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

Phototransformation in water

Link to relevant study record(s)

Reference

Endpoint:

phototransformation in water

Type of information:

experimental study

Adequacy of study:

supporting study

Reliability:

1 (reliable without restriction)

Rationale for reliability incl. deficiencies:

guideline study

Study type:

direct photolysis

Qualifier:

according to guideline

Guideline:

EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)

Deviations:

no

Qualifier:

according to guideline

Guideline:

other: BBA Guideline IV/6-1 (Aqueious Photolysis)

Deviations:

no

GLP compliance:

yes

Specific details on test material used for the study:

- Radiolabeled test substance name: 14C-XDE-795
- Label: Labeled in the 2 position of the quinoline ring
- Purity: 99+%
- Reference no. A925-161

Radiolabelling:

yes

Analytical method:

high-performance liquid chromatography

other: liquid scintillation counting

Light source:

Xenon lamp

Light spectrum: wavelength in nm:

298

Duration:

8 h

Temp.:

20 °C

Initial conc. measured:

10 mg/L

Reference substance:

yes

Remarks:

DCHQ

Dark controls:

yes

Key result

% Degr.:

27

St. dev.:

12

Sampling time:

45 min

Test condition:

298 ± 8 nm and 20°C [solvent:acetonitrile:water (80:20 v/v)]

Quantum yield (for direct photolysis):

0.012

Key result

DT50:

> 1.7 - < 22.8 h

Remarks on result:

other: The half-lives (medium values assuming normal climate conditions) were between 1.7 (June) and 22.8 h (December)

Transformation products:

yes

Remarks:

One main radio-labeled component was found which contained between 6 and 30% of the radioactivity (was not identified). A minor degradation product (1-11 % of the initial radioactivity) corresponding to 5,7-dichloro-4-hydroxyquinoline

Validity criteria fulfilled:

yes

Conclusions:

Analysis of irradiated 14C-test substance solutions indicated the presence of two main photoproducts. The major product, which accounted between 6 and 30% of the radioactivity after 8 hours irradiation, was not identified during this study. A second product, 5,7-dichloro-4-hydroxyquinoline, which accounted for 1-11% of the radioactivity after 8 hours was identified by chromatographic comparison with an analytical standard.

Executive summary:

The degree of photolytic degradation and the quantum yield of the test substance were determined by irradiation at 298 ± 8 nm at 20°C in accordance with BBA guideline IV/6-1 (aqueous photolysis). Due to the low solubility of the test substance in water, the irradiations were performed in a mixture of acetonitrile and purified, de-ionized water (80:20 v/v), after showing that the acetonitrile had no effect on light absorption. HPLC analysis showed that test substance was degraded under these conditions (between 15 and 44 % within 45 min depending on concentration and lamp intensity). The quantum yield of the photodegradation was determined to be 1.2E-2 (±19%; n = 4; independent from concentration and lamp intensity).

Additionally, 14C-test substance was irradiated under the same conditions. Samples were analyzed by radio-HPLC after irradiation times of 4 to 8 h (with different lamp intensities). Test substance accounted for 55-93% of the radioactivity and one main radio-labeled component was found which contained between 6 and 30% of the radioactivity. This degradate was not identified within this study. A minor degradation product (1-11 % of the initial radioactivity) corresponding to 5,7-dichloro-4-hydroxyquinoline was identified by chromatographic comparison with an analytical standard.

Environmental half-life periods were predicted using a computer program. The determined UV/Vis absorption coefficients and quantum yield were used as input and no dissipation processes other than photolysis were considered. The half-lives (medium values assuming normal climate conditions) were between 1.7 (June) and 22.8 h (December).

Description of key information

Half-life = 18 minutes at 40ºN summer sunlight. CFBPQ (2-chloro-10-fluoro[1]benzopyrano[2,3,4-de]quinoline) was identified as the primary photodegradate of the test substance.

CFBPQ is formed very quickly under natural conditions. Once formed there is a rapid degradation of CFBPQ to material which is polar and multicomponent in nature. When sediment is present the amount of radioactivity present in the aqueous layer is greatly reduced due to partitioning of CFBPQ to the sediment.

Key value for chemical safety assessment

Half-life in water:

18 min