol. 2, 1409 - 1421.
After the harsh extraction procedures the remaining soil sample was mixed with about 50 ml 0.5 N aqueous NaOH solution and extracted by shaking at room temperature for about 17 hours at 300 rpm followed by centrifugation at 2500 rpm for 10 min. To the decanted supernatant concentrated HCl was added until a pH ≤1 was reached. The resulting suspension was centrifuged as described above, the supernatant decanted, the volume determined (fulvic acid fraction) and the radioactivity determined. The remaining solid (humic acid fraction) was dissolved in ca. 40 ml 0.5 N NaOH and also radioassayed by LSC.
The insoluble humin fraction was determined by subtraction the radioactivity released by basic treatment from the residual radioactivity remaining in the soil after harsh extraction.

Determination of Non-extractables: Residual radioactivity remaining in the soil after extraction was determined by combustion and LSC. For this purpose, samples were air-dried, homogenised and then three aliquots of about about 0.5 g to 1g each combusted in a stream of oxygen at about 900 °C with copper oxide as catalyst (OX-500 sample oxidiser, R. J. Harvey Instrument Corporation, Hillsdale, New Jersey). The liberated 14CO2 was trapped in 15 ml Scintillator and submitted to LSC measurement.
Soil No.:
#1
% Recovery:
99
St. dev.:
0.6
Remarks on result:
other: min: 98.0%, max: 99.9%, n: 8
Soil No.:
#2
% Recovery:
98.8
St. dev.:
0.9
Remarks on result:
other: min: 97.8%, max: 100.5%, n: 8
Key result
Soil No.:
#1
% Degr.:
ca. 98
Parameter:
radiochem. meas.
Sampling time:
56 d
Key result
Soil No.:
#2
% Degr.:
ca. 95
Parameter:
radiochem. meas.
Sampling time:
56 d
Key result
Soil No.:
#1
DT50:
0.2 d
Type:
other: first-order two compartment
Temp.:
20 °C
Key result
Soil No.:
#2
DT50:
0.2 d
Type:
other: first-order two compartment
Temp.:
20 °C
Transformation products:
yes
No.:
#1
Details on transformation products:
IUPAC name: [(5-chloroquinolin-8-yl)oxy]acetic acid
CAS#: 88349-88-6
CAS name: Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-
Molecular Formula: C11H8ClNO3
Molar mass: 237.639 g/mol
SMILES notation: O=C(O)COc1ccc(Cl)c2cccnc12
InChI: InChI=1S/C11H8ClNO3/c12-8-3-4-9(16-6-10(14)15)11-7(8)2-1-5-13-11/h1-5H,6H2,(H,14,15)
Structural formula: see attachment in Illustration (picture/graph)
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes
Details on results:
For further details see Tables 1-6 (given further below).
x% AR: x% of the applied radioactivity

soil #1 (Gartenacker):
CO2: 13.0% AR after 56 days
extractables: 98.2% AR (after 0 d), 5.5% AR (after 56 d)
non-extractables: 1.7% AR (after 0 d), 79.4% AR (after 56 d)
main degradation product: CGA153433, maximum found: 19.3 % AR (after 0.21 d), 18.4% AR (after 3 d)
Cloquintocet-mexyl: DT50: 0.2 d, DT90: 1.0 d (first-order two compartment model)
Metabolite: DT50: 9.7 d, DT90: 32.2 d (formation & decline, single first order model)

soil #2 (Pappelacker):
CO2: 5.7% AR after 56 days
extractables: 98.9% AR (after 0 d), 8.2% AR (after 56 d)
non-extractables: 1.6% AR (after 0 d), 84.7% AR (after 56 d)
main degradation product: maximum found: 32.9% AR (after 1 d)
Cloquintocet-mexyl: DT50: 0.2 d, DT90: 1.0 d (first-order two compartment model)
Metabolite: DT50: 5.5 d, DT90: 18.2 d (formation & decline, single first order model)

Harsh (neutral: water-acetonitrile) extraction of selected soil samples from day 56 of incubation removed only little radioactivity (Gartenacker: 3.2%, Pappelacker: 3.3% of the applied radioactivity, AR). Harsh (acidic) extraction with acetonitrile / 0.1 N HCl liberated additional 0.8 % (Gartenacker) and 2.2% AR. Due to the verly low amounts of radioactivity no further analyses were performed with the various harsh extracts.

Subsequent organic matter fractionation released 16.6% (Gartenacker soil) and 13.7% (Pappelacker soil) AR as fulvic acids from non-extractables. Humic acids represented 6.2 % (Gartenacker) and 4.8% (Pappelacker) AR. The insoluble humin fraction amounted to 52.6% (Gartenacker) and 60.6% (Pappelacker) AR.

Table 1: Degradation parameters of CGA185072 in two agricultural soils incubated under aerobic conditions

Soil

Gartenacker

Pappelacker

A10 (% of applied radioactivity)

93.7

89.6

A20 (% of applied radioactivity)

4.5

9.2

k1 (days-1)

2.961

4.828

k2 (days-1)

0.010

0.002

DT50 (days)

0.2

0.2

DT90 (days)

1.0

1.0

A(t)=A10*exp(-k1*t) + A20*exp(-k2*t)

A: CGA185072

 

 

Table 2: Degradation parameters of CGA153433 in two agricultural soils incubated under aerobic conditions

Soil

Gartenacker

Pappelacker

A0 (% of applied radioactivity)

20.1

36.1

k1 (days-1)

16.689

5.336

k2 (days-1)

0.071

0.127

DT50 (days)

9.7

5.5

DT90 (days)

32.2

18.2

B(t)=A0*k1/(k2-k1)*(exp(-k1*t)-exp(-k2*t))

A: CGA185072, B: CGA153433

 

 

Table 3: Balance of Radioactivity Applied to Soil Treated with14C-CGA185072 - Gartenacker Soil
Values in percent of the applied radioactivity. All Values are mean of duplicate samples.

Incubation Time (days)

0

0.21

1

3

7

14

28

56

Extractables

 

 

 

 

 

 

 

 

               Extractables

98.16

42.98

28.51

22.97

22.77

14.15

10.15

5.49

               Soxhlet

0.00

0.33

0.09

0.00

0.00

0.00

0.00

0.00

               Subtotal

98.16

43.32

28.60

22.97

22.77

14.15

10.15

5.49

Non-extractables

1.70

56.40

70.12

76.26

75.46

82.63

82.50

79.44

CO2

0.00

0.00

0.01

0.17

0.55

1.89

6.03

13.01

Total:

99.86

99.71

98.74

99.40

98.78

98.66

98.69

97.95

 

 

Table 4: Balance of Radioactivity Applied to Soil Treated with14C-CGA185072 - Pappelacker Soil
Values in percent of the applied radioactivity. All Values are mean of duplicate samples.

Incubation Time (days)

0

0.21

1

3

7

14

28

56

Extractables

 

 

 

 

 

 

 

 

               Extractables

98.90

65.55

47.11

31.25

30.99

14.19

11.15

8.24

               Soxhlet

0.00

0.28

0.23

0.00

0.00

0.00

0.00

0.00

               Subtotal

98.90

65.83

47.33

31.25

30.99

14.19

11.15

8.24

Non-extractables

1.59

33.47

51.91

66.95

66.63

83.08

84.09

84.69

CO2

0.00

0.00

0.02

0.12

0.31

1.03

2.52

5.69

Total:

100.49

99.31

99.27

98.32

97.93

98.31

97.76

98.63

 

 

Table 5: Pattern of CGA185072 and its Metabolites in Soil - Gartenacker Soil.
Values in percent of the applied radioactivity. All Values are mean of duplicate samples.

Time (days)

CGA185072

CGA153433

UK1

UK2

UK3

UK4

UK5

UK6

NA

Total

0

98.16

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

98.16

0.21

23.69

19.30

0.00

0.00

0.00

0.00

0.00

0.00

0.33

43.32

1

9.26

15.84

0.87

1.64

0.68

0.22

0.00

0.00

0.09

28.60

3

4.10

18.41

0.33

0.12

0.00

0.00

0.00

0.00

0.00

22.96

7

4.05

15.75

1.50

1.15

0.33

0.00

0.00

0.00

0.00

22.77

14

3.72

5.18

3.84

0.49

0.36

0.27

0.29

0.00

0.00

14.15

28

4.44

0.98

0.20

0.62

0.00

0.00

0.24

3.67

0.00

10.15

56

1.97

1.40

0.74

0.69

0.00

0.00

0.00

0.69

0.00

5.49

UK1, ..., UK6, NA: unknown compounds (not further analysed)

 

 

Table 6: Pattern of CGA185072 and its Metabolites in Soil - Pappelacker Soil.
Values in percent of the applied radioactivity. All Values are mean of duplicate samples.

Time (days)

CGA185072

CGA153433

UK1

UK2

UK3

UK4

UK5

UK6

NA

Total

0

98.90

0.00

0.00

0.00

0.00

0.00

0.00

0.00

0.00

98.90

0.21

41.62

23.93

0.00

0.00

0.00

0.00

0.00

0.00

0.28

65.83

1

11.20

32.92

2.38

0.62

0.00

0.00

0.00

0.00

0.23

47.33

3

8.96

21.73

0.25

0.21

0.09

0.00

0.00

0.00

0.00

31.25

7

8.05

22.59

0.00

0.29

0.07

0.00

0.00

0.00

0.00

30.99

14

7.80

0.48

5.05

0.49

0.25

0.12

0.00

0.00

0.00

14.19

28

10.35

0.35

0.00

0.25

0.00

0.00

0.00

0.21

0.00

11.15

56

5.33

0.84

0.80

0.37

0.00

0.00

0.18

0.71

0.00

8.24

UK1, ..., UK6, NA: unknown compounds (not further analysed)

 

Conclusions:
The substance dissipated rapidly from aerated soils at 20 °C.
Executive summary:

The metabolism and rate of degradation of cloquintocet-mexyl under aerobic conditions in two soils at 20 °C and a humidity of 40% of the maximum water holding capacity was studied under GLP to a guideline similar to OECD TG 307. The kinetics of formation and decline of its major degradate [(5-chloroquinolin-8-yl)oxy]acetic acid were also studied.

Two soils were used in the study, a loam/silt loam (Gartenacker) and a loamy sand (Pappelacker), which were kept at a humidity of 40% of the maximum holiding capacity. Test substance was applied at a concentration of about 0.1 mg/kg soil dw. The test was conducted at a temperature of 20 °C, for a period of 56 days. 

The DT-50 value (degradation, first-order two compartment model) of the test substance was determined as 0.2 days in both soils.

Besides the parent substance, one major metabolite ([(5-chloroquinolin-8-yl)oxy]acetic acid) was detected, reaching its highest concentration after 3 days and 1 day with 18.4% and 32.9% in Gartenacker and Pappelacker soil, respectively. At the end of the study its concentration in both soils was 1.4% and 0.8% of the applied radioactivity. Its half-life was found to be 9.7 and 5.5 days, for Gartenacker and Pappelacker soil, respectively. All other metabolites were ≤5% of the applied radioactivity.

From day three of the study on significant formation of carbon dioxide was observed. At the end of the study (i.e. after 56 days) carbon dioxide amounted to 13.0% and 5.7% for Gartenacker and Pappelacker soil, respectively. These figures indicate significant mineralisation of the quinoline-ring moiety. Non-extractables residues increased from 1.7% and 1.6% at day 0 to 79.4% and 84.7% of the applied radioactivity at day 56 for Gartenacker and Pappelacker soil, respectively.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1990-02-20 – 1991-03-26 (experimental phase)
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: Richtlinie für die amtliche Prüfung von Pflanzenschutzmitteln; Teil IV, 4 - 1: Verbleib von Pflanzenschutzmitteln im Boden - Abbau, Umwandlung und Metabolismus; Stufe 1; Biologische Bundesanstalt fur Land- und Forstwirtschaft, Bundesrepublik Deutschland,
Qualifier:
according to guideline
Guideline:
other: Environmental Chemistry and Fate Guidelines for Registration of Pesticides in Canada; Section 6.2.C: Biotransformation; 1. Soil - Degradation Pathways and Persistence, July 15, 1987.
Qualifier:
according to guideline
Guideline:
other: Danish Law of the Ministry of Environment, September 1, 1987.
Qualifier:
according to guideline
Guideline:
other: Dutch Registration Guidelines, January 1980, Section G.1: Behaviour in the Soil.
GLP compliance:
yes
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
loamy sand
% Clay:
5.7
% Silt:
38.4
% Sand:
55.9
% Org. C:
2.7
pH:
6
CEC:
10 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
sandy loam
% Clay:
6.2
% Silt:
34.7
% Sand:
59.1
% Org. C:
2.3
pH:
6.9
CEC:
6.3 meq/100 g soil d.w.
Details on soil characteristics:
soil #1:
- German Standard Soil 2.2 (supplied by LUFA Speyer, origin: Neuhausen, Germany; reported as "loamy sand")
- maximum water holding capacity (g water /100 g dry soil): 52.1
- field capacity (g water /100 g dry soil): 30.6
- microbial biomass (mg C / 100 g soil):
at start: 28
after 84 days (incubation): 0
after 168 days (incubation): 3

soil #2:
- Sandy Loam (origin: Mosimannacker, Les Barges, VS, Switzerland)
- maximum water holding capacity (g water /100 g dry soil): 46.9
- field capacity (g water /100 g dry soil): 31.3
- microbial biomass (mg C / 100 g soil):
at start: 84
after 84 days (incubation): 17
after 168 days (incubation): 17

The soils were stored in the greenhouse under natural conditions to keep biologically active until use.

Soil preparation: Before use the soils were partially air-dried at room temperature and passed through a 2mm sieve. After treatment the moisture content was adjusted to 40% of the maximum water holding capacity.
Soil No.:
#1
Duration:
336 d
Soil No.:
#2
Duration:
336 d
Soil No.:
#1
Initial conc.:
ca. 1 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
ca. 1 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 °C
Humidity:
40% MWHC
Soil No.:
#2
Temp.:
20 °C
Humidity:
40% MWHC
Details on experimental conditions:
Test system:
75 g soil samples (dry weight) were weighed into 150 ml crystallisation dishes and incubated in incubation chambers. They were continuously ventilated with moistened air with a flow rate of about 100 ml/min. The outcoming air was passed through four absorption flasks, two containing 100 ml 2N NaOH, one ethyleneglycol and the other one 0.1N H2S04,
For the measurement of the biomass 100 g soil samples (dry soil weight) were incubated as described above.

Temperature:
The soil was incubated at 20°C in the dark.

Soil Moisture:
The soil moisture held at 40 % of the water holding capacity is corresponding to 17.2 % and 15.8 % water in soil (or 20.8 and 18.8 g water per 100 g dry soil) Neuhofen and Mosimannacker, respectively.

Concentrations:
The test substance was applied at a concentration of ca. 1 mg/kg (based on dry soil).

Incubation: The soil samples were incubated at 20 ± 2°C in the dark. Soil moisture was checked regularly and water added if necessary.

Sampling: Soil samples were taken for analysis immediately after application and after 7, 14, 28, 56, 84, 168, 252 and 336 days.
The absorption solutions were exchanged and analyzed for radioactivity in weekly intervals during the first month and thereafter in about two weeks intervals.

Extraction procedure and analysis: The soil was transferred into a 250 ml centrifuge tube and extracted twice for 30 min by shaking with 100 ml of a methanol-water mixture (80:20). Thereafter, the suspensions were centrifuged at about 4000 rpm for 5 min at 20°C and the supernatant filtered into a round bottom flask. The extracts were concentrated using a vacuum evaporator. Aliquots were analysed for radioactivity. The extraction was completed by refluxing the soil with acetone for 4 - 5 hours in a Soxhlet apparatus. The Soxhlet-extract was concentrated and the radioactivity determined in aliquots. The extracts were analysed by TLC. The extracted soil was air-dried, weighed, homogenized and the residual activity determined by combustion and LSC.
Soil No.:
#1
% Recovery:
93.1
St. dev.:
2.9
Remarks on result:
other: n=9, min 89.9%, max 98.6, mean 93.1%, std. dev. (abs) 2.9%
Soil No.:
#2
% Recovery:
96
St. dev.:
1.7
Remarks on result:
other: n=9, min 93.5%, max 99.3, mean 96.0%, std. dev. (abs) 1.7%
Key result
Soil No.:
#1
DT50:
2.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Key result
Soil No.:
#2
DT50:
1.3 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Transformation products:
yes
No.:
#1
Details on transformation products:
#1:
IUPAC name: [(5-chloroquinolin-8-yl)oxy]acetic acid
CAS#: 88349-88-6
CAS name: Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-
Molecular Formula: C11H8ClNO3
Molar mass: 237.639 g/mol
SMILES notation: O=C(O)COc1ccc(Cl)c2cccnc12
InChI: InChI=1S/C11H8ClNO3/c12-8-3-4-9(16-6-10(14)15)11-7(8)2-1-5-13-11/h1-5H,6H2,(H,14,15)
Structural formula: see attachment in Illustration (picture/graph)
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes
Details on results:
For details see Tables 1-3

The 14C02-formation increased steadily during the experiments reaching 2.8% (Neuhofen soil) and 17.8 % (Mosimannacker soil) of the applied radioactiviy.

The non-extractable radioactivity reached values of 80.0% (Neuhofen soil) and 81.3% (Mosimannacker soil) of the applied radioactivity after 7 days of incubation. In the biologically more active Mosimannacker soil a decrease of the bound radioactivity was observed after 168 days.

Table 1: Disappearance times for the substance CGA185072 and its main transformation product CGA153433

CGA185072

CGA153433

DT50
[days]

DT90
[days]

DT50
[days]

DT90
[days]

German Standard Soil 2.2 (Neuhofen)

2.4

8.1

Sandy Loam Soil (Mosimannacker), original report

1.3

4.2

Sandy Loam Soil (Mosimannacker), re-evaluation

1.1

3.6

72.4

260.4

DT 50/90 = Disappearance Time for 50% respectively 90% of the compound.

 

 

Table 2: Dissipation of CGA185072 in German Standard Soil 2.2 (Neuhofen under Aerobic Conditions (Values listed are given in % of the dose applied)

Time
(days)

Extractable

Non-extractable

14CO2

Total
(Recovery)

CGA185072

CGA153433

(acid)

0.01

95.6

3.0

---

98.6

95.6

n.d.

7

15.7

80.0

< 0.1

95.7

11.7

4.0

14

12.2

77.7

< 0.1

89.9

6.6

5.6

28

10.3

84.5

0.1

94.9

5.8

4.6

56

8.1

84.2

0.2

92.5

2.7

4.5

84

7.4

82.2

0.3

89.9

2.5

4.9

168

6.6

85.2

1.1

92.9

2.4

3.8

252

6.1

83.8

1.9

91.8

1.9

3.7

336

4.8

84.0

2.8

91.6

1.7

2.6

n.d. = not detected

 

 

Table 3: Dissipation of CGA185072 in a Sandy Loam Soil (Mosimannacker) under Aerobic Conditions (Values listed are given in % of the dose applied)

Time
(days)

Extractable

Non-extractable

14CO2

Total
(Recovery)

CGA185072

CGA153433

(acid)

0.01

93.3

3.5

---

96.8

93.3

n.d.

7

17.8

81.3

0.2

99.3

1.9

15.9

14

14.6

81.3

0.3

96.2

1.3

13.2

28

15.7

80.6

0.7

97.0

1.2

14.5

56

13.4

81.1

1.8

96.3

0.2

10.9

84

10.1

82.3

3.3

95.7

0.5

8.9

168

6.6

80.1

8.5

95.2

0.4

5.1

252

4.5

76.1

13.4

94.0

0.6

2.7

336

3.2

72.5

17.8

93.5

0.6

1.6

n.d. = not detected

Conclusions:
The substance degrades rapidly in soils under aerobic conditions.
Executive summary:

The degradation of cloquintocet-mexyl was studied in the German Standard Soil 2.2 (Neuhausen, loamy sand) and a Sandy Loam (Mosimannacker) under aerobic conditions at 20 °C at an initial concentration of about 1 mg/kg. The substance degraded with dissipation times (DT50, single first order kinetics) of 2.4 and 1.3 days for soils Neuhofen and Mosimannacker, respectively. The DT50 for the second soil from Mosimannacker was re-calculated in a later study and determined to be 1.1 days.

The main degradation product was [(5-chloroquinolin-8-yl)oxy]acetic acid, which appeared transiently, and in the sandy loam also carbon dioxide. The 14C02-formation increased steadily during the experiments reaching 2.8 and 17.8% of the applied dose in soil Neuhofen and Mosimannacker, respectively, after 336 days of incubation, thus demonstrating the low microbial activity of the German Standard Soil. Other degradation products were found in very low amounts only.

In soil Mosimannacker, the main metabolite degraded with a DT50 of 72.4 days (single first order kinetics). In soil Neuhofen, most probably due to its low biological activity, the degradation kinetics of the main metabolite could not be evaluated.

After 7 days of incubation the non-extractable radioactivity reached values of 80.0 and 81.3% in soils Neuhofen and Mosimannacker, respectively. In the microbiologically more active soil Mosimannacker the bound radioactivity started to decrease after 168 days.

The results indicate that the disappearance of cloquintocet-mexyl in soils is due to mineralization by soil microorganisms and to the formation of soil non-extractables by the compound and/or the acid.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1990-02-28 - 1991-05-22 (experimental phase)
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: Pesticide Assessment Guidelines, Subdivision N, Chemistry: Environmental Fate. Guidelines 162-1 and 162-2: Aerobic and Anaerobic Soil Metabolism Studies. (U.S.) Environmental Protection Agency, Washington, DC., October 18, 1982.
GLP compliance:
yes
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic/anaerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
sand
% Clay:
8.7
% Silt:
0
% Sand:
91.3
% Org. C:
2.3
pH:
7.3
CEC:
12.8 meq/100 g soil d.w.
Soil no.:
#2
Soil type:
loam
% Clay:
23.1
% Silt:
40.2
% Sand:
36.7
% Org. C:
3.2
pH:
6.5
CEC:
19.7 meq/100 g soil d.w.
Details on soil characteristics:
soil #1:
- origin: Collombey (VS, Switzerland)
- maximum water holding capacity (MWC): 38.7 g water / 100 g dry soil
- field capacity (FC): 27.2 g water / 100 g dry soil
- microbial biomass (mg C/100g soil)
at start: 339
after 84 d: 51
after 168 d: 48
after 350 d: 47

soil #2:
- origin: Les Evouettes (VS, Switzerland)
- maximum water holding capacity (MWC): 86.1 g water / 100 g dry soil
- field capacity (FC): 56.9 g water / 100 g dry soil
- microbial biomass (mg C/100g soil)
at start: 67
after 84 d: 96
after 168 d: 55
after 350 d: 50

Soil preparation: Before use the soils were partly air-dried at room temperature to a humidity suitable for sieving through a 2 mm sieve. Thereafter an aliquot was taken for determination of the initial microbial biomass. The remaining soil was stored until treatmint at ca. 4 °C.

For experiments under aerobic-sterile conditions: Sieved soil (200 g on a dry weight basis) was placed into Steilbrust flasks and sterilized by autoclaving. Until treatment soil samples were kept under sterile conditions at room temperature.
Soil No.:
#1
Duration:
350 d
Soil No.:
#2
Duration:
350 d
Soil No.:
#1
Initial conc.:
ca. 1 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#2
Initial conc.:
ca. 1 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 °C
Soil No.:
#2
Temp.:
20 °C
Details on experimental conditions:
Aerobic, aerobic/anaerobic and sterile/ aerobic at 20 °C in a loamy sand(Les Evouettes) and under aerobic conditions 20 °C in a sandy soil (Collombey).

Metabolism apparatus
open gas-flow system with the following components:
- gas washing bottle filled with distilled water to saturate the incoming air
- needle valve for adjustment of the air flow rate
- 1-liter glass bottle (Steilbrust) containing the treated soil
- gas absorption bottles filled with 50 mL ethylene glycol, sulfuric acid (0.1 N) and sodium hydroxide (2 N) to trap volatiles and radioactive carbon dioxide.
- flow meter measuring the gas flow rate

Aerobic and aerobic/anaerobic Incubation:
200 g soil samples (dry weight) for each sampling interval were transferred to 1 liter Steilbrust flasks and thereafter 5.0 mL of the application solution (solvent: acetone/water) added to the soil surface by means of a pipette. Afterwards the soil was mixed thoroughly. By this procedure a CGA185072-concentration of 1.1 mg/kg (calculated on dry soil) was achieved.
After completion of the treatment, the soil moisture was adjusted with deionized water to 75% of its field capacity.

Aerobic/sterile Incubation:
The sterile soil samples were treated with 5.0 mL of the application solution (solvent: acetone/water) each under aseptic conditions by using sterile glass ware and ultramembrane filter. The amount of radioactivity remaining in the filters and glassware was washed out with ethanoVwater (1+1) and determined by LSC. The resulting countings were subtracted from the determined amount in the 5.0 ml of application solution. After treatment the soil moisture was adjusted to 75% field capacity by adding sterile water. Finally the flasks were connected to the other parts of the metabolism apparatus in a way that sterile conditions were maintained.

Incubation
The incubation (Steilbrust) flasks were connected to the other parts of the metabolism apparatus which were installed in an incubation chamber held at 20±2 °C. The room was kept in the dark. For sterile incubation, the inlet was connected to a sterile ultra-membrane and the outlet was protected against infections by a sterile cotton wool plug. Thereafter, the aerobic and aerobic/sterile experiments were continuously ventilated with moist air at a flow rate of about 60 ml/min.
For anaerobic incubation, the soils were flooded with a water layer of 2-3 cm (about 200 mL) after an aerobic pre-incubation period of 28 days and thereafter ventilated four times per day with nitrogen for about 15 minutes at a flow rate of about 60 ml/min. During incubation soil moisture content of the soils was controlled and adjusted if necessary.

Sampling:
- absorption solutions were exchanged and monitored for radioactivity in intervals of one week during the first month and thereafter in two-weeks intervals.
- soil samples were taken for analysis up to about one year for the aerobic experiments and up to 120 days and 90 days for the aerobic/anaerobic and aerobic-sterile experiments.
- microbial biomass: untreated soil samples were taken prior to the treatment and 84, 168 and 350 days after treatment.

Extraction:
-extraction at room temperature: soil samples were extracted in 5 portions at room
- extraction at room temperature: Soil samples (about 180 g, wet) were extracted in 5 portions at room temperature by shaking (160 rpm) for about 30 minutes with methanol/deionized water 8+2 v/v (1-2 ml per g of soil) in 250 mL centrifuge tubes. Thereafter, the suspensions were centrifuged at 2500 rpm for 3 minutes at 20° C and the supernatant filtered into an adequate measuring cylinder. This extraction procedure was repeated four times. Filtered cold extracts were combined, their volumes recorded and triplicate aliquots submitted to radioactivity measurements by liquid scintillation counting (LSC).
Soxhlet Extraction: Following extraction at room temperature, soil sediments were combined and thereafter submitted to an extraction with methanol in a Soxhlet apparatus (about 2 mL/g of soil) for about 5 hours. The radioactivity in the the extract was determined by LSC. The extract was further analyzed when exceeding about 0.5 % of the dose applied. The residual radioactivity in the remaining soil sediment was determined by combustion.

Clean-up and Analysis of Extracts Cold Extracts: The combined extracts were concentrated to about 100 ml using a vacuum rotary evaporator with a water bath at 40 °C. The radioactivity in the extracts was determined by LSC. Aliquots of the extracts were analysed by TLC.
Soxhlet Extracts: The Soxhlet extract was concentrated as described for the cold extracts. Aliquots of these concentrates accounting for 0.6% or greater of the dose applied were submitted to analysis by TLC.
Water Layers of Anaerobic Studies: The water layers of anaerobic studies were decanted and their radioactivity determined. Neither under neutral nor under acidic conditions significant amounts were extractable from the water phases with dichloromethane. This indicated that no parent and no acid were present.

Isolation of Metabolites: The major metabolite from aerobic incubation of the test substance was isolated by liquid/liquid partition of acidified (pH 2 - 3) extracts with dichloromethane. Under these conditions the acid, and also the methylated acid was extractable. The methylation of the acid happened relatively easily, e.g. it was observed by concentrating methanolic extracts or by TLC with solvent systems containing methanol.
Soil No.:
#1
% Recovery:
93.7
St. dev.:
7.4
Remarks on result:
other: aerobic conditions
Soil No.:
#2
% Recovery:
92
St. dev.:
4.6
Remarks on result:
other: aerobic conditions
Key result
Soil No.:
#1
DT50:
0.5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Key result
Soil No.:
#1
DT50:
0.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Transformation products:
yes
No.:
#1
Details on transformation products:
IUPAC name: [(5-chloroquinolin-8-yl)oxy]acetic acid
CAS#: 88349-88-6
CAS name: Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-
Molecular Formula: C11H8ClNO3
Molar mass: 237.639 g/mol
SMILES notation: O=C(O)COc1ccc(Cl)c2cccnc12
InChI: InChI=1S/C11H8ClNO3/c12-8-3-4-9(16-6-10(14)15)11-7(8)2-1-5-13-11/h1-5H,6H2,(H,14,15)
Structural formula: see attachment in Illustration (picture/graph)
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes
Details on results:
see also Tables 1-8

Summary of kinetic results:
soil #1 (Collombey), aerobic conditions
DT50: 0.5 d; DT90: 1.7 d; k: 0.5235 / day

soil #2 (Les Evouettes), aerobic conditions
DT50: 0.4 d; DT90: 1.2 d; k: 0.3656 / day

soil #2 (Les Evouettes), aerobic-sterile conditions
DT50: 1328 d; DT90: 4413 d; k: 0.000522 / day


Under aerobic conditions extractable radioactivity steadily decreased from ca. 75% at starting time to ca. 6% of the applied radioactivity after 350 days. The non-extractable fraction increased in both soils up to 28 days reaching ca. 80% AR and decreased thereafter to amouints of 60-70 % AR after 350 days.

Under aerobic/anaerobic conditions (test withLes Evouettes soil) the extractable fraction decreased within the 28 days aerobic incubation period to 13.5 % AR. During anaerobic incubation no drastic changes were observed. At the end of the study after three months extractables accounted for 7.8% AR and the non-extractable radioactivity for 80.6 % AR.

Under aerobic-sterile conditions no significant changes in the amounts of extractable and non-extractable radioactivity were observed during 84 days of incubation.

Under aerobic incubation the evolution of 14-CO2 reached 19.9% AR (Collombey) and 27.5% AR (Les Evouettes) after 350 days of incubation. Only negligible amounts of volatile radioactivity other than CO2 were found.

Under aerobic/anaerobic conditions 14-CO2 was mainly observed during the aerobic phase, accounting for 4.1% AR. After the anaerobic phase a total of 5.8% AR was observed. The amounts of other volatile radioactive products were very low.

Under aerobic-sterile conditions practically no volatile radioactivity was observed (<0.2 % AR).

Under aerobic conditions the test substance showed a rapid breakdown.

Under aerobic/anaerobic conditions a rapid degradation was observed during the 28 days aerobic period. During the following two months of anaerobic incubation only minor amounts (ca. 1.5% AR) of the test substance were additionally brolen down.

Under aerobic-sterile conditions, the test substance degraded very slowly.

Under aerobic conditions, the main degradation product was CGA153433 (proven by co-chromatography with the corresponding reference substance). CGA153433 degraded with DT50 values of 19.3 d (Collombey soil) and 5.5 d (Les Evouettes soil).

An unknown polar metabolite was observed mainly in soil Collombey. It amounted to 8.9 % Ar after 28 days of aerobic incubation and decreased thereafter. Due to the low amount, no identification procedure was made. In addition at least two unknown metabolites were observed in amounts of max. 2.5% AR.

%AR: % of applied radioactivity

Table 1: Distribution of14C-Activity for the Degradation of CGA185072 in Soil Collombey (Sandy Soil) under Aerobic Conditions (Values listed are given in % of the radioactivity applied).

Time
(days)

Cold
extraction

Soxhlet
extraction

Non-extractable

14CO2

Combustion

Total
Recovery

0.5

73.96

0.47

21.16

100.0

95.59

7

25.21

0.30

72.08

0.41

103.5

98.00

14

22.11

0.42

75.71

1.20

94.9

99.44

28

20.88

0.38

80.77

1.68

89.7

103.71

56

16.01

0.57

68.48

6.33

85.0

91.39

84

12.86

0.58

66.29

9.26

83.3

88.99

168

7.70

0.46

59.30

12.19

69.8

79.65

350

5.37

0.42

67.36

19.90

68.0

93.05

 

 

Table 2: Analysis of CGA185072 and Metabolites in the Extracts from Soil Collombey under Aerobic Conditions (Values listed are given in % of the radioactivity applied).

Time
(days)

CGA185072

CGA153433

Unknown
met. A

Unknown
metabolites

Total
extractables

0

96.0 *

n.d.

 

 

 

0.5

49.47

24.48

n.d.

0.47

74.42

7

5.69

17.09

2.42

0.29

25.49

14

3.78

11.89

6.44

0.42

22.53

28

2.26

9.31

8.93

0.75

21.25

56

3.56

5.99

6.05

0.97

16.57

84

4.05

3.99

4.38

1.02

13.44

168

1.18

3.91

1.79

1.27

8.15

350

2.68

1.39

n.d.

1.72

5.79

n.d. = not detected                            * = application solution

 

 

Table 3: Distribution of14C-Activity for the Degradation of CGA185072 in Soil Les Evouettes (Loamy Soil) under Aerobic Conditions (Values listed are given in % of the radioactivity applied).

Time
(days)

Cold
extraction

Soxhlet
extraction

Non-extractable

14CO2

Combustion

Total
Recovery

0.5

74.72

1.28

21.08

93.0

97.08

7

18.12

0.43

77.18

0.43

96.8

96.30

14

15.10

0.57

74.44

1.63

92.2

91.75

28

12.84

0.71

77.44

4.09

90.0

95.08

56

9.20

0.74

72.55

7.75

83.0

90.23

84

8.16

0.34

73.05

8.67

80.7

90.20

168

5.93

0.52

60.97

15.32

73.6

82.74

350

5.03

0.64

59.26

27.47

66.2

92.40

 

 

Table 4: Analysis of CGA185072 and Metabolites in the Extracts from Soil Les Evouettes under Aerobic Conditions (Values listed are given in % of the radioactivity applied)

Time
(days)

CGA185072

CGA153433

Unknown
met. A

Unknown
metabolites

Total
extractables

0

96.0 *

n.d.

 

 

 

0.5

38.12

37.87

n.d.

n.d.

75.99

7

6.18

11.09

0.83

0.58

18.68

14

4.37

9.22

1.49

0.59

15.67

28

3.77

6.62

2.02

1.15

13.56

56

3.06

3.37

1.49

2.03

9.95

84

3.49

2.85

1.19

0.92

8.48

168

2.09

2.01

n.d.

2.34

6.44

350

1.64

1.53

n.d.

2.50

5.67

n.d. = not detected                            * = application solution

 

 

Table 5: Distribution of14C-Activity for the Degradation of CGA185072 in Soil Les Evouettes (Loamy Soil) under Aerobic / Anaerobic Conditions (Values listed are given in % of the radioactivity applied).

Time
(days)

Paddy-water

Cold
extraction

Soxhlet
extraction

Non-extractable

14CO2

Combustion

Total
Recovery

0.5

 

74.72

1.28

21.08

93.0

97.08

7

 

18.12

0.43

77.18

0.43

96.8

96.30

14

 

15.10

0.57

74.44

1.63

92.2

91.75

28

 

12.84

0.71

77.44

4.09

90.0

95.08

28

Installation of Anaerobic Conditions:

56

0.52

10.38

0.56

76.18

5.20

 

92.84

84

0.44

7.85

0.41

79.62

4.72

 

93.04

112

0.40

7.41

0.38

80.60

5.72

 

94.51

 

 

Table 6: Analysis of CGA185072 and Metabolites in the Extracts from Soil Les Evouettes under Aerobic / Anaerobic Conditions (Values listed are in % of the radioactivity applied)

Time
(days)

CGA185072

CGA153433

Unknown
met. A

Unknown
metabolites

Total
extractables

0.5

38.12

37.87

n.d.

n.d.

75.99

7

6.18

11.09

0.83

0.58

18.68

14

4.37

9.22

1.49

0.59

15.67

28

3.77

6.62

2.02

1.15

13.56

28

Installation of Anaerobic Conditions:

56

2.39

5.90

1.54

1.63

11.46

84

0.88

5.46

1.13

1.23

8.70

112

1.69

3.78

1.18

1.54

8.19

 

 

Table 7: Distribution of14C-Activity for the Degradation of CGA185072 in Soil Les Evouettes (Loamy Soil) under Sterile / Aerobic Conditions (Values listed are given in % of the radioactivity applied).

Time
(days)

Cold
extraction

Soxhlet
extraction

Non-extractable

14CO2

Combustion

Total Recovery

0.5

90.99

1.18

2.68

118.2

94.85

28

88.95

0.65

4.92

0.05

86.5

94.57

56

86.68

1.30

5.82

0.10

98.0

93.90

84

88.46

1.79

6.94

0.16

84.1

97.35

 

 

Table 8: Analysis of CGA185072 and Metabolites in the Extracts from Soil Les Evouettes under Sterile / Aerobic Conditions (Values listed are in % of the radioactivity applied)

Time
(days)

CGA185072

CGA153433

Unknown
metabolites

Total
extractable

0.5

92.17

n.d.

n.d.

92.17

28

88.96

n.d.

0.64

89.60

56

87.76

0.12

0.08

87.96

84

90.07

0.18

n.d.

90.25

 

Conclusions:
The substance dissipated rapidly from aerated soils at 20 °C.
Executive summary:

The degradation of cloquintocet-mexyl in soil under aerobic conditions was studied under GLP to guidelines similar to OECD TG 307. Degradation of the substance was tested in two soils, a sand from Collombey and a loam from Les Evouettes. The initial test concentration applied to the soil was about 1 mg/kg soil dw. The studies were conducted at a temperature of about 20 °C and the moisture of soil was adjusted to about 75% of natural moisture. The dissipation rate in the two soils under aerobic conditions was very fast, with observed half-lives of 0.6 days in Collombey sand (re-calculated value, original DT50 = 0.5 days) and 0.4 days in the loam from Les Evouettes. One major metabolite was observed, [(5-chloroquinolin-8-yl)oxy]acetic acid, which also dissipated quickly from the two soils with half-lives of 3 days and 2 days, respectively.

Endpoint:
biodegradation in soil
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1991-06-27 - 1992-06-23 (experimental phase)
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: Environmental Chemistry and Fate Guidelines for Registration of Pesticides in Canada; Section 6.2.C: Biotransformation; 1. Soil - Degradation Pathways and Persistence, July 15, 1987.
Qualifier:
according to guideline
Guideline:
other: Danish Law of the Ministry of Environment, September 1, 1987.
Qualifier:
according to guideline
Guideline:
other: Dutch Registration Guideline, Section G.l: Behaviour in Soil; Ministry of Agriculture and Fisheries, Ministry of Public Health and Environmental Hygiene, Ministry of Social Affairs, January 1987.
GLP compliance:
yes
Test type:
laboratory
Radiolabelling:
yes
Oxygen conditions:
aerobic
Soil classification:
USDA (US Department of Agriculture)
Soil no.:
#1
Soil type:
sandy loam
% Clay:
18.1
% Silt:
24.8
% Sand:
57.1
% Org. C:
1.26
pH:
7
CEC:
13.1 meq/100 g soil d.w.
Details on soil characteristics:
soil #1:
- source of soil: greenhouse Ciba-Geigy, Stein, AG, Switzerland (collection date: 1990-10-22)
- maximum water holding capacity (g water /100 g dry soil): 38.7
- field capacity (g water /100 g dry soil): 27.6
- microbial biomass (mg C / 100 g soil):
at start: 49.7
after 84 days (incubation): 50.0
after 168 days (incubation): 43.8

The soil was stored in the greenhouse under natural conditions (overgrown with grass) to keep it biologically active until use.


Soil preparation: Before use the soils were partially air-dried at room temperature and passed through a 2mm sieve. After treatment the moisture content was adjusted either to 38% of the field capacity (fc) or to 60 % fc.
Soil No.:
#1
Duration:
329 d
Soil No.:
#1
Initial conc.:
1.05 mg/kg soil d.w.
Based on:
test mat.
Soil No.:
#1
Initial conc.:
10.3 mg/kg soil d.w.
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
Soil No.:
#1
Temp.:
20 °C
Humidity:
38% fc
Soil No.:
#1
Temp.:
10 °C
Humidity:
60% fc
Soil No.:
#1
Temp.:
20 °C
Humidity:
60% fc
Details on experimental conditions:
Test System:
75 g soil samples (dry weight) were weighed into 150 ml crystallisation dishes and incubated in incubation chambers. They were continuously ventilated with moistened air with a flow rate of 60 to 100 ml/min. The outcoming air was passed through two absorption flasks, containing 100 ml 2N NaOH. For the measurement of biomass 100 g soil samples (dry soil weight) were incubated as described above (without absorption solutions).

Soil Moisture:
The soil moistures of 38 % and 60 % of the field capacity is corresponding to 10.4 and 16.6 g water per 100 g dry soil, respectively.

Concentrations:
The test substance was applied at concentrations of 1.05 ppm (samples 1 to 22) and 10.3 ppm (samples 23 to 33), calculated on soil dry weight.
Soil No.:
#1
% Recovery:
93.7
St. dev.:
7.8
Remarks on result:
other: 1 mg/kg / 20 °C / 38% FC
Soil No.:
#1
% Recovery:
94.2
St. dev.:
8.1
Remarks on result:
other: 1 mg/kg / 10 °C / 60% FC
Soil No.:
#1
% Recovery:
96.9
St. dev.:
4.4
Remarks on result:
other: 10 mg/kg / 20 °C / 60% FC
Soil No.:
#1
DT50:
1.5 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 1 mg/kg / 20 °C / 38% FC
Soil No.:
#1
DT50:
1.6 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 1 mg/kg / 10 °C / 60% FC
Soil No.:
#1
DT50:
1.5 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: 10 mg/kg / 20 °C / 60% FC
Transformation products:
yes
No.:
#1
Details on transformation products:
IUPAC name: [(5-chloroquinolin-8-yl)oxy]acetic acid
CAS#: 88349-88-6
CAS name: Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-
Molecular Formula: C11H8ClNO3
Molar mass: 237.639 g/mol
SMILES notation: O=C(O)COc1ccc(Cl)c2cccnc12
InChI: InChI=1S/C11H8ClNO3/c12-8-3-4-9(16-6-10(14)15)11-7(8)2-1-5-13-11/h1-5H,6H2,(H,14,15)
Structural formula: see attachment in Illustration (picture/graph)
Evaporation of parent compound:
no
Volatile metabolites:
yes
Residues:
yes
Details on results:
for details see Tables 1-4 (further below)

The non-extractable radioactivity reached maximum values after 56 to 112 days (about 80% AR) and declined after about 168 days.

The 14-CO2 formation increased steadily in all experiments, reaching 5.86% AR (1 mg/kg / 20°C / 38% FC), 4.44% AR (1 mg/kg / 10°C / 60% FC) and 8.56% AR (10 mg/kg / 20°C / 60% FC) after 329 days (% AR: % of the applied radioactivity).

The main degradation product (CGA153433) was always found in amounts lower than 20% AR. The half-lives of CGA153433 were estimated as 90 days (1 mg/kg / 10°C / 60% FC) and 168 days (10 mg/kg / 20°C / 60% FC). Other degradation products were found in very low amounts only (<5% AR).

There was practically no change of the amount of biomass from day 0 to 168. Therefore no measurement was made after 329 days of incubation.

Table 1: Dissipation Times (DT) and rate-constants (k rate) of the test substance

 

DT50

DT90

k rate (day-1)

1 mg/kg/20°C/38%FC

1.5 days

5.0 days

0.4654

1 mg/kg/10°C/60%FC

1.6 days

5.2 days

0.4401

10 mg/kg/20°C/60%FC

1.5 days

4.8 days

0.4775

DT 50/90 = Disappearance Time for 50% respectively 90% of the compound.

 

 

Table 2: Dissipation of CGA185072 in Soil Stein under the following Aerobic Conditions: Concentration 1 ppm, Temperature 20 °C, 38 % of Field Capacity. (Values listed are given in % of the dose applied)

Time
[days]

Extractable

Non extractable

14CO2

Total
(Recovery)

CGA185072

CGA153433
(Acid)

Unknown metabolites

0

105.17

7.43

n.d.

112.60

97.23

7.94

n.d.

7

13.47

78.08

0.02

91.57

3.68

9.76

0.03

14

10.54

82.38

0.06

92.98

0.93

9.15

0.46

28

10.12

77.45

0.17

87.74

0.49

8.87

0.76

56

10.67

79.47

0.37

90.51

0.33

8.64

1.70

84

17.81

79.79

0.62

98.22

9.95

6.70

1.16

112

8.44

81.30

1.07

90.81

0.29

5.65

2.50

168

7.61

81.52

3.00

92.13

n.d.

3.96

3.66

329

6.53

74.02

5.86

86.41

n.d.

1.96

4.56

n.d. = not detected

 

 

Table 3: Dissipation of CGA 185072 in Soil Stein under the following Aerobic Conditions: Concentration 1 ppm, Temperature 10 °C, 60 % of Field Capacity. (Values listed are given in % of the dose applied)

Time
[days]

Extractable

Non extractable

14CO2

Total
(Recovery)

CGA185072

CGA153433
(Acid)

Unknown metabolites

0

106.11

7.97

n.d.

114.08

89.66

16.45

n.d.

7

14.84

77.20

0.04

92.08

3.99

10.35

0.50

14

11.95

83.81

0.09

95.85

1.68

10.27

n.d.

28

11.41

81.75

0.25

93.41

1.01

9.82

0.58

56

11.09

84.04

0.55

95.68

0.78

9.56

0.76

84

9.86

77.55

0.96

88.37

0.70

7.85

1.31

112

10.70

74.23

1.40

86.33

0.79

8.43

1.48

168

9.19

81.70

2.28

93.17

0.15

6.92

2.13

329

7.72

77.05

4.44

89.21

0.46

3.46

3.81

n.d. == not detected

 

 

Table 4: Dissipation of CGA 185072 in Soil Stein under the following Aerobic Conditions: Concentration 10 ppm,Temperature 20 °C, 60 % of Field Capacity. (Values listed are given in % of the dose applied)

Time
[days]

Extractable

Non extractable

14CO2

Total
(Recovery)

CGA185072

CGA153433
(Acid)

Unknown metabolites

0

103.54

3.34

n.d.

106.88

83.32

14.95

5.27

7

15.90

78.32

0.03

94.25

2.81

13.09

n.d.

14

14.75

78.07

0.09

92.91

2.05

12.71

n.d.

28

13.94

80.52

0.30

94.76

1.25

12.10

0.59

56

14.17

82.82

0.82

97.81

0.51

11.77

1.89

84

12.96

86.52

1.38

100.86

0.43

10.94

1.58

112

14.00

78.64

1.99

94.63

0.61

10.88

2.51

168

11.03

79.80

3.77

94.60

n.d.

6.92

4.12

329

7.60

79.45

8.56

95.61

0.34

3.74

3.52

n.d. = not detected

Conclusions:
The substance dissipated rapidly from soil under aerobic conditions at 10 °C or 20 °C.
Executive summary:

The aerobic degradation of the test substance was studied under GLP to a guidance similar to OECD TG 307 in soil from Stein (sandy loam) at three different combinations of test substance concentration, temperature and soil moisture content (expressed as % of the field capacity (FC)). The corresponding DT50 values were 1.5 d (1 mg/kg / 20 °C / 38% FC), 1.6 d (1 mg/kg / 10 °C / 60% FC) and 1.5 d (10 mg/kg / 20 °C / 60% FC).


The main degradation product, [(5-chloroquinolin-8-yl)oxy]acetic acid, was always found in amounts lower than 20% AR (% AR: % of the applied radioactivity). Other degradation products were found in very low amounts only (<5% AR).


The 14-CO2 formation increased steadily in all experiments, reaching 5.86% AR (1 mg/kg / 20°C / 38% FC), 4.44% AR (1 mg/kg / 10°C / 60% FC) and 8.56% AR (10 mg/kg / 20°C / 60% FC) after 329 days.


The non-extractable radioactivity reached maximum values after 56 to 112 days (about 80% AR) and declined after about 168 days.


Under the conditions used, neither the test substance concentration, nor the temperature nor the moisture content had a significant influence on the DT50 of the test substance.

Description of key information

The geometric mean DT50 in aerobic soil at 20 °C is 0.7 days. Converting to the EU average outdoor temperature of 12 °C (in accordance with ECHA R.16 guidance) gives a normalised DT50 of 1.33 days. In sterile and anaerobic conditions the degradation rate is considerably slower; >1 year in sterile conditions.

The main metabolite also degraded quickly in most soils (geometric mean of 7.46 days) except in Mosimannacker soil where a DT50 of 72 days was determined. Converting to the EU average outdoor temperature of 12 °C gives a normalised DT50 of 14.14 days.

Key value for chemical safety assessment

Half-life in soil:
0.7 d
at the temperature of:
20 °C

Additional information

The rate of degradation of cloquintocet-mexyl was investigated in five GLP compliant studies, three of which also investigate degradation of the metabolite, Acetic acid, 2-[(5-chloro-8-quinolinyl)oxy]-. The experimental parameters selected were 10 °C and 20 °C, viable and sterile soils, as well as aerobic and anaerobic conditions. Soils used were as follows:


1) sandy loam, Mosimannacker, 2.3% organic carbon, pH 6.9, microbial biomass 84 mg/100 g dw, Keller 1991


2) loamy sand, German standard soil 2.2, 2.7% organic carbon, pH 6.0, microbial biomass 28 mg/100 g dw, Keller 1991


3) sandy loam, Stein, 1.26% organic carbon, pH 7.0, microbial biomass 49.7 mg/100 g dw, Keller 1992


4) sand, Collombey, 2.3% organic carbon, pH 7.3, microbial mass 339 mg/100 g dw, Keller 1992


5) loam, Les Evouettes, 3.2% organic carbon, microbial biomass 67 mg/100 g dw, Keller 1992


6) loam, silt loam, Gartenacker, 2.35 - 2.6% organic carbon, pH 7.1 - 7.2, microbial mass 65.3 mg/100 g dw, Ellgehausen 2001


7) loamy sand, Pappelacker, 1.0% organic carbon, pH 7.5 - 7.6, microbial mass 29.4 mg/100 g dw, Ellgehausen 2001


The degradation rates were derived for all studies. It should be noted that the data obtained in the Keller (1991) and Keller (1992) studies have been re-evaluated in order to calculate the degradation kinetics of the main metabolite.


The geometric mean DT50 under aerobic conditions, and at an environmental temperature of 20 °C is 0.7 days for cloquintocet mexyl. The corresponding geometric mean DT90 is 2.5 days. The geometric mean DT50 for the main metabolite is 7.46 days, and the geometric mean DT90 for the main metabolite is 24.66 days.


When incubated under aerobic conditions, cloquintocet-mexyl is degraded very rapidly under concurrent formation of the free acid, irrespective of soil moisture, temperature and analyte concentration. The half-lives of the parent compound are found to be between 0.2 days and 2.4 days, the DT90-values between 1 day and 8 days. The relatively low rate of degradation found in German standard soil 2.2 resulting in a half-life of 2.4 days is due to the low microbial activity of this soil.


Degradation of the acid metabolite is observed in all soils tested. The DT50- and DT90-values in the soil from Collombey and Les Evouettes are very short (2 - 3 days and 6.6 - 10 days, respectively), the values obtained in the other soils are between 5.5 - 72 days and 18 - 240 days, respectively. 
Only small quantities of further degradates of unknown structure are detected (always <5% of applied).


Shortly after incubation, the non-extractable residues increased and reached the maximum amounts in the range of 77% to 87% between day 28 and day 84. The non-extractable components started to decrease slowly during further incubation and reached final values between 59% and 84% after 329 and 360 days, respectively. At the same time, the formation of 14C-carbon dioxide increased in parallel. Until study termination, mineralisation amounted to 6 - 13% after 56 days incubation in the Pappelacker loamy sand and Gartenacker loam/silt loam, 6 - 9% after 329 days in Stein sandy loam, 18% after 336 days in the Mosimannacker sandy loam, 20% after 350 days in the Collombey sand and 28% after 360 days in the Les Evouettes loam.


The results of these studies give a consistent picture of the processes occurring in soil. The most important steps are the degradation of cloquintocet-mexyl yielding the intermediate acid metabolite, as well as the formation of non-extractable components which are strongly bound to soil organic matter. However, traces of these residues can be partly released and become extractable again before they are finally mineralised to 14C-carbon dioxide in viable soils.


The dissipation of cloquintocet-mexyl was also investigated in a number of field dissipation studies in a wide range of soil types at sites in Germany, France, Italy, Spain and Switzerland. After application of up to 150 g/ha to bare soil, the residues of cloquintocet-mexyl in the 0 - 10 cm soil layer disappeared completely within 1 - 3 months. The residues of the acid metabolite declined to 0.01 mg/kg or less within 3 - 5 months. No residues above 0.5 μg/kg were detected below 10 cm soil depth. Therefore, it is concluded that accumulation in soil into the next growing season can be completely excluded. Additionally, the potential of cloquintocet-mexyl and its metabolites to penetrate deeper soil layers and contaminate the shallow groundwater is negligible. The field studies regarding the dissipation of cloquintocet-mexyl are not included in the IUCLID dossier, as these are not a standard data requirement under the REACH regulation.