(2RS,3RS)-3-(2-chlorophenyl)-2-(4-fluorophenyl)-[(1H-1,2,4-triazol-1-yl)methyl]oxirane

Biodegradation in soil

Key value for chemical safety assessment

Half-life in soil:

189 d

at the temperature of:

20 °C

Additional information

Parent compound:

Experimental data are available for the assessment of the aerobic and anaerobic degradation of epoxiconazole in soil. Studies on the route of degradation of the test substance in soil conditions were performed with oxirane and fluorophenyl labeled test compound.

In the GLP study with oxirane labelled test substance metabolism in soil was investigated in two soils (clay loam and sand). The test was conducted according to EPA 162-1 Guideline under dark conditions at 20 °C for up to 336 days. At the end of the study 34 and 67% TAR were recovered as parent. Two minor unidentified components were detected at levels < 4% TAR. Non-extractable residues accounted for 15.1 to 23.2% TAR at the end of the test procedure (Baranowski, rep. no.: 093014, 1989).

The degradation kinetics were re-evaluated using the experimental data given in the study and analyzing the kinetic parameters according to the current FOCUS guidance. The SFO kinetic model resulted in the best fit for this study. The half-life DegT50 was calculated to be 390.1 days for the clay loam soil and 173.2 days for the sand soil (at 20 °C, Voss, 2016).

Additionally, one study on the anaerobic degradation of epoxiconazole is available. This GLP study was conducted according to german BBA Guideline IV 4-1. The study was investigated at 20 °C for 120 days with the fluorophenyl labelled test compound in a loamy sand soil. At the end of the study, 55% TAR were recovered as parent. Non-extractable residues accounted for 24.2% TAR at the end of the study (BASF AG, rep.no.: 58246, 2003). In both studies the biggest amount of the non-extractable residues was assigned to the humin fraction.

The degradation kinetics were re-evaluated using the experimental data given in the study and analyzing the kinetic parameters according to the current FOCUS guidance. The DFOP model resulted in the best fit for this study. The half-life DegT50 was calculated to be 187.8 days for the loamy sand soil (at 20 °C, Sachers, 2016).

Metabolites

Regarding the metabolism of epoxiconazole under aerobic conditions, it can be concluded that during metabolism of the test substance (oxirane labeled) in soil, no metabolites appeared in major amounts. Only very small amounts unknown metabolites appeared (max 4 % TAR). According to the TLC analytics the analyzed fraction with unknown metabolites could be separated into at least four further fractions of which two spots migrated similar to the reference compound BF 480-11. For further characterization, isolated fractions and BF 480-11 were tried to derivatize with diazomethane. After the methylation procedure, the moieties were analysed again by TLC. These additional investigations demonstrated that - if at all - only very trace amounts could be contributed to BF 480-11 in the soil extracts.

The concentration of the non-extractable residues amounted up to about 20% TAR. The residual fraction after alkaline extraction was the humin fraction, the fraction soluble after acidification was the fulvic acid fraction and that soluble in alkaline but insoluble in acidic solution the humic acid fraction (for details see the Table 1 below).

Table 1. Characterization of non-extractable residues (% TAR)

	Clay/clay loam	Sand
Fulvic acid	2.3	5.1
Humic acid	2.2	5.4
Humin	18.7	9.5

 

The results show that the most portion of radioactivity was bound to the humin fraction. This makes it very likely that there is no concern to be expected with regard to release of active substance from the bound residues, because the number of bound residues is low and because they are tightly incorporated onto the humins being insoluble.

Two metabolites were identified for the parent compound as relevant degradation products under anaerobic test conditions in terms of PBT/vPvB assessment, with an estimated quantity of ≥ 0.1%. The metabolite BF 480-entriazole was identified with a maximum amount of 8.6% TAR after 120 days. The second metabolite BF 480-Alcohol remained constant at 1.2% TAR during the test procedure. From the pattern of identified metabolites, it is concluded that the first step in the degradation of the parent compound in anaerobic conditions consists of a cleavage of the oxirane ring, resulting in the formation of the alcohol BF 480-alchol which is readily dehydrated to the alkene BF 480-entriazol. Further outcomes are the formation of bound residues and to a minor extent the formation of CO2. However, for the metabolite BF 480-entriazol, no reliable degradation endpoints could be derived as no acceptable fit was obtained.

The concentration of the non-extractable residues amounted up to about 20% TAR. The residual fraction after alkaline extraction was the humin fraction, the fraction soluble after acidification was the fulvic acid fraction and that soluble in alkaline but insoluble in acidic solution the humic acid fraction (for details see the Table 2 below).

Table 2. Characterization of non-extractable residues, anaerobic conditions (% TAR)

Duration (d)	NaOH extract	Humin
14	2.0	7.0
29	3.3	8.6
63	3.7	11.5
91	3.7	13.5
120	3.7	14.8

The results show that the most portion of radioactivity remained unextractable and was assigned to the humin fraction.