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Diss Factsheets

Administrative data

Endpoint:
phototransformation in air
Type of information:
experimental study
Adequacy of study:
key study
Study period:
1997-1998
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: non-GLP, non-guideline study conducted using scientifically valid principles

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1998
Report date:
1998

Materials and methods

Test guideline
Qualifier:
no guideline available
Deviations:
not applicable
Principles of method if other than guideline:
The value for the rate constant of the OH reaction was obtained by monitoring the rate of disappearance of the test substance relative to that of a reference compound (CH4 or CH3Cl) in the presence of OH radicals.
GLP compliance:
no

Test material

Constituent 1
Reference substance name:
HFE s-601
IUPAC Name:
HFE s-601
Details on test material:
- Name of test material (as cited in study report): L-14787

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.
- Filters used and their purpose: Vycor jacket on light source to remove 185 nm mercury line. Vycor typically filters all wavelengths less than ca. 210 nm.
- Light intensity at sample and area irradiated: Not reported
Details on test conditions:
Phototransformation of HFE s-601 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). 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 800). 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 in the presence of water vapor (ca. 3 mm Hg). Ozone was produced by first trapping the effluent of an ozonizer in cold silica gel, then desorbing the sample into a 12-L glass reservoir and subsequently mixing with helium. Experiments were conducted at room temperature with ca. 200 mm Hg helium as buffer gas.

Concentrations of test and reference substance were measured at varying time points. Fractions of each substance relative to its initial concentration (C/Co) were calculated and log transformed. The log-transformed test substance and reference substance fractions were plotted in ordered pairs, as a function of reference substance concentration, and fitted using a least squares with the curve forced through the origin to obtain relative photolysis rate. Relative photolysis rate was multiplied by accepted values of the reference substances' photolysis rates to obtain absolute photolysis rates for HFE s-601.
Duration of test at given test condition
Duration:
12 min
Temp.:
295 K
Reference substance:
yes
Remarks:
methane and chloromethane

Results and discussion

Dissipation half-life of parent compound
DT50:
2.6 yr
Test condition:
by comparison relative rate with atmospheric lifetime of methane
Degradation rate constant
Reaction with:
OH radicals
Rate constant:
0 cm³ molecule-1 d-1

Any other information on results incl. tables

See Table 1 → Attachments for tabulated fractions with time.

See Figure 1 → Illustration for plot of log-transformed relative fractions. The relative reaction rates (k-test/k-ref) were

k-test/k-methane: 2.33±0.25

k-test/k-chloromethane: 0.43±0.02. The absolute reaction rates were

k-test = 1.47(±0.22)e-14 cm³/(molecule*s) using k-methane of 6.3e-15 cm³/(molecule*s) and

k-test = 1.56(±0.17)e-14 cm³/(molecule*s) using k-chloromethane of 3.6e-14 cm³/(molecule*s)

Applicant's summary and conclusion

Conclusions:
The atmospheric lifetime of HFE s-601 is 3.8 years.
Executive summary:

The phototransformation of HFE s-601 was addressed in a chamber study using hydroxyl radical (*OH), with methane (CH4) and chloromethane (CH3Cl) as reference substances. A number of other fluorinated organic chemicals were tested in the experimental series. Hydroxyl radicals were produced by photolysis of ozone in the presence of water vapor. A medium pressure mercury lamp (typically emitting in discrete wavebands rather than as a continuous spectrum) was used for photolysis. HFE s-601 and one of the reference substances were introduced to the chamber simultaneously, and FTIR was used to monitor concentrations of both over the course of the reaction to obtain relative reaction rates. The relative reaction rate was 2.33±0.25 v. methane and 0.43±0.02 v. chloromethane. The absolute reaction rates for HFE s-601 were 1.47(±0.22)e-14 cm³/(molecule*s) using a rate of 6.3e-15 cm³/(molecule*s) for methane and 1.56(±0.17)e-14 cm³/(molecule*s) using a rate of 3.6e-14 cm³/(molecule*s) for chloromethane. The aggregated photolysis rate for HFE s-601 is 1.51e-14 cm³/mol*s. Based on an atmospheric lifetime of 9 years for methane and the reaction rates, the atmospheric lifetime of HFE s-601 is 3.8 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. Purity and source of the tested materials is not stated. Validation data for the testing apparatus is not provided. Therefore, this study reliable with restrictions.

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