Methyl (R)-2-(4-(3-chloro-5-trifluoromethyl-2-pyridyloxy)phenoxy)propionate

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:

test procedure in accordance with generally accepted scientific standards and described in sufficient detail

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: Japan MAFF 9 Nohsan 5089

Deviations:

no

GLP compliance:

no

Remarks:

The report represents data generated after the effective date of GLP

Specific details on test material used for the study:

Pyridine label:
Specific activity: 28.1 mCi/mmol
Average purity: 98.2%

UL phenyl label:
Specific activity: 18.3 mCi/mmol
Average purity: 97.8%

Radiolabelling:

yes

Analytical method:

high-performance liquid chromatography

Light source:

Xenon lamp

Duration:

9 d

Temp.:

20 °C

Initial conc. measured:

2 other: µg/mL

Duration:

16 d

Temp.:

20 °C

Initial conc. measured:

2 other: µg/mL

Reference substance:

yes

Dark controls:

yes

Quantum yield (for direct photolysis):

0.004

Key result

DT50:

20 d

Test condition:

pH 5 buffer at 40° N latitude summer sun

Key result

DT50:

2 d

Test condition:

Natural water

Transformation products:

yes

Remarks:

DE-535-acid and three degradates (DE-535-furan, DE-535-acid-phenone, DE-535-acid-furan) exceeding 10% of applied radiocarbon were observed.

Conclusions:

In pH 5 buffer, the expected half-life for the test substance was 20 and DT90 value was 66 days. Degradation was faster in natural water with DT50 value of 2 days and DT90 value of 7 days. The quantum yield value was 3.8E-3. Results indicate that in aqueous environments it is likely that the test substance will be photodegraded to form small naturally occurring organic acids and CO2.

Executive summary:

This study determined the rate and route of photodegradation of the test substance in sterile pH 5 buffer and non-sterile natural water. The study was conducted following EPA guideline 161-2. 14C-test substance, radiolabeled either uniformly in the phenyl ring or in the 3,4-positions of the pyridine ring was applied to buffer and natural water to give a concentration of 2.0 µg/mL test substance and 0.8% acetonitrile co-solvent. Because test substance was quickly photolyzed to form DE-535-acid in natural water, the natural water samples were also used to calculate DT50 and DT90 values for DE-535-acid photolysis in natural water. 14C DE-535-acid, radio labeled either uniformly in the phenyl ring or in the 4,5-positions of the pyridine ring was applied only to buffer to give a concentration of 1.0 µg/mL DE-535-acid and less than 0.4% acetonitrile co-solvent.

Samples were continuously irradiated using a xenon arc lamp to simulate average summer sunlight at 40 °N latitude. Irradiated samples and dark controls for test substance and DE-535-acid were collected for buffer and natural water samples at 0, 0.8, 1.8, 4.8, 6.8, 8.8, 15.8, and 16.7 days after treatment (DAT) and analyzed by reverse phase high pressure liquid chromatography (HPLC). Additional sampling times for the DE-535 in natural water were collected at 0, 0.04, 0.3, 0.1, 0.8, and 1.8 DAT.

In pH 5 buffer, the expected half-lives for the test substance and DE-535-acid at 40° N latitude summer sun were 20 and 12 days, respectively, and DT90 values were 66 days (test substance) and 40 days (DE-535-acid). Degradation was faster in natural water with DT50 values of 2 days (test substance) and 8 days (DE-535-acid) and DT90 values of 7 days (test substance) and 24 days (DE-535-acid). The quantum yield values were 3.8E-3 for test substance and 1.7E-2 for DE-535-acid.

Description of key information

Study Type	Study Details	Value	Guideline	Reliability
Phototransformation in water	pH 5 buffer and natural water	DT50 = 20 and 2 days	EPA 161-2	1

Key value for chemical safety assessment

Half-life in water:

2 d