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Environmental fate & pathways

Biodegradation in water: screening tests

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biodegradation in water: ready biodegradability
Data waiving:
study scientifically not necessary / other information available
Justification for data waiving:

Description of key information

Conducting a ready biodegradability study in water is considered not scientifically necessary as other fluorochemical products SOLVENT N1 is not be expected to undergo significant biodegradation in water.

Key value for chemical safety assessment

Biodegradation in water:
under test conditions no biodegradation observed

Additional information

SOLVENT N1 is a reaction mass where all the components have fluorinated structure. Basing on the assessment of the molecular structure no significant biodegradation of SOLVENT N1 in water is expected.

Fluorinated products are recalcitrant chemicals in respect of biodegradation. The high stability in respect of biodegradation is related to the stability of the C–F bond, which is known to be the stronge st existing covalent bond (450 kJ/mol) in organic chemistry. Fluorochemical products are reported to be stable in respect to degradation by acids, bases, oxidants, reductants, photolytic processes, microbes, and metabolic processes (Schultz et al. 2003). Also the presence of three pairs of nonbonding electrons around each fluorine atom and the effective shielding of carbon by the fluorine atoms is reported as a cause preventing significant attacks to the C-F bond. (Kissa2001).

In some conditions, evidence of biodegradation of some poly- and per-fluorinated compounds is reported in literature, but such biodegradation is incomplete and may not result in mineralization (Parson et al., 2008).

The lack of mineralization observed is ascribed the stability of the C–F bond while the not -fluorinated functionalities present in the molecule are more easily degraded.

For polyfluoroalkyl chemicals it is reported that the observed partial biodegradability is largely owing to its non-fluorinated functionality, whose breakdown precedes the breakdown of the perfluorinated carbons, if the later occurs. (Liu & Mejia Avendaño, 2013). In contrast, perfluoroalkyl chemicals in general resist biotransformation and defluorination under natural conditions. (Liu & Mejia Avendaño, 2013). Long perfluoroalkyl chains are known to be persistent in the environment (Fromel T & Knepper TP, 2010).

Defluorination has been described as a potential mechanism of degradation of fluorinated compounds. However, although reductive defluorination is expected in theory basing on thermodynamic properties and there are examples of microbially catalyzed defluorination reactions, the mechanism has rarely been observed, probably due to the less available enzymatic systems in nature, high C-F bond strength, and the absence of structures that are susceptible to electrophilic or nucleophilic attack. (Parson et al, 2006; Liu& Mejia Avendaño, 2013).

It can be therefore reasonably expected that SOLVENT N1 would not fulfill the conditions of ready biodegradability under a standard OECD 301 test. SOLVENT N1 is considered not readily biodegradable.