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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Data waiving:
other justification
Justification for data waiving:
other:
Transformation products:
not measured
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
28 Jul 1998 - 06 Jan 1999
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
other: EU Council Directive 91/414 EEC as amended by Commission Directive 95/36/EC of July 1995, Section 7.2.1.3.2
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
other: water: aerobic/sediment: anaerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of surface water:
- Details on collection: Samples of sediment and water were collected according to ISO/DIS 10381-6 from two sites, a stream located on Aldhams Farm, Manningtree, Essex, UK. (Sediment No 98/29, Manningtree, Ordinance Survey TM 100302) and from the River Roding, Boarded Barns Farm, Ongar, Essex, UK. (Sediment No 98/30, Ongar, Ordinance Survey TL 566048).
- Storage conditions: Water and sediment samples were maintained separately in the dark at 4 °C.
- Date of collection: 23 and 24 Jul 1998
- Temperature (°C) at time of collection: (98/29) 13.6 °C, (98/30) 17 °C
- pH at time of collection: (98/29) 6.35, (98/30) 7.75
- Redox potential (mv) initial/final: Initial: (98/29) 401, (98/30) 7.0
- Oxygen concentration (%) initial/final: (98/29) 34, (98/30) 56
- Hardness (ppm as CaCO3): (98/29) 337, (98/30) 401
- Total organic carbon (ppm): (98/29) 3.5, (98/30) 5.6
- Total Nitrogen (ppm): (98/29) 15.0, (98/30) 2.0
- Total Phosphorous (ppm): (98/29) 0.7, (98/30) 0.6
- Water filtered: yes
- Type and size of filter used: 0.2 mm filter
Details on source and properties of sediment:
- Details on collection: Samples of sediment and water were collected according to ISO/DIS 10381-6 from two sites, a stream located on Aldhams Farm,Manningtree, Essex, UK. (Sediment No 98/29, Manningtree, Ordinance Survey TM 100302) and from the River Roding, Boarded Barns Farm, Ongar, Essex, UK. (Sediment No 98/30, Ongar, Ordinance Survey TL 566048).
- Storage conditions: Water and sediment samples were maintained separately in the dark at 4 °C.
- Date of collection: 23 and 24 Jul 1998
- Textural classification (ADAS): (98/29) Sandy silt loam, 39% sand, 44.5% silt, 16.4% clay; (98/30) Clay loam, 36.5% sand, 31.5% silt, 32.0% clay
- pH in water at time of collection: (98/29) 6.2, (98/30) 7.6
- Organic carbon (%): (98/29) 5.6, (98/30) 4.4
- CEC (meq/100 g): (98/29) 9.7, (98/30) 37.6
- Biomass (in µg C/g soil): Initial: (98/29) 1269, (98/30) 318; Final: (98/29) 256, (98/30) 112
- Sediment samples sieved: yes, through a 2 mm mesh screen
Duration of test (contact time):
100 d
Initial conc.:
183.14 other: µg/flask
Based on:
test mat.
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Details on study design:
TEST CONDITIONS
- Test temperature: 20 ± 2 °C
- Aeration of incubation flasks: Moistened air was passed through the flasks at 26.6 mL/min
- Continuous darkness: yes
- Other: The water/sediment samples were acclimated for 27 days until there was complete phase separation.

TEST SYSTEM
- Culturing apparatus: glass incubation flasks of 6 cm diameter
- Sediment dry weight : water ratio: (98/29) 1:7.5, (98/30) 1:6; the water level in each flask was maintained during the study by addition of deionised water
- Number of culture flasks/concentration: 2
- Method used to create aerobic conditions: aeration with moistened air
- Details of trap for CO2 and volatile organics if used: The effluent air was passed through an ethylene glycol trap to trap volatiles, followed by two 2M potassium hydroxide traps to trap evolved 14CO2.
- Measurement of water and sediment parameters: The redox potential of the sediment and the pH and the oxygen content of the water at these time points were recorded in untreated control flasks.

SAMPLING
- Sampling frequency: Duplicate flasks of each sediment type were removed for analysis at the following time points: zero hours (immediately after dose application), 24, 48 hours, and 7, 14, 30, 61 and 100 days after application.
- Sampling method: The water was decanted from the sediment taking care not to disturb the sediment. If any sediment was disturbed, the water was centrifuged at 3000 rpm for 10 minutes.
- Sample storage before analysis: All samples were extracted on the day of sampling and analysed by HPLC within the following two weeks. The extracted samples were stored in a freezer at - 20 °C.

CONTROL AND BLANK SYSTEM
- Inoculum blank: yes, untreated control flasks

STATISTICAL METHODS
The half-life, DT50 and where, possible, the DT90 values for the decline in the amount of ethiprole in the two water/sediment systems were calculated using Excel (first order kinetics), Timme-Frehse and the kinetic modelling program (KIM). Values were calculated based on the amount of ethiprole (in % of applied) as determined by HPLC results.
% Degr.:
97
Parameter:
other: Radiochem. meas. and Test mat. analysis
Sampling time:
100 d
Remarks on result:
other: Sediment
% Degr.:
96
Parameter:
other: Radiochem. meas. and Test mat. analysis
Sampling time:
100 d
Remarks on result:
other: Water
Compartment:
water
DT50:
> 12 - < 13.5 d
Type:
other: KIM Power Rate
Remarks on result:
other: r2 = - 0.9989; DT90 = 57.4 - 68.1
Compartment:
entire system
DT50:
> 15 - < 16.1 d
Type:
other: KIM Power Rate
Remarks on result:
other: r2 = - 0.9946 to - 0.9976; DT90 = 67.5 - 86.1
Compartment:
water
DT50:
> 18.5 - < 21.1 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r2 = 0.9873 - 0.9906; DT90 = 61.6 - 70.1
Compartment:
entire system
DT50:
> 20.3 - < 23.7 d
Type:
(pseudo-)first order (= half-life)
Remarks on result:
other: r2 = 0.9821 - 0.9951; DT90 = 67.6 - 78.7
Compartment:
water
DT50:
> 25.5 - < 28.7 d
Type:
other: KIM Power Rate
Temp.:
12 °C
Compartment:
entire system
DT50:
> 31.8 - < 34.2 d
Type:
other: KIM Power Rate
Temp.:
12 °C
Compartment:
water
DT50:
> 39.3 - < 44.8 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Compartment:
entire system
DT50:
> 43.1 - < 50.3 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
No.:
#4
Details on transformation products:
- Pathways for transformation: reduction, oxydation and hydrolysis
Evaporation of parent compound:
no
Volatile metabolites:
no
Residues:
yes
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes

TRANSFORMATION PRODUCTS (WATER)
RPA 107566 (reduction product)
- 5 - 6% of the applied radioactivity from day 14 to day 100 in system (98/29)
- 11% of the applied radioactivity at day 14, 3% at day 100 in system (98/30)
RPA 097973 (oxidation product)
- 5% of the applied radioactivity at day 100 in both systems
RPA 112916 and RPA 112917 (hydrolysis products)
- < 1% of the applied radioactivity at day 100

TRANSFORMATION PRODUCTS (SEDIMENT)
RPA 107566 (reduction product)
- maximum of 71.7% of the applied radioactivity at day 100 in system (98/29)
- maximum of 77.2% of the applied radioactivity at day 100 in system (98/30)
RPA 097973 (oxidation product)
- maximum of 8.65% of the applied radioactivity at day 100 in system (98/29)
- maximum of 10.5% of the applied radioactivity at day 100 in system (98/30)
RPA 112917 (hydrolysis product)
- appeared in only one sample at day 100 (0.46%)

TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT
- Three unknown metabolites, each accounting for < 2.8% of the applied radioactivity

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 102% for both systems
- % of applied amount at end of study period: 98.5% for (98/29), 102% for (98/30)

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: 0% in both systems
- % of applied amount at end of study period: 5.27% in (98/29) and 7.05% in (98/30)

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

MATERIAL (MASS) BALANCE
- System (98/29): Mean recovery of 104% (range 98 - 108%)
- System (98/30): Mean recovery of 106% (range 101 - 111%)

DISTRIBUTION OF RADIOACTIVITY
In both systems, the radioactivity recovered from the water at time zero was slightly above 100% then declined to approximately 50% at day 14 in the Manningtree system (98/29) and at day 30 in the Ongar system (98/30), then down to approximately 15 and 12% at day 100 for the Manningtree and the Ongar systems, respectively. This was due to the transfer of radioactivity from the water phase to the sediment phase. The radioactivity recovered from the sediment increased steadily from zero at time zero to approx. 90% (83.5% Manningtree, 90.0% Ongar) at day 100.

Under aerobic aquatic conditions, ethiprole is rapidly transferred from the water to the sediment where it is reduced via the sulphoxide group to one major metabolite, RPA 107566, and a minor metabolite, RPA 097973. Small amounts of RPA 112916 and RPA 112917 and three unknown compounds were also detected.

Table 1. Mean distribution and recovery of radioactivity in Manningtree System (98/29) (in % of applied radioactivity)

Days

Water

Sediment extract

Total extract

Volatiles

Unextracted

Total

0

102.8

0.06

102.14

N/A

0.01

102.15

1

94.01

9.58

103.59

0.00

0.37

103.96

2

89.57

12.77

102.35

0.00

0.49

102.84

7

67.81

34.29

102.10

0.01

1.39

103.51

14

49.61

54.20

103.81

0.02

1.79

105.61

30

38.68

63.05

101.73

0.03

2.53

104.29

61 (2 mo)

22.81

75.31

98.12

0.09

3.99

102.20

100 (3 mo)

14.96

83.53

98.49

0.09

5.27

103.85

Mean recovery

103.55

N/A = not applicable

Note: Sediment was extracted using acetonitrile and 80:20 v/v acetonitrile/water mix

 

Table 2. Mean distribution and recovery of radioactivity in Ongar System (98/30) (in % of applied radioactivity)

Days

Water

Sediment extract

Total extract

Volatiles

Unextracted

Total

0

102.6

0.01

102.08

N/A

0.00

102.08

1

98.25

6.82

105.07

0.00

0.22

105.30

2

92.69

11.20

103.89

0.00

0.56

104.45

7

75.04

29.01

104.04

0.01

1.07

105.12

14

64.06

40.35

104.41

0.01

1.64

106.06

30

43.97

60.99

104.96

0.06

3.26

108.28

61 (2 mo)

18.71

85.68

104.39

0.12

5.26

109.77

100 (3 mo)

12.25

90.02

102.27

0.11

7.05

109.43

Mean recovery

106.31

N/A = not applicable

Note: Sediment was extracted using acetonitrile and 80:20 v/v acetonitrile/water mix

Validity criteria fulfilled:
not applicable
Conclusions:
Ethiprole was degraded by one major pathway, reduction of the sulphoxide group to the sulphide, RPA 107566. Oxidation of the sulphoxide group to the corresponding sulphone RPA 097973 also occured. Hydrolysis of the nitrile group led to the formation of small amounts of the amide RPA 112916. Further hydrolysis of the sulphone RPA 097973 at the nitrile group or oxidation of the amide RPA 112916 led to the formation of RPA 112917. Three unknowns were also detected but each accounted for < 2.8 % of the applied radioactivity for individual samples. The overall mean recoveries were 103.55 % and 106.31% for the two systems. No significant volatile products were formed and unextracted residues remained below 8% of the applied radioactivity.
Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
21 Jul 1997 - 6 Oct 1998
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
EPA Subdivision N Pesticide Guideline 162-4 (Aerobic Aquatic Metabolism)
Version / remarks:
1982
GLP compliance:
yes
Radiolabelling:
yes
Oxygen conditions:
aerobic
Inoculum or test system:
other: microbially active pond water and pond sediment (hydrosoil)
Details on source and properties of surface water:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Fresh pond water used in this study was collected from a pond at the Rhone-Poulenc Ag Company Research Station in Clayton, North Carolina. The water was sieved through a 2-mm sieve to remove extraneous debris before removal from the pond. A 5 gallon bucket approximately 1/4 full of sediment was procured, and then the bucket was filled with additional pond water. Four 1/2 gallon jugs were filled with more pond water. The bucket and jugs were capped and transported to the Rhone-Poulenc Ag Company research facility in Research Triangle Park, North Carolina.
- Storage conditions: The jugs containing the pond water were uncapped and stored at room temperature.
- Storage length: The pond water and sediment were stored in this manner for four days prior to test system set up in the growth chamber.
- pH at time of collection: 7.2
- Redox potential (mv) initial/final: 192.7 mV / 353.6 mV
- Oxygen concentration (mg/l) initial: 10 mg/L
- Hardness (CaCO3): 70 mg/L
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): 525 Aug CFU/g (heterotrophic plate count)
- Water filtered: yes
- Type and size of filter used, if any: 2-mm mesh size sieve
Details on source and properties of sediment:
- Details on collection (e.g. location, sampling depth, contamination history, procedure): Fresh sediment (hydrosoil) used in this study was collected from a pond at the Rhone-Poulenc Ag Company Research Station in Clayton, North Carolina. The sediment was sieved through a 2-mm sieve to remove extraneous debris before removal from the pond. A 5 gallon bucket approximately 1/4 full of sediment was procured, and then the bucket was filled with additional pond water. Four 1/2 gallon jugs were filled with more pond water. The bucket and jugs were capped and transported to the Rhone-Poulenc Ag Company research facility in Research Triangle Park, North Carolina.
- Storage conditions: The 5 gallon bucket containing the pond sediment was loosely capped and stored at room temperature.
- Storage length: The pond water and sediment were stored in this manner for four days prior to test system set up in the growth chamber.
- Textural classification (i.e. %sand/silt/clay): 3.08% organic matter; 78.8% sand; 14.4% slit; 6.8% clay
- pH at time of collection: 5.7
- Redox potential (mv) initial/final: - / -4.2 mV
- CEC (meq/100 g): 4.57
- Bulk density (g/cm³): 1.27
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): 710000 Aug CFU/g (heterotrophic plate count); 173 µg C/g soil (start of study); 108 µg C/g soil (end of study)
- Sediment samples sieved: yes
Duration of test (contact time):
12 mo
Initial conc.:
0.52 other: kg a.i./ha
Based on:
test mat.
Remarks:
equivalent to approximately 0.46 ppm of the oven-dry weight of the sediment and 87% of the maximum anticipated use rate.
Parameter followed for biodegradation estimation:
radiochem. meas.
test mat. analysis
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: To each container approximately 51 g of centrifuged sediment (equivalent to 33 g of dry soil) was added. The sediment was covered with 100 mL of associated pond water. The ratio of dry equivalent weight of sediment to water was approximately 1:4 (w/w)
- Composition of medium: microbially active pond water and sediment (loamy sand)
- Solubilising agent (type and concentration if used): Acetonitrile
- Test temperature: Flasks were maintained at 20± 1 °C, except for 2 weeks when the temperature ranged from 20 to 22 °C under aerobic conditions in a growth chamber.
- pH adjusted: no
- Continuous darkness: yes
- Other: Radiolabelled test substance was tested in 2 different concentrations, a 1X and a 10X dose. The 1X dose solution was prepared as follows: The calculated volume of stock 14C-ethiprole (361 µL) was added to an 8 mL glass vial. Then 4.049 mL (enough to bring the total volume to 4.4 mL) of acetonitrile was added to the glass vial and mixed. Each test container received 103 µL of dose solution equivalent to 14 µg of 14C-ethiprole (1,550,329 DPM). The 10X dose solution was prepared as follows: A stock solution of 10 mg/mL of non-labeled ethiprole was prepared in acetonitrile. Then 60 µL of the non-labeled ethiprole stock solution and 361 µL of the 14C-ethiprole stock solution were added to a 4 mL screw cap glass vial. Finally 479 µL of acetonitrile was added to bring the final volume to 900 µL. Each test container received 100 µL of dose solution equivalent to 133 µg of ethiprole (7,253,400 DPM).

TEST SYSTEM
- Culturing apparatus: 250 mL glass flasks connected to an aerobic aquatic incubation apparatus, which consisted of a hydrated air supply connected in parallel to the test flasks and the flaks were then connected in series to 4 standard midget bubblers. Each bubbler
was closed with a ground glass top fitted with a glass inlet tube and an outlet. The inlet tube with a gas dispersing end extended into the reservoir. The inlet tube allows the gas to flow into each bubbler and continuously stirred the trapping solvent with bubbling gas. The outlet from each bubbler was connected by Tygon® tubing to the inlet tube of the next bubbler. The first and third bubblers were empty backflow traps. The second bubbler contained 15 mL of ethylene glycol which served as an organic volatile trap while the fourth bubbler contained a CO2 trap composed of 15 mL of 2-ethoxyethanol: mono-ethanolamine (2:1 v/v). Air supplied from an air gas cylinder was hydrated through a container of distilled water before being passed over the samples. The air flow was determined by visual evaluation. The prepared test systems were placed in a Lab-Line Biotronette Plant growth chamber at 20±1 °C and allowed to acclimatize for about three weeks before dosing.
- Number of culture flasks/concentration: 2, In addition, 4 samples were prepared for the 10X treatment rate and 4 samples were prepared as untreated controls
- Method used to create aerobic conditions: Moistened air was supplied under positive pressure on the surface of the water in each
unit.
- Method used to control oxygen conditions: Hydrated air supply
- Test performed in closed vessels due to significant volatility of test substance: Test was performed in a closed vessel, but no significant volatility of test substance
- Details of trap for CO2 and volatile organics if used: See above

SAMPLING
- Sampling frequency: Duplicate samples were analyzed at intervals of 0, 3, 7 and 14 days and 1, 2, 3, 6, 9 and 12 months after application. Control samples were analyzed at the beginning and end of the study. Trapping solutions were also sampled at 17, 49, 70, 99, 127, 197, 233, 273, and 309 days after treatment.
- Sampling method used per analysis type: The pond water was carefully separated from the pond sediment by decanting the water through a Whatman #1 filter paper. The volume of the pond water was recorded and aliquots were taken for liquid scintillation analysis (LSA). The volume of the trapping solutions for each sample pair was recorded and aliquots were taken for LSA analysis. Trapping solutions were also sampled and analyzed by LSA. After recording the volumes and taking aliquots for LSA analysis, trapping solutions were replaced with fresh trapping solutions.
- Sample storage before analysis: The collected samples or sample extracts were stored in the refrigerator between 4°C and 9°C.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION
CONTROL AND BLANK SYSTEM
- Inoculum blank: The control solution was the same solvent, acetonitrile, used in the preparation of the treated dose solution without the active ingredient.

STATISTICAL METHODS:
- The mean, standard deviation, and relative standard deviation were calcualted using acceptable methods. All combustions, extractions and analyses were conducted at least in triplicate. Where possible, data are presented as the mean of at least triplicate analyses. The parent concentrations at various time intervals was subjected to correlation and regression analysis. Rate constant and half-life (ti/2) were calculated by using a linear regression (assuming pseudo-first order reaction kinetics): Log Ct = -Kt + Log C0, where K = rate constant, Ct = parent concentration at time t, C0 = Initial parent concentration. The half-life (t1/2) of the test substance was calculated by the following equation: t1/2 = Ln 2/K = 0.693/K. The disappearance time (DT) values were determined as the time taken for the calculated maximum concentration to decline to half (DT50) and one tenth (DT90) that maximum value respectively.
Compartment:
other: natural pond water
% Recovery:
5.08
Remarks on result:
other: percent of applied recovery in pond water at 12 months
Compartment:
other: natural pond sediment
% Recovery:
85.86
Remarks on result:
other: percent of applied radioactivity measured in pond sediment at 12 months
Compartment:
entire system
% Recovery:
90.94
Remarks on result:
other: percent of applied radioactivity at 12 months in pond water/sediment system
% Degr.:
> 87.6 - < 89.5
Parameter:
radiochem. meas.
Sampling time:
12 mo
Remarks on result:
other: Degradation of ethiprole in the entire system
Compartment:
other: natural pond water
DT50:
4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Compartment:
other: natural pond sediment
DT50:
11 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Compartment:
entire system
DT50:
5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Compartment:
other: natural pond water
DT50:
8.5 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Compartment:
other: natural pond sediment
DT50:
23.4 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Compartment:
entire system
DT50:
10.6 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Other kinetic parameters:
pseudo-first order rate constant
Transformation products:
yes
No.:
#1
No.:
#2
Details on transformation products:
- Pathways for transformation: Reduction and oxidation
Evaporation of parent compound:
no
Remarks:
Volatile radioactivity remained very low throughout the test period and, overall, was negligible.
Volatile metabolites:
not specified
Residues:
yes
Remarks:
The unextractable residues as determined by combustion after the solvent extractions were at or below 5% of applied radioactivity at all sampling intervals.
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes
- Anomalies or problems encountered (if yes): A loss of 10% or greater of the radioactivity was obserbed in organic extracts of sediment samples at 12 months. The same concentration procedure was used for organic extracts from all sediment samples. During this concentration and filtration process no loss of recovered radioactivity was observed in the one month sample, <10% loss in the other samples. It is suggested that the loss of radioactivity in one of the replicate samples was not due to loss of any volatile metabolites because (1) no compounds were detected in the organic volatile traps throughout the test period and (2) the metabolite profile of the sample with good recovery was not different from that of the other sample with >10% loss of radioactivity.

MAJOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: The concentration of RPA107566 in the total system increased from 14% of the initial application at day 3 to 80% of the applied dose at 1 month.
- Range of maximum concentrations in % of the applied amount at end of study period: The concentration of RPA107566 in the total system declined to 41% at 12 months.

MINOR TRANSFORMATION PRODUCTS
- Range of maximum concentrations in % of the applied amount and day(s) of incubation when observed: RPA097973 in the total system was initially detected from 2 to 12 months and the levels detected ranged from 1 to 9% of the applied dose.


TOTAL UNIDENTIFIED RADIOACTIVITY (RANGE) OF APPLIED AMOUNT:
- An unknown of less than 0.5% of applied (HPLC retention time ~10.8 minutes) was detected in the duplicate flasks at 6 months in pond water. Several unknowns of equal to or less than 2% of dose applied were detected in 2, 6 and 12 months pond water. The presence of unknown was detected only in one of the duplicate flasks. The following unknowns were detected in the water samples: in 2 months at 7.3 minutes; in 6 months at 2.6 6.3, 8.4, and 9.6 minutes; and in 12 months at 2.6, 6.0, 9.6 and 10.0 minutes. None of these unknowns were found in the sediment.

EXTRACTABLE RESIDUES
- % of applied amount at day 0: 107.36%
- % of applied amount at end of study period: 90.94%

NON-EXTRACTABLE RESIDUES
- % of applied amount at day 0: < 5%
- % of applied amount at end of study period: < 5%

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: Not detectable

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: < 1% at all sampling intervals

Ethiprole rapidly degraded in both water and in sediment, but remained at detectable levels throughout the test. RPA107566 (sulfide) is the major metabolite detected only in the sediment of this study. This compound is a reduction

product of ethiprole. The formation of this degradate can be explained in terms of the anaerobic nature of the sediment during the study. At the end of the study (day 365), approximately 40% of the applied radioactivity was detected as RPA107566 in the sediment. RPA097973, an oxidation product of ethiprole, was detected at low and variable levels of the applied dose.

Table 1. Mean Recovery (% of Applied Radioactivity) in Aerobic Aquatic Total System

Time (days)

0

3

7

14

30

60

90

180

270

365

% of applied radioactivity

107.36

96.25

97.27

97.23

90.91

91.47

87.42

93.85

94.86

90.94

% Overall mean recovery

94.76

 

Table 2. Distribution of Radioactivity between Water and Sediment as%Applied Radioactivity

Time (days)

0

3

7

14

30

60

90

180

270

365

Water

89.41

71.13

37.46

19.76

11.95

10.58

15.76

10.49

5.15

5.08

Sediment

17.95

25.12

59.81

77.47

78.96

80.89

71.66

83.36

89.71

85.86

Total

107.36

96.25

97.27

97.23

90.91

91.47

87.42

93.85

94.86

90.94

 

Table 3. Mean distribution of 14C-Ethiprole and metabolites in surface water and sediment concentrates (% of applied radiocarbon)

 

RPA 107382

RPA107566

RPA097973

Sampling time

Water

Sediment

Total

Water

Sediment

Total

Water

Sediment

Total

0 days

89.42

8.15

97.56

-

-

-

-

-

-

3 days

71.13

8.36

79.49

-

14.34

14.34

-

-

-

7 days

33.82

5.64

39.46

1.89

50.90

52.79

-

-

-

14 days

9.28

3.74

13.02

10.70

63.91

74.61

-

-

-

1 month

3.90

5.08

8.98

7.12

72.83

79.95

-

-

-

2 months

7.11

3.36

10.47

2.62

57.88

60.50

-

1.38

1.38

3 months

10.86

8.21

19.07

3.04

52.22

55.59

1.79

-

1.79

6 months

7.36

3.35

10.71

-

55.03

55.03

1.72

3.19

4.91

9 months

4.28

40.23

44.51

-

28.04

28.04

0.79

5.89

6.68

12 months

2.15

6.86

9.01

-

40.74

40.74

1.43

7.73

9.16

Validity criteria fulfilled:
not applicable
Conclusions:
Ethiprole rapidly degraded in this aerobic aquatic environment. The degradation is mainly through oxidation of the parent to the sulfone and reduction of the parent to the sulfide. The degradation of ethiprole appeared to follow pseudo-first-order kinetics with a degradation rate constant (K) of-0.1473 day1 and a half life of 5 days (r2 = 0.9717) in the entire system. Total identified radioactivity accounted for 53% to 97% of the applied dose. The main identified degradate was RPA107566 (sulfide), a reduction product of ethiprole, which accounted for up to 82% (0.46 ppm) of the applied dose. The formation of this metabolite is due to the quick transfer of parent into the sediment where anaerobic conditions even very early in the incubation period are prevalent. At the end of the study (day 365), approximately 40% of the applied radioactivity was detected as RPA107566 in the sediment. RPA097973 (sulfone), an oxidation product of ethiprole, was detected at low and variable levels of the applied dose in water and sediment. The appearance of sulfone in the aqueous phase and sediment is attributed to increasingly oxidative nature of the system towards the end of the study. In the sediment an unknown (10.8 minutes) was detected in 6 month water samples with a maximum concentration of less than 1% of applied dose was also present. Four minor unknowns were detected and each was less than 2% of the applied radioactivity. The appearance of these unknowns did not follow an obvious pattern.

Description of key information

DT50 = 12 - 13.5 days (25.5 - 28.7 days, recalculated to 12 °C), 96 - 97% degradation in water and sediment (EU Council Directive 91/414 EEC).

DT50 = 4 - 11 days (8.5 - 23.4 days, recalculated to 12 °C), 87.6 - 89.5% degradation in a natural pond water/sediment system (US EPA Subdivision N Pesticides guideline 162-4, 1982).

Key value for chemical safety assessment

Additional information

One simulation test was carried out to assess the degradation of the substance in two aquatic sediment systems and to determine the metabolites formed under aerobic aquatic conditions. The study followed GLP and EU Council Directive 91/414 EEC as amended by Commission Directive 95/36/EC. The duration of the test with two different water/sediment-samples was 100 days. Under aerobic aquatic conditions ethiprole was rapidly transferred from the water to the sediment (with a transformation of 96 and 97% in water and sediment, respectively), where it was reduced via the sulphoxide group to one major metabolite and a minor metabolite. The half-life of the parent substance in water was determined to be 12 - 13.5 days (25.5 - 28.7 days, recalculated to 12 °C).

An additional simulation study was carried out to assess the degradation of the target substance in a natural pond water/sediment system and to determine the metabolites formed under aerobic conditions. The study followed GLP and US EPA Subdivision N Pesticide guideline 162-4 (1982). The duration of the test was 365 days (12 months). The target compound ethiprole rapidly degraded in both water and in sediment but remained at detectable levels throughout the test. Under aerobic aquatic conditions, the substance was found to be degraded by 87.6 to 89.5% in the entire system, forming one major metabolite, which was detected only in the sediment of this study. This compound is a reduction product of ethiprole. The formation of this degradate can be explained in terms of the anaerobic nature of the sediment during the study. At the end of the study (day 365), approximately 40% of the applied radioactivity was detected as the reduction product in the sediment. A second metabolite, an oxidation product of ethiprole, was detected at low and variable levels of the applied dose. The half-life of the target compound in the water/sediment system was determined to be 4 - 11 days (8.5 - 23.4 days, recalculated to 12 °C).