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

Biodegradation in water and sediment: simulation tests

Key value for chemical safety assessment

Half-life in freshwater:

3.9 d

at the temperature of:

20 °C

Half-life in freshwater sediment:

392 d

at the temperature of:

20 °C

Additional information

Parent:

The assessment of the degradation and partitioning behavior of epoxiconazole in water and sediment is performed with a weight of evidence approach. This approach consists of two available experimental studies conducted with epoxiconazole (OECD 309 and OECD 308).

In a study the distribution and degradation of epoxiconazole was investigated in two natural water/sediment systems using two different labelling positions (chlorophenyl-U and fluorophely-U- [14C]epoxiconazole). This GLP study was conducted according to OECD Guideline 308 (draft and proposal) under the dark test conditions at 20 °C for 100 days. The test substance concentration was 125 g/ha. In general, the results for the two different radiolabeled test items in both test systems were in very good agreement within the test systems. In both systems, the radioactivity in the water phase continuously decreased ( <10% TAR after 100 days, Schnoeder, 2003). In the sediments phase of the Millstream Pond, the amounts of the test item increased until 7 days after application to 66% TAR and, then the amount of extractable test item in the sediment remained on a plateau and slightly decreased towards the end of the test procedure. In the sediment phase of the Swiss Lake the extractable amount of expoxiconazole reached a maximum of 50% TAR after 13 days after application. Thereafter, a clear decrease towards the end of the experiment was determined (33.6 – 37.2% TAR after 100 days, Schnoeder, 2003).

The degradation kinetics of the parent test substance was re-evaluated based on the latest guidance document of the FOCUS workgroup on degradation kinetics. The results are summarized in the Table below.

Table 1. Summary of trigger endpoints (DT50, d) for expoxiconazole.

	Water phase, FOMC kinetic model		Sediment phase, SFO kinetic model
	Trigger endpoints	Modeling Endpoints	Trigger endpoints	Modeling Endpoints
Swiss Lake	6.4	25.9	n.d.	n.d.
Millstream Pond	2.4	8.2	391.9	391.9

n.d. not acceptable fit was obtained

Apart from the sediment phase in system Swiss Lake, the evaluation resulted in reliable trigger and modeling endpoints for all compartments of both systems. For the water phase, the trigger DT50 ranged from 2.4 to 6.4 days (geometric mean DT50: 3.9 days, n=2). The corresponding modeling DT50 ranged from 8.2 to 25.9 days. For the sediment phase, the trigger DT50 in system Millstream Pond were 391.9 and the corresponding modeling DT50 was also 391.9 days.

Additionally, the GLP study was performed according to OECD guideline 309 (Aerobic mineralization in surface water – Simulation biodegradation test) with a pelagic test system. The test was performed at two test item concentrations (10 and 100 µg/L) using triazole-3(5)-14C-labelled test item. Sterile samples were tested at the higher concentration. The test substance was not significantly degraded in the natural water environment. At least 93.9% TAR was recovered as the unchanged parent substance after 60 days of exposure (Kelly, 2016). There was no change in the enantiomer ratio (50:50) of the test substance during the study and the rate of mineralization was low (<0.1% TAR). Degradation kinetics were not reported as no significant degradation was observed.

The substance has a very high experimental Koc value varying in the range from 945 to 2451 L/kg (@pH 5.9 – 7.3, see IUCLID Ch. 5.4.1). In an aerobic water/sediment study under dark conditions (OECD 308, Schnoeder, 2003) epoxiconazole was observed to quickly partition from the water phase to the sediment phase as expected due to the high Koc value. Therefore, the sediment and soil are determined to be the major degradation compartments for epoxiconazole.

Metabolite

 

In a study performed according to OECD guideline 309 (Aerobic mineralization in surface water – Simulation biodegradation test) with a pelagic test system no metabolites, were identified as relevant degradation products in terms of PBT/vPvB assessment. However, in the key study, conducted according OECD Guideline 308 (draft and proposal) under the dark test conditions the metabolite BF 480-entriazole was detected. This metabolite was identified in the sediment phase at a maximum amount of 32.3% TAR after 59 days (Swiss Lake, Schnoeder, 2003). In the water phase, the metabolite was detected only sporadically at concentrations below 2% TAR at all sampling occasions for both labels and water/sediment systems.

The degradation kinetics of the metabolite was re-evaluated based on the latest guidance document of the FOCUS workgroup on degradation kinetics. The results are summarized in the Table below.

Table 2. Summary of trigger endpoints (DT50, d) for metabolite BF 480-entriazole.

	Sediment phase, SFO kinetic model
	Trigger endpoints	Modeling Endpoints
Swiss Lake	n.d.	n.d.
Millstream Pond	46.6	46.6

n.d. not acceptable fit was obtained

The kinetic evaluation of metabolite degradation revealed no reliable trigger and modeling endpoints for the system Swiss Lake. For the system Millstream Pond, reliable trigger and modeling endpoints were derived. The trigger and the corresponding modelling DegT50 were 46.6 days.