Environmental Fate
Environmental modeling of long-chain (C9-C20) PFCAs cannot be conducted using widely accepted models as they cannot be applied to ionizable surfactants. Kow (octanol-water partition coefficient) is a problematic parameter for surfactants because they tend to aggregate at the interface of a liquid-liquid system and therefore cannot be measured directly.
Long-chain (C9-C20) PFCAs and/or their salts are expected to partition primarily to the aqueous medium as a result of their high water solubility and low volatility. The presence of the acid functional group imparts a large proportion of the nature and character of the long-chain (C9-C20) PFCAs. The acid functional group is hydrophilic and is completely dissociated in the aqueous phase (Ellis et al. 2004a). Substances containing a perfluoroalkyl moiety may have surfactant properties due to the combined properties of oleophobicity, hydrophobicity and hydrophilicity over portions of a particular molecule, whereas unsubstituted hydrocarbon chains are oleophilic and hydrophobic (Key et al. 1997). Furthermore, a functional group attached to the perfluorinated chain (e.g., a charged moiety such as a carboxylate anion) can impart hydrophilicity to part of the molecule. However, as the length of the perfluorinated chain increases, the PFCA molecule will likely become more hydrophobic and its water solubility diminishes (Ellis et al. 2004a).