picoxystrobin (ISO); methyl (2E)-3-methoxy-2-[2-({[6-(trifluoromethyl)pyridin-2-yl]oxy}methyl)phenyl]acrylate

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Endpoint:

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

Type of information:

experimental study

Adequacy of study:

key study

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)

Deviations:

no

Qualifier:

according to guideline

Guideline:

EPA OPPTS 835.3190 (Aerobic Mineralisation in Surface Water - Simulation Biodegradation Test)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

Radiochemical Purity: 98.8% (Pyridine-3- labeled with specific activity of 53.58 μCi/mg)
98.4% (Phenyl(U)- labeled with specific activity of 51.48 μCi/mg)

Radiolabelling:

yes

Oxygen conditions:

aerobic

Inoculum or test system:

other: Surface water

Details on source and properties of surface water:

- Details on collection: The water was collected from a pond at ABC Laboratories located in Columbia, Missouri. The pond is fed by wet weather springs as well as surface water run-off. The run-off mainly originates from a grassy area around pastureland that has been pesticide free in the previous 5 years. The water was collected by scooping the water from the pond using a 5-gallon bucket over the sample area.
- pH at time of collection: 8.0
- Electrical conductivity: 0.71 mmhos/cm
- Redox potential initial: 181.6 mv
- Oxygen concentration initial: 7.27 mg/L
- Hardness (CaCO3): 190 mg equivalent CaCO3/L
- Dissolved organic carbon: 3.0 ppm
- Water filtered: no

Duration of test (contact time):

60 d

Initial conc.:

50 µg/L

Based on:

act. ingr.

Initial conc.:

500 µg/L

Based on:

act. ingr.

Parameter followed for biodegradation estimation:

radiochem. meas.

Details on study design:

TEST CONDITIONS
- Volume of test solution/treatment: Pyridinyl-test Substance (50 μg/L): 1.20 mL
Pyridinyl-test Substance (500 μg/L): 3.40 mL
Phenyl-test Substance (50 μg/L): 0.74 mL
Phenyl-test Substance (500 μg/L): 3.40 mL
- Solubilising agent (type and concentration if used): Acetonitrile (<0.15% co solvent in sample)
- Test temperature: 20 ± 2°C
- pH: 7.68
- Continuous darkness: yes
- Any indication of the test material adsorbing to the walls of the test apparatus: No

TEST SYSTEM
- Culturing apparatus: 1 L capacity bioreactors sealed with a plastic cap and continuously agitated using a magnetic stirrer and bar.
- Number of culture flasks/concentration: Four bioreactors were prepared for each radiolabelled form [pyridine or phenyl] of the test substance, with two replicates at each nominal concentration (50 μg/L or 500 μg/L). Surface water (700 mL) was measured with a graduated cylinder and transferred to each bioreactor. The samples were designated with the label prefix FT, and were sub-sampled at each interval for mineralization testing. Testing intervals consisted of zero time, 7, 14, 29, 46, and 60 days after application. Eight additional bioreactors were similarly prepared for mass balance determinations at Day 0 and termination (Day 60). Bioreactors for these sampling intervals were designated with the label prefix FM.
Two bioreactors were also prepared, as described above, for the reference compound, sodium benzoate, at a nominal concentration of 500 μg/L. Bioreactors for these sampling intervals were designated with the label prefix FC and were sampled in parallel with the FT samples.
- Method used to create aerobic conditions: Aerobic conditions were maintained in all samples by constant stirring of the surface water. Oxygen in the headspace, which was replenished during sampling, was deemed sufficient to maintain aerobic conditions.
- Measuring equipment: graduated cylinder
- Test performed in closed vessels: Yes, except for the bioreactors designated for termination mass balance
- Details of trap for CO2 and volatile organics if used: The headspace of acidified samples purged and passed through 2 x 1N NaOH traps at Day 60.

SAMPLING
- Surface Water Sub-Samples for Mineralization Test (FT and FC Bioreactors)
Sub-samples (40-mL) from the FT and FC bioreactors were sampled at zero time (immediately after treatment), 7, 14, 29, 46, and 60 days after application. Sub-samples of the surface water were removed via a serological pipette and transferred to pre-labeled tared vials. The weight of transfer was recorded to verify the amount of water removed from the bulk sample.
- Surface Water Mass Balance Samples (FM Bioreactors)
Mass balance samples (FM) were analyzed at zero time and then again at termination (Day 60). At sampling, the entire sample was assayed for radioactive content. For the termination samples, the headspace and bulk water was purged with air and any carbon dioxide potentially in the headspace dissolved in the water phase was purged and in to two traps (1 M NaOH) in series.
- Sample Storage Conditions
Water samples were analyzed for total radioactivity and analyzed by HPLC immediately. Sub-samples prior to acidification and post-acidification were stored at -20˚C.

Reference substance:

benzoic acid, sodium salt

Key result

Remarks on result:

other: Test substance degradation was less than 10% AR.

Key result

Remarks on result:

other: DT50 and DT90 values for the test substance in surface water were not calculated since test substance degradation was less than 10% AR.

Transformation products:

no

Details on transformation products:

In the surface water, levels of the test substance, prior to acidification decreased from 97.2% and 99.2% AR at Day 0 to 89.1% and 96.8% AR at the end of 60 days of incubation in the [pyridine-3-14C] and [phenyl(U)-14C test substance, respectively. No single degradation product was found in the water at levels exceeding 3.4% AR throughout the course of the study.

Residues:

yes

Details on results:

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

MAJOR TRANSFORMATION PRODUCTS
No single degradation product was found in the water at levels exceeding 3.4% AR throughout the course of the study.

MINERALISATION
- % of applied radioactivity present as CO2 at end of study: Analysis of the traps showed that the 14CO2 formed in the system after 60 days was only 2% AR at maximum.

Validity criteria fulfilled:

yes

Conclusions:

The test substance did not mineralize significantly during the 60-day study.
Though the total radioactivity in the water was observed to decrease after acidification, the results of the study indicate that these losses were a symptom of the acidification and not due to losses of 14CO2 via mineralization. The test substance accounted for 93% AR at Day 60 and direct trapping of 14CO2 showed that negligible mineralization occurred (max 2% AR as 14CO2). No major products were observed >10% AR in this study.

Executive summary:

The aerobic mineralization of [14C]-test substance was studied in one surface water system under pelagic conditions at 20 ± 2ºC in the dark.

The surface water collected for this study was representative of a typical pond. The water was collected from a pond (ABC Lane) located in Columbia, Missouri. The pH, biological oxygen demand, and total suspended solids were 8.0, 5.1 mg-O2/L, and 20 ppm, respectively.

A total of fourteen bioreactors (1-liter capacity) containing 700 mL of surface water were used. To twelve bioreactors, pyridine or phenyl labeled [14C]-test substance was applied at nominal rates of 50 μg a.i./L and 500 μg a.i./L. Four bioreactors, one for each radiolabel and concentration, were used for mineralization testing at zero time, 7, 14, 29, 46 and 60 days after dosing. To confirm microbial viability of the surface water, two additional bioreactors were prepared with a reference compound (sodium benzoate) at 500μg/L and were analyzed in parallel for mineralization. Eight bioreactors, one for each radiolabel, concentration, and two intervals were prepared and analyzed for material balance at study initiation and termination.

For mineralization testing, a sub-sample of the surface water was removed and assayed for radioactivity followed by acidification (pH 2-3 using concentrated hydrochloric acid) and purging with air to expel any CO2. Decreases in radioactivity following acidification were evaluated as possible mineralization. The potential for biotransformation was determined by HPLC analysis of the surface water prior to acidification. Material balance was determined by direct measurement of the mass balance bioreactor flasks.

The results indicated that the test substance did not significantly mineralize (<5% in phase) over the study duration. Though the total radioactivity in the water was observed to decrease after acidification, the results of the study indicate that these losses were a symptom of the acidification and not due to losses of 14CO2 via mineralization. The test substance accounted for 93% AR at day 60 and direct trapping of 14CO2 showed that negligible mineralization occurred (max 2% AR as 14CO2). Due to the lack of mineralization, no rate constants were derived for this study. The reference compound (sodium benzoate) was mineralized up to a mean of 90.9% after 14 days confirming the viability of the system.

The mean material balance at study initiation of the low and high dose rates in the mass balance bioreactors (FM) were 101.2% and 103.1% of the dosed radioactivity, respectively. At termination (Day 60), the mean material balance of the low and high dose rates were 54.4% and 92.8% of the dosed radioactivity, respectively. The low recoveries in the low dose samples at termination may have been due in part to the losses associated with the glassware, which have a large impact at such low levels of dosed radioactivity.

The amount of [14C]-test substance in the surface water, as determined by LSC of the high dose samples prior to acidification, ranged from a mean of 98.2% at time zero and decreased to 93.0% by Day 60.

DT50 and DT90 values for the test substance in surface water were not calculated since test substance degradation was less than 10% AR. Subsequently, no metabolic pathway is presented in this study.

Description of key information

DT50 and DT90 values for the test substance in surface water were not calculated since test substance degradation was less than 10% AR.