Estimation of the acid dissociation constant of perfluoroalkyl carboxylic acids through an experimental investigation of their water-to-air transport

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  • L. Vierke
  • Urs Berger
  • Ian T. Cousins

The acid dissociation constants (pK as) of perfluoroalkyl carboxylic acids (PFCAs) have been the subject of discussion in the literature; for example, values from -0.2 to 3.8 have been suggested for perfluorooctanoic acid (PFOA). The dissociated anionic conjugate bases of PFCAs have negligible air-water partition coefficients (K AWs) and do not volatilize from water. The neutral acids, however, have relatively high K AWs and volatilization from water has been demonstrated. The extent of volatilization of PFCAs in the environment will depend on the water pH and their pK a. Knowledge of the pK as of PFCAs is therefore vital for understanding their environmental transport and fate. We investigated the water-to-air transfer of PFCAs in a novel experimental setup. We used ∼1 μg L -1 of PFCAs in water (above environmental background concentrations but below the concentration at which self-association occurs) at different water pH (pH 0.3 to pH 6.9) and sampled the PFCAs volatilized from water during a 2-day experiment. Our results suggest that the pK as of C 4-11 PFCAs are <1.6. For PFOA, we derived a pK a of 0.5 from fitting the experimental measurements with a volatilization model. Perfluoroalkane sulfonic acids were not volatilized, suggesting that their pK as are below the investigated pH range (pK a <0.3).

Original languageEnglish
JournalEnvironmental Science & Technology
Issue number19
Pages (from-to)11032-11039
Number of pages8
Publication statusPublished - 01.10.2013

    Research areas

  • Chemistry - Acid dissociation constants, Background concentration, Environmental transport, Experimental investigations, Partition coefficient, Perfluoroalkyl carboxylic acids, Perfluorooctanoic acid, Volatilization models