4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-5-oxo-4,5-dihydro-1H-tetrazole-1-carboxamide

Biodegradation in water and sediment: simulation tests

Link to relevant study record(s)

Reference

Reference 1

Endpoint:

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

Data waiving:

other justification

Justification for data waiving:

other:

Transformation products:

not measured

Reference 2

Endpoint:

biodegradation in water: sediment simulation testing

Data waiving:

other justification

Justification for data waiving:

other:

Transformation products:

not measured

Description of key information

The worst case “very persistent” is concluded for the test substance.

Additional information

In a biodegradation screening study (EU Method C.4-E) 0% biodegradation was observed, thus the test substance is not readily biodegradable. Further simulation studies with paddy soils resulted in a maximum half-life of 46 days. However, according to the ECHA document "Guidance on Information Requirements and Chemical Safety Assessment. Chapter R.7b: Endpoint specific guidance. Version 4.0" (2017) the preferred temperature for simulation degradation studies is 12 °C, which corresponds to average temperature of European surface waters. Where this condition is not met a temperature correction should be considered based on the Arrhenius equation and half-lives be re-calculated. For first order kinetics this was done and the half-life of 46 days (at 28 °C) was re-calculated to 199 days (at 12 °C). Thus, based on a worst case assumption significant biodegradation in the environment is not expected.

Available simulation data on soil biodegradation were gained in studies with paddy soils systems, reflecting similar conditions as in water/sediment tests. In the key study available for soil biodegradation the degradation and partitioning behavior of [phenyl-UL-14C] and [cyclohexyl-1-14C]-labeled test substance and its metabolites occurring in submerged soil (alluvial and volcanic ash soil) and water layer under paddy conditions without plants. During the entire study period a significant formation of CO2 could be observed in both soil systems. After 105 days of incubation the portion of unchanged parent that was located in the solids, amounted to 11.4% (alluvial) and 18.1% (Volcanic ash) of applied dose, only. The main metabolite resulting from C-label #1, the 2-chlorophenyltetrazolinone (CRT), was found in the water phase as well as the soil extracts and reached its maximum portion at about 35 to 70 days yielding 39% in alluvial by 32% of applied RA in volcanic ash soil system. Finally, the CRT content declined to about 31% and 26% at day 105. A further metabolite, CPT-Me (M1), reached its maximum at day 105 by about 11% and 13% of applied RA in alluvial and volcanic ash soil system, but was mainly found in the soil extracts. Further metabolites (i.e. >5%) resulting from the before-mentioned label were not found. The main metabolite resulting from the cyclohexyl-1-14C-label, cyclohexylethylamine (CEA), was mainly extracted from the soils and reached a maximum portion of 7% and 10% of applied RA at the 16 to 35 days intervals in alluvial and volcanic ash soil system. Finally, the CEA content declined to about 2 and 5% at day 105. Further metabolites (i.e. >5%) resulting from the 2nd label were not found. DT50 values for the test substance in the paddy soil systems (submerged soil plus water) were estimated to be a maximum of 46 days at 28 °C (Guideline for the Experiment of Pesticide Residue in Soil, Environmental Agency of Japan (1978) and B59 NOSAN No. 4200, MAFF Japan (1985)). However, according to the ECHA document "Guidance on Information Requirements and Chemical Safety Assessment. Chapter R.7b: Endpoint specific guidance. Version 4.0" (2017) the preferred temperature for simulation degradation studies is 12 °C, which corresponds to the average temperature of European surface waters. Where this condition is not met a temperature correction should be considered based on the Arrhenius equation and half-lives be re-calculated. For first order kinetics this was done and a half-live of 46 days (at 28 °C) was re-calculated to 199 days (at 12 °C). Thus, based on the criteria given in the “Guidance on information requirements and chemical safety assessment, chapter R.11: PBT Assessment” (ECHA, 2017) a substance fulfills the “very persistent” criterion (vP) if the degradation half-life in soil is higher than 180 days. Thus, the substance has to be regarded as being very persistent based on a worst case assumption (DT50 = 199 days at 12°C).

No alternative metabolism pathway is expected in a new biodegradation simulation study in water/ sediment than in the biodegradation study in soil. Due to the results from the biodegradation screening study (0% biodegradation after 28 days, EU Method C.4-E) and simulation data on soil biodegradation with paddy soils systems (DT50 = 199 days at 12°C) it is expected that further simulation tests will not gain additional information. Furthermore, additional testing cannot contribute to a stricter assessment and thus, no further simulation test is proposed.

Furthermore, based on a study investigating the potential for bioaccumulation, the substance is not bioaccumulative in the context of the PBT-assessment. In case bioaccumulation can be excluded, the evaluation of the persistence (P) is not relevant and the overall evaluation result is “not PBT”. Radiolabeled test substance was used in the study investigating the potential for bioaccumulation. The substance accumulated in bluegill sunfish with a total residue kinetic bioconcentration factor of about 275.5 to 289.8 X for whole fish (sum of radio labelled compounds, parent substances, metabolites and mineralization products). When exposure ceases, the residues were depurated with a half-life of about 0.42 to 0.55 days. After 14 days in uncontaminated water 100 % of the mean plateau radioactivities were depurated from whole fish in both test levels. Accumulations of total residues in edible parts were less (116.9 – 153.6 X) than in whole fish (275.5 – 289.8 X). Taking into account that about 30 % parent compound were detected in edible parts and about 16% parent compound in non-edible (viscera) parts after 15 days of exposure the steady-state-BCF for parent (based on whole fish, wet weight) is about 71, the steady-state-BCF for parent (normalised to 6% lipid content) is about 54. Thus, bioaccumulation can be excluded and the overall evaluation result is “not PBT”.

Overall, due to the results from the biodegradation screening study (0% biodegradation after 28 days, EU Method C.4-E) and simulation data on soil biodegradation with paddy soils systems (DT50 = 199 days at 12 °C) the worst case “very persistent” is concluded for the test substance and additional testing cannot contribute to a stricter assessment.