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Environmental fate & pathways

Phototransformation in water

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Reference
Endpoint:
phototransformation in water
Type of information:
other: Data from publications
Adequacy of study:
supporting study
Study period:
Not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Remarks:
Review document of publicy available data.
Study type:
not specified
Qualifier:
no guideline followed
GLP compliance:
not specified
Specific details on test material used for the study:
Details on properties of test surrogate or analogue material (migrated information):
Molecular weight: 129.91 (Weast 1977)
Melting point: -158°C (Weast 1977)
Boiling point at 760 torr: -29.8°C (Weast 1977)
Vapour pressure at 20°C: 4306 torr (Pearson and McConnell 1975)
Solubility in water at 25°C: 280 mg/l (Pearson and McConnell 1975)
Log octanol/water partition coefficient: 2.16 (Hansch et al. 1975)
Radiolabelling:
not specified
Analytical method:
not specified
Details on sampling:
Not specified
Buffers:
Not specified
Light source:
not specified
Details on light source:
not specified
Type of sensitiser:
not specified
Details on test conditions:
Not specified
Reference substance:
not specified
Dark controls:
not specified
Computational methods:
Not specified
Parameter:
not specified
Transformation products:
not specified
Details on results:
Not specified

No information was found pertaining specifically to the rate of photolysis of dichlorodifluoromethane in the aquatic environment under ambient conditions. Due to the high vapour pressure of dichlorodifluoromethane, volatilization to the atmosphere is quite rapid. The compound is tropospherically stable (Environment Protection Agency 1975; Hanst 1975; Howard and Durkin 1973); it does not react readily with hydroxyl radicals, nor does it photodissociate in the troposphere since it exhibits no absorption of light greater than 200nm (Hanst 1978; Howard et al. 1975). Lovelock at el. (1973) have suggested a tropospheric residence time of 30 years for dichlorodifluoromethane before diffusion to the stratosphere. In the stratosphere, dichlorodifluoromethane is broken down by the absorption of higher energy; shorter wavelength ultraviolet light (Hanst 1978; Rebbert and Ausloos 1975; Jayanty et al 1975). The initial step in photodissociation is the abstraction of the chlorine atom (Environmental Protection Agency 1975): CCl2F2→CClF2+ Cl· . Eventually, the photodissociation proceeds as follows: F2Cl2→·CF2Cl + Cl · →:CF2+ Cl2→: CF2+2Cl· Thus, accoding to Rebbert and Ausloos (1975) the photodissociation of dichlorodifluoromethane results in the release of two chlorine atoms since less energy is required for the cleavage of the C-Cl bond than for the cleavage of the C-F bond. According to Jayanty et al. (1975), the photolysis of dichlorodifluoromethane in the presence of O2at 213.9nm and 25°C leads to the production of CF2O and Cl2and, potentially, chlorine atoms. Chlorine atoms, release by reactions such as these, are theorized to be catalysts in the destruction of the stratospheric ozone layer (Hanst 1978; Environmental Protection Agency 1975).

Validity criteria fulfilled:
yes
Conclusions:
Dichlorodifluoromethane introduced into aqueous systems will most likely volatize to the atmosphere. Once in the troposphere, dichlorodifluoromethane remains stable. It eventually diffuses into the stratosphere or is carried back to the earth during the precipitation process. Once in the stratosphere dichlorodifluoromethane is photolyzed by shorter wave-length, higher energy ultraviolet light with the subsequent formation of chlorine atoms.
Executive summary:

Dichlorodifluoromethane introduced into aqueous systems will most likely volatize to the atmosphere. Once in the troposphere, dichlorodifluoromethane remains stable. It eventually diffuses into the stratosphere or is carried back to the earth during the precipitation process. Once in the stratosphere dichlorodifluoromethane is photolyzed by shorter wave-length, higher energy ultraviolet light with the subsequent formation of chlorine atoms.

Description of key information

Key information taken from published data.
Photolysis is probably not significant in aquatic systems; photodissociation in the stratosphere is the primary fate of this compound.

Key value for chemical safety assessment

Additional information

Dichlorodifluoromethane introduced into aqueous systems will most likely volatize to the atmosphere. Once in the troposphere, dichlorodifluoromethane remains stable. It eventually diffuses into the stratosphere or is carried back to the earth during the precipitation process. Once in the stratosphere dichlorodifluoromethane is photolyzed by shorter wave-length, higher energy ultraviolet light with the subsequent formation of chlorine atoms.