Organic Pollutants

Partition Coefficients

Koc And Kow Correlation

Partitioning of PCBs into other organic compound mixtures or phases found in the environment alters environmental parameters used to estimate their fate and transport. For example, dissolved phase humic substances (i.e., DPHS) can increase the apparent solubility of organic pollutants 381-390 (see Chap. 2). The most common partition coefficient encountered in environmental work (Sect. 2.1.4) is the octanol water partition coefficient (KOW) and the solid phase carbon-water partition coefficient...

Aliphatic Compounds

Moisture And Hydrocarbon Scrubbers

Aliphatic hydrocarbons, a diverse suite of compounds, are an important lipid fraction which is either natural (i. e., from photosynthesis by marine biota inhabiting the surface waters or by terrestrial vascular plants) or anthropogenic (i. e., of petroleum origin from land runoff, and or industrial inputs). Aliphatic hydrocarbons have been studied and characterized from various environmental multimedia 1,53-56,99-109 . Aliphatic hydrocarbons of petroleum origin (Fig. 1) (also coal) in the...

Factors Affecting Acclimation

Acclimation of a microbial community to one substrate frequently results in the simultaneous acclimation to some, but not all, structurally related molecules. Because individual species often act on several structurally similar substrates, the species favored by the first addition may then quickly destroy the analogues 100,107,108,110,111,127 . The duration of acclimation is affected by several environmental factors, such as temperature, pH, aeration status, and nutrients. The concentration of...

Fractionation

Chemical Structure Humic Sustances

A fractionation procedure has been established and widely applied to studies of humic materials 42-44 . The procedure begins with natural OM (i.e., humus) and uses an aqueous basic solution (e.g., 0.1-0.5 mol l NaOH and Na2CO3) to solubilize a fraction of the OM. The basic extract is then acidified which causes a precipitate to form, i.e., humic acids (HA). The fraction, which remains in solution, is called fulvic acids (FA). Humin is the name given to the insoluble organic fraction that...

Clay Fraction

Isomorphism Mineral

Much of the early work in characterizing the environmental behavior of chemicals was accomplished in the area of agricultural chemistry. Work surrounding the behavior of plant nutrients in the soil has provided a large base of information about the processes of environmental chemistry. Workers investigating the effectiveness of soil-applied herbicides determined that the herbicidal activity of organic chemicals varied with soil properties. It was determined that clay and OM contents of the soil...

Aliphatic Hydrocarbons

Branched Aliphatic Hydrocarbon

Aliphatic hydrocarbons are straight chain and branched-chain structures (see Chap. 1). Most aliphatic hydrocarbons introduced into the environment come from industrial solvent waste, the petroleum industry, and vehicular traffic. Liquid aliphatic hydrocarbons readily degrade under aerobic conditions, especially when the number of carbons is between 8 and 16. Longer chain aliphatic compounds are usually waxy substances. Biodegradation of these longer carbon chains is slower due to limited water...

Polycyclic Aromatic Compounds

Aromatic Organic Molecules

Polycyclic aromatic hydrocarbons (PAHs, sometimes also called polynuclear aromatics, PNA) are a hazardous class of widespread pollutants. The parent structures of the common PAHs are shown in Fig. 4 and the alkylated homologs are generally minor in combustion emissions. PAHs are produced by all natural combustion processes (e. g., wild fires) and from anthropogenic activity such as fossil fuels combustion, biomass burning, chemical manufacturing, petroleum refining,metallurgical processes, coal...

Alicyclic Hydrocarbons

Hydrocarbon Plume Degradation Aerobic

Alicyclic hydrocarbons are saturated carbon chains that form ring structures. Naturally occurring alicyclic hydrocarbons are common (Chap. 1). For example, alicyclic hydrocarbons are a major component of crude oil, comprising 20-67 vol. . Other examples of complex, naturally occurring alicyclic hydrocarbons include camphor (a plant terpene) and cyclohexyl fatty acids (components of microbial lipids).Anthropogenic sources of alicyclic hydrocarbons to the environment include fossil-fuel...

Verification of Intrinsic Bioremediation

Techniques traditionally used to verify the occurrence of intrinsic bioremedia-tion at contaminated field sites include monitoring indirect indicators of biological activity such as depletion of contaminant and electron acceptors and production of dissolved inorganic carbon DIC 310 or methane CH4 475 , and the enumeration of BTEX-degrading microorganisms 134 . Although determining the geochemical and microbiological characteristics at a specific contaminated location is essential to any...

Henrys Law Constant

Generally, the higher the pressure, the higher is the solubility of a gas in a liquid. This relationship is expressed quantitatively by Henry's Law which states that the mass of gas (m) dissolved by a given volume of solvent at a constant temperature is proportional to the gas pressure (p) with which it is in equilibrium If the mass of gas dissolved by the given volume is converted to a concentration term, the pressure to vapor density, the Henry's Law relation may be expressed as where C V and...

Aromatic Hydrocarbons

Metabolite Pathway Organic Pollutants

The aromatic hydrocarbons contain at least one unsaturated ring system with the general structure C6R6, where R is any functional group (see Chap. 1). The parent hydrocarbon of this class of compounds is benzene (C6H6), which exhibits the resonance, or delocalization of electrons, typical of unsaturated cyclic structures. Owing to its resonance energy, benzene is remarkably inert. Aromatic compounds, excluding polycyclic aromatic hydrocarbons (PAHs), which contain one or more benzene rings, are...

Dealkylation

Organic Pollutants

Pesticides containing methyl or other alkyl substituents may be linked to N or O (i.e., N- or O-alkyl substitution). An N- or O-dealkylation catalyzed by microorganisms frequently results in loss of the pesticide activity. Phenylurea (see Chap. 1) becomes less active when microorganisms N-demethylate the molecules (e.g., the conversion of Diuron to the normethyl derivative, Fig. 7). The subsequent removal of the second N-methyl group renders the molecule fully nontoxic 169 . On the other hand,...

Dehalogenation

Dehalogenation

Many pesticides contain chlorine or other halogens, and removal of the halogen often converts the toxicant to an innocuous product. The enzymes are designated dehalogenases. These dehalogenations may involve replacement of the halogen by H (i.e., reductive dehalogenation, reaction 11), by OH (i.e., hydro-lytic dehalogenation, reaction 12) or it may result in removal of the halogen and an adjacent H (i. e., dehydrodehalogenation, reaction 13) Fig. 6. Detoxification of DDT, Lindane, and Dalapon...

Dichlorobenzidine

Several million kilograms of 3,3'-dichlorobenzidine (DCB) and benzidine were produced in the United States up to 1977 for the production of dyes and pigments 363 . Recognition of the carcinogenic nature of DCB and its lesser-chlorinated congeners including benzidine resulted in a reduction of their use 362,363 ). Benzidine has been found to be carcinogenic in the human bladder and in oral passages in animals. DCB has likewise been acknowledged to induce cancer in animals and is considered a...

CoMetabolism

Partial Oxidation

The transformation of an organic compound by a microorganism that is unable to use the substrate or one of its constituent elements as a source of energy is termed co-metabolism. The active microbial populations thus derive no nutritional benefit from the substrates they co-metabolize. The energy sufficient to sustain growth fully is not acquired even if the conversion is an oxidation and releases energy, and the C, N, S, or P that may be in the molecule is not used as a source of these...

Sorption Desorption of Organic Pollutants from Complex Mixtures Modeling Kinetics Experimental Techniques and Transport

T. Simoneit2 1 Department of Civil, Construction and Environmental Engineering, College of Engineering, Oregon State University, 202 Apperson Hall, Corvallis, OR 97331, USA 2 Environmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA, Sorption desorption is one of the most important processes influencing movemement of organic pollutants in natural systems. Sorption with...

Nonionic Compounds

Halogenated Hydrocarbon Compounds Ims

Pesticides of this category (Fig. 10, Table 3) do not ionize significantly in aqueous systems and vary widely in their chemical composition and properties (i.e., water solubility, polarity, molecular volume, and tendency to volatilization). Chlorinated hydrocarbon insecticides are among the most widely known and studied group of nonionic pesticides 151 . DDT, in particular, has been studied more than any other pesticide (Fig. 10, Table 3). It has been implicated as detrimental to numerous...

Detoxification

The most important role of microorganisms in the transformation of pollutants at aqueous-solid phase interfaces is their ability to bring about detoxification (i. e., the change in a molecule that renders it less harmful to one or more susceptible species). Detoxification results in inactivation, with the toxicologically active substance being converted to an inactive product. Because toxicological activity is associated with many chemical entities, substituents, and modes of action,...

Free Wilson Mathematical Model

The idea that substituents should contribute constant increments or decrements to biological response in a related series of compounds has probably been a long held intuition of medicinal chemists trained in organic chemistry. However, in the recent past are a few demonstrations of this reported in the literature. The same time that the Hansch model was proposed, Free and Wilson demonstrated a general mathematical method for assessing both the occurrence of additive substituent effects and...

Formation and Complex Composition

Formation Humic Acid

Several mechanisms have been proposed to explain the formation and complex composition of solid phase humic substances (i.e., SPHS, Fig. 3). Selman Waksman's classical theory 17 , the so called Lignin Theory , was that HS are modified lignins which remain after microbial attack (pathway 4, Fig.3), and undergo further modifications yielding first humic acids (HA) and then fulvic acids (FA). Pathway 1 (Fig. 3), which is not considered significant, assumes that HS form from sugars 25 . The...

Case Study

In the next few sections, a case study of the environmental impact of highway construction and repair materials as well as hazardous solid waste materials is presented and discussed from the view points of sorption desorption processes. Assessment, prediction, and management of the environmental impact of solid waste material (SWM) disposal in landfills and recycled wastes mixed with asphalt that are used as highway construction and repair (C& R) materials on surface and ground waters across...

Humic Mineral Associations

Complexation Metal Ions

In addition to the ability of HS to form associations with hydrophobic organic species, humic material also reacts readily to form associations with inorganic minerals as well as polar and ionic organic materials. These types of associations are involved in colloid formation with a wide variety of materials 58-61 . FA can interact with clay minerals and are known to form stable complexes with metal ions and hydrous oxides 59,61 . The operational technique for isolation of HA involves a...

References

Dissertation. Department of Civil, Construction and Environmental Engineering, Oregon State University, Corvallis, Oregon, USA 2. Ruthven DM 1984 Principles of adsorption and adsorption processes.Wiley, New York, p 445 3. Scheidegger AM, Sparks DL 1996 A critical assessment of sorption-desorption mechanisms at the soil mineral water interface. Soil Science 161 813 4. Schlebaum W, Schraa G, van Riemsdijk WH 1999 Environ Sci Technol 33 1413 5. Schwarzenbach...

Introduction On Organic Pollutant

The Mechanism Soil Organic Pollutant

The mechanism of sorption and or desorption for various toxic organic pollutants (see Chap. 1) by various solid phases has long been a subject of profound interest because of its direct impact on the mobility and activity of the organic pollutants in both soils and aquatic sediments 1-11 . A sorption-desorption transformation mechanism, a part of the environmental chemodynamic changes to environmental organic pollutants, occurs when a thermodynamically favorable reaction occurs to these...

Bioavailability and Reductive Dechlorination

Intrinsic reductive dechlorination of PCBs at sites, where residual petroleum products are often found, is often limited or nonexistent 34 . Both commercial PCBs and petroleum exist in the environment as complex mixtures of structurally related compounds. The compounds comprising these mixtures typically have low water solubilities and high sorption coefficients. At relatively low concentrations in the environment,the constituents of these mixtures partition into soil and sediment organic...

Organic Pollutants in Aqueous Solid Phase Environments Types Analyses and Characterizations

T. Simoneit2 1 Department of Civil, Construction and Environmental Engineering, College of Engineering, Oregon State University, 202 Apperson Hall, Corvallis, OR 97331, USA 2 Environmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA e-mail simoneit oce.orst.edu In order to study the chemodynamic behavior (i.e., fate and transport) of organic pollutants in the environment and...

Interaction Mechanisms Between Organic Pollutants and Solid Phase Systems

Simoneit2 1 Department of Civil, Construction and Environmental Engineering, College of Engineering, Oregon State University, 202 Apperson Hall, Corvallis, OR 97331, USA e-mail Tarek.Kassim orst.edu 2 Environmental and Petroleum Geochemistry Group, College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, OR 97331, USA The chemical and structural constitutions of solid phase surfaces in the environment make them active sorbing sites...

Alkylphenol Polyethoxylates

Alkylphenol polyethoxylates (APEO) are a major class of nonionic surfactants over 230 million kg were sold in the United States in 1990 434,435 . They are most important in industrial applications but are also used in institutional and household cleaners and personal care products 436 . In recent years,APEs have received widespread attention in the United States and abroad because of their incomplete elimination during sewage treatment and the detection of their biodegradation intermediates in...

Role of Dissolved Humic Substances in Pollutant Solid Phase Interactions

Dissolved humic substances (DHS) are the main constituents of the dissolved organic carbon (DOC) pool in surface waters (freshwaters and marine waters), groundwaters, and soil porewaters and commonly impart a yellowish-brown color to the water system. Despite the different origins responsible for the main structural characteristics of DHS, they all constitute refractory products of chemical and biological degradation and condensation reactions from plant or animal residues and play a crucial...

Free Energy Models

Among the first models proposed using QSAR methods is the one by Hansch and co-workers 60-62,80,102-110,152,195,296 -298 . They proposed that the early observations of the importance of relative lipophilicity to biological potency into the useful formalism of Linear Free Energy Relationships (LFER) to provide a general QSAR model in biological contexts.As a suitable measure of lipophilicity,the partition coefficient (log KOW) between Z-octanol and water was proposed, and it was further...

Surfactants

Surfactants (Fig. 23) represent one of the major and most versatile groups of organic compounds produced around the world 314 . Their main uses are industrial, 54 (cleaning products, food, and industrial processing), household, 29 (laundry, dishwashing, etc.) and personal care, 17 (soaps, shampoos, cosmetics). The worldwide production in 1988 315 was 2.8 million tons. Surfactants, natural 316,317 or synthetic, change the solubility and physico-chemical state of other environmental...

Gel Permeation Chromatography

Gel permeation chromatography (GPC) with SX3 Biobeads (200-400 mesh) in a range of column sizes and solvents is used by most workers 189,366,400,402, 453,454,487-489 . Separation has been made primarily between lipid material > 500 A which is the first to elute from such columns followed by the smaller molecules which include most of the organic pollutants that accumulate in sample matrices. GPC or size exclusion chromatography (SEC) has several key advantages over all other methods currently...

Basic Compounds

The most important and extensively studied pesticides of this group (Fig. 10, Table 3) are Amitrole and several members of the family of s-triazines 89,151, 153,155,156 .Amitrole had been widely used as a herbicide, but its uses as a registered product for application on food crops were canceled starting in 1971 because it was suspected of inducing thyroid tumors in rats 157-162 . Amitrole is soluble in water, with a weak basic character (PKb 10) and behaves chemically as a typical aromatic...

Amphoteric Zwitterionic

Amphoteric surfactants (Fig. 23) are surface-active agents containing both anionic and cationic functional groups or moieties capable of carrying both ionic charges 314 . However, the term amphoteric surfactants or amphoterics is used generally to refer to materials that show amphoteric properties. The term ampholytes or ampholytic surfactants, though synonymous with amphoterics, is used to refer more specifically to surfactants which can accept or donate a proton, such as amino acids. A simple...

Anaerobic Conditions

Anaerobic conditions are not uncommon in the environment and can develop in water or saturated sediment soil environments. However, even in well-aerated solid phase systems, there are interfacial microenvironments with little or no oxygen. In all of these environments, anaerobiosis occurs when the rate of oxygen consumption by microorganisms is greater than the rate of oxygen diffusion through either air or water. In the absence of oxygen, organic compounds can be mineralized through anaerobic...

Fragmentation Pattern and Environmental Applications

Hopanes Pattern

The combination of high-resolution capillary columns with fast scanning qua-drupole or magnetic sector mass spectrometers provides an excellent method for the identification of a large proportion of the compounds in complex organic materials (COMs). It is worth mentioning that GC-MS analysis of environmental samples has the added advantage over GC of providing structural information on many unknown components responsible for the chromatographic peaks, as well as components that appear to be...

Future Developments in Organic Pollutant Identification and Characterization

Most of the development work on organic pollutants has resulted from the use of GC-MS and synthesis of authentic standards or surrogate standards. However, with advances in other techniques it is clear that this field will benefit by making greater use of alternative identification and characterization methods. The following is a summary of some advances and instrument combinations - Fourier transform infrared spectroscopy (FTIR) can now be combined with GC to provide IR spectra on peaks...

Chlorinated Hydrocarbons

1,1,2,2-Tetrachloroethane (TeCA) was the first chlorinated hydrocarbon solvent produced in large quantities before World War I 371 . It was used as a solvent for cellulose acetate, fat, waxes, greases, rubber, and sulfur. In a few cases, TeCA is used as a carrier or reaction solvent in manufacturing processes for other chemicals and as an analytical reagent for polymers 371 . TeCA was largely replaced by less toxic solvents after 1945. TeCA release in the United States varied from 44,000 pounds...

Assimilation of Carbon

Many measurements have been made of the carbon in the organic substrate which is converted into the cells that are carrying out the biodegradation. Such measurements are simple and straightforward in liquid media with water-soluble substrates since the biomass is particulate and thus can be readily distinguished from carbon in solution 47,56,84 - 86 . In contrast, the measurements in soils, wastewater, sewage, or sediments are complicated because (1) other organic particulate matter is present...

Acclimation

Prior to the degradation of many organic compounds, a period is noted in which no destruction of the compound is evident. This time interval is designated as an acclimation period or, sometimes, an adaptation or lag period 93-98 . It may be defined as the length of time between the addition or entry of the compound into an environment and evidence of its detectable loss. During this interval, no change in concentration is noted, but then the disappearance becomes evident and the rate of...

NNitrosation of Secondary Amines

Many activations involve compounds which are used as pesticides. In the case of N-nitrosation, the precursors are secondary amines and nitrate. The former are common synthetic compounds and the latter is an anion found in nearly all solid and aqueous phases. The N-nitrosation of a secondary amine R-NH-R' occurs in the presence of nitrite formed microbiologically from nitrate. The product is an N-nitroso compound (i.e., a nitrosamine RR'-N-N O ). The reason for concern with nitrosamines is their...

Methyl Bromide

Methyl bromide is presently the most important preplanting soil fumigant commercially available 402 . This compound is used extensively in the United States in the production of many economically important crops for the management of plant-pathogenic nematodes, soil-borne fungi and bacteria, and weeds 403 . This compound is also used as a space fumigant for commodities, for structural pest control, and for quarantine and regulatory purposes. For preplanting soil fumigation, methyl bromide is...

Nonylphenol Ethoxylates

Nonylphenol ethoxylates (NPEOs) are extensively used as surfactants in industrial products (see Chap. 1). NPEOs are a mixture of polyethoxylated mono-alkylphenols, predominantly para-substituted, and are used in the manufacturing of paints, detergents, inks, and pesticides 435, 446 . Surfactants are common water pollutants because of their use in aqueous solutions, which are discharged into the environment in the form of wastewater from treatment plants or sludge stored in landfills....

Conclusions

Understanding environmental partitioning mechanisms of organic pollutants at aqueous-solid phase interfaces (i.e., water-soil, water-sediment, water-suspended solids, water-biosolids) requires the complete knowledge and analysis of most of the important physical and chemical properties of such pollutants. These properties, in some degrees of precision and accuracy, can initially determine the chemodynamics of the pollutants once they are released to the environment. Even through the predicted...

Bioremediation Enhancement

There is tremendous interest in using in situ bioremediation for the cleanup of contaminated soil sediment sites and ground waters. However, biodegradation biotransformation rates, especially in the subsurface aqueous-solid phase environment, are often constrained by a limited oxygen supply and by factors related to bioavailability e.g., solubility, dissolution rate, sorption 150, 191, 200 . Recent research has examined the possibility of enhancing the bioavailability of low solubility and...

Factors Affecting Biodegradation

It is often difficult to predict the fate of a pollutant in an interfacial microenvironment because the interactions between the microbial, chemical, and physical components of the environment are still not well understood. The total microbial activity at aqueous-solid phase interfaces depends on a variety of factors, such as numbers of microbes, available nutrients, environmental conditions, and pollutant chemical structure. The impact of some of the most important factors affecting microbial...

Hydrolysis of Esters

Several esters marketed as herbicides are activated by hydrolysis to give the actual phytotoxin, which is the free acid 94,127 This reaction occurs in soils amended with Flamprop-methyl 205 , Benzoyl-prop-ethyl, and Diclofop-methyl 206 . As the names of these pesticides indicate, R' is CH3 or CH2CH3, respectively. The second product of the conversion is presumably the non-toxic alcohol R'-OH . Chlorinated dibenzo-p-dioxins and dibenzofurans are among the most toxic substances known, especially...

Molecular ConnectivityQSAR Model for PAH Chronic Toxicity Prediction

A QSAR (see Sect. 2.2) is a mathematical model between a property (activity) of a certain compound, in this case the chronic toxicity value of a certain PAH compound, and the descriptors of that PAH. The descriptors are chemical or physical characteristics obtained experimentally or from the structure of the compound itself. In order to develop the MOLCONN-QSAR model, Aboul-Kassim 1 1. Prepared a training data set of chronic toxicity measurements to statistically establish the relationship...

Vapor Pressure

Vapor pressure (i.e., VP) is a measure of the amount of contaminant present in the air at a particular temperature (see Sect. 2.1.2).VP is one of the main factors controlling the vaporization of PCBs from aqueous or solid phase environments into the atmosphere. Figure 7 shows the vapor pressure at 25 C for PCB isomers, indicating that VP decreases as the degree of chlorination increases. Many of the PCBs found in the aquatic environment (e. g., in lakes and in the Arctic and Antarctic) have...

PCB Compositions

Monsanto Chemical Company was the sole producer of PCBs in the United States, marketing them under the trade name Aroclor.A four-digit number identified the mixture of biphenyls found in a particular product. The first two digits (usually 12) indicated that the mixture contained polychlorinated biphenyls. The second two numbers indicated the percentage of chlorine in the mixture. For example, the name Aroclor 1254 indicates a PCB mixture with 54 chlorine. The only exception to this numbering...

Toxic Unit Concept

In quantifying the joint actions of PAHs in mixtures, for instance, the concept of toxic unit (TU) is used. It is defined as where z is the concentration of compound i in a mixture that causes a certain response, and Zj is its concentration causing the same response when acting singly. In fresh water algal toxicity this response could be 50 inhibition of the algal growth. If the TUs of all PAHs in a mixture are equal, then the PAH mixture is referred to as an equitoxic or a uniform mixture....

The Cluster and Path Cluster MCIs

The main characteristic of cluster-type indices is that all bonds are connected to the common, central atom (star-type structure). The third-order cluster molecular connectivity index (3cc) is the first, simplest member of the cluster-type indices where three bonds are joined to the common central atom 102-104, 111-113,152-154,166,167,269 . The simplest chemical structure it refers to is the non-hydrogen part of tert-butane. This index is then calculated using where i, j, k, and l correspond to...

Nomenclature of Molecular Connectivity Indices

The most successful of all topological indices at present is the molecular connectivity index (MCI) or a system of molecular connectivity indices. Their numerous applications in various areas of physics, chemistry, biology, pharmacology (drug design), and environmental sciences outnumber all other existing topological indices, the number of which is approaching 100 108, 221, 222,224-226,254-261 . There are two major reasons for this 1. These indices are based on sound chemical, structural...

Partition Coefficient

The concentrations of any single molecular species in two phases, which are in equilibrium, have a constant ratio to each other and this is defined as follows It assumes that there are no significant solute-solute interactions and no strong solute-solvent interactions which would influence the distribution process. Concentrations are expressed as mass unit volume, and usually C1 refers to an aqueous phase and C2 to a non-aqueous phase. The equilibrium constant (P or K) defining this system is...

Equilibrium Vapor Pressure

The equilibrium vapor pressure of organic compounds is comparable to solubility in that it is a measure of the volatilization tendency from liquid or solid phases. The equilibrium vapor pressure of a gas can be conceived as its solubility in air. The vapor pressure of a liquid or solid is the pressure of the gas in equilibrium with the liquid or solid at a given temperature. The thermodynamic Clausius-Clapeyron expression (Eq. 1, 31 ) describing this equilibrium is where AH is the heat of...

Ideal Adsorbed Solution Model

The most common model for describing adsorption equilibrium in multi-component systems is the Ideal Adsorbed Solution (IAS) model, which was originally developed by Radke and Prausnitz 94 . This model relies on the assumption that the adsorbed phase forms an ideal solution and hence the name IAS model has been adopted. The following is a summary of the main equations and assumptions of this model (Eqs. 22-29). The IAS model relates the concentration of solute i in a complex mixture (C1) to a...

Multicomponent Langmuir Model

The Langmuir model for competitive adsorption can be used as a common model for predicting adsorption equilibria in multicomponent systems. This was first developed by Butler and Ockrent 77 and is based on the same assumptions as the Langmuir model for single adsorbates. It assumes, as in the case of the Langmuir model, that the rate of adsorption of a species at equilibrium is equal to its desorption rate. This is expressed by Eq. (18) where Q and b are the Langmuir constants determined from...

Linear Model

When the Freundlich isotherm n values approximate one, that indicates a linear relationship between the amount sorbed and the equilibrium concentration in solution. Thus, the distribution of any organic pollutant in the aqueous-solid system can be defined by a simple proportionality constant. Equation (8) can be modified as follows where Kd is a simple measure of the distribution of an organic pollutant between the two phases. A variation of this relationship is used to account for the...

Van der Waals Attractions

Ionic species can induce a dipole in a nonpolar molecule over a short range. London forces exist between instantaneous and induced dipoles, and are operative between all bodies when they are close together. For molecular systems they are also commonly called van der Waals attractive forces after the Dutch physicist (J.D. van der Waals) who described these forces as being active in crystals 65 . The London van der Waals force is also frequently referred to as the dispersion force and is...

Ionic Bonding Ion Exchange

Adsorption by this mechanism applies only to a relatively small number of organic pollutants, which are cations in solution or can accept a proton (i. e., protonate) to become cationic. Adsorption via cation exchange or ionic bonding operates through ionized carboxylic and phenolic hydroxyl functional groups of SPHS 17 . For example,Diquat and Paraquat,being divalent cationic pesticides, can react with more than one negatively charged site on an SPHS (e.g., two COO-groups or a COO- plus a...

Hydrogen Isotope Analysis

GC-IRMS systems that allow for the measurement of the hydrogen isotopic composition of individual contaminant compounds have recently become commercially available. The difficult problem of measuring 2H 1H ratios in an excess of helium carrier gas has been tackled by Prosser and Scrimgeour 661 , who designed a flight tube with two spurs to provide a large mass separation between 1H1H+ and 2H1H+ and at the same time to prevent any tailing from 4He+ into the Faraday cup set for m z 3. The...

OnLine Coupling of IRMS

The following section provides information about on-line coupling of IRMS to both GC and MS for environmental applications. For work of the highest accuracy and precision using GC coupled to IRMS through a combustion furnace (GC-C-IRMS), on-line isotopic calibration is essential. The standard practice is to introduce pulses of an isotopically standardized gas (e.g., CO2) via an independent inlet directly into the ion source. The disadvantage of this calibration method is that it fails to...

Sample Preparation and Handling

As for all trace-level analyses, sample preparation and handling are of crucial importance. In addition to all the usual problems of GC-MS, measurements of isotope ratios must ensure that none of these steps introduce any isotope discrimination. Any chemical reactions, including conversion of the organic sample molecules to the simple gases which are those actually analyzed, must be quantitative (100 conversion) to avoid kinetic isotope effects 627 . Until relatively recently, all gas IRMS...

Comparative Extraction Studies

Ideally, the pollutants to be determined should be removed from the matrix as completely as possible with a minimum amount of the other non-target components. This type of selectivity was certainly anticipated from supercritical fluid extraction. However, trace organic pollutants cover a wide range of polarity, volatility, and molecular size, making selective extraction very difficult to achieve. Currently the most popular extraction methods are Soxhlet 191,400, 402-404 , blending 189, 408,...

Liquid Liquid Extraction

Liquid-liquid extraction (LLE) is based on the partition of organic compounds between the aqueous sample and an immiscible organic solvent. The efficiency of an extracting solvent depends on the affinity of the compound for this solvent, as measured by the partition coefficient (i. e., on the ratio of volumes of each phase and on the number of extraction steps). Solvent selection for the extraction of environmental samples is described and reported in many reviews and recent articles...

Blending and Ultrasonic Extraction

The simplest extraction technique is to blend or ultrasonically agitate a sample with an appropriate organic solvent at room temperature.Apart from the polarity of the solvent, the efficiency of the extraction is dependent upon the homogeneity of the sample and the mixing ultrasonication blending soaking time. The mixture of sample and organic solvent are separated from each other by centrifugation or filtration and washing with solvent. Blending has been used for solid phase and other...

Supercritical Fluid Extraction

The first use of supercritical fluid extraction (SFE) as an extraction technique was reported by Zosel 379 . Since then there have been many reports on the use of SFE to extract PCBs, phenols, PAHs, and other organic compounds from particulate matter, soils and sediments 362, 363, 380-389 . The attraction of SFE as an extraction technique is directly related to the unique properties of the supercritical fluid 390 . Supercritical fluids, which have been used, have low viscosities, high diffusion...

Organotin Compounds

Organotin compounds (Fig. 21) are used worldwide as insecticides, fungicides, bactericides, acaricides, wood preservatives, plastic stabilizers, and antifouling agents 75, 59, 255, 256 and are therefore found in numerous environmental compartments as for example water, sediments, biological tissue, sewage sludge, etc. 257 . Due to their high toxicity for aquatic organisms, the application of tributyltin (TBT) and triphenyltin (TPT) (Fig. 21) as marine antifouling agents Fig. 21. Structures of...