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

Toxicity to terrestrial plants

Link to relevant study record(s)

Reference

Endpoint:

toxicity to terrestrial plants: long-term

Data waiving:

exposure considerations

Justification for data waiving:

the study does not need to be conducted because direct and indirect exposure of the soil compartment is unlikely

Additional information

In accordance with Regulation (EC) No 1907/2006, Annex IX, column 2, testing of effects on terrestrial organisms is not required since direct and indirect exposure of the soil compartment for the substance 4-(2-chlorophenyl)-N-cyclohexyl-N-ethyl-5-oxo-4,5-dihydro-1H-tetrazole-1-carboxamide is unlikely. Furthermore, the evaluation of the PEC/PNEC ratio indicates no risk for the terrestrial compartment (RCR << 1). For detailed information, see Chemical Safety Report (CSR) chapter 9 and 10.

In addition, two studies were conducted to investigate the metabolism of the test substance in Japanese rice (1997a, 1997b). But these studies are not relevant for hazard and risk assessment of the test substance. In order to present a comprehensive overview of available data, both studies are summarised here.

Both studies were conducted according to GLP principles and followed EPA-Guidelines OPPTS 860.1300 (Nature of the Residue - Plants, Livestock) and MAFF Japan-Guideline (59 NOSAN No. 4200) from Jan. 1985. The conduct of the two studies is almost identical; the main difference between the studies is the difference in the location of the radiolabelling.

The metabolism of the test substance was investigated in Japanese rice (cultivar: Nihonbare) grown under paddy conditions. The 14C-labeled test substance was formulated as 30 GR (30 g a.i./kg granular formulation) and applied uniformly to each of 6 plant containers 10 days after transplanting of young rice plants (3-4 leaf stage). The application rate corresponded to 266 g active ingredient/ha and was based on the projected field rate of 200 - 300 g a.i./ha. Forage sample was taken at day 59 (69 days after transplanting). Straw and hulled rice were harvested at day 131 (1997a) or day 142 (1997b). These materials were analysed for the total radioactive residues (TRR) by combustion analysis (data expressed as mg/kg a.i. equivalents) and the qualitative and quantitative nature of metabolites were determined in forage, straw and hulled rice.

In the first study (1997a) the total radioactive residues in forage, straw and hulled rice amounted to 0.164 mg/kg, 0.624 mg/kg and 0.040 mg/kg, respectively. From forage 93.5% of the TRR were extracted with a combination of conventional and microwave extraction steps and 6.5% remained in the solids. From straw, a total of 95.6% of the TRR was extracted. In the lignin and cellulose fraction 0.2% and 4.2% of the TRR, respectively, were found. From hulled rice 27.1% of the TRR was dissolved in the first conventional extracts and 69.8% in the microwave extracts. Approximately 40% of the TRR was assumed as to be attributable to natural constituents such as starch. On the basis of the nature and amount of metabolites found in the extracts of forage, straw and hulled rice a degradation pathway were proposed. In all samples no parent compound was found. This was also observed in the second rice metabolism study (1997b). The metabolic degradation of the parent compound in paddy soil primarily occurred by hydrolytic cleavage with the formation of cyclohexylethylamine (CEA) and 2-chlorophenyltetrazolinone (CRT). The CEA part of the molecule was better degradable than the CPT part, but led to a higher portion of radioactivity bound to soil constituents [compare endpoint biodegradation in soil]. Since the TRRs in rice plants were very low in contrast to the results of the phenyl label study, it was considered that the test substance was mainly cleaved in soil/water before uptake. The primary metabolite CEA was further metabolized in rice plants. Hydroxylation of the cyclohexyl ring of CEA yielded three isomers (hydroxy-CEA). The finding of urea-dihydroxy-CEA indicated urea-CEA (N-cyclohexyl-N-ethylurea) as a possible intermediate. In forage and straw 49.1% (0.081 mg/kg) and 59.3% (0.369 mg/kg) of the TRR, respectively, were identified or characterized. From a total of 15 metabolites in the conventional and exhaustive extracts of forage and straw six metabolites were identified (forage: 3.0 - 13.4%, 0.005 mg/kg - 0.022 mg/kg; straw: 2.8 - 17.0%, 0.017 - 0.107 mg/kg). Nine unknown metabolites were present in very small quantities (forage: 2.1 - 9.1%, 0.004 - 0.015 mg/kg; straw: 1.1 - 7.5%, 0.007 - 0.04 7 mg/kg). In hulled rice all metabolites were equal to or less than 0.001 mg/kg (0.5 - 3.8%) except for radioactivity at the TLC origin (6.8%, 0.003 mg/kg). A total of 75.8% (0.031 mg/kg) of the TRR was identified or characterized. Comparing the individual amounts of metabolites in this study with the ones from the study (1997b) using another 14C-label, it was evident that the representative compounds for the residue definition were the CPT-acetic acid and CPT-lactic acid. As an example, the residue levels of the main metabolite CEA (forage: 0.017 mg/kg; straw: 0.107 mg/kg; hulled rice: 0.001 mg/kg) were only 1/9 - 1/28 times that of the main metabolite CPT-acetic acid (forage: 0.471 mg/kg; straw 0.919 mg/kg; hulled rice 0.024 mg/kg).

From the second study (1997b) the following conclusions were drawn. At harvest, most of the recovered radioactivity was found in the straw, followed by the rachis and the chaff. The lowest amount was detected in hulled rice (0.14 %; 0.048 mg/kg a.i. equiv.). These data indicated a rather low importance of the total radioactive residues in hulled rice which is for this crop the only commodity for human consumption. The extractability of the radioactivity from the forage, straw and hulled rice was enhanced by using microwave treatment after the standard extraction. In this way more than 90% of the radioactivity could be extracted from forage and straw. In case of hulled rice, ca. 30% (0.015 mg/kg a.i. equiv.) remained in the solids. The radioactive residue in this sample was characterised as to be incorporated into natural constituents (amino acid, starch and protein fraction). On the basis of the nature and amount of metabolites found in the extracts of forage, straw and hulled rice a degradation pathway could be proposed. After uptake of the test item and/or the soil degradation compound 2-chlorophenyltetrazolinone (CPT), this primary metabolite was conjugated with acetyl serine (cysteine synthase) or serine (tryptophane synthase) forming the conjugate CPT-alanine. Via the intermediate compound CPT-pyruvic acid which could not be detected the final metabolites CPT-lactic acid and especially CPT-acetic acid were formed. In all samples no parent substance was found. The most important metabolite was CPT-acetic acid because it was found in high yield in all raw agricultural commodities (forage: 50.28 % of TRR, 0.471 mg/kg; straw: at least 43.02 % of TRR, 1.023 mg/kg; hulled rice: 48.42 % of TRR, 0.024 mg/kg a.i. equiv.). Similar metabolites were also found for example in case of several triazole-ring containing fungicides (i.e. Tebuconazole), and aminotriazole. These highly effective detoxification reactions are therefore of common importance for the metabolism in plants of such compounds.

The low amount of CPT/CPTmethyl found in the different samples (< 5 %, < 0.05 mg/kg) additionally proved the given considerations of the main biodegradation pathway of the 14C-labeled test substance in rice plants. The major metabolites CPT-acetic acid and CPT-lactic acid were proposed as important for the residue definition.