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Environmental fate & pathways

Biodegradation in water: screening tests

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Reference
Endpoint:
biodegradation in water: ready biodegradability
Type of information:
experimental study
Adequacy of study:
key study
Study period:
Not specified
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
data from handbook or collection of data
Principles of method if other than guideline:
No guideline followed. Report details overview of aerobic biodegradation for CFC products overall.
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)
Oxygen conditions:
not specified
Inoculum or test system:
not specified
Details on inoculum:
Not specified
Details on study design:
Not specified
Reference substance:
not specified
Parameter:
not specified
Value:
0
Remarks on result:
other: Dichlorodifluoromethane introduced into aqueous systems will most likely volatize to the atmosphere. Once in the troposphere, dichlorodifluoromethane remains stable.
Details on results:
Not specified
Results with reference substance:
Not specified

No information was found pertaining to the biodegradability of dichlorodifluoromethane. According to Howard et al. (1975) the volatility of dichlorodifluoromethane, as well as other fluorocarbons, would limit, if not preclude, biodegradation. Su and Goldberg (1976), however, report that dichlorodifluoromethane, as well as other synthetic organic compounds, is persistent in natural waters.

Validity criteria fulfilled:
yes
Interpretation of results:
under test conditions no biodegradation observed
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. No evidence was found for significant biodegradation.

It has been observed in laboratory experiments with contaminated soil-samples that CFCs are slowly biodegradable in anaerobic aquatic environments. Nevertheless, these compounds are persistent in the environment because of their chemical stability.

The “Handbook on Biodegradation and Biological Treatment of Hazardous Organic Compounds By M.H. van Agteren, Sytze Keuning, D. Janssen”states that the biological degradation of chlorofluorocarbons has not been studied extensively. In general, the order of reactivity of reactions in which the carbon-halogen bond is involved is C-I > C-Br > C-CI > C-F. Lesser halogenated aliphatics are more susceptible to hydrolysis and aerobic degradation , while higher halogenated aliphatics are more susceptible to reductive dehalogenation. Therefore, it is not surprising that the substance CFC-12 is very persistent under aerobic conditions. as has been observed in several biological studies, for example with Methylosinus trichosporium strain OB3b.

Description of key information

Key value taken from published data. 
No evidence was found for significant biodegradation.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

Volatility probably precludes biodegradation. It has been observed in laboratory experiments with contaminated soil-samples that CFCs are slowly biodegradable in anaerobic aquatic environments. Nevertheless, these compounds are persistent in the environment because of their chemical stability.

The “Handbook on Biodegradation and Biological Treatment of Hazardous Organic Compounds By M.H. van Agteren, Sytze Keuning, D. Janssen” states that the biological degradation of chlorofluorocarbons has not been studied extensively. In general, the order of reactivity of reactions in which the carbon-halogen bond is involved is C-I > C-Br > C-CI > C-F. Lesser halogenated aliphatics are more susceptible to hydrolysis and aerobic degradation , while higher halogenated aliphatics are more susceptible to reductive dehalogenation. Therefore, it is not surprising that the substance CFC-12 is very persistent under aerobic conditions. as has been observed in several biological studies, for example with Methylosinus trichosporium strain OB3b.