imidacloprid (ISO); 1-(6-chloropyridin-3-ylmethyl)-N-nitroimidazolidin-2-ylidenamine

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

key study

Study period:

Oct 1987 - Jun 1988

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Subdivision N Pesticide Guideline 162-4 (Aerobic Aquatic Metabolism)

Qualifier:

according to guideline

Guideline:

other: FOCUS, 2006: Guidance Document on Estimating Persistence and Degradation Kinetics from Environmental Fate Studies on Pesticides in EU Registration. Report of the FOCUS Work Group on Degradation Kinetics, EC Document Reference Sanco/10058/2005 version 2

Version / remarks:

2006

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

natural water / sediment: freshwater

Details on source and properties of surface water:

- Details on collection (e.g. location, sampling depth, contamination history, procedure): The water and sediment samples originated from the drainage ditch of a fruit orchard near Ijzendoorn (NL) and a recultivated gravel quarry nead Lienden (NL).
- Temperature (°C) at time of collection: 22 °C
- pH at time of collection: 7.9 – 8.9
- Oxygen saturation: >70%
- Total organic carbon: 4 g/L (Ijzendoorn), 5 mg/L (Lienden)
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): All samples were biologically active.
- Water filtered: no

Details on source and properties of sediment:

- Details on collection (e.g. location, sampling depth, contamination history, procedure): The water and sediment samples originated from the drainage ditch of a fruit orchard near Ijzendoorn (NL) and a recultivated gravel quarry nead Lienden (NL).
- Textural classification (i.e. %sand/silt/clay):
Ijzendoorn sediment: Loamy silt, 15.3% sand, 69.7% silt, 14.9% clay
Lienden sediment: Loamy sand, 73.9% sand, 16.8% silt, 9.2% clay
- Organic carbon (%): 4.09 (Ijzendoorn), 0.89 (Lienden)
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): All samples were biologically active.
- Sediment samples sieved: The sediment phase was passed through a 2 mm mesh sieve.

Initial conc.:

0.2 mg/L

Based on:

test mat.

Parameter followed for biodegradation estimation:

radiochem. meas.

test mat. analysis

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment: 500 mL, including a 1.5 cm sediment layer (10% w/w)
- Test temperature: 22 °C
- Continuous darkness: yes
- Other: Preparation of the system: After brief, vigorous stirring up followed by sedimentation, the sediments were separated into water phase and solid sediment phase. Subsequently the sediment phase was passed through a 2 mm mesh sieve. The dry weight (% dry mass = T) of the thoroughly mixed sediment phase was determined. Fifty g sediment relative to dry mass were weighed into each incubation vessel. Then this was filled up to 500 g with the decanted aqueous phase of the respective sediment. The systems were pre-incubated in the climatic cabinet at 22°C for 2 weeks to acclimatize them to the laboratory conditions. The shaker operated at a speed of 60 rpm.

TEST SYSTEM
- Culturing apparatus: The aquatic model ecosystem used is characterized by the following features: the stagnant sediment is covered by a water layer being in motion, the dribbling water surface guarantees an oxygen uptake from the air, the stagnant sediment provides the biotop for microorganisms having a different oxygen demand, the air in the incubation vessel has the natural oxygen content of the atmosphere and volatile radioactive metabolites including 14C02 are absorbed in a trap attachment. The experiments were carried out at 22°C in the dark in an incubation shaking cabinet KF 4 of Infers Co.
- Number of culture flasks/concentration: Ten test vessels per sediment were treated with active ingredient solution. Two additional vessels (no. 11 and 12) without active ingredient were incubated for comparison. Two further vessels per sediment were prepared for metabolite production with 20 µCi 14C-labeled NTN 33 893 as well as about 1 mg unlabeled active ingredient.
- Measuring equipment: A pH-meter of Knick with a glass electrode (Schott Co.) was used for measurement of the pH-value and an oxygen electrode according to Clark (WTW OXI 521) was used for measurement of the oxygen content of the water phase.
- Test performed in open system: No, the test was performed in a closed system.
- Details of trap for CO2 and volatile organics if used: The used CO2 trap was a glass tube (overall length 14.5 cm) filled as follows: Quartz wool (0.2 g), soda lime (4 g) for sorption of atmospheric CO2, quartz wool (0.2 g), soda lime (10 g) for sorption of CO2 emanating from the system, quartz wool (0.3 g) and oil-coated quartz wool for sorption of volatile organic compounds (1 g, moistened with 2% paraffine in hexane).

SAMPLING
- Sampling frequency: Two duplicate determinations were carried out in each of the two sediments after 0, 14, 29, 60 and 92 days.
- Sampling method used per analysis type: At each sampling time duplicate samples of each of the two sediments were sacrificed. The separation into water and sediment was carried out in a pressure filter unit with an 0.2 µm Durapore filter. Volatile components were determined by analysis of the constituents in the sorption tube. The CO2 still being present in the solution or in the sediment was liberated in an aliquot by means of HCl and again adsorbed in the sorption tube.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION
CONTROL AND BLANK SYSTEM
- Inoculum blank: No

STATISTICAL METHODS:
Assuming a reaction kinetic pseudo 1st order for the degradation of NTN 33 893 in the water/sediment system, the half-lives were determined by linear regression.

Compartment:

natural water / sediment: freshwater

% Recovery:

98.8

St. dev.:

0.2

Remarks on result:

other:

Remarks:

Sediment identification: Ijzendoorn; total recovery after 92 days

Compartment:

natural water / sediment: freshwater

% Recovery:

98.6

St. dev.:

0.4

Remarks on result:

other:

Remarks:

Sediment identification: Lienden; total recovery after 92 days

% Degr.:

2

Parameter:

CO2 evolution

Sampling time:

92 d

Remarks on result:

other:

Remarks:

Sediment identification: Lienden

% Degr.:

1.4

Parameter:

CO2 evolution

Sampling time:

92 d

Remarks on result:

other:

Remarks:

Sediment identification: Ijzendoorn

Compartment:

natural water / sediment: freshwater

DT50:

162 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Sediment identification: Lienden

Compartment:

natural water / sediment: freshwater

DT50:

412.5 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Sediment identification: Lienden; Calculated DT50 based on experimental data at 22 °C

Compartment:

natural water / sediment: freshwater

DT50:

30 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Sediment identification: Ijzendoorn

Compartment:

natural water / sediment: freshwater

DT50:

76.4 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Sediment identification: Ijzendoorn; Calculated DT50 based on experimental data at 22 °C

Compartment:

natural water: freshwater

DT50:

6.1 d

Type:

other: Kinetic evaluation using FOCUS 2006

Temp.:

22 °C

Compartment:

natural sediment: freshwater

DT50:

1 000 d

Type:

other: Kinetic evaluation using FOCUS 2006

Temp.:

22 °C

Transformation products:

yes

Remarks:

Four degradation products were found. Not all of which could be identified. Please refer to "Details on transformation products".

No.:

#1

Details on transformation products:

- Formation and decline of each transformation product during test: During the first sampling dates the radioactivity in the water phases consisted predominantly of unchanged parent compound. As the test period progressed, increasing amounts of a main metabolite (WLF 230) were formed besides that, the chemical structure of which corresponded to that of the reference compound NTN 33 823 and which derives from NTN 33 893 by replacement of the N02-group by a H-atom. This metabolite occurred in amounts of up to 6.0% (IJzendoorn) and/or 4.5% (Lienden) of the applied radioactivity on day 92. While NTN 33 823 greatly dominated in the water phase of the system IJzendoorn, two further degradation products were formed in the system Lienden in amounts of 1-4% of the applied radioactivity: 6-chloronicotinic acid and an open-chain diamine corresponding to the reference compound DIJ 9646-2. The metabolite pattern in the sediment extracts was similar to that in the water phases. NTN 33 823 as main metabolite occurred with increasing content of up to 6.3% (IJzendoorn) and 4.3% (Lienden) of the applied radioactivity on day 92. Only small amounts of 6-chloronicotinic acid (1%) were found besides that in both systems.

Evaporation of parent compound:

no

Remarks:

< 0.1% of the applied radioactivity were found in the traps for volatile compounds

Volatile metabolites:

no

Remarks:

< 0.1% of the applied radioactivity were found in the traps for volatile compounds

Details on results:

TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: pH and O2 saturation remained relatively constant in the water phase, of both test systems “Lienden” and “Ijzendoorn”, throughout the testing period.

EXTRACTABLE RESIDUES IN THE SEDIMENT
- % of applied amount at day 0: 5.9 (Lienden), 15.2 (Ijzendoorn)
- % of applied amount at end of study period: 15.4 (Lienden), 18.0 (Ijzendoorn)

NON-EXTRACTABLE RESIDUES IN THE SEDIMENT
- % of applied amount at day 0: 0.4 (Lienden), 1.1 (Ijzendoorn)
- % of applied amount at end of study period: 16.1 (Lienden), 66.9 (Ijzendoorn)

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 2.0 (Lienden), 1.4 (Ijzendoorn)

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: < 0.1% of the applied radioactivity were found in the traps for volatile compounds.

Table 1: Radioactivity Balance in the Water-Sediment System Lienden

 

	% applied radioactivity, mean of two samples
sampling time (days)	0	14	29	60	92
aqueous phase	92.5	80.8	74.3	73.9	65.2
sediment extract	5.9	11.9	12.6	14.4	15.4
not extractable residues and filter residues	0.4	5.9	12.0	9.6	16.1
C02	n.d.	<0.1	0.1	0.7	2.0

n.d. = not detected

 

 

Table 2: Radioactivity Balance in the Water-Sediment System Ijzendoorn

 

	% applied radioactivity, mean of two samples
sampling time (days)	0	14	29	60	92
aqueous phase	80.7	44.2	31.0	15.7	12.5
sediment extract	15.2	35.7	32.4	23.1	18.0
not extract able residues and filter residues	1.1	19.1	36.0	58.7	66.9
C02	n.d.	0.1	0.2	0.6	1.4

n.d. = not detected

Validity criteria fulfilled:

not applicable

Conclusions:

Summarizing the degradational behaviour of NTN 33 893 in the two investigated water/sediment systems can be described as follows: The active ingredient was degraded relatively rapidly in the system IJzendoorn (half-life 30 days). During this process NTN 33 823 as main metabolite as well as residues bound to the sediment were formed. In the system Lienden the degree of degradation was considerably lower (extrapolated half-life: 162 days). In this case amounts of 6-chloronicotinic acid and DIJ 9646-2 were found - particularly in the water phase - in an order of magnitude of 1-4%.

Reference 2

Endpoint:

biodegradation in water: simulation testing on ultimate degradation in surface water

Type of information:

experimental study

Adequacy of study:

key study

Study period:

04 May 1995 - 26 Nov 1996

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: Agriculture Canada. 1987. Guidelines for Determining Environmental Chemistry and Fate of Pesticides. Agriculture Canada, Ottawa, Canada.

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

natural water: freshwater

Details on source and properties of surface water:

- Details on collection (e.g. location, sampling depth, contamination history, procedure): The Canadian pond water used for the study was obtained from the following location: Lot 2, Concession 10, Norfolk Township, Norfolk County, Ontario Canada.
- pH at time of collection: 8.37
- Initial oxygen concentration (mg/l): 8.2
- Hardness (CaCO3): 210 mg/L
- Water filtered: no

Duration of test (contact time):

> 123 d

Initial conc.:

0.66 mg/L

Based on:

test mat.

Remarks:

Nonsterile, light exposed test system

Initial conc.:

0.672 mg/L

Based on:

test mat.

Remarks:

Nonsterile, nonexposed test system

Initial conc.:

0.706 mg/L

Based on:

test mat.

Remarks:

Sterile, light exposed test system

Initial conc.:

0.706 mg/L

Based on:

test mat.

Remarks:

Sterile, nonexposed test system

Parameter followed for biodegradation estimation:

radiochem. meas.

test mat. analysis

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment: 100 mL
- Composition of medium: Each borosilicate culture tube was dosed with 923 µL of 14C-imidacloprid stock solution (0.519 mg/mL stock solution in acetonitrile diluted to 75.8 µg/mL in reagent water [obtained from a Milli-Q Water Purification System]) and swirled to mix. The nominal concentration of test substance in the pond water was 0.70 ppm.
- Solubilising agent (type and concentration if used): acetonitrile in stock solution (see section “Composition of medium”)
- Test temperature: 22 ± 1 °C
- pH: 8.37 (initial pH of the pond water), pH measurements were performed on all samples
- pH adjusted: no
- Aeration of dilution water: In the metabolism vessel, individual tube was aerated by an air pulsing system to maintain dissolved oxygen and redox levels. The metabolism vessel was connected to a trapping system consisting of three 250 mL 1N KOH traps, one 250 mL 1N H2SO4 trap, one 250 mL ethylene glycol trap and a small trap at the end containing two foam plugs for 14C-organic volatiles. The test system was aerated by passing air from compressed air tanks over Ascarite and Drierite, through a flow control manifold and into a 1N KOH pre-trap, to remove CO2, followed by a DI water pretrap to humidify the air.
- Continuous darkness: depending on treatment (The definitive study was conducted with the following four test systems. 1) Nonsterile, light exposed (12 hours on/off daily), 2) Nonsterile, nonexposed, 3) Sterile, light exposed (12 hours on/off daily), 4) Sterile, nonexposed)
- Any indication of the test material adsorbing to the walls of the test apparatus: For some test systems and sample points, the mass balance calculated from the summation of 14C-activity in water samples and 14C-volatiles was less than 90%. In these instances, the borosilicate tubes which contained the sample were extracted by adding extractant to the tube (extractants were methanol, and/or THF, and/or 1N KOH, and/or 1N H2SO4) shaking for 1/2 hour, saving the extractant, then repeating the extraction twice more for a total of 3 extractions.

TEST SYSTEM
- Culturing apparatus: The test containers were 40 x 200 mm borosilicate glass tubes.
- Number of culture flasks/concentration: 40
- Method used to control oxygen conditions: Air pulsing system
- Measuring equipment: Radioactivity measurements were made with either a Beckman model 6000 or model 3801 Liquid Scintillation Counting System (Beckman Instruments, Fullerton, CA); HPLC equipped with a UV detector was used for identification of radiolabeled imidacloprid and its degradates; GC-MS was applied for conformational analysis of derivatized degradate isolates (Hewlett-Packard 5890 A Series II GC-MS with a Hewlett-Packard 5971A Mass Selective Detector [Hewlett-Packard, Avondale, PA]).; LC-MS/MS analysis of parent and degradate isolates was performed on a PE Sciex API 300 LC-MS/MS system (Perkin-Elmer Sciex Instruments, Ontario, Canada); The pH meters used during the study were either an Accumet Model 50 pH meter (Denver Instrument Co., Arvada, CO) or a Corning Model 125 pH meter (Corning Inc. Corning, NY) that were calibrated before use; The meter used to measure redox potential was a Corning model 125 pH/millivolt meter (Corning Inc., Corning, NY) operating in the millivolt mode; Dissolved oxygen was measured using either a YSI model 58 dissolved oxygen meter (Yellow Springs Instrument Co., Yellow Springs, OH) or a Corning M90 meter with a dissolved oxygen probe (Corning Inc. Corning, NY); Conductivity was measured using a YSI model 33 conductivity meter (Yellow Springs Instrument Co., Yellow Springs, OH)
- Details of trap for CO2 and volatile organics if used: The metabolism vessel was connected to a trapping system consisting of three 250 mL IN KOH traps, one 250 mL 1N H2SO4 trap, one 250 mL ethylene glycol trap and a small trap at the end containing two foam plugs for 14C-organic volatiles. Trapping systems were sampled and analyzed for volatile 14C -residues and replenished at each sampling interval with fresh trapping solutions and foam plugs. The evolution of 14C-volatiles was quantified by analyzing 3 x 1.00-mL aliquots of each trapping solution from each test system by LSC at each time point.

SAMPLING
- Sampling frequency: Depending on the respective test system duplicate flasks were removed from the testing environment for analysis at the following time points:
1) Nonsterile, light exposed (12 hours on/off daily): days 0, 1,3, 7, 14, 18, 25, 31, 61, 91, and 123 (termination); 2) Nonsterile, nonexposed: days 0, 1, 3, 7, 14, 31, 60, 92, 123, 183, 274, and 366 (termination); 3) Sterile, light exposed (12 hours on/off daily): days 0, 1, 3, 7, 14, 31, 60, 92, 123, 183, 274, and 366 (termination); 4) Sterile, nonexposed: days 0, 1, 3, 7, 14, 31, 60, 92, 123, 183, 274, and 366 (termination).
- Sterility check if applicable: In the sterile test systems microbial samples were taken on days 92, 183, 274, and 366 in addition to those taken at initiation. Dilutions of test water ranged from 10E-01 to 10E-05 for bacterial and fungal counts. Dilutions were added to sterile plastic petri dishes. Then, the appropriate agar solution, DIFCO plate count agar for bacteria and Sabouraud agar for fungi, was added to the plates. The bacterial plates were incubated in the dark at 26 ± 2 °C, and the fungal plates were incubated in the dark at ambient temperature; In addition to microbial plate counts, the microbial biomass of the pond water from the control system after 274 days incubation was determined using a modified version of the Anderson and Domsch method. The method was modified such that 14C-glucose was used instead of nonradiolabled glucose to measure microbial respiration.

DESCRIPTION OF CONTROL AND/OR BLANK TREATMENT PREPARATION CONTROL AND BLANK SYSTEM
- Other: One hundred milliliters of pond water was also added to each of 20 nonsterile or sterile (depending on testsystem) borosilicate culture tubes, which were used as controls. Eighteen of these control tubes were inserted into a separate metabolism vessel and placed in the environmental chamber. One of the remaining two was used for microbial evaluation, while the other was used as a blank sample for day-0 LSC analysis. The metabolism vessel containing the control tubes was placed on a similar aeration system as the nonsterile, light exposed test samples, with a trapping system consisting of 250 mL traps containing 1N KOH, 1N H2SO4 and ethylene glycol.

Compartment:

natural water: freshwater

% Recovery:

90.4

Remarks on result:

other:

Remarks:

Recovery and distribution of 14C-radioactivity after 123 days— nonsterile, light exposed test system

Compartment:

natural water: freshwater

% Recovery:

96.3

Remarks on result:

other:

Remarks:

Recovery and distribution of 14C-radioactivity after 366 days — nonsterile, nonexposed test system

Compartment:

natural water: freshwater

% Recovery:

93.8

Remarks on result:

other:

Remarks:

Recovery and distribution of 14C-radioactivity after 366 days — sterile, light exposed test system

Compartment:

natural water: freshwater

% Recovery:

92

Remarks on result:

other:

Remarks:

Recovery and distribution of 14C-radioactivity after 366 days — sterile, nonexposed test system

% Degr.:

5

Parameter:

test mat. analysis

Sampling time:

123 d

Remarks on result:

other:

Remarks:

Nonsterile, light exposed test system

% Degr.:

4.3

Parameter:

test mat. analysis

Sampling time:

366 d

Remarks on result:

other:

Remarks:

Nonsterile, nonexposed test system

% Degr.:

26.2

Parameter:

test mat. analysis

Sampling time:

366 d

Remarks on result:

other:

Remarks:

Sterile, light exposed test system

% Degr.:

0.2

Parameter:

test mat. analysis

Sampling time:

366 d

Remarks on result:

other:

Remarks:

Sterile, nonexposed test system

Compartment:

natural water: freshwater

DT50:

4.19 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Nonsterile, light exposed test system

Compartment:

natural water: freshwater

DT50:

10.7 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Nonsterile, light exposed test system; Calculated DT50 based on experimental data at 22 °C

Compartment:

natural water: freshwater

DT50:

331 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Nonsterile, nonexposed test system

Compartment:

natural water: freshwater

DT50:

842.8 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Nonsterile, nonexposed test system; Calculated DT50 based on experimental data at 22 °C

Compartment:

natural water: freshwater

DT50:

28.4 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Sterile, light exposed test system

Compartment:

natural water: freshwater

DT50:

72.3 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Sterile, light exposed test system; Calculated DT50 based on experimental data at 22 °C

Compartment:

natural water: freshwater

DT50:

499 d

Type:

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

Temp.:

22 °C

Remarks on result:

other:

Remarks:

Sterile, nonexposed test system

Compartment:

natural water: freshwater

DT50:

1 270.6 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Sterile, nonexposed test system; Calculated DT50 based on experimental data at 22 °C

Transformation products:

yes

Remarks:

Ten degradation products were found. Not all of which could be identified. Please refer to "Details on transformation products".

No.:

#1

No.:

#2

No.:

#3

Details on transformation products:

- Formation and decline of each transformation product during test:
Nonsterile, light exposed test system:
Radiolabeled imidacloprid declined rapidly from 99.3% at day 0 to less than 10% of the initial measured dose (IMD) at day 14, declining subsequently with time until it was not detected on days 91 and 123. The test substance metabolized into ten quantifiable degradate products, four of which, (degradates A [#1], B [#2], C [#3], and F) exceeded 10% of the IMD. As the parent declined, degradate C showed the most rapid increase, from 0.2% at day 0 to 82% of IMD at day 25. Degradate C tended to decline after this sampling time, while other degradates increased. Degradate A increased to 10.9% of IMD at day 91 and 16.4% of IMD at day 123. Degradate B increased from 1% at day 31 to 11.6% at day 61, reaching a maximum of 18.4% of IMD at day 91, then declining to less than 10% of IMD at day 123. Degradate F reached a maximum concentration of approximately 10.6% of IMD at day 61. At termination 14-CO2 evolution reached 5%. The test was terminated after day 123 based on the depletion of the parent and formation and decline of degradates.
Nonsterile, nonexposed test system:
Radiolabeled imidacloprid declined slowly from 97.0% at day 0 to 47.8% of IMD at termination. The test substance metabolized into nine quantifiable degradate products, two of which (degradates C and D) exceeded 10% of the IMD. As the parent declined, degradate C increased to 26.4% at day 274, then decreased to 19.2% at termination. Degradate D increased to 10.6% of IMD at termination. 14-CO2 evolution reached 4.3% at termination.
Sterile, light exposed test system:
Radiolabeled imidacloprid declined from 97.1% of IMD to 12.7% at 92 days. The test substance metabolized into nine quantifiable degradates, two of which, (degradates C and J) exceeded 10% of the IMD in 92 days. As the parent declined, degradate J showed an increase to 32.8% of IMD at 60 days, after which it declined to 18.8% at 92 days. Degradate C increased more gradually, from 1.7% at day 7 to 20.2% of IMD at 92 days. 14-CO2 evolution reached 8.3% at 92 days.
Sterile, nonexposed test system:
Radiolabeled imidacloprid declined from 97.1% of IMD to 90.4% at 92 days. Six different degradates were observed between day 0 and 92 days, but none exceeded 10% of IMD.

Evaporation of parent compound:

no

Remarks:

In all test systems no significant amounts (<0.1%) of 14C-organic volatiles were trapped in ethylene glycol, sulfuric acid and foam plugs.

Volatile metabolites:

no

Remarks:

In all test systems no significant amounts (<0.1%) of 14C-organic volatiles were trapped in ethylene glycol, sulfuric acid and foam plugs.

Residues:

not specified

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): In the nonsterile light exposed test system, the test was terminated after 123 days due to rapid degradation of 14C-imidacloprid. The sterile systems did not remain completely sterile after 92 days. However, the difference in half-lives in exposed (nonsterile = 4.19 days; sterile = 28.4 days) and the nonexposed (nonsterile = 331 days; sterile = 499 days) suggested that the sterile systems remained partially sterile and less microbially active than nonsterile.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: 14-CO2 Cumulative production, after 123 days, in the nonsterile light exposed, nonsterile nonexposed, sterile light exposed and sterile nonexposed test systems was 5.0, 1.0, 13.1 and 0.1% respectively. After 366 days, 14-CO2 cumulative production in the nonsterile nonexposed, sterile light exposed and sterile nonexposed test systems was accounted for 4.3, 26.2 and 0.2% respectively.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Production of organic volatiles was < 0.1 %, for all test systems, indicating that organic volatile production was not a significant sources of test substance removal.

RESULTS OF SUPPLEMENTARY EXPERIMENT (if any):
- Storage stability: The stability of14C-imidacloprid stored under freezer conditions was demonstrated by comparing 14C-HPLC chromatograms of day-0 samples and a stability sample analyzed after 123 days of freezer storage. No change in the concentration of parent by HPLC was observed, after 123 days of freezer storage indicating that 14C-imidacloprid was stable under freezer storage.

Table 1: Comparison of Mass balance, Percent Metabolized, Major Degradates and Half-life of the Nonsterile, Light Exposed; Nonstenle, Nonexposed; Sterile, Light Exposed; and Sterile, Nonexposed Test Systems

 

	Nonsterile, Light Exposed	Nonsterile, Nonexposed	Sterile, Light Exposed	Sterile, Nonexposed
Average Mass Balance	96.5 + 4.6	95.3 ± 2.2	94.9 ± 2.5	102 ± 5
% Parent (Time)	ND (Day 91)	47.1% (Day 274)	12.7% (Day 92)	90.4% (Day 92)
			1.0% (Day 274)	37.7% (Day 366)
% Degradate (Time)	A 16.4% (Day 123)	C 26.4% (Day 274)	C 20.2% (Day 92)
	B 18.4% (Day 91)	D 10.6% (Day 366)	J 32.8% (Day 60)
	C 82.0% (Day 25)
	F 10.6% (Day 61)
Half-Life	4.19 days	331 days	28.4 days	499 days

 

A:          6-Chloro-nicotinic Acid

B:           Urea NTN

C:           Des-Nitro Imidacloprid

D:          Unknown

F:           Unknown

J:            Unknown

ND = Not Detected

Degradate E was less than 10% in all systems

Validity criteria fulfilled:

not applicable

Conclusions:

These results showed that in open water systems such as ponds or lakes, imidacloprid would degrade rapidly through light- and microbial- mediated degradation mechanisms into des-nitro imidacloprid, urea imidacloprid, 6-chloro nicotinic acid and possibly other more polar degradates. These degradates may further mineralize to CO2.

Reference 3

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Study period:

29 Aug 1995 - 15 Dec 1996

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)

GLP compliance:

yes

Radiolabelling:

yes

Oxygen conditions:

anaerobic

% Degr.:

< 0.2

Parameter:

radiochem. meas.

Sampling time:

366 d

Remarks on result:

other:

Remarks:

Nonsterile Test

% Degr.:

< 0.2

Parameter:

radiochem. meas.

Sampling time:

366 d

Remarks on result:

other:

Remarks:

Sterile Test

Compartment:

natural water / sediment: freshwater

DT50:

121 d

Type:

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

Temp.:

5 °C

Remarks on result:

other:

Remarks:

Nonsterile Test

Compartment:

natural water / sediment: freshwater

DT50:

60.4 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Nonsterile Test; Calculated DT50 based on experimental data at 5 °C

Compartment:

natural water / sediment: freshwater

DT50:

657 d

Type:

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

Temp.:

5 °C

Remarks on result:

other:

Remarks:

Sterile Test

Compartment:

natural water / sediment: freshwater

DT50:

328.1 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Sterile Test; Calculated DT50 based on experimental data at 5 °C

Validity criteria fulfilled:

not applicable

Conclusions:

The anaerobic aquatic biotransformation of the test substance [pyridinyl-14C-methyl]imidacloprid was studied in pond water and sediment obtained from Stilwell, Kansas. The test systems were kept in the dark, over a period of one year, in an environmental chamber maintained at 5 + 1 °C. The study, dosed at a nominal concentration of 0.6 ppm, was conducted under both nonsterile and sterile conditions. The dose rate was calculated based on a water layer of 10 cm depth, and is approximately 1.5 times the maximum commercial use rate (0.5 Ib a.i./acre) for agricultural application. Anaerobic conditions were confirmed by dissolved oxygen and redox measurements. Microbial viability was confirmed by microbial biomass and microbial plate count determinations. The results of the metabolism of 14C-imidacloprid under each condition are summarized below.

Nonsterile Condition:
Over the course of the study for the nonsterile system, residues from water decreased from 15.0% of the initial measured dose (IMD) at day 0 to 0.7% at day 366. Extractable residues from sediment decreased from 79.7% at day 0 to 27.0% at day 366. Non-extractable residues in the sediment increased from 5.3% at day 0 to 68.9% at termination (day 366). 14C-volatile residues never exceeded 0.2% of the IMD during the entire period of incubation. The average 14C-mass balance was 97.5%, with values ranging from 91.1% to 101.7%. Non-extractable residues comprising > 10% of IMD were subjected to further extraction. The humic and fulvic acid fractions accounted for 3.70 and 6.08% of IMD of the non extractable radioactivity, respectively, at termination. Reflux extraction of the humin fraction further released 14.17% of IMD. The non-extractable bound residues at termination were 33.04% of IMD. The parent concentration declined from 94.2% at day 0 to 11.9% at day 366. The half-life of 14C-imidacloprid under nonsterile, anaerobic aquatic conditions was calculated to be 121 days, using the data from day 0 to day 366 (R2= 0.989; half-life range calculated from the standard error of the slope coefficient was 117 to 125 days). The major biotransformation product (> 10% of IMD) found at study termination was NTN 33893 des-nitro, which represented 13.9% of IMD. The identity of this metabolite was confirmed by mass spectrometry.

Sterile Condition:
Degradation of 14C-imidacloprid under sterile anaerobic conditions was less rapid than nonsterile conditions. The sterile system was not completely sterile after 55 days. Residues from water decreased from 31.3% of the initial measured dose (IMD) at day 0 to 2.6% at day 359. Extractable residues from sediment decreased from 65.1 % at day 0 to 37.8% at day 359. Non-extractable residues in the sediment increased from 3.6% at day 0 to 56.6% at day 359. 14C-volatile residues never exceeded 0.2% of the IMD during the entire period of incubation. The average 14C-mass balance was 96.8%, with values ranging from 90.1 % to 100.9% Non-extractable residues comprising > 10% of IMD were subjected to further extractions. The humic and fulvic acid fractions accounted for 2.90 and 6.44% of IMD of the non-extractable radioactivity at termination. Reflux extraction of the humin fraction further released 11.38% of IMD. The non-extractable bound residues were 26.69% of IMD. The parent concentration declined from 96.0% at day 0 to 86.7% at day 55, after which the test system remained only partially sterile. The half-life of 14C-imidacloprid under sterile, anaerobic aquatic conditions was calculated to be 657 days, using the data from day 0 to day 55 (R2= 0.469; half-life range calculated from the standard error of the slope coefficient was 444 to 1238 days). The major biotransformation product (> 10% of IMD) found at study termination was NTN 33893 des-nitro, which represented 16.0% of IMD. The identity of this metabolite was confirmed by mass spectrometry.

Comparison of Test Systems:
Although the sterile system did not remain completely sterile after 55 days, the difference in half-lives (nonsterile = 121 days; sterile = 657 days) and the biotransformation of 14C-imidacloprid (nonsterile = 65.3%; sterile = 86.7% at 55 days) suggested that the sterile system remained less microbially active than nonsterile. These results showed that in anaerobic water systems such as benthic regions of ponds and lakes, imidacloprid would degrade through microbial-mediated degradation mechanisms mainly to NTN 33893 des-nitro.

Reference 4

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

anaerobic

% Degr.:

0.2

Parameter:

radiochem. meas.

Sampling time:

249 d

Compartment:

natural water / sediment: freshwater

DT50:

27.12 d

Type:

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

Temp.:

22 °C

Compartment:

natural water / sediment: freshwater

DT50:

69.1 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 based on experimental data at 22 °C

Validity criteria fulfilled:

not applicable

Conclusions:

The degradation and metabolism of the insecticidal active ingredient imidacloprid was investigated under anaerobic conditions in an aquatic model ecosystem with sediment portion.
Water and accompanying sediment originated from a pond in Stanley (Kansas). After adjustment of the system to anaerobic conditions [pyridinyl-14C-methylene] imidacloprid was appplied to the water surface at a concentration of 0.6 mg/L. This was incubated for 0, 3, 7, 14, 30, 60, 120, 249 and 358 days.
The active ingredient content in the supernatant water phase declined to about 54% until day 30, to about 3% until day 120 and to 0.1% until day 249. A maximum concentration of about 19% active ingredient could be detected in the sediment after an incubation period of 14 days. About 4% of the applied amount of active ingredient were recovered on day 60 and only 0.1% on day 249.
The half-life of imidacloprid in water and sediment was calculated to be 27 days.
The only main metabolite was the free base (NTN 33823). The maximum concentration of 20% in the water was measured after 60 days. Relative to the applied amount of radioactivity about 14% of this metabolite could still be detected in the water after 358 days. Large amounts of the metabolite were bound to the sediment. Under stringent extraction conditions about 50% were still extracted from the sediment and detected after 358 days.

Reference 5

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

other: EPA Pesticide Assessment Guidelines, Subdivision N: § 161-4

Version / remarks:

1982

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

aerobic

% Degr.:

0.7

Parameter:

radiochem. meas.

Sampling time:

30 d

Compartment:

natural water / sediment: freshwater

DT50:

129 d

Type:

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

Temp.:

22 °C

Compartment:

natural water / sediment: freshwater

DT50:

328.5 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 based on experimental data at 22 °C

Validity criteria fulfilled:

not applicable

Conclusions:

The degradation of the insecticidal active ingredient imidacloprid in an aquatic microecosystem with sediment portion was investigated. The samples originated from a pond in an agriculturally used area in Stilwell (Kansas, USA). The applied amount of [methylene-14C] imidacloprid was 0.68 mg/L water. The incubation period of the experiment was limited to 30 days.
After an incubation period of 30 days, 64.0 % of the applied radioactivity could be detected in the surface water as parent compound (TLC-evaluation), and 20.4 % of unchanged parent compound could still be detected in the sediment after 30 days.
The first half-life (DT50) for the degradation of the active ingredient in the test system was 129 days.
The active ingredient was degraded in the test system to the point of the final mineralization product 14CO2. After an incubation period of 30 days, 0.7 % of the applied radioactivity were detected as 14CO2.
In the course of the mineralization, small amounts of several metabolites were detected in water and sediment, with only WAK 4103 occurring in amounts worth mentioning (2.8 %).
The percentage of bound residues in the sediment was 8.2 % of the applied radioactivity after an incubation period of 30 days.

Reference 6

Endpoint:

biodegradation in water: sediment simulation testing

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

2 (reliable with restrictions)

Rationale for reliability incl. deficiencies:

guideline study with acceptable restrictions

Qualifier:

according to guideline

Guideline:

EPA Subdivision N Pesticide Guideline 162-4 (Aerobic Aquatic Metabolism)

Version / remarks:

1982

GLP compliance:

yes (incl. QA statement)

Radiolabelling:

yes

Oxygen conditions:

aerobic

% Degr.:

5.8

Parameter:

radiochem. meas.

Sampling time:

21 d

Remarks on result:

other:

Remarks:

14CO2 under artificial sunlight

% Degr.:

9.8

Parameter:

radiochem. meas.

Sampling time:

21 d

Remarks on result:

other:

Remarks:

14CO2 under xenon light

Compartment:

natural water / sediment: freshwater

DT50:

< 14 d

Type:

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

Temp.:

20 °C

Compartment:

natural water / sediment: freshwater

DT50:

29.7 d

Type:

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

Temp.:

12 °C

Remarks on result:

other:

Remarks:

Calculated DT50 based on experimental data at 20 °C

Validity criteria fulfilled:

not applicable

Conclusions:

Under the influence of artificial light (xenon lamp) and sunlight, the degradation of the insecticidal active ingredient imidacloprid was investigated in an aquatic micro ecosystem with sediment portion. The samples originated from a pond in an agriculturally used area in Stilwell (Kansas, USA). The choosen concentration (0.62 mg/L) in this part of the study is the same as in the anaerobic aquatic study. The concentration in the main test was 0.34 mg/L. The applied amount of [methylene-14C-] imidacloprid was 0.62 mg/L water. The incubation period of the test was determined to be 30 days.
The active ingredient is very quickly degraded under the influence of sunlight as well as also of xenon light. The first half-life for the xenon light variant is estimated to be less than 5 days. The mineralization rates after an incubation period of 21 days are 5.8% of the applied radioactivity for the sunlight variant and 9.8% for the xenon light variant. Several metabolites were formed during the mineralization in the water as well as also in the sediment, with 6-chloronicotinic acid as key metabolite accounting for the greatest percentage for the further degradation. There is no difference in the qualitative distribution pattern of the metabolites between the two test variants. In the main test without irradiation only slight mineralisation was observed. The test with additional light conditions showed after 30 days a amount of 10.5% 14CO2. Relative to the applied amount of radioactivity the percentage of bound residues after an incubation period of 21 days was 67.6% in the sunlight variant and 47.7% in the xenon light variant. After the fractionation of the humic substances with 0.5 N NaOH solution under nitrogen, 4.0% of the applied radioactivity in the sunlight variant were localized in the humic acids, 21.2% in the fulvic acids and 35.1% in the humin. The respective values for the xenon light variant were 1.1% for the humic acids, 15.7% for the fulvic acids and 14.8% for the humin.

Description of key information

DT50 = 10.7 - 1271 days, degradation in water recalculated to 12 °C

 

DT50 = 29.7 – 412.5 days, degradation in sediment recalculated to 12 °C

Key value for chemical safety assessment

Half-life in freshwater:

843 d

at the temperature of:

12 °C

Half-life in freshwater sediment:

412.5 d

at the temperature of:

12 °C

Additional information

For the degradation of (2E)-1-[(6-chloropyridin-3-yl)methyl]-N-nitroimidazolidin-2-imine in water and water/sediment systems ten studies are available.

 

The first laboratory simulation study assessed the degradation of the radioactively labeled test substance and the formation of metabolites in natural surface water under aerobic aquatic conditions, following GLP and the guideline “Agriculture Canada. 1987. Guidelines for Determining Environmental Chemistry and Fate of Pesticides. Agriculture Canada, Ottawa, Canada”. The definitive study was conducted at 22 °C with the following four test systems: 1) Nonsterile, light exposed (12 hours on/off daily), 2) Nonsterile, nonexposed, 3) Sterile, light exposed (12 hours on/off daily), 4) Sterile, nonexposed. In these test systems the half-life of the substance was accounted for 4.19 days (10.7 days, recalculated to 12 °C), 331 days (842.8 days, recalculated to 12 °C), 28.4 (72.3 days, recalculated to 12 °C) and 199 days (1270.6 days, recalculated to 12 °C) at 22 °C. Highest mineralization was recorded for the system “sterile, light exposed” with 26.2% of the applied radioactivity after 366 days.

These results showed that in open water systems such as ponds or lakes, the test substance would degrade through light- and microbial- mediated degradation mechanisms into des-nitro imidacloprid, urea imidacloprid, 6-chloro nicotinic acid and possibly other more polar degradates.

 

The second laboratory simulation study assessed the degradation of the test substance under aerobic conditions in two water/sediment systems with radioactively labeled active ingredient, according to GLP and the guideline “EPA Subdivision N Pesticide Guideline 162-4 (Aerobic Aquatic Metabolism)”. The study was conducted at 22 °C in the dark for 92 days. Under aerobic aquatic conditions the test substance was rapidly transferred from the water to the sediment with a formation of 66.9 and 19.1%, respectively, of non extractable residues after 92 days. The half-life of the test substance was 162 days (412.5 days, recalculated to 12 °C) in the system Lienden and 30 days (76.4 days, recalculated to 12 °C) in the system Ijzendoorn. The main metabolite occurred in amounts up to 12.3% of the applied radioactivity (System Ijzendoorn, day 92). After 92 days of incubation 2.0 and 1.7% of the applied radioactivity were mineralized.

 

In a third study, according to GLP and “EPA Subdivision N Pesticide Guideline 162-4 (Aerobic Aquatic Metabolism)”, the degradation of the test substance was investigated in an aerobic aquatic micro ecosystem with sediment portion under the influence of artificial light (xenon lamp) and sunlight. The incubation period of the test was determined to be 30 days at 20 °C. The active ingredient was very quickly degraded under the influence of sunlight as well as also of xenon light. The first half-life for the xenon light variant was estimated to be less than 5 days (<10.6 days, recalculated to 12 °C) and less than 14 days for the sunlight variant (<29.7 days, recalculated to 12 °C). The mineralization rates after an incubation period of 21 days are 5.8% of the applied radioactivity for the sunlight variant and 9.8% for the xenon light variant. Several metabolites were formed during the mineralization in the water as well as also in the sediment, with 6-chloronicotinic acid as key metabolite accounting for the greatest percentage for the further degradation. The test with additional light conditions showed after 30 days an amount of 10.5% 14-CO2. Relative to the applied amount of radioactivity the percentage of bound residues after an incubation period of 21 days was 67.6% in the sunlight variant and 47.7% in the xenon light variant.

 

A fourth study determined the degradation of the test substance in an aquatic microecosystem with sediment portion under aerobic conditions, following GLP and the guideline “EPA Pesticide Assessment Guidelines, Subdivision N: § 161-4”. After an incubation period of 30 days at 22 °C, 64.0 % of the applied radioactivity could be detected in the surface water as parent compound, and 20.4 % of unchanged parent compound could still be detected in the sediment after 30 days. After an incubation period of 30 days, 0.7 % of the applied radioactivity were detected as 14-CO2. The determined half-life (DT50) was 129 days (328.5 days, recalculated to 12 °C).

 

Two more GLP studies assessed the anaerobic degradation of the test substance in water/sediment systems according to “EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)”. In both tests incubation was performed in darkness. The first study (incubation for 358 days at 22 °C) determined a half-life of 27.1 days (69.1 days, recalculated to 12 °C), while the second study (incubation for 366 days at 5 °C) revealed a half-life of 121 days (60.4 days, recalculated to 12 °C). In the latter study 68.9 % of the initially applied radioactivity was bound to the sediment as non-extractable residues.

 

Four more studies on the degradation of the test substance in water and sediment are available. Half-life determinations range from 1.4 to 10 days in water and from 10 days to 1000 days in sediment.