Modeling the environmental fate of perfluorooctanoic acid and perfluorooctanoate: An investigation of the role of individual species partitioning

Abstract

A multimedia multi-species environmental fate model was developed for the conjugate pair perfluorooctanoic acid (PFOA):perfluorooctanoate (PFO). The model allows assessment of the relative contribution of each individual species, in equilibrium with each other, to the overall environmental movement of the pair. The Lake Ontario (Canada/USA) watershed system was selected for this investigation and is simulated in a single-region, seven-compartment model, including a water surface microlayer, and aqueous aerosol generation and redeposition. Results indicate that in the equilibrated presence of both PFOA and PFO, the environmental fate of the pair can be accomplished by consideration of the physical properties of the neutral acid, which govern the intermedia distribution of the pair, coupled with processes of media advection, such as air or water flow. The role of the anion, while the most populous species in the aqueous phase, appears merely to be as a source of the neutral acid for subsequent partitioning. Thus, when only the bulk aqueous phase anion concentrations are of interest a multimedia fate model is not required because these concentrations are largely predictable from the magnitude of emissions to and the advection of the phase. With neutral species partitioning, all local field measurement concentrations of the conjugate pair, PFO(A), are explained by the model to within approximately an order of magnitude, with the exception of lake sediment solids. Model results indicate that bulk aqueous phase PFO acts as a net source for PFOA to the atmosphere, where it may be subject to long-range transport (LRT). Initial calculations suggest an atmospheric LRT potential for PFO(A) of thousands of kilometers, rendering it comparable to hexachlorobenzene.

Using COSMOtherm to predict physicochemical properties of poly- and perfluorinated alkyl substances (PFASs)

“…For some PFAAs, especially the strongly acidic PFSAs, the neutral form represents only a small fraction of all molecules at pH values typical in the environment, and likely does not play a major role in controlling environmental behaviour. In contrast, for PFCAs it has been suggested that the neutral form may be relevant in environmental transport and partitioning processes [18] as well as in bioaccumulation. [33] In addition, COSMOtherm estimates made here represent only the properties of PFAS monomers.…”

“…However, recent studies have shown that PFASs can also adsorb to interfaces as previously discussed and that these adsorption properties could have a strong influence on the environmental distribution of PFASs. [18] Goss has tested the possibility using COSMOtherm to predict adsorption constants for the air-water interface for a set of more than 200 organic compounds [57] that included some FTOHs and fluorotelomer olefins. Moreover, Arp and Goss have developed a COSMOthermbased model to predict the partitioning behaviour at the gasparticle interface and evaluated it with some measurement for C 6 -C 8 PFCAs.…”

“…[12][13][14][15][16][17][18] To date, these studies have mainly focussed on perfluorocarboxylic acids (PFCAs) with perfluorinated chain lengths of 7-12 carbons (which are often termed C 8 -C 13 PFCAs including the carboxylic acid carbon), C 8 perfluorosulfonic acid (PFOS) and a few related substances.…”

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

“…Hence, the relative importance of each species and its related processes should become apparent through application of the models. Multimedia fate models that rely on these standard equilibrium equations have already been used but without directly addressing the question of their applicability [20][21][22][23][24][25][26]. The apparent success of the equilibria equations in the multimedia models may have been due to a masking effect from the multimedia model complexity.…”

Coking wastewater treatment plant as a source of polycyclic aromatic hydrocarbons (PAHs) to the atmosphere and health-risk assessment for workers

“…However, the common used wastewater treatment plant (WWTP) can not achieve the complete removal of pollutants, thus appearing the point sources of water pollution (Pham and Proulx, 1997). Also, WWTPs can become the atmospheric sources of some organic pollutants, such as volatile organic compounds (Simonich et al, 2000;Escalasa et al, 2003;Wu et al, 2006), perfluorooctanoic acid (Webster et al, 2010), polyfluoroalkyl compounds (Ahrens et al, 2011) and PAHs (Byrns, 2001;Seth et al, 2008). Recently, intense attention has been paid on PAHs in the atmosphere (Simcik et al, 1999;Park et al, 2002;Omar et al, 2006;Zhang et al, 2011a), as the most carcinogenic, mutagenic and toxic contaminants (Deng et al, 2006).…”