Response to Comment on “Experimental pKa Determination for Perfluorooctanoic Acid (PFOA) and the Potential Impact of pKa Concentration Dependence on Laboratory-Measured Partitioning Phenomena and Environmental Modeling”

Burns, Darcy C.; Ellis, David; Webster, Eva; McMurdo, Colin J.

doi:10.1021/es900815a

Cited by 15 publications

(9 citation statements)

References 17 publications

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“…[41][42][43] This surfactant-like nature complicates the understanding of the environmental behaviour of PFASs, as there is still no clear and coherent interpretation of how the accumulation of aggregates at interfaces influences the environmental fate of PFASs. [44][45][46] Performance evaluation of COSMOtherm for FTOHs and some other PFASs As shown in Fig. 2, most estimated property data for the FTOHs are close to the experimental data.…”

Section: Limitations Of Property Estimationssupporting

confidence: 60%

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

et al. 2011

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Environmental context. Poly-and perfluorinated alkyl substances (PFASs) include a wide range of individual compounds that are used in many consumer products, but only a few physicochemical property data are available for these chemicals. Here we provide estimates of physicochemical properties (vapour pressure, water solubility, etc.) of 130 individual PFASs derived with a quantum-chemical model. Our results provide insight into the effect of molecular structure on the properties of PFASs and a basis for estimating the environmental partitioning and fate of PFASs.Abstract. Recently, there has been concern about the presence of poly-and perfluorinated alkyl substances (PFASs) in the environment, biota and humans. However, lack of physicochemical data has limited the application of environmental fate models to understand the environmental distribution and ultimate fate of PFASs. We employ the COSMOtherm model to estimate physicochemical properties for 130 individual PFASs, namely perfluoroalkyl acids (including branched isomers for C 4 -C 8 perfluorocarboxylic acids), their precursors and some important intermediates. The estimated physicochemical properties are interpreted using structure-property relationships and rationalised with insight into molecular interactions. Within a homologous series of linear PFASs with the same functional group, both air-water and octanol-water partition coefficient increase with increasing perfluorinated chain length, likely due to increasing molecular volume. For PFASs with the same perfluorinated chain length but different functional groups, the ability of the functional group to form hydrogen bonds strongly influences the chemicals' partitioning behaviour. The partitioning behaviour of all theoretically possible branched isomers can vary considerably; however, the predominant isopropyl and monomethyl branched isomers in technical mixtures have similar properties as their linear counterparts (differences below 0.5 log units). Our property estimates provide a basis for further environmental modelling, but with some caveats and limitations.

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Section: Limitations Of Property Estimationssupporting

confidence: 60%

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

et al. 2011

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“…The pK a value of PFOS was estimated to be À3.3 (Brooke et al, 2004) implying PFOS always being dissociated at environmental conditions. In contrast, modelled pK a values for PFOA reach from À0.5 to 0.9 (Goss, 2008;Wang et al, 2011;Vierke et al, 2013a) and experimentally obtained pK a values are in the range of <1-3.8 (Igarashi and Yotsuyanagi, 1992;Burns et al, 2008Burns et al, , 2009Cheng et al, 2009;Goss and Arp, 2009;Kutsuna et al, 2012;Vierke et al, 2013a). Note that higher PFOA pK a values may overestimate the true pK a values due to experimental artefacts (Vierke et al, 2013a and references therein).…”

Section: Aerosol Propertiesmentioning

confidence: 98%

Particle-size distribution of airborne poly- and perfluorinated alkyl substances

et al. 2015

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“…The mean calculated p K a values were 3.1 ± 0.5 and 0.4 ± 0.5 for FHEA and PFOA, respectively. In contrast, experimental results, which were completed using a potentiometric method in methanol/water and rigorously extrapolated to pure water and infinite PFOA dilution returned a p K a value of 3.8 ± 0.1 for the PFOA monomers (Burns et al ). Focusing on the comparison of n ‐octanoic acid and FHEA, we observed that the effect of replacing the alkyl chain CH 3 ‐(CH 2 ) 5 ‐ with a perfluoroalkyl group CF 3 ‐(CF 2 ) 5 ‐ resulted in an increased acidity (i.e., decrease in the p K a by 1.6 units).…”

Section: Resultsmentioning

confidence: 99%

“…The method we present based on CP-MIMS allows the acid-base behavior of sparingly soluble compounds to be investigated at concentrations below the aggregation threshold observed for some fatty acids (Small et al 1984;Burns et al 2008), allowing measurements of the free monomer forms. Furthermore, there is a significant advantage of in situ MS techniques, which have the ability to measure partitioning behavior under complex conditions relevant to a particular application (e.g., biological fluids for pharmaceuticals or natural waters containing colloidal suspensions for environmental contaminants).…”

Section: Resultsmentioning

confidence: 99%

Direct Measurement of Acid Dissociation Constants of Trace Organic Compounds at Nanomolar Levels in Aqueous Solution by Condensed Phase–Membrane Introduction Mass Spectrometry

Feehan

Monaghan

Gill

et al. 2019

Environmental Toxicology and Chemistry

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We report the use of condensed phase–membrane introduction mass spectrometry as a novel method for the determination of acid dissociation constants for hydrophobic organic acids in aqueous solution at nanomolar concentrations. The technique is based on the pH‐dependent permeation of analytes through a semipermeable polydimethylsiloxane membrane probe that is immersed directly in aqueous samples. We describe the method and report the dissociation constant (pKa) values for compounds of biological and environmental relevance, including contaminants, pharmaceuticals, and naphthenic acids. The approach can be applied to individual compounds, combined suites, and complex mixtures at parts‐per‐billion levels. We report pKa values for 10 carboxylic acids with precision estimates and relative errors (where reliable literature values are available) of <0.1 log units. We report acidity constants for 2‐methyl‐3‐methoxy‐4‐phenyl butanoic acid (a biomarker for microcystin algal toxins) and 4‐t‐butylcyclohexane carboxylic acid (a model naphthenic acid) as 4.28 ± 0.03 and 5.15 ± 0.05, respectively. Furthermore, we employ this approach to measure the effect of both temperature and deuterium oxide (heavy water) on acid dissociation, reporting the enthalpy and entropy changes for the ionization of a representative carboxylic acid and substituted phenol. Environ Toxicol Chem 2019;38:1879–1889. © 2019 SETAC.

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Response to Comment on “Experimental pK_a Determination for Perfluorooctanoic Acid (PFOA) and the Potential Impact of pK_a Concentration Dependence on Laboratory-Measured Partitioning Phenomena and Environmental Modeling”

Cited by 15 publications

References 17 publications

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

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

Particle-size distribution of airborne poly- and perfluorinated alkyl substances

Direct Measurement of Acid Dissociation Constants of Trace Organic Compounds at Nanomolar Levels in Aqueous Solution by Condensed Phase–Membrane Introduction Mass Spectrometry

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