Samuel W. Karickhoff

Sorption of hydrophobic pollutants on natural sediments

The sorption of hydrophobic compounds (aromatic hydrocarbons and chlorinated hydrocarbons) spanning a concentration range in water solubility from 500 parts per trillion (ppt) to 1800 parts per million (ppm) on local (North Georgia) pond and river sediments was investigated. The sorption isotherms were linear over a broad range of aqueous phase pollutant concentrations. The linear partition coefficients (Kp) were relatively independent of sediment concentrations and ionic strength in the suspensions. The Kp ś were directly related to organic carbon content for given particle size isolates in the different sediments. On an organic carbon basis (Koc = Kp/fraction) organic carbon), the sand fraction (> 50 μm particle size) was a considerably less effective sorbent (50–90% reduction in Koc) than the fines fraction (> 50 μm particles). Differences in sorption within the silt and clay fractions were largely related to differences in organic carbon content. Reasonable estimates of Kocś can be made from octanol/water distribution coefficients, which are widely catalogued or easily measured in the laboratory.

Semi-empirical estimation of sorption of hydrophobic pollutants on natural sediments and soils

Methods were developed for estimating the equilibrium sorption behavior of hydrophobic pollutants. At low pollutant concentration (aqueous phase concentration less than half the solubility), sorption isotherms were linear, reversible, and characterized by a partition coefficient, Kp. Partition coefficients normalized to organic carbon, KOC (KOC = Kpfraction organic carbon), were highly invariant over a set of sediments and soils collected from throughout the nation. Equations for estimating KOC from water solubility (including crystal energy) and octanol/water partition coefficients were developed. The predictive equations were tested on literature sorption data and found to estimate measured KOCs generally within a factor of two.

OPTICAL ABSORPTION SPECTRA OF CLAY MINERALS

A preliminary survey of electronic absorption spectra of clay minerals reveals the utility of u.v.-visible spectroscopy in the elucidation of structural, physical, and chemical properties of such systems. Spectra, which were obtained in the suspension, film, and single crystal states (where applicable), are interpreted in terms of iron-associated transitions. Microcrystalline clay minerals typically show Fe(lll) in octahedral oxo-ligand geometry whereas mica-type minerals may show a range of iron species, including octahedral Fe(III), tetrahedral Fe(III), and octahedral Fe(II). Iron affects the local site geometry and in “high iron” minerals may dictate layer geometry and subsequently the crystalline form.Résumé Un tour d’horizon préliminaire des spectres d’absorption électronique des minéraux argileux révèle l’utilité de la spectroscopic ultraviolet-visible si l’on veut élucider les propriétés structurales, physiques et chimiques de tels systèmes. Les spectres, obtenus avec des suspensions, des films ou des monocristaux (quand c’est possible) sont interprétés en terme de transitions associées au fer. Les minéraux argileux microcristallins montrent d’une façon typique le Fe (III) dans une géométrie octa-édrique d’oxo-ligands, tandis que les minéraux du type mica peuvent montrer toute une série d’espèces du fer, comprenant Fe (III) octaédrique, Fe III tétraédrique et Fe (II) octaédrique. Le fer affecte la géométrie locale du site et dans les minéraux “riches en fer” peut imposer une géométrie au feuillet et par là, imposer la forme cristalline.KurzreferatEine Voranalyse der elektronischen Absorptionsspektren von Tonmineralien erweist den Wert ultraviolett-sichtbarer Spektroskopie für die Erforschung der strukturellen, physischen und chemischen Eigenschaften derartiger Systeme. Spektren, die in den Suspensions-, Film- und Einkristallzuständen (je nach Verfügbarkeit) erzielt wurden, werden als Übergangsphasen in Verbindung mit Eisen interpretiert. Mikrokristalline Tonmineralien weisen typisch Fe(III) in oktahedralem Oxoverband auf, während glimmerartige Mineralien eine Reihe von Eisenarten wie oktahedralem Fe(III), tetrahedralem Fe(III) und oktahedralem Fe(II) enthalten mögen. Eisen übt auf die lokale Lagerstättengeometrie einen Einfluß aus und kann in eisenreichen Mineralien für die Schichtengeometrie und daher die Kristallform entscheidend sein.РезюмеПредварительное исследование спектра электронного поглощения глинистых минералов выявило ценность видимой ультрафиолетовой спектроскопии в разъяснении структурных физических и химических особенностей таких систем. Спектры полученные от суспензии, на пленке и на сростке отдельных кристаллов (где относится) расшифровывались как соединения с железом. Микрокристаллические глинистые минералы обычно включают Fe(III) в восьмигранной оксо-лигиндной конфигурации, в то время как слюдистые минералы могут состоять из ряда железистых групп, включая октаэдральный Fe(III) тетраэдральный Fe(III) и октаэдральный Fe(II). Железо влияет на конфигурацию места заложения и в минералах с высоким содержанием железа оно может влиять на конфигурацию слоев и на форму кристаллов.

Biosorption of hydrophobic organic pollutants by mixed microbial populations

Abstract In recognition of the need to estimate biosorption for natural microbial populations, the variability of partition coefficients for two hydrophobic pollutants to natural populations from a variety of aquatic systems was investigated. Biosorption partition coefficents for pyrene [2.46(±0.6) × 10 4 ] and phenanthrene [6.34(±1) × 10 3 ] were nearly constant over 14 different microbial sources, consisting of sediments and soils from eight states. For these condensed ring aromatics, semi-empirical equations were developed relating biosorption partition coefficients to octanol/water partition coefficients and to water solubility and melting point. Concepts and relationships developed for these materials should extend to other families of hydrophobic compounds.

Estimation of microscopic, zwitterionic ionization constants, isoelectric point and molecular speciation of organic compounds.

Mathematical models based on structure-activity relationships and perturbed molecular orbital theory have been developed to calculate the ionization pK(a)s for a large number of organic molecules. These models include resonance, direct and indirect electrostatic field effects, sigma induction, steric effects, differential solvation and hydrogen bonding. The thermodynamic microscopic ionization constants, pk(i), of molecules with multiple ionization sites and the corresponding complex speciation as a function of pH have been determined using these chemical reactivity models. For a molecule of interest SPARC (SPARC performs automated reasoning in chemistry) calculates all of the microscopic ionization constants and the fraction of each species as a function pH along with the titration (charge) curve. The system has been tested on several biologically and environmentally important compounds.

PROTONATION OF ORGANIC BASES IN CLAY-WATER SYSTEMS

The extent of protonation of organic bases in clay—water systems depends upon the adsorptive properties of the organo-clay species involved, and upon the structure and degree of hydration of the clay system. Organic molecules that can disperse cationic charge over two or more condensed aromatic rings give rise to greater surface-induced protonation than do single-ring organic molecules with similar solution pKa. Protonation in clay suspensions is frequently far in excess of that predicted on the basis of electrolytic suspension pH and solution pKa of the organic base. For a given organic base, protonation in a clay film exceeds that in the suspended clay system. Protonation in an organo-clay film increases as the film moisture content decreases. The extent of protonation in organo—clay systems varies with cationic species, cationic saturation, and clay type.

Estimation of gas-liquid chromatographic retention times from molecular structure

A new type of a computer program called SPARC (SPARC Performs Automated Reasoning in Chemistry) was developed to predict chemical reactivity parameters and physical properties of organic molecules from their molecular structures based on fundmental chemical structure theory. SPARCs physical models for vapor pressure and activity coefficient were used to calculate the Henrys constant, which can be related to the Kovats retention index. The Kovats indices for a wide range of compounds at any temperature on a squalane liquid phase were calculated. The Root Mean Square deviation error was found to be less than 7 Kovats units, a value that is close to interlaboratory experimental error.

Competitive Hydration of Quinazoline at the Montmorillonite-Water Interface

Ultraviolet spectroscopic analyses of suspensions of quinazoline and Na+-saturated montmorillonite have indicated that covalent hydration of the monovalent organic cation is inhibited at or near the clay surface. A similar lack of hydration was observed in solutions of quinazoline and high-ionic-strength calcium chloride. The inhibition is attributed to a local competition between quinazoline and the inorganic cations for water of hydration.