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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Nov 1995 - Sep 1996
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
guideline study with acceptable restrictions
Qualifier:
according to guideline
Guideline:
other: BBA-Guidelines for Testing of Plant Protectants in the Registration Process Part IV, 5-1, Degradability and Fate of Plant Protectants in the Water/Sediment System
Version / remarks:
1990
Qualifier:
according to guideline
Guideline:
other: Commission Directive 95/36/EC, Placing Plan Protection Products on the Market; Official Journal of the European Communities, 14. July 1995
Version / remarks:
1995
Qualifier:
according to guideline
Guideline:
other: SETAC-Europe Procedures for Assessing the Environmental Fate and Ecotoxicity of Pesticides, March 1995
Version / remarks:
1995
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): see “Details on source and properties of the sediment”
- Temperature (°C) at time of collection: 7.6 (Hönniger), 9.4 (Lienden)
- pH at time of collection: 7.8 (Hönniger), 7.9 (Lienden)
- Redox potential (mv) initial: 93 (Hönniger), 196 (Lienden)
- Oxygen saturation (%): 76 (Hönniger), 81 (Lienden)
- Hardness (grad DH): 3.6 (Hönniger), 9.6 (Lienden)
- Dissolved organic carbon (mg C/L): 2.0 (Hönniger), 2.7 (Lienden)
Details on source and properties of sediment:
- Details on collection (e.g. location, sampling depth, contamination history, procedure):
Hönniger Pond (Hönniger Weiher. Wipperfürth. Germany): Water and sediment samples were collected from an artificially dammed pond (mesotroph/oligotroph) in the course of the "Hönniger Creek" forming "Hönniger Pond". On account of its in- and outlet the pond (about 1,000 m2 in surface area) had a strong water current. Water and sediment were freshly sampled on November 14, 1995.
Lienden Lake (Lienden. Netherland): Water and sediment samples were collected from a lake (oligotroph) resulting from re-cultivation of a gravel pit. Water and sediment were freshly sampled on November 15, 1995.
- Storage conditions: Water and sediment collected from both origins were kept under aerated conditions in the laboratory. They were used within the next few days after sampling.
- Textural classification according to DIN 19682 (i.e. %sand/silt/clay):
Hönniger: 24.3% sand, 63.4% silt, 12.3% clay
Lienden: 97.8% sand, 1.8% silt, 0.4% clay
- pH (dest. H2O) at time of collection: 6.0 (Hönniger), 8.4 (Lienden)
- Organic carbon (%): 3.84 (Hönniger), 0.39 (Lienden)
- CEC (meq/100 g): 11 (Hönniger), 3 (Lienden)
- Sediment samples sieved: Yes. The collected water-sediment samples were separated in the laboratory by decanting the supernatant water each. The aqueous sediment was passed through a 0.5 cm mesh sieve and mixed. After settling the remaining water was decanted, the sediment was mixed again and the dry weight was de termined. - Other: The dry matter content (mean of duplicates) of sediment Hönniger was 41.2% and of the sediment Lienden was 77.3%.

Duration of test (contact time):
> 0 - < 100 d
Initial conc.:
120.71 µg/L
Based on:
test mat.
Remarks:
Corresponding to a direct spray of 359 g/ha; test system: Hönniger
Initial conc.:
126.53 µg/L
Based on:
test mat.
Remarks:
Corresponding to a direct spray of 376 g/ha; test system: Lienden
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: Amounts of the aqueous sediments (stones and plant debris were taken out) corresponding to 50 g dry matter (DM) were weighed into each incubation vessel which was equal to 121.4 g fresh weight for Hönniger and 64.7 g for Lienden sediment. The respective water was filtered through a 0.2 mm sieve and 374.1 mL (Hönniger) and 430.8 mL (Lienden) corresponding to a total volume of 445.5 mL of water each were added to each incubation vessel. The total mass of sediment plus water/vessel was about 500 g for both systems.
- Test temperature: The test systems were incubated in the dark at 20°C
- Other: Assuming a direct spray onto a water body of 30 cm depth, the applied amount of test substance corresponds to a projected concentration of about 0.12 mg substance/1L of water (i.e. about 54 µg a.i. per incubation vessel in case of a total volume of water of approx. 450 mL). The actual amount of test substance used in this study was 53.78 (Hönniger) or 56.37 (Lienden) µg a.i. per incubation vessel.

TEST SYSTEM
- Culturing apparatus: The system used for the present study (see Appendices 1 and 2 in the “Attached background material”) is a special glass vessel with an inner diameter of about 10.5 cm and a volume of about 1,000 mL. The test system is characterised by the following features:
1) the stagnant sediment is covered by a water layer being in motion,
2) the rippling surface of the water guarantees oxygen uptake from the air,
3) the static sediment provides the biotope for micro-organisms having differing oxygen demand,
4) the air in the vessel has the same oxygen content as the atmosphere,
5) volatile radioactive metabolites including 14CO2 are absorbed in a trapping attachment
- Number of culture flasks/concentration: 16

SAMPLING
- Sampling frequency: Processing dates were 0, 1 3 7 14 35 62 and 100 days after application.
- Sampling method used per analysis type: At each processing date two batches per water-sediment system treated with active ingredient were completely processed.
- Other: At each sampling interval (except day 0) and before taking off the trap attachment, gaseous compounds contained in the test vessel were purged into the trap by slightly pressurised, freshly moistened air for about 2 minutes.

Compartment:
natural water / sediment: freshwater
% Total extractable:
48.8
% Non extractable:
22.3
% CO2:
4
% Other volatiles:
0
Remarks on result:
other:
Remarks:
Total recovery in water-sediment system Hönniger after 100 days: 100.4%
Compartment:
natural water / sediment: freshwater
% Total extractable:
7
% Non extractable:
17.5
% CO2:
4.3
% Other volatiles:
0
Remarks on result:
other:
Remarks:
Total recovery in water-sediment system Lienden after 100 days: 97.5%
Parent/product:
parent
Compartment:
total system
Remarks:
Water-sediment system: Hönniger
% Degr.:
4
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
Mineralisation to CO2.
Parent/product:
parent
Compartment:
total system
Remarks:
Water-sediment system: Lienden
% Degr.:
4.3
Parameter:
radiochem. meas.
Sampling time:
100 d
Remarks on result:
other:
Remarks:
Mineralisation to CO2
Compartment:
natural water / sediment: freshwater
DT50:
20.3 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Water-sediment system: Hönniger
Compartment:
natural water / sediment: freshwater
DT50:
43.1 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 at 12 °C, based on results at 20 °C. Water-sediment system: Hönniger
Compartment:
natural water / sediment: freshwater
DT50:
12.1 d
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Water-sediment system: Lienden
Compartment:
natural water / sediment: freshwater
DT50:
25.7 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 at 12 °C, based on results at 20 °C. Water-sediment system: Lienden
Compartment:
natural water / sediment: freshwater
DT50:
20 d
Type:
other: Kinetic evaluation using FOCUS 2006
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Water-sediment system: Hönniger
Compartment:
natural water / sediment: freshwater
DT50:
12.4 d
Type:
other: Kinetic evaluation using FOCUS 2006
Temp.:
20 °C
Remarks on result:
other:
Remarks:
Water-sediment system: Lienden
Transformation products:
yes
Remarks:
see "Details on transformation products"
No.:
#1
No.:
#2
Details on transformation products:
TRANSFORMATION PRODUCTS IN THE SUPERNATANT
- The main degradation products were thiacloprid-amide (KKO 2254) and thiacloprid-sulfonic acid (WAK 6999). The identity of substances was verified by overlapping co-chromatography of water phase with the authentically reference standards and by HPLC.
- The maximum residue of the main metabolite KKO 2254 was reached on day 35 with about 17% of applied amount for the Hönniger system and about 62% of applied amount for the Lienden system.
- The maximum residue of WAK 6999 in the supernatant water of both systems was below 10% of applied radioactivity at each sampling interval (day 100: Hönniger 5.3%; Lienden 9.5% of applied radioactivity).
- Further one minor metabolite M1 (polarity higher than the polarity of WAK 6999) was observed in the supernatant water of both systems. The maximum portion was about 1.0% (Hönniger) and 2.3% (Lienden).

TRANSFORMATION PRODUCTS IN THE SEDIMENT
- The main metabolite was KKO 2254. The maximum was reached after about 35-62 days (Hönniger 37.8% of dose on day 62; Lienden 7.2% of dose on day 35). At study termination (day 100) 36% of dose for Hönniger and 6.4% of dose for Lienden sediment was measured.
- Further metabolites resulting from both 14C-labels were not relevant in the extracts of the submerged sediments, including WAK 6999 with a maximum of 1.2% of dose in Hönniger sediment on day 100.
Evaporation of parent compound:
no
Remarks:
In all test systems less than 0.01 % of applied radioactivity could be found in the PU traps at each sampling time during the entire incubation period.
Volatile metabolites:
no
Remarks:
In all test systems less than 0.01 % of applied radioactivity could be found in the PU traps at each sampling time during the entire incubation period.
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes
The respiration rate in the test vessels indicated that the systems were biologically active during the entire period of the test.
In the Hönniger System, which indicated about 4-fold higher activity, a reduction (factor of 2) of the microbial activity in the course of the experiment was observed.
In the Lienden system the respiration rate remained at a very low level during the entire study and also a reduction (factor of 2) of the microbial activity in the course of the experiment was observed.
The pH-value (1-N-KCI) measured in the sediments of the BIO vessels was constant during the entire study period. Also the direct records of pH in the supernatant water of the incubated test systems indicated constant pH-values between 6.9 and 7.9 (Hönniger system) and 7.9 to 8.6 for Lienden system.
In general, sufficient oxygen was available in the individual vessels at each sampling time. Thus, the data showed that the supernatant water was aerobic during the entire incubation period.

RADIOACTIVITY BALANCE
- The material balance of dosed radioactivity in the individual vessels ranged from 99.9 to 105.7% (Hönniger system; mean 101%) and 97.3 to 102.5% (Lienden system, mean 99%). A clear time-dependent tendency was not found.
- The test substance was quickly eliminated from the water body, either via translocation into the sediment or via degradation.
- A portion of less than 2% (Hönniger system) or about 6% (Lienden system) of applied could be detected in the supernatant water after 35 days. Parent compound in the water was not detectable after 100 days.

NON-EXTRACTABLE RESIDUES
- % of applied amount at end of study period: During the entire study period the portion of ,,bound residue" increased from both sediments continually in case of Hönniger system to 31.9% and in case of Lienden system to 17.2% of dose at interval 100 days

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: At termination of the test, the 14CO2 recoveries were 4.0% (Hönniger system) and 4.3% (Lienden system) of applied amount.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: In all test systems less than 0.01 % of applied radioactivity could be found in the PU traps at each sampling time during the entire incubation period.
Validity criteria fulfilled:
not applicable
Conclusions:
From this study it can be concluded that the test substance has to be regarded as a well dissipating compound from the water phase of a water-sediment system.
The rate of total mineralisation in both systems was relatively low with a maximum of 4.0% or 4.3% of dose at study termination.
Endpoint:
biodegradation in water: simulation testing on ultimate degradation in surface water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
13 Nov 2012 - 31 May 2013
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Qualifier:
according to guideline
Guideline:
OECD Guideline 309 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)
Version / remarks:
2004
Qualifier:
according to guideline
Guideline:
other: DG Sanco 11802/2010/rev 1 amending the Regulation (EC) No. 1107/2009 of the European Parliament and of the council of 21 October 2009 and repealing Council Directives 79/117/EEC and 91/414/EEC
Version / remarks:
2010
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): Water was freshly sampled from a pond in Biederthal, France in September, 2012. The water was sampled from the surface at a depth of about 0 to 10 cm. The sampling location was in an area not submitted to effluent discharges and located far from human activity.
- The sample was transported to IES Ltd in sealed containers and filtered through a 0.2 mm sieve.
- Storage conditions: The water was stored at about 4 °C in the dark, until use.
- Temperature (°C) at time of collection: 7.7
- pH at time of collection: 7.47
- Redox potential (mv) initial/final: 91
- Oxygen concentration (mg/l) initial: 11.9
- Dissolved organic carbon (mg/L): 4.92
- Biomass (e.g. in mg microbial C/100 mg, CFU or other): As more than 90% of benzoic acid degraded within 7 days, the test water could be considered as microbially active

Duration of test (contact time):
> 0 - < 62 d
Initial conc.:
0.1 mg/L
Based on:
test mat.
Initial conc.:
0.01 mg/L
Based on:
test mat.
Initial conc.:
0.1 mg/L
Based on:
test mat.
Remarks:
Performed under sterile conditions in order to gain information about abiotic degradability of the test item.
Parameter followed for biodegradation estimation:
radiochem. meas.
Details on study design:
TEST CONDITIONS
- Volume of test solution/treatment: Radiolabelled test item was applied to 100 mL of natural pond water at concentrations of 0.1 and 0.01 mg/L.
- Other: The high concentration experiment was additionally performed under sterile conditions in order to gain information about abiotic degradability of the test item.
Samples were incubated at a controlled temperature of 21.0 ± 0.1 °C, in the dark under aerobic conditions.

TEST SYSTEM
- Culturing apparatus: Each test system consisted of an open gas-flow-system with 350 mL conical flasks, containing 100 mL of natural water.
- Method used to create aerobic conditions: Each flask was aerated with moistened air. The samples were continuously and gently stirred to maintain particles and micro-organisms in suspension. Agitation also facilitated oxygen transfer from headspace to liquid, in a way that aerobic conditions were maintained.
- Details of trap for CO2 and volatile organics if used: After treatment, samples were connected to a trapping system equipped with a total of two absorption traps, one containing ethylene glycol and the other 2N NaOH (in this sequence) to trap organic volatiles and 14CO2, respectively.
- Other: Degradation of 14C(U)] benzoic acid was monitored using the same experimental set-up in order to test the microbial activity of the test water.

SAMPLING
- Sampling frequency: Duplicate samples (replicate A and B) per system were worked up to incubation day 0, 3, 7, 14, 28, 40 and 62.
- Sampling method used per analysis type:
Mineralisation of benzoic acid was monitored by LSC measurement and HPLC analysis of sub-samples at 3 different intervals (e.g. 0, 3 and 14 days) and the amount of radioactivity in NaOH traps determined (LSC).
At each sampling interval, pH value and oxygen content of the water was measured in the respective treated samples and in two untreated control samples.

Reference substance:
benzoic acid, sodium salt
Compartment:
natural water: freshwater
% Total extractable:
103.5
% CO2:
0.2
% Other volatiles:
< 0.1
Remarks on result:
other:
Remarks:
Recovery after 62 days of incubation: 103.7% of applied radioactivity in the high dose treatment (0.1 mg/L).
Compartment:
natural water: freshwater
% Total extractable:
102.2
% CO2:
0.7
% Other volatiles:
< 0.1
Remarks on result:
other:
Remarks:
Recovery after 62 days of incubation: 102.9% of applied radioactivity in the low dose treatment (0.01 mg/L).
Compartment:
abiotic control measured at end of test
% Total extractable:
110.5
% CO2:
0.1
% Other volatiles:
< 0.1
Remarks on result:
other:
Remarks:
Recovery after 62 days of incubation: 110.6% of applied radioactivity in the high dose treatment (0.1 mg/L) under sterile conditions.
Parent/product:
parent
Compartment:
total system
% Degr.:
0.2
Parameter:
radiochem. meas.
Sampling time:
62 d
Remarks on result:
other:
Remarks:
Based on 14CO2 measurement after 62 days of incubation in the high dose treatment (0.1 mg/L).
Parent/product:
parent
Compartment:
total system
% Degr.:
0.7
Parameter:
radiochem. meas.
Sampling time:
62 d
Remarks on result:
other:
Remarks:
Based on 14CO2 measurement after 62 days of incubation in the low dose treatment (0.01 mg/L).
Parent/product:
parent
Compartment:
total system
% Degr.:
0.1
Parameter:
radiochem. meas.
Sampling time:
62 d
Remarks on result:
other:
Remarks:
Based on 14CO2 measurement after 62 days of incubation in the high dose treatment (0.1 mg/L) under sterile conditions.
Compartment:
natural water: freshwater
DT50:
117.9 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other:
Remarks:
DT50 in the high dose treament (0.1 mg/L) at 21 °C.
Compartment:
natural water: freshwater
DT50:
274.2 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the high dose treament (0.1 mg/L) at 12 °C, based on results at 21 °C.
Compartment:
natural water: freshwater
DT50:
57.7 d
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other:
Remarks:
DT50 in the low dose treament (0.01 mg/L) at 21 °C.
Compartment:
natural water: freshwater
DT50:
134.2 d
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the low dose treament (0.01 mg/L) at 12 °C, based on results at 21 °C.
Compartment:
natural water: freshwater
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Temp.:
21 °C
Remarks on result:
other:
Remarks:
DT50 in the high dose sterile treament (0.1 mg/L) at 21 °C.
Compartment:
natural water: freshwater
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
Calculated DT50 in the high dose sterile treament (0.1 mg/L) at 12 °C, based on results at 21 °C.
Transformation products:
yes
Remarks:
see "Details on transformation products".
No.:
#1
Details on transformation products:
- One metabolite was observed, which was identified by co-chromatography using HPLC and TLC as [3-(6-Chloro-pyridin-3-ylmethyl)-thiazolidin-(2Z)-ylidene]-urea.
- The metabolite was first detected after 28 days of incubation and represented 14.4% and 12.9% of AR in the high and low dose systems respectively.
- After 62 days, the amount of the metabolite increased to 30.0% and 42.8% of AR in the high and low dose systems respectively.
Evaporation of parent compound:
no
Remarks:
Volatile products other than 14CO2 did not exceed 0.1% of AR throughout the study.
Volatile metabolites:
no
Remarks:
Volatile products other than 14CO2 did not exceed 0.1% of AR throughout the study.
Details on results:
TEST CONDITIONS
- Aerobicity (or anaerobicity), moisture, temperature and other experimental conditions maintained throughout the study: Yes. The results demonstrated that the test item had no significant effects on the physico-chemical parameters of the test system.
Oxygen: The oxygen concentration measured in the water phase ranged from 6.01 to 8.32 mg/L in the high dose, from 6.40 to 8.59 mg/L in the high dose sterile and from 5.42 to 8.25 mg/L in the low dose experiment.
pH: Corresponding values for pH were 8.03 to 8.35, 8.03 to 8.34 and 7.82 to 8.32 respectively.
Similar values were observed in the untreated control samples ranging from 6.28 to 8.13 mg/L for oxygen concentration and from 7.99 to 8.47 with for the pH values.
Temperature: The mean temperature during incubation was 21.0 ± 0.1 °C for all systems.
- Other: Within 7 days of incubation, the amount of benzoic acid decreased rapidly from initially 93.3% to 0% under formation of 55.0% radioactive carbon dioxide. As more than 90% of benzoic acid degraded within 7 days, the test water could be considered as microbially active.

EXTRACTABLE RESIDUES
- % of applied amount at end of study period: After 62 days of incubation, the amount of radioactivity in the water phase still represented 103.7%, 110.6% and 102.9% of AR in the respective systems.
- Other: The total mean recoveries were 103.9 ± 1.7% of applied radioactivity (AR) for the high dose, 105.9 ± 3.6% AR for the high dose sterile and 102.0 ± 1.6% AR for the low dose experiments.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: Formation of radioactive carbon dioxide never exceeded 0.3% of AR in the high dose, 0.1% in the sterile and 0.9% in the low dose systems. The amount of radioactive carbon dioxide dissolved in the water layer was negligible.

VOLATILIZATION
- % of the applied radioactivity present as volatile organics at end of study: Volatile products other than 14CO2 did not exceed 0.1% of AR throughout the study.

Validity criteria fulfilled:
yes
Conclusions:
In conclusion, the test substance, regardless of its concentration, degraded slowly in natural surface water systems with a lag phase of approx. 14 days. Thereafter, degradation started, i.e. more rapidly in the low dose then in the high dose test. Since the concentration of the test substance remained stable in the sterile system, its degradation in the surface water can be attributed to microbial activity. However, prior to starting the biodegradation, a biological matrix (bio-film, etc.) has to be formed in the test flasks. The main metabolite was [3-(6-Chloro-pyridin-3-ylmethyl)-thiazolidin-(2Z)-ylidene]-urea, reaching values of 30.0% and 42.8% of AR in the high and low dose systems respectively within 62 days, respectively.
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)
Version / remarks:
1982
GLP compliance:
yes (incl. QA statement)
Radiolabelling:
yes
Oxygen conditions:
anaerobic
Inoculum or test system:
natural water / sediment: freshwater
Duration of test (contact time):
>= 0 - <= 360 d
Parent/product:
parent
Compartment:
total system
% Degr.:
0.4
Parameter:
radiochem. meas.
Sampling time:
360 d
Remarks on result:
other:
Remarks:
14CO2 formation after 360 days under anaerobic conditions.
Compartment:
natural water / sediment: freshwater
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Temp.:
20 °C
Compartment:
natural water / sediment: freshwater
DT50:
> 1 yr
Type:
(pseudo-)first order (= half-life)
Temp.:
12 °C
Remarks on result:
other:
Remarks:
DT50 recalculated based on results at 20 °C
Conclusions:
The fate of 3-(2-chloro-5-pyridylmethyl)-2-cyaniminothiazolidine, in an anaerobic aquatic system was investigated using pond water and sediment from Stilwell, Kansas. The test systems were preincubated anaerobically prior to treatment with 17.5 µg a.i./L of [methylene-14C]-labelled test substance. The test systems were incubated in the dark at 20 ± 1 °C for 360 days.
Material balance from 0 to 360 days post treatment ranged from 93.3 to 99.3% of applied radioactivity. Radiocarbon residues in the water layer decreased at succeeding sampling intervals. At 0 and 360 days post-treatment 86.6% and 9.9% were recovered in the water, respectively. Radioactive residues in the sediment increased to a maximum of 88.9% at 360 days post-treatment.
Low levels of 14CO2 were detected (i.e. maximum of 0.4% of applied radioactivity at day 360 post-treatment). The calculated half-life DT50 of the test substance was > 1 year.
The test results show that the degradation rate in the sterile systems was lower than in the non-sterile systems.

Description of key information

DT50 in natural pond water at 21 °C: 58 to 118 days (135 to 274 days, recalculated to 12 °C).

The test substance, regardless of its concentration, degraded slowly in natural surface water systems with a lag phase of approx. 14 days.

 

DT50 in sediment at 20 °C: 12.1 to 20.3 days (25.7 to 43.1 days, recalculated to 12 °C), aerobic conditions

 

DT50 in sediment at 20 °C: > 1 year, anaerobic conditions

Key value for chemical safety assessment

Half-life in freshwater:
274 d
at the temperature of:
12 °C
Half-life in freshwater sediment:
41.3 d
at the temperature of:
12 °C

Additional information

One simulation test was carried out to assess the aerobic biodegradation of 14C-labelled (Z)-3-(6-chloro-3-pyridylmethyl)-1,3-thiazolidin-2-ylidenecyanamide, at 21 °C, in natural pond water according to GLP and OECD Guideline 309. The study was conducted over a period of 62 days at two concentration levels (0.1 and 0.01 mg/L), whereas the higher dosage level was additionally tested under sterile conditions. After 62 days of incubation, radioactive carbon dioxide did not exceed 0.3% of AR in the high dose, 0.1% of AR in the sterile and 0.9% of AR in the low dose systems throughout the study. Volatile products other than 14CO2 did not exceed 0.1% of AR during the entire incubation period. The calculated half-life (DT50), based on single first-order (SFO) kinetics, for the test substance in the different systems, ranged from 58 to 118 days (135 to 274 days, recalculated to 12 °C).

Another simulation study was carried out, according to GLP, to investigate the fate of the test substance in an aquatic model ecosystem consisting of two sediment/water systems under aerobic conditions. The formation of 14CO2 after 100 days accounted for 4.0 and 4.3%, respectively, of the applied radioactivity. The determined DT50 of the test compound ranged from 12.1 to 20.3 days (25.7 to 43.1 days, recalculated to 12 °C).

In addition, a simulation study on the anaerobic degradation of the test substance in water/sediment following GLP and “EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism)” was conducted at 20 °C. The study revealed low levels of 14CO2 (i.e. maximum of 0.4% of applied radioactivity) at day 360 post-treatment. The calculated half-life DT50 of the test substance was > 1 year.