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Environmental fate & pathways

Biodegradation in soil

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Description of key information

Aerobic Biodegradation in soil ( Japan MAFF Test Guideline, 12-Nousan-No. 8147 Part 2-5-2):

DT50 soil: 12.3 – 18.3 days at 25 °C, M-398551-01-1

temperature corrected values DT50 soil: 40.9 – 60.9 days at 12 °C, M-398551-01-1

Aerobic Biodegradation in soil (OECD 307; EPQ OPPTS 4100; Draft SANCO 11802/20; Japan MAFF Test Guideline, 12-Nousan-No. 8147 Part 2-5-2):

DT50 soil: 2.7 - 14.7 days at 20.3 °C, M-443672-01-1

temperature corrected values DT50 soil: 5.9 – 32.1 days at 12 °C, M-443672-01-1

Anaerobic Biodegradation in soil (OECD 307; EPQ OPPTS 4200; Japan MAFF Test Guideline, Annex No.: 2-5-3):

DT50 soil: > 1000 days at 20 °C, M-482008-01-1

Key value for chemical safety assessment

Half-life in soil:
60.9 d
at the temperature of:
12 °C

Additional information

Aerobic Biodegradation in Soil (M-398551-01-1)

The degradation of the [14C-A ([cyclohexane-UL-14C]), -B ([phenyl-UL-14C]) and –C ([tetrahydrofuranyl-2-14C]) ring labeled test substance was investigated according to Japan MAFF Test Guideline, 12-Nousan-No. 8147 Part 2-5-2 in freshly collected Japanese paddy soil under aerobic conditions in the dark in the laboratory for 120 days at 25 ± 1 °C and at 50% of the maximum water holding capacity (M-398551-01-1). The study application rate was 0.3 mg/kg soil (dry weight). Single replicate viable samples were collected for each label at time 0 and following 3, 7, 14, 30, 62 and 120 days incubation.

 

Average radiocarbon recoveries ranged from 98.2 ± 1.8% to 99.2 ± 0.9% of applied dose for all sets. In viable soils, radiocarbon recovered in the NaOH traps represented an average of 23.5%, 11.5% and 28.5% of the applied dose in A-label, B-label and C-label sets, respectively, at the end of the 120 days of incubation. Minimal radiocarbon was recovered in the traps for organic volatiles.

 

Extractable radiocarbon decreased from >93% of dose at time zero to less than 46% of dose at the end of the study for all viable sets tested. Unextracted residues increased to > 34% of dose by the end of the incubation period. Additional extraction of the Day 14 and 120 bound residues by soxhlet with acetonitrile/0.1M HCl released an additional 20.7-22.7% of the applied radiocarbon (AR) in the 14 day samples and 12.1- 18.1% AR in the 120 day samples. The remaining unextracted radiocarbon was characterized by partitioning the humic and fulvic acid fractions from the soil residues (humin). Thus, the fulvic acid fraction contained an average of 15.4% of the dose, with an average of 2.2% of the dose recovered in the humic acid fractions and 5.1% of the dose associated with the humin.

 

The degradation rates were similar for the viable soil A-, B- and C-label samples. In the viable soils at time 0, the test substance represented 95.4% (A-label), 92.5% (B-label), and 93.0% AR (C-label). The test substance degraded quickly to 44.8% (A-label), 42.9% (B-label), and 43.5% (C-label) by day 30. As the treated soils aged the rate of decline slowed and by day 120 the soil extracts contained 28.9% (A-label), 32.6% (B-label), and 26.2% (C-label) of the applied test substance. The metabolite, benzoic acid, was detected in both the B- and C-labeled samples indicating that some cleavage did occur. Benzoic acid represented 4.4% and 4.5% of applied at day 120 for B- and C-labels, respectively. LC/MS analysis confirmed the identity of parent and benzoic acid in the day 120 soil extracts for A-, B-, and C-labels.

 

In the sterile B-labeled soil, the test substance represented 93.3% AR at time 0 and degraded to 61.2% AR by the end of the incubation period.

 

In viable soils, the test substance degraded quickly in the first month of the study then the rate of decline slowed as the experiment progressed. Since the degradation did not conform well to a first order linear model, the DT50 and DT90 values for the test substance were calculated using a biphasic model, which yielded values that more closely resembled the experimental results. Additionally, the DT50 and DT90 were determined for the total amount of the test substance present in the samples including percent test substance recovered in the soxhlet extracts. The test substance degraded slowly in sterile soils. The half-life of the test substance in sterile soil was determined as 108 days (r2 0.83) using first order kinetics.

 

The calculated half-lives of test substance under aerobic conditions were 18.3 days in the [14C-A ([cyclohexane-UL-14C]) labeled, 15.2 days in the-B ([phenyl-UL-14C]) labeled and 12.3 days in the –C ([tetrahydrofuranyl-2-14C]) ring labeled test substance. The mean DT50 equaled 14.6 days, which corresponds to a temperature corrected DT50 value of 48.6 days (based on an average environmental temperature of 12°C). 

 

Aerobic Biodegradation in Soil (M-443672-01-1)

  The biotransformation of [Phenyl-UL-14C]test substance was studied in soil Laacher Hof AXXa, loamy sand (pHCaCl2 6.4, OC (organic carbon) 1.6%, Monheim, Germany), soil Dollendorf II, clay loam (pHCaCl2 7.2, OC 5.0%, Blankenheim, Germany), soil Laacher Hof Wurmwiese, sandy loam (pHCaCl2 5.6, OC 1.8%, Monheim, Germany) and soil Hoefchen am Hohenseh 4a, silt loam (pHCaCl2 6.3, OC 1.7%, Burscheid, Germany) for 120 days under laboratory aerobic conditions in the dark at 20 ± 2 °C and 55 ± 5% maximum water holding capacity (MWHC) (M-443672-01-1). 

 

The experiments were conducted in accordance to the OECD Guideline for the Testing of Chemicals No. 307, with additional US and EU requirements (US EPA OCSPP Fate, Transport and Transformation Test Guideline Nos. OPPTS 835.4100 and OPPTS, the EU DRAFT SANCO 11802/2011/rev 1, the EU regulation No. 1107/2009) and the Japanese MAFF New Test Guidelines for Supporting Registration of Chemical Pesticides 12 Nousan 8147, Annex No. 2-5-2.

 

The intended maximum single field use rate of the test substance is 300 g/ha, corresponding to a nominal test concentration of 800 μg/kg soil dry weight. The test system consisted of Erlenmeyer flasks each containing 100 g dry soil, equipped with traps for the collection of CO2 and volatile organic compounds. Duplicate samples were analyzed after 0, 1, 3, 7, 14, 29, 58, 90 and 120 days of incubation. The test conditions outlined in the study protocol were maintained throughout the study. Overall mean material balances were 95.0, 94.7, 95.3 and 95.7% of the applied radioactivity (% of the AR) for soils Laacher Hof AXXa, Dollendorf II, Laacher Hof Wurmwiese, and Hoefchen am Hohenseh 4a, respectively.

 

The maximum amount of 14CO2 was 63.2% of the AR at study end (soil Dollendorf II, DAT-120). Formation of other volatile organic compounds was insignificant as demonstrated by values of ≤ 0.1% of the AR at all sampling intervals for all soils. Extractable 14C-residues decreased from 94.4, 93.2, 93.8, and 94.3% of the AR at DAT-0 to 4.6, 2.1, 15.6 and 2.7% of the AR at study end (DAT-120) in soils Laacher Hof AXXa, Dollendorf II, Laacher Hof Wurmwiese, and Hoefchen am Hohenseh 4a, respectively. Non-extractable 14C-residues (NER) increased from 2.3 – 4.7% of the AR at DAT-0 to 28.9 – 33.0% at study end (DAT-120).

 

The test item declined from 92.1, 90.4, 91.7 and 91.7% of the applied radioactivity (AR) at DAT-0 to 0.3 to 8.5% of the AR at DAT-120 in soils Laacher Hof AXXa, Dollendorf II, Laacher Hof Wurmwiese, and Hoefchen am Hohenseh 4a, respectively.

 

Besides the formation of carbon dioxide, one transformation product > 10% AR, benzyl alcohol, was identified with a maximum amount of 61.0% of the AR at DAT-14 in soil Hoefchen am Hohenseh 4a. Furthermore, one transformation product < 10% of the AR, benzoic acid, was found with a maximum amount of 7.3% of the AR at DAT-3 in soil Hoefchen am Hohenseh 4a.

 

The experimental data could generally be well described by first order kinetic models. The half-lives for the test substance under laboratory aerobic conditions ranged from approximately 3 to 15 days in the tested soils. Specifically in the soil Laacher Hof AXXa, the DT50 equaled 8.0 days (via SFO); soil Dollendorf II, the DT50 equaled 2.7 days (via SFO); soil Laacher Hof Wurmwiese, the DT50 equaled 14.7 days (via FOMC) and finally for the soil Hoefchen am Hohenseh 4a, the DT50 equaled 5.0 days (via SFO). Taking a temperature correction to 12°C into account (average environmental temperature Europe) the calculated half-lives ranged between 5.9 and 32.1 days.

 

Anaerobic Biodegradation in Soil (M-482008-01-1)

The route and rate of degradation of [phenyl-UL-14C]test substance were studied in three soils Dollendorf II (DD) (Blankenheim, Germany), soil Hoefchen am Hohenseh 4a (HH) (Burscheid, Germany) and soil (WW) Laacher Hof Wurmwiese, (Monheim, Germany) under anaerobic conditions for 120 days, after an aerobic incubation phase of up to 7 days, in the dark in the laboratory at 20.0 °C (total study duration of up to 127 days).

 

The study followed the OECD Guideline for the Testing of Chemicals No. 307, the US EPA OCSPP Fate Transport and Transformation Test Guideline No. 835.4100 /835.4200 with additional NAFTA Requirements and the Japanese MAFF New Test Guidelines for Supporting Registration of Chemical Pesticides 12 Nousan 8147, Annex No. 2-5-3.

 

After application of the test item, the test systems were incubated under aerobic conditions in the dark at 55% of the maximum water holding capacity for 3 days for soils DD and HH and for 7 days for soil WW. Subsequently, the soil of each test system was flooded with oxygen-depleted water, mimicking a field flooding scenario, and set under an atmosphere of nitrogen.

 

For soils DD and HH duplicate samples were processed and analyzed 0 and 3 days after treatment (DAT) during the aerobic incubation phase and at DAT-3, -10, -17, -31, -61, -95 and -123 of the anaerobic incubation phase. For soil WW duplicate samples were processed and analyzed at DAT-0 and -7 in the aerobic incubation phase and at DAT-7, -14, -21, -35, -65, -99 and -127 in the anaerobic incubation phase. The sampling intervals of the anaerobic incubation phase correspond to 0, 7, 14, 28, 58, 92 and 120 days after soil flooding (DASF) for all three soils.

 

Mean material balances were 101.3% AR for soil DD, 100.6% AR for soil HH and 98.8% AR for soil WW. The maximum amount of carbon dioxide formed at the end of the aerobic incubation phase was 1.0, 0.3 and 1.6% AR in soil DD, HH and WW, respectively, and remained at the same level during the anaerobic incubation phase. Formation of volatile organic compounds (VOC) during the aerobic and anaerobic incubation phase was insignificant as demonstrated by values of < 0.1% AR at all sampling intervals for all soils. Extractable residues decreased from 97.0% AR at DAT-0 to 79.0% AR at DASF-92 in soil DD and slightly increased to 81.3% AR at DASF-120. In soil HH, extractable residues decreased from 96.2% AR at DAT-0 to 74.4% AR at DASF-28 and slightly increased to 78.4% AR at DASF-120. In soil WW, extractable residues decreased from 92.9% AR at DAT-0 to 64.8% AR at DASF-58 and slightly increased to 73.2% AR at DASF-120. Non-extractable residues (NER) increased during the aerobic incubation phase from 5.3% AR at DAT-0 to 11.8% AR at DAT-3 in soil DD, from 4.9% AR at DAT-0 to 11.2% AR at DAT-3 in soil HH and from 6.1% AR at DAT-0 to 18.4% AR at DAT-7 in soil WW. During the following anaerobic incubation phase, NER increased in soil DD to 19.6% AR at DASF-92 and slightly declined to 18.4% AR at DASF-120. In soil HH, NER increased to 25.1% AR at DASF-58 and slightly declined to 22.2% AR at DASF-120. In soil WW, NER increased to 32.9% AR at DASF-58 and slightly declined to 25.3% AR at DASF-120.

 

Within the aerobic incubation phase, the amount of the test substance decreased rapidly from 94.3% AR at DAT-0 to 59.2% AR at DAT-3 in soil DD, from 93.3% AR at DAT-0 to 70.5% AR at DAT-3 in soil HH and from 90.8% AR at DAT-0 to 64.1% AR at DAT-7 in soil WW. During the following anaerobic incubation phase, the amount of the test substance slightly further decreased to 44.6, 56.4 and 52.3% AR at DASF-120 in soil DD, HH and WW, respectively.

 

Two degradation products were identified with the following maximum amounts: benzoic acid with 7.1% AR (aerobic, DAT-3) and 8.9% AR (anaerobic, DASF-58) in soil DD. Benzyl alcohol with 13.1% AR (aerobic, DAT-3) and 18.9% AR (anaerobic, DASF-58) in soil DD. The total unidentified residues amounted to a maximum of 9.4% AR and no single component exceeded 4.5% AR at any sampling interval for all soils.

 

The experimental data of the anaerobic incubation phase could be well described by a double first order (DFOP) kinetic model. The half-life of the test substance under anaerobic conditions was > 1000 days in all soils.