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Environmental fate & pathways

Phototransformation in water

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phototransformation in water
Type of information:
experimental study
Adequacy of study:
key study
Study period:
23 Apr 1998 - 30 Dec 1999
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Study type:
direct photolysis
according to guideline
EPA Guideline Subdivision N 161-2 (Photodegradation Studies in Water)
according to guideline
other: EU Directive 91/414/EEC, Annex IIA 2.9.2
according to guideline
other: SETAC: Procedures for assessing the environmental fate and ecotoxicity of pesticides, 1995, 10. Aqueous photolysis
GLP compliance:
Analytical method:
high-performance liquid chromatography
Details on sampling:
- Sampling intervals for the parent/transformation products: Sampling was carried out after 0, 3, 5, 8, 12.3 and 16 hours of irradiation. For the dark controls, the sampling time was 16 h.
- Sampling method: Sampled aliquots were split up: Radioactivity was counted in 2 x 200 µL, 2 x 1.5 mL were removed for HPLC analysis, 5 mL were removed for HPLC analysis
- Sampling intervals/times for pH measurements: pH was checked at each sampling time point.
- Sampling intervals/times for sterility check: Sterility was checked in aliquots from 16 h samples.
- Sample storage conditions before analysis: Instant analysis or storage at -20 °C; stability of the compounds under this condition was shown.
- pH: 5
- Type and final molarity of buffer: 18.25 mM citric acid
- Composition of buffer: 8.4 g of citric acid was dissolved in 2 L deionised water and the pH was adjusted with 1M NaOH
Light source:
Xenon lamp
Light spectrum: wavelength in nm:
> 290
Details on light source:
- Emission wavelength spectrum: > 290
- Filters used and their purpose: Special ultra-violet glass was used to remove radiation below 290 nm and give a spectral distribution approximating D65 radiation.
- Light intensity at sample and area irradiated: The intensity of the incident light measured was found to be 730 W/m2.
- Relative light intensity based on intensity of sunlight: 5.06 hours of Suntest irradiation under experimental conditions are equivalent to one day of summer sunlight at the latitudes 20°-50° North or 1 hour of Suntest irradiation = 0.198 days of summer sunlight.
Details on test conditions:
- Type, material and volume of test apparatus/vessels: Pyrex photochemical reactors, 100 mL
- Sterilisation method: 35 min at 121 °C
- If no traps were used, type of test system: closed
- Test temperature: 24.8 - 25.2 °C

- Volume used/treatment: 100 mL
- Kind and purity of water: Deionised water, further purified by means of an Elgastat UHP apparatus, resistivity > 18 MΩ*cm
- Preparation of test medium: 99 mL of buffer pH 5 solution was poured into the photochemical reactors using a sterilised graduated measuring cylinder. 1.0 mL of a solution containing 14C-RPA107382 at a nominal concentration of 0.303 mg/mL in acetonitrile was added to each reactor using an automatic pipette fitted with a sterile tip. The final concentration of the test substance was 3.03 µg/mL.
- Identity and concentration of co-solvent: acetonitrile, 1% (v/v)

- No. of replicates (dark): 2
- No. of replicates (irradiated): 2

16 h
25 °C
Initial conc. measured:
3.03 other: µg/mL (nominal)
Reference substance:
Dark controls:
Two Schott bottles were placed at 25 ± 1 °C in the dark for 16 h.
Computational methods:
- Half-lives or DT50 values: Calculations were made with Excel v7.0 (Microsoft). r2 = 0.9952 for Ethiprole degradation kinetics which was found to be pseudo-first order.
max lambda
203 nm
neutral medium
max lambda
278.5 nm
neutral medium
max lambda
329 nm
neutral medium
% Degr.:
Sampling time:
16 h
6.46 h
Test condition:
16 hours continuous Xenon-lamp irradiation
1.3 d
Test condition:
Calculated for summer sunlight in Florida, USA
Transformation products:
Details on results:
- pH, sterility, temperature, and other experimental conditions maintained throughout the study: Yes

TRANSFORMATION PRODUCTS in the dark controls
- No degradation was observed.

TRANSFORMATION PRODUCTS in the irradiated test samples
- RPA 157925: 21.0% on day 3 and 18.5% at test end
- Met 10.3: 5.5% on day 3 and 37.2% at test end
- Met 9.3: 1.5% on day 3 and 9.2% at test end
- Met 6.5: 1.5% on day 5 and 7.5% at test end

- No volatiles were generated.

Mass balance: For each individual sample, the total radioactivity balance ranged from 94.2 to 101.1% of the initial applied radioactivity (mean: 97.3% of applied).

Validity criteria fulfilled:
not applicable

Description of key information

DT50 = 1.3 d in summer sunlight (20 - 50 °North) (EPA Guideline Subdivision N, 161-2)

Key value for chemical safety assessment

Half-life in water:
1.3 d

Additional information

One study investigating the Phototransformation of the substance in water is available following GLP and EPA Guideline Subdivision N, 161-2. A half-life of 6.46 hours was determined at continuous irradiation (Xenon lamp) corresponding to 1.3 days of summer sunlight in Florida (20 - 50 °North). Photodegradation can be considered as an important route of degradation in an aqueous environment.