5,7-dichloro-4-(4-fluorophenoxy)quinoline;quinoxyfen (ISO)

Phototransformation in soil

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in soil

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Qualifier:

according to guideline

Guideline:

other: EC Directive 91/414/EEC

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

[14C]-DE-795 labelled at position 2 of the quinoline ring
Batch GHD-3058-19
Radiopurity: 99%

Radiolabelling:

yes

Analytical method:

high-performance liquid chromatography

other: thin layer chromatography

Light source:

other: sun simulation lamps

Duration:

30 d

% Moisture:

4.04

Temp.:

25 °C

Initial conc. measured:

250 other: g a.i. per ha

Reference substance:

yes

Remarks:

unlabeled test substance

Dark controls:

yes

Key result

DT50:

205 d

Test condition:

25°C

Remarks on result:

other: This corresponds to an estimated t1/2 of between 424 and 2565 days in natural sunlight according to season at Letcombe, England

Transformation products:

yes

Remarks:

The main degradation product reached up to 6.5% of applied radioactivity (AR) at 30 days and was not identified. Small amounts (up to 2.5% AR) of DCHQ, non-extractable residue generally increased with time to a maximum of ca 12% AR

Validity criteria fulfilled:

yes

Conclusions:

The t1/2 estimated for test substance under natural sunlight conditions (>1 year; spring at Letcombe, England) has indicated that soil photolysis will not be a significant route of degradation for the test substance in the environment

Executive summary:

The photolysis of the active substance of the test substance has been investigated on the surface of Speyer 2.2 soil. The study was conducted to meet the requirements of the FAO Annex to revised guidelines on environmental criteria for the registration of pesticides, as accepted under EC Directive 91/414/EEC.

Portions of Speyer 2.2 soil were surface treated with [14C]-test substance to give an application rate equivalent to 250 g a.i. per ha. Samples were then placed inside a chamber, sealed with a quartz glass lid and exposed to an artificial light source using a light/dark cycle. An actinometer was used to compare the intensity of the artificial light with natural sunlight. The samples were maintained at ca 25°C and ca 18°C during the light and dark cycles respectively. Control samples were maintained under the same conditions but with light excluded. At 1, 3, 7, 14, 21 and 30 days after treatment for the irradiated experiment, any evolved organic volatiles and CO2 were removed by purging the headspace. Soil samples from the irradiated and control experiments were then taken for analysis, in addition to zero-time samples. The results are as follows.

In the irradiated experiment, test substance degraded under the artificial light conditions with a t1/2 (Timme-Frehse) of 205 days, corresponding to an estimated t1/2 of greater than 1 year in natural sunlight (spring at Letcombe, England). The main degradation product, which had chromatographic properties similar to parent compound, reached up to 6.5% of applied radioactivity (AR) at 30 days. It was not identified. Small amounts (up to 2.5% AR) of 5,7-dichloro-4-hydroxyquinoline (DCHQ) were also seen together with a polar fraction (up to 4% AR at 14 days). Non-extractable residue generally increased with time to a maximum of ca 12% AR. Little or no organic volatiles or CO2 were detected (<1% AR in total).

In the control experiment where light was excluded, little or no degradation of test substance occurred over the 30-day study period. In addition, less non-extractable residue was formed. These results indicated that the degradation seen in the irradiated experiment resulted abiotically from the photodegradation of test substance on soil.

In conclusion, the t1/2 estimated for the test substance under natural sunlight conditions (>1 year; spring at Letcombe, England) has indicated that soil photolysis will not be a significant route of degradation for the test substance in the environment.

Description of key information

The t1/2 estimated for test substance under natural sunlight conditions (>1 year; spring at Letcombe, England) has indicated that soil photolysis will not be a significant route of degradation for the test substance in the environment.

Key value for chemical safety assessment

Half-life in soil:

1 yr