Registration Dossier

Administrative data

Endpoint:
phototransformation in air
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Scientifically reliable study, non-GLP

Data source

Reference
Reference Type:
other: MS thesis
Title:
Unnamed
Year:
1993
Report Date:
1993

Materials and methods

Test guideline
Qualifier:
no guideline followed
Principles of method if other than guideline:
Indirect photolysis with *OH radical or O(1D) initiation, direct photolysis
GLP compliance:
no

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
- Name of test material (as cited in study report):[CF3]2CFCF=CFCF3, dimer of hexafluoropropene, 4-trifluoromethyl-2-perfluoropentene
- Physical state: liquid

Study design

Light source:
other: mercury lamp
Details on light source:
- The reactor contained an Ace Hanovia medium-pressure mercury lamp.
- Emission wavelength spectrum: No spectrum provided. Medium pressure mercury lines typically emit light at specific frequencies rather than as a continuous spectrum. The mercury lamp emits ca. 5.8 watts of its radiated energy at 254 nm wavelength and ca. 3.8 watts at 222 nm wavelength.
- Filters used and their purpose: Vycor jacket on light source to remove 185 nm mercury line. Vycor typically filters all frequencies less than ca. 210 nm.
- Light intensity at sample and area irradiated: Not reported.
Details on test conditions:
Phototransformation of HFP kinetic dimer was done as part of a larger experiment covering a variety of fluorinated organic chemicals.

Indirect photolysis was measured with respect to reaction with hydroxyl radical (*OH), as well as direct photolysis, using the same chamber. The long-path absorption cell, made of Pyrex glass, had a volume of 7.6 L and a base length of 60 cm, which was adjusted to give a total of 24 passes and an optical path length of 14.4 m. The chamber had a medium pressure Ace-Hanovia mercury lamp contained within a jacket to allow forced gas cooling. Concentrations of the reactants and products were monitored using a FTIR spectrometer (Nicolet 20SX). Decays of the test and reference substances were determined by subtracting the reference IR spectra of all of the reactants from the initial and final total IR spectra of the reaction mixture.

Hydroxyl radical was produced by photolysis of ozone at 254 nm in the presence of water vapor. Ozone was produced offline and had a typical mole fraction of ca. 0.9. A Vycor lamp jacket and air cooling were used to attenuate wavelengths <210 nm and limit direct photolysis of some of the other compounds in the experimental series. The mole fraction ozone was reduced to 0.3-0.4 by mixing with helium. The reactions were done using 5-30 mTorr of test substance, ca. 30 mTorr of methane, and 1 Torr of ozone in helium as buffer gas, with water vapor was added at ca. 10 Torr to allow complete conversion to hydroxyl radical. Total pressures during experiments ranged 200-700 Torr. Reactions were stopped after 3-8 minutes seconds. Tests using methane, which was used to verify operation of the apparatus, showed that disappearance of methane was independent of total pressure in the range of 100-760 Torr.
Duration of test at given test condition
Duration:
5 min
Temp.:
298 K
Reference substance:
yes
Remarks:
methane

Results and discussion

Preliminary study:
No degradation was observed in preliminary study done without ozone. No direct photolysis under reaction conditions
% Degradation
Key result
% Degr.:
77.8
Sampling time:
5 min
Test condition:
rate constant (k[OH]): 7.7(±0.8)E-14 cm³ molecule-¹ s-¹
Dissipation half-life of parent compound
Key result
DT50:
0.57 yr
Test condition:
by comparison with lifetime of methane (reference substance)

Any other information on results incl. tables

Dissipation half-life was calculated as follows:

Hydroxyl reaction lifetime:

lifetime of methane: 9.6 years

rate constant for methane: 6.5E-15 cm³ molecule-¹ s-¹

rate constant for HFP kinetic dimer: 7.7E-14 cm³ molecule-¹ s-¹

lifetime = 9.6 * rate constant for methane/rate constant for HFP kinetic dimer

lifetime = 9.6 * 6.5E-15/7.7E-14 = 0.82 years

half-life = lifetime * 0.693 = 0.57 years

(at time of the study report, atmospheric lifetime of methane was considered to be 12 years. The currently accepted value is 9.6 years, which value was used in this calculation)

Applicant's summary and conclusion

Validity criteria fulfilled:
not applicable
Conclusions:
The half-life for phototransformation of HFP kinetic dimer is 0.57 years
Executive summary:

The phototransformation of HFP kinetic dimer was addressed in a chamber study using hydroxyl radical (*OH) as indirect photooxidant, with methane as reference substance. A number of other fluorinated organic chemicals were tested in the experimental series. FTIR was used to monitor concentrations of HFP kinetic dimer and methane using a subtraction technique. A medium pressure mercury lamp (typically emitting in discrete wavebands rather than as a continuous spectrum) was used to photolyze ozone and produce the radical species of interest. No direct photolysis of HFP kinetic dimer was observed under reaction conditions. HFP kinetic dimer reacted more rapidly than methane. The rate constant for this reaction was 7.7(±0.8)E-14 cm³ molecule-¹ s-¹. The HFP kinetic dimer atmospheric lifetime is 0.82 years with respect to hydroxyl radical induced photolysis. The corresponding atmospheric half-life 0.57 years.

The study was conducted using scientifically sound principles. However, there is very little information on the specifics of the study. Lamp power, model, and emission characteristics are not provided, nor are purity and source of the tested materials stated. Summary data only are provided on validation of the test apparatus and on decay of the tested compounds. Therefore, this study is reliable with restrictions. It is suitable for use in Risk Assessment, Classification & Labelling, and PBT Analysis.