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Environmental fate & pathways

Biodegradation in water and sediment: simulation tests

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Description of key information

Aerobic Aquatic Water/Sediment Systems (OECD 308):

Pikeville System

DT50 in water: 38.0 days at 25 °C (M-267001-01-2)

DT50 in water/sediment: 69.0 days at 25 °C (M-267001-01-2)

Lawrence System

DT50 in water: 327 days at 25 °C (M-267001-01-2)

DT50 in water/sediment: 578 days at 25 °C (M-267001-01-2)

Anaerobic Aquatic Water/Sediment Systems (EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism):

DT50 in water: 75.0 days at 20 °C (M-250846-01-1)

DT50 in water/sediment: 227.0 days at 20 °C (M-250846-01-1)

Anaerobic Aquatic Water/Sediment Systems (EPA Subdivision N Pesticide Guideline 162-3 (Anaerobic Aquatic Metabolism):

DT50 in water: 84.0 days at 20 °C (M-250839-01-2)

DT50 in water/sediment: 273.0 days at 20 °C (M-250839-01-2)

Key value for chemical safety assessment

Half-life in freshwater:
327 d
at the temperature of:
25 °C
Half-life in freshwater sediment:
578 d
at the temperature of:
25 °C

Additional information

Aerobic Aquatic Water/Sediment Systems

The aerobic biotransformation of [pyrazol-3-14C]-test substance and [phenyl-UL-14C]-test substance was studied in a pond water-sandy loam sediment system (water pH 6.4, sediment pH 5.4, organic carbon 4.1%) from Pikeville, North Carolina, USA, for 132 days and a pond water-silty clay loam sediment system (water pH 8.0, sediment pH 7.5, organic carbon 0.81%) from Lawrence, Kansas, USA, for 131 days (M-267001-01-2).
Both sediments were incubated in the dark at 25 ± 1°C. [14C]test substance was applied at two rates of 3.8 and 19
μg a.i./L each. The sediment/water ratio used was 1:6 (38.4 g dry wt. sediment: 225 mL water) for the water-sandy loam sediment system and 1:3 (65.6 g dry wt. sediment: 225 mL water) for the water-silty clay loam sediment system. The experiment was conducted in accordance with the Pesticide Assessment Guidelines, Subdivision N, Environmental Fate, US EPA, 162-4 and in compliance with the GLP standards US EPA Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA): Good Laboratory Practice Standards. The test systems consisted of 47 (sandy loam system) and 50 (silty clay loam system) 500 mL straight-sided glass flasks containing sediment/water connected to a series of trapping solutions for the collection of CO2 and volatile products. Samples were analyzed at 0, 11, 26, 55, 81, 109, and 132 days of incubation in the sandy loam system and at 0, 21, 42, 64, 83, 104, and 131 days of incubation in the silty clay loam system. The water samples were not extracted and were concentrated by rotary evaporation. Sediment samples were extracted with ACN: water (4:1 v:v) using a shake method followed by an accelerated solvent extraction using ACN:water (9:1 v:v). Water layers and sediment extracts were analyzed for [14C]test substance and its transformation products using reverse phase high performance liquid chromatography with 14C-radiodection and identified by comparison to reference substances. Identification of the parent compound was confirmed using LC/MS/MS with turbo-ionspray interface in multiple reaction monitoring mode.

Overall material balances averaged 96.8 ± 3.3% (range 89.8-101.9%, n=28) and 99.9 ± 1.9% (range 95.3-103.7%, n=28) in the water-sandy loam and water-silty clay loam sediment systems, respectively.

In the water-sandy loam sediment system, overall [14C]-residues in the water phase decreased from 97.1% at day 0 to 7.1% of the applied amount at the end of the incubation period. Extractable [14C]residues in sediment increased from 0.7% at day 0 to 13.4% of the applied amount at the end of incubation period. Non-extractable [14C]-residues in sediment increased from 14.1% at day 11 to 73.2% of the applied amount at study termination. At the end of the study, <1% of the applied radioactivity was present as either CO2 or organic volatile compounds.

In the water-silty clay loam sediment system, overall [14C]residues in the water phase decreased from 100.7% at day 0 to 64.4% of the applied amount at the end of the incubation period. Extractable [14C]-residues in sediment increased from 0.8% at day 0 to 22.0% of the applied amount at the end of incubation period. Non-extractable [14C]-residues in sediment increased from 0.7% at day 0 to 11.8% of the applied amount at study termination. At the end of the study, <0.1% of the applied radioactivity was present as either CO2 or organic volatile compounds.

In the water-sandy loam system, the percentage of [14C]test substance in water decreased from 97.6% at day 0 to 5.5% of the applied amount by the end of the study. The percentage of [14C]test substance in the sediment phase increased from 0.9% at day 0 to a maximum of 25.1% at day 26, before decreasing to 12.7% at the end of the study period. In the water-silty clay loam sediment system, the percentage of [14C]test substance in water decreased from 100.9% at day 0 to 63.9% of the applied amount by the end of the study. The percentage of [14C]test substance in the sediment phase increased from 0.5% at day 0 to 24.0% at the end of the study period.

No major transformation products were detected in the water or sediment phases. The sole minor transformation product was 2-methylsulfonyl-4-(trifluorormethyl)benzoic acid which did not exceed 3% in the total system of either water-sediment system. The unidentified [14C]residues during the study, consisting of three separate peaks, accounted for < 2% and < 3% of the applied radioactivity in the water-sandy loam and water-silty clay loam sediment systems, respectively.

The 50% decline times (DT50) via biphasic kinetics of [14C]test substance in aerobic water were 38 and 327 days for the water-sandy loam and water-silty clay loam sediment systems, respectively. DT50 values using first-order non-linear kinetics of [14C]-test substance in the entire system were 69 and 578 the days for the water-sandy loam and water-silty clay loam sediment systems, respectively. 

Anaerobic Aquatic Water/Sediment Systems [Pyrazole-3 -14C]

The anaerobic biotransformation of radiolabeled test substance, was studied in a pond water/sediment system (water: pH 7.5, dissolved organic carbon = 11.7 ppm, sediment: texture = silty clay, pH 7.0, organic carbon = 1.1%) from Lawrence, Kansas, United States for 365 days in the dark at 20 ± 1 °C (M-250846-01-1). Test substance was applied at a rate of 0.004 mg a.i./L. The sediment/water ratio used was 1:3. The experiment was conducted in accordance with Pesticide Assessment Guidelines, Subdivision N, Environmental Fate, US EPA, 162-3, Environmental Chemistry and Fate, Guidelines for Registration of Pesticides in Canada, and in compliance with the GLP standards (40 CFR part 160; FR, August 17, 1989). The test system consisted of twenty-four 250-mL Erlenmeyer flasks with double-valve sealable tops containing sediment and water. Samples were analyzed at 0, 3, 14, 17, 28, 63, 91, 106, 120, 184, 275 and 365 days of incubation. The water samples were concentrated and the sediment samples were extracted with 9:1 ACN:water using a shaking method followed by an ASE extraction (accelerated solvent extraction) using the same solvents. Test substance residues were analyzed by HPLC coupled to a 14C detector. Identification of the parent was achieved by co-chromatography and liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS). The total material balance in the water/sediment system was 94.1 ± 2.8% (mean ± SD) of the applied amount. The mean percent of applied radioactivity recovered at day 365 in water, extractable from sediment, and unextractable from sediment was 37.3% (± 0.5), 22.4% (± 1.5), and 36.4% (± 2.0), respectively. Extractable [14C] residues in sediment increased from 0.0% at day 0, to 22.7% of the applied at 63 days and remained constant through the remainder of the study. Non-extractable [14C] residues in sediment increased from 0.0% at day 0 to 26.5% of the applied amount at day 63, and increased to 36.4% by the end of the study. At the end of the study, 1.8% and 0.0% of the applied radioactivity was present as CO2 and volatile organic compounds, respectively. The concentration of [14C]test substance in water decreased from 100.0% at day 0 to 43.3% of the applied amount at 63 days, and decreased to 37.3% by the end of the study. The concentration of test substance in the sediment increased from 0.0% at day 0 to 22.7% of the applied amount at 63 days, and remained constant through the end of the study period. On day 365 at study termination 58.8% of the applied radioactivity was partitioned from water to sediment (sum of extractable and non-extractable in sediment).

No major transformation products were detected in the water or sediment phases. The unidentified [14C] during the study was <1.6% on day 106 consisting of two peaks, none of which were greater than 0.9% of the applied amount. The half-lives using first-order nonlinear degradation kinetics for test substance in anaerobic water and in the entire system were 75 days (k = 0.0093 day-1; r2 = 0.56) and 227 days (k = 0.0031 day-1; r2 = 0.46), respectively. The data for the total system better fit a biphasic model (r2 = 0.95), characterized by a fast dissipation rate (k = 0.167 day-1) resulting in a half life of 4.2 days for the first phase, and a slower dissipation rate (k = 0.0004 day-1) resulting in a half-life for the second phase of greater than 1 year. There was no degradation of test substance in the anaerobic test system, but test substance dissipated to the sediment and formed bound residues.

 

Anaerobic Aquatic Water/Sediment Systems [Phenyl UL-3 -14C]

The anaerobic biotransformation of radiolabeled test substance, was studied in a pond water/sediment system (water: pH 7.5, dissolved organic carbon = 11.7 ppm, sediment: texture = silty clay, pH 7.0, organic carbon = 1.1%) from Lawrence, Kansas, United States for 365 days in the dark at 20 ± 1 °C (M-250839-01-2). Test substance was applied at a rate of 0.004 mg a.i./L. The sediment/water ratio used was 1:3. The experiment was conducted in accordance with Pesticide Assessment Guidelines, Subdivision N, Environmental Fate, US EPA, 162-3, Environmental Chemistry and Fate, Guidelines for Registration of Pesticides in Canada, and in compliance with the GLP standards (40 CFR part 160; FR, August 17, 1989). The test system consisted of twenty-four 250 mL Erlenmeyer flasks with double-valve sealable tops containing sediment and water. Samples were analyzed at 0, 3, 7, 10, 22, 31, 63, 92, 120, 183, 273 and 365 days of incubation. The water samples were concentrated and the sediment samples were extracted with 90:10 ACN:water using a shaking method followed by an ASE extraction (accelerated solvent extraction) using the same solvents. Test substance residues were analyzed by HPLC coupled to a 14C detector. Identification of the parent was achieved by co-chromatography and liquid chromatography-electrospray ionization mass spectrometry (LC-ESI/MS). The total material balance in the water/sediment system was 96.6 ± 2.3 % (mean ± SD) of the applied amount. The mean percent of applied radioactivity recovered at day 365 in water, extractable from sediment, and unextractable from sediment was 40.0% (± 0.6), 25.5% (± 5.0), and 33.8% (± 3.3), respectively. Extractable [14C] residues in sediment increased from 0.0% at day 0, to 18.1% at day 63, and remained constant through the remainder of the study. Non-extractable [14C] residues in sediment steadily increased from 0.0% at day 0 to 33.8% of the applied amount at day 365. At the end of the study, 2.8% and 0.0% of the applied radioactivity was present as CO2 and volatile organic compounds, respectively. The concentration of [14C]test substance in water decreased from 99.2% at day 0 to 44.8% at day 63, and remained constant though the end of the study. The concentration of test substance in the sediment increased from 0.0% at day 0 to 17.2% at day 63, and slowly increased to 25.5% of the applied amount at the end of the study period. On day 365 at study termination 59.3% of the applied radioactivity was partitioned from water to sediment (sum of extractable and non-extractable in sediment). No major transformation products were detected in the water or sediment phases. The unidentified [14C] during the study was =3.1% on day 31 consisting of an average of 3 peaks, none of which were greater than 2.6% of the applied amount. The half-lives using first-order nonlinear degradation kinetics for test substance in anaerobic water and in the entire system were 84 days (k= 0.0083 day-1; r2 = 0.63) and 273 days (k = 0.0025 day-1; r2 = 0.40), respectively. The data for the total system better fit a biphasic model (r2 = 0.95), characterized by a fast dissipation rate (k = 0.112 day-1) resulting in a half-life of 6.2 days for the first phase, and a slower dissipation rate (k =0.00007 day-1) resulting in a half-life for the second phase of greater than 1 year. There was no degradation of test substance in the anaerobic test system, but test substance dissipated to the sediment and formed bound residues.