KIA Values Research Articles

Molecular Dynamics Simulation Prediction of the Partitioning Constants (KH, Kiw, Kia) of 82 Legacy and Emerging Organic Contaminants at the Water-Air Interface.

The tendency of organic contaminants (OCs) to partition between different phases is a key set of properties that underlie their human and ecological health impacts and the success of remediation efforts. A significant challenge associated with these efforts is the need for accurate partitioning data for an ever-expanding list of OCs and breakdown products. All-atom molecular dynamics (MD) simulations have the potential to help generate these data, but existing studies have applied these techniques only to a limited variety of OCs. Here, we use established MD simulation approaches to examine the partitioning of 82 OCs, including many compounds of critical concern, at the water-air interface. Our predictions of the Henry's law constant (KH) and interfacial adsorption coefficients (Kiw, Kia) correlate strongly with experimental results, indicating that MD simulations can be used to predict KH, Kiw, and Kia values with mean absolute deviations of 1.1, 0.3, and 0.3 logarithmic units after correcting for systematic bias, respectively. A library of MD simulation input files for the examined OCs is provided to facilitate future investigations of the partitioning of these compounds in the presence of other phases.

Predicting Concentration- and Ionic-Strength-Dependent Air-Water Interfacial Partitioning Parameters of PFASs Using Quantitative Structure-Property Relationships (QSPRs).

Air-water interfacial retention of poly- and perfluoroalkyl substances (PFASs) is increasingly recognized as an important environmental process. Herein, column transport experiments were used to measure air-water interfacial partitioning values for several perfluoroalkyl ethers and for PFASs derived from aqueous film-forming foam, while batch experiments were used to determine equilibrium Kia data for compounds exhibiting evidence of rate-limited partitioning. Experimental results suggest a Freundlich isotherm best describes PFAS air-water partitioning at environmentally relevant concentrations (101-106 ng/L). A multiparameter regression analysis for Kia prediction was performed for the 15 PFASs for which equilibrium Kia values were determined, assessing 246 possible combinations of 8 physicochemical and system properties. Quantitative structure-property relationships (QSPRs) based on three to four parameters provided predictions of high accuracy without model overparameterization. Two QSPRs (R2 values of 0.92 and 0.83) were developed using an assumed average Freundlich n value of 0.65 and validated across a range of relevant concentrations for perfluorooctane sulfonate (PFOS), perfluorooctanoate (PFOA), and hexafluoropropylene oxide-dimer acid (i.e., GenX). A mass action model was further modified to account for the changing ionic strength on PFAS air-water interfacial sorption. The final result was two distinct QSPRs for estimating PFAS air-water interfacial partitioning across a range of aqueous concentrations and ionic strengths.

Air-water interfacial adsorption of C4-C10 perfluorocarboxylic acids during transport in unsaturated porous media

The impact of chain length on air-water interfacial adsorption of perfluorocarboxylic acids (PFCAs) during transport in unsaturated quartz sand was investigated. Short-chain (C4-C7: PFBA, PFPeA, PFHxA, PFHpA) and long chain (C8-C10: PFOA, PFNA, PFDA) PFCAs were selected as a representative homologous series. Surface tensions were measured to characterize surface activities of the selected PFCAs. Miscible-displacement column experiments were conducted for each of the PFCAs to characterize the magnitudes of air–water interfacial adsorption under transport conditions. The transport of the long-chain PFCAs exhibited greater retardation than the short-chain PFCAs. Air–water interfacial adsorption (AWIA) was the predominant source of retention (≥63%) for the long-chain PFCAs. Conversely, AWIA contributed less to retention than did solid-phase sorption for the short-chain PFCAs, with the former contributions ranging from 4% to 40%. Direct examination of the breakthrough-curve profiles as well as mathematical-modeling results demonstrated that transport of the two longest-chain PFCAs was influenced by nonlinear AWIA, whereas that of the shorter-chain PFCAs was not. This disparate behavior is consistent with the input concentration used for the transport experiments in comparison to the respective surface activities and critical reference concentrations of the different PFCAs. Quantitative-structure/property-relationship (QSPR) analysis was applied to characterize the influence of molecular size on air-water interfacial adsorption. The logs of the air-water interfacial adsorption coefficients (Kia) determined from the transport experiments are a monotonic function of molar volume, consistent with prior QSPR analyses of surface-tension measured values. The Kia values determined from the transport experiments are very similar to those measured from surface-tension data, indicating that the transport experiments produced robust measurements of AWIA.

Impact of a Hydrocarbon Surfactant on the Retention and Transport of Perfluorooctanoic Acid in Saturated and Unsaturated Porous Media.

The transport and retention behavior of perfluorooctanoic acid (PFOA) in the presence of a hydrocarbon surfactant under saturated and unsaturated conditions was investigated. Miscible-displacement transport experiments were conducted at different PFOA and sodium dodecyl sulfate (SDS) input ratios to determine the impact of SDS on PFOA adsorption at solid-water and air-water interfaces. A numerical flow and transport model was employed to simulate the experiments. The PFOA breakthrough curves for unsaturated conditions exhibited greater retardation compared to those for saturated conditions in all cases, owing to air-water interfacial adsorption. The retardation factor for PFOA with a low concentration of SDS (PFOA-SDS ratio of 10:1) was similar to that for PFOA without SDS under unsaturated conditions. Conversely, retardation was greater in the presence of higher levels of SDS (1:1 and 1:10) with retardation factors increasing from 2.4 to 2.9 and 3.6 under unsaturated conditions due to enhanced adsorption at the solid-water and air-water interfaces. The low concentration of SDS had no measurable impact on PFOA air-water interfacial adsorption coefficients (Kia) determined from the transport experiments. The presence of SDS at the higher PFOA-SDS concentration ratios increased the surface activity of PFOA, with transport-determined Kia values increased by 27 and 139%, respectively. The model provided very good independently predicted simulations of the measured breakthrough curves and showed that PFOA and SDS experienced various degrees of differential transport during the experiments. These results have implications for the characterization and modeling of poly-fluoroalkyl substances (PFAS) migration potential at sites wherein PFAS and hydrocarbon surfactants co-occur.

Measuring snow scavenging of two airborne cyclic volatile methylsiloxanes under controlled conditions

The objective of this study was to determine snow scavenging of cVMS and its potential effect on the cVMS concentrations in snowmelt water and surrounding soil. Snow scavenging of two cVMS, octamethylcyclotetrasiloxane (D4) and decamethylcyclopentasiloxane (D5), was examined in two steps. First, sorption and desorption of D4 and D5 on snowflakes, including snow sorption coefficients (KiA), were measured against a benchmark compound, cyclopentanone, at different temperatures from 0 to −20 °C. Measurements were made using a custom-made snow chamber and 14C-labeled D4 and D5. In addition, the transfer of snow-bound cVMS to snowmelt water and surrounding soil was studied with 14C-D4 and 14C-D5-spiked snowpack placed both in a closed snow chamber and on top of a layer of frozen soil in an open chemical hood. KiA values measured in both sorption and desorption processes were very small (<10−2 m). They increased with decreasing temperature and were higher for the D5 compared to D4. The calculated gas scavenging of D4 and D5 was small because of the small KiA values, while particle scavenging of cVMS is predicted to be negligible due to their low octanol/air partition coefficients (KOA). Most importantly, almost all 14C-D4 and 14C-D5 sorbed by a snowpack was lost during the snow melting process through re-volatilization and hydrolysis and became non-detectable in snowmelt water. In short, the experimental measurements demonstrated that snow scavenging could not be a valid deposition mechanism for these volatile hydrophobic compounds.

Examining the robustness and concentration dependency of PFAS air-water and NAPL-water interfacial adsorption coefficients

Determining robust values for the air-water or NAPL-water interfacial adsorption coefficient, KIA, is key to characterizing and modeling PFAS transport and fate in several environmental systems. Direct, high-resolution measurements of surfactant adsorption at the fluid-fluid interface were aggregated from the literature. This data set was used to examine the accuracy and applicability of Γ and KIA measurements determined for three PFAS from transport experiments and surface-tension data. The transport-measured Γ and KIA data were observed to be fully consistent with the directly-measured data. Specifically, Γ values for the two methods were entirely coincident in the region of overlapping concentrations, which spanned ~4 orders-of-magnitude. Furthermore, the two data sets adhered to an identical Γ-C profile. These results conclusively demonstrate the accuracy of the transport-measured values. Γ and KIA values determined from the application of the Gibbs adsorption equation to measured surface-tension data were fully consistent with the directly-measured and transport-measured data sets, demonstrating their applicability for representing PFAS transport in environmental systems. The directly-measured data were used to examine the concentration dependency of KIA values, absent the potential confounding effects associated with the use of surface-tension or transport-measured data. The directly-measured data clearly demonstrate that KIA attains a constant, maximum limit at lower concentrations. Two separate analyses of the transport-measured data both produced observations of constant KIA values at lower concentrations, consistent with the directly-measured data. These outcomes are discussed in terms of surface activities, relative surface coverages, and critical concentrations.

Large Bubbles Reduce the Surface Sorption Artifact of the Inert Gas Stripping Method

Accurate Henry’s law constants between air and water (H) are crucial for understanding a chemical’s environmental behavior. During inert gas stripping (IGS) H is derived from the rate of a chemical’s disappearance from aqueous solution as a result of air bubbling through a water-filled column. While H of many semivolatile organic compounds has been measured by IGS, inconsistent results between different studies have been attributed to chemical adsorption to the bubble surface. This surface adsorption artifact is expected to increase with a chemical’s interface–air partition coefficient (KIA) and decreasing bubble size. Previous work with normal alkanols of variable chain length identified a KIA threshold of approximately 0.001 m, above which IGS is compromised by the surface sorption artifact. In this study, we repeated IGS measurements of H of normal alkanols at different temperatures of 298.15 K, 305.65 K, 323.15 K, and 343.15 K using a modified gas inlet mechanisms that results in the formation of large bubbles (diameter approximately 5.5 mm). The new H values agreed very well with those measured with a head space technique that is much less susceptible to surface adsorption. The method is judged suitable for measuring H of surface active chemicals with KIA values below 0.02 m.

An automated satellite image classification design using object-oriented segmentation algorithms: A move towards standardization

Abstract Numerous segmentation algorithms have been developed, many of them highly specific and only applicable to a reduced class of problems and image data. Without an additional source of knowledge, automatic image segmentation based on low level image features seemed unlikely to succeed in extracting semantic objects in generic images. A new region-merging segmentation technique has recently been developed which incorporates the spectral and textural properties of the objects to be detected and also their different size and behaviour at different stages of scale, respectively. Linking this technique with the FAO Land Cover Land Use classification system resulted in the development of an automated, standardized classification methodology. Testing on Landsat and Aster images resulted in mutually exclusive classes with clear and unambiguous class definitions. The error matrix based on field samples showed overall accuracy values of 92% for Aster image and 89% for Landsat. The KIA values were 88% for Aster images and 84% for the Landsat image.

Mechanical and microstructural investigations into the crack arrest behaviour of a modern 2¼Cr‐1 Mo pressure vessel steel

Tests were performed on a 2¼ Cr–1 Mo steel to measure the fracture toughness at initiation, KIc and at arrest, KIa . The results were compared with those obtained on another pressure vessel steel (A508) of similar strength. Two techniques were used to measure KIa : (i) isothermal compact crack arrest (CCA) tests, and (ii) specially designed thermal shock experiments using an externally notched ring. These specimens were cooled to −196 °C and then heated by induction in the centre of the ring to produce very steep thermal gradients. This caused crack initiation from the notch. The crack propagates very rapidly (∼500 m s−1 ) and stopped when it reached the warmer region of the specimen. The specimens were analysed using an elastic–plastic finite element method to determine KIa values. These tests reveal a greater temperature shift (∼100 °C) between KIc and KIa in 2¼ Cr–1 Mo steel than in A508 steel. Detailed metallographical examinations of the micromechanisms of crack propagation and arrest in the 2¼ Cr–1 Mo steel showed that this involves the nucleation of a three‐dimensional network of cleavage microcracks which change their direction at bainitic packet boundaries. The remaining uncracked ligaments between the cleavage microcracks break by ductile rupture mechanism

Binding Constants of Dextrans and Isomaltose Oligosaccharides to Dextran-Specific Myeloma Proteins Determined by Affinity Electrophoresis

Abstract In polyacrylamide electrophoresis, mobilities of dextran-specific myeloma proteins W3129 and QUPC52 were retarded when dextrans were added to the separating gel. Retardation by dextran was reversed by adding isomaltose oligosaccharides to the gel. From measurements of the extent of retardation by dextran or of reversal by hapten as a function of concentration, association constants of dextrans (Ka) and of oligosaccharides (Kia) were determined. With W3129, NRRL dextrans B 742 FR.S, B 742 FR.L, N279, B 1355 FR.S, B 1399, B 1299 FR.S, and NRC fractions 6, 7, and 8 have Kα values ranging from 2 to 6 × 104 ml/g. With QUPC52, dextrans in general show lower Ka than with W3129; N279, NRC fractions 6, 7, and 8, and B 1399 have Ka values ranging from 1 to 7 × 104 ml/g, whereas B-742 FR.S, B-1299 FR.S, and B-1355 FR.S have Ka values ranging from 3 to 6 × 102 ml/g. Dextran D3, a completely linear α(1 → 6)-linked glucosyl chain having a m.w. of 36,500 has a relative high affinity for QUPC52 (Ka = 2.3 × 103 ml/g or 8.3 × 104 M-1), although it does not show any affinity for W3129. This result confirms that myeloma protein W3129 is specific for a terminal chain of α(1 → 6)-linked glucosyl residues, whereas QUPC52 reacts with the nonterminal portion of α(1 → 6)-linked glucosyl chains. Kia values obtained coincided with those by other methods reported earlier by Cisar et al. With W3129, affinity increases with chain length up to isomaltopentaose (IM5) with the highest affinity Kia = 6.7 × 104 M-1; Kia of isomaltohexaose (IM6) and isomaltoheptaose (IM7) being 6.3 × 104 and 2.3 × 104 ml/g, respectively. With QUPC52, affinity increases as the number of residues in the glucosyl chain increases, reaching an upper limit with IM6 and IM7, 1.2 and 1.4 × 104 M-1. This method of affinity electrophoresis is useful for obtaining binding constants ranging from 102 to 106 M-1. It may be performed on antibodies, lectins, and other binding proteins by using not only the purified proteins but also crude protein mixtures such as the ascitic fluid used in this study.

The Scattering of Underwater Plane Ultrasonic Waves by Liquid Cylindrical Obstacles

An experimental investigation of sound scattering from liquid cylindrical obstacles was performed by Tamarkin following on the work of Bauer and others. A series of scattering patterns, confined to the region about the extended axis of the incident beam and on the opposite side of the obstacle from the source, were determined for ten liquids. The special kia values chosen (ki; = 2π/λi, λi = wavelength of the sound in the medium of the obstacle, a = radius of the cylindrical obstacle) lie in the range 26.0&amp;lt;kia&amp;lt;41.0 and are below and above the corresponding value for the water medium surrounding the obstacle. On the assumption of a plane incident wave, a series solution was found for the total scattered wave and numerical calculations were carried out for conditions approximating those of the actual experiments. The results of this theoretical investigation confirm the experimental findings that scattering of an underwater ultrasonic beam, from the special liquid cylindrical obstacles examined, lies in the zone between the geometrical region and the region of Rayleigh scattering. In this zone, diffraction predominates and the diffraction patterns based on theory agree quantitatively quite well with the positions of the experimental maxima and minima. A rather detailed and extended theoretical study of the resonance curve found experimentally was made and the plotted theoretical resonance curve shows a similar oscillating behavior with amplitude decreasing with increasing kia.

Scattering of Underwater Plane Ultrasonic Waves by Liquid Cylindrical Obstacles

This paper is a report of a theoretical investigation of sound scattering from liquid cylindrical obstacles immersed in water following closely the conditions prevailing in the previous experimental work of Tamarkin, Bauer, and others. An incident plane wave being assumed, series solution was found for the total scattered wave. Numerical calculations were carried out using parameters approximating those of Tamarkin's experiments (radius of obstacle, 0.635 cm; sound frequency, 1.145 mc/sec; wavelength, 0.13 cm). A series of scattering patterns, confined principally to the forward direction for an angular spread of about 14° (with the obstacle at the vertex) were calculated for eight liquids, chosen to give a spread of kia values (ki the wave parameter inside the liquid and a the radius) between 26.0 and 41.0. The results of this theoretical investigation confirm the experimental findings that for the liquids examined the scattering is diffractive and lies in the zone between the geometrical region and the region of Rayleigh scattering. Quantitative comparisons are made between the theoretical and experimentally plotted results with special emphasis on the experimental resonance curve and its theoretically computed counterpart.