TY - JOUR

T1 - Estimation of the acid dissociation constant of perfluoroalkyl carboxylic acids through an experimental investigation of their water-to-air transport

AU - Vierke, L.

AU - Berger, Urs

AU - Cousins, Ian T.

PY - 2013/10/1

Y1 - 2013/10/1

N2 - 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).

AB - 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).

KW - Chemistry

KW - Acid dissociation constants

KW - Background concentration

KW - Environmental transport

KW - Experimental investigations

KW - Partition coefficient

KW - Perfluoroalkyl carboxylic acids

KW - Perfluorooctanoic acid

KW - Volatilization models

UR - http://www.scopus.com/inward/record.url?scp=84885169336&partnerID=8YFLogxK

U2 - 10.1021/es402691z

DO - 10.1021/es402691z

M3 - Journal articles

C2 - 23952814

AN - SCOPUS:84885169336

VL - 47

SP - 11032

EP - 11039

JO - Environmental Science & Technology

JF - Environmental Science & Technology

SN - 0013-936X

IS - 19

ER -