Equilibrium modeling: A pathway to understanding observed perfluorocarboxylic and perfluorosulfonic acid behavior

Abstract

Equilibrium distribution models of hydrophobic neutral partitioning of the perfluorinated carboxylic and sulfonic acids were shown, without the need for any physical chemical properties, to successfully predict the sediment-water distribution (D(SW) ) directly from independently measured equilibrium tissue distributions known as the bioconcentration factor (BCF). The constant of proportionality required by the models successfully predicted the correlation between the biotic and abiotic distributions of both sets of chemicals, thus demonstrating the applicability of the assumptions inherent in the models, that is, hydrophobically driven partitioning of the neutral species, and thus the applicability of the models themselves. Colloquially speaking, the models are thus validated as applicable to these chemicals. Subsequent application of the standard equilibrium models showed order of magnitude agreement for 83% of measured BCF values and 88% of measured D(SW) for the perfluorinated carboxylic acids, confirming the physical chemical properties used. The applicability of the models to perfluorooctane sulfonic acid (PFOSA) was shown by the successful prediction of D(SW) from BCF. Therefore, the measured D(SW) and BCF could be used to calculate the octanol-water distribution, D(OW) , and hence the corresponding pK(a):K(OW) solution set, thus providing independent experimentally based estimates of these properties. For both the perfluorinated carboxylic and sulfonic acids, the existing standard equilibrium models are shown to be applicable.

Understanding the atmospheric measurement and behavior of perfluorooctanoic acid

“…The observed agreement between calculated and expected values for the correlation constants for atmospheric systems at or near equilibrium supports the magnitude of the correction suggested by Ahrens et al 13. Consistent with recent studies 22, 32–33, the excellent agreement with accepted values of α for neutral organics suggests the absence of any anomalous PFOA partitioning behavior, that is, PFOA is behaving similarly to any other normal, neutral organic in natural atmospheric environments. The excellent agreement seen with Equations 1 and 3, where octanol is used as the surrogate for the organic matter in the particulate, suggests the applicability of octanol‐based modeling to PFOA.…”

Influence of global climate change on chemical fate and bioaccumulation: The role of multimedia models

“…Fugacity-based multimedia fate models 50 are most commonly applied for neutral organic chemicals, but other models are available for ionizing chemicals 51–55 and some metals, including mercury 56–59. At the hemispheric to global scale, fate and transport models have been parameterized at a variety of spatial resolutions (e.g., broad latitudinal bands → 1 × 1° resolution) 60–64 and can be used for either steady-state or dynamic calculations.…”

“…Based on how the model has been parameterized, these simulations are most relevant to neutral organic compounds, but the approach described here could also be adopted to include ionogenic organic chemicals (e.g., 51–55). …”

Development and evaluation of a mechanistic bioconcentration model for ionogenic organic chemicals in fish

“…The majority of currently available bioaccumulation models specifically developed for IOCs in fish are regression-based [9][10][11][12], although an equilibrium partitioning approach considering the role of sorption to proteins was recently proposed to characterize the bioaccumulation potential of some PFAAs [13]. Generic methods for estimating the tissue-plasma partitioning of IOCs have also been described in the literature [14,15].…”