Polychlorinated biphenyls, examples

The aim of the first example is to look for polychlorinated biphenyls (PCB) for which C-NMR spectra, measured in deuterochloroform, as well as the partition coefficients between 1-octanol and water arc known. Since it is not reliable to per-... 

Common examples of compounds that are amenable to carbon adsorption are aromatics (benzene, toluene) and chlorinated organics (trichloroethylene, trichloroethane [71-55-6, 75 -(9(9-j5y, tetrachloroethylene, polychlorinated biphenyls (PCBs), DDT /T(9-77-77, pentachlorophenol [87-86-5J. Compounds that are not adsorbed effectively by carbon include ethanol [64-17-5], diethylene glycol [111-46-6], and numerous amines (butylamine [109-73-9, 13952-84-6, 75-64-9], triethanolamine [102-71-6], cyclohexylamine [108-91-8], hexamethylenediamine [108-91-8] (1). Wastewater concentrations that are suitable for carbon adsorption are generally less than 5000 mg/L. 

It is known that the brain is one of the most sensitive sites of action of steroids in utero, and recently there have been suggestions that EDs may affect normal brain development and behaviour. For example, it has been alleged that in utero exposure to polychlorinated biphenyl compounds (PCBs) resulted in adverse effects on neurologic and intellectual function (memory and attention) in young children born to women who had eaten PCB contaminated fish in the USA." It has also been speculated that exposure to environmental pollutants with steroidal activity may be infinencing human sexual development and sexually controlled behavioiir." ... 

The values of n and the corresponding N which are necessary to resolve 50-90% of the constituents of a mixture of 100 compounds are listed in Table 1.5, thus making clear the limitations of one-dimensional chromatography. For example, to resolve over 80 % of the 100 compounds by GC would require a column generating 2.4 million plates, which would be approximately 500 m long for a conventional internal diameter of 250 p.m. For real mixtures, the situation is even less favourable to resolve, for example, 80 % the components of a mixture containing all possible 209 polychlorinated biphenyls (PCBS) would require over lO plates. 

Unfortunately, processes are not always so simple. The members of groups such as polychlorinated biphenyls (PCBs) and PAHs, for example, do not all operate through the same principal mechanism of action. Also, some individual pollutants such as p,p -DDT or tributyl tin work through more than one mode of action. 

Chemicals that possess a common structural feature are called congeners. Some common examples are polychlorinated biphenyls (PCBs), polyaromatic hydrocarbons (PAHs), poly-brominated diphenylethers (PBDE) and chlorofluorocarbons (CFC). The common features... 

The most critical decision to be made is the choice of the best solvent to facilitate extraction of the drug residue while minimizing interference. A review of available solubility, logP, and pK /pKb data for the marker residue can become an important first step in the selection of the best extraction solvents to try. A selected list of solvents from the literature methods include individual solvents (n-hexane, " dichloromethane, ethyl acetate, acetone, acetonitrile, methanol, and water ) mixtures of solvents (dichloromethane-methanol-acetic acid, isooctane-ethyl acetate, methanol-water, and acetonitrile-water ), and aqueous buffer solutions (phosphate and sodium sulfate ). Hexane is a very nonpolar solvent and could be chosen as an extraction solvent if the analyte is also very nonpolar. For example, Serrano et al used n-hexane to extract the very nonpolar polychlorinated biphenyls (PCBs) from fat, liver, and kidney of whale. One advantage of using n-hexane as an extraction solvent for fat tissue is that the fat itself will be completely dissolved, but this will necessitate an additional cleanup step to remove the substantial fat matrix. The choice of chlorinated hydrocarbons such as methylene chloride, chloroform, and carbon tetrachloride should be avoided owing to safety and environmental concerns with these solvents. Diethyl ether and ethyl acetate are other relatively nonpolar solvents that are appropriate for extraction of nonpolar analytes. Diethyl ether or ethyl acetate may also be combined with hexane (or other hydrocarbon solvent) to create an extraction solvent that has a polarity intermediate between the two solvents. For example, Gerhardt et a/. used a combination of isooctane and ethyl acetate for the extraction of several ionophores from various animal tissues. 

Figure 8.9 is an example of the use of solvent extraction to isolate polychlorinated biphenyls from a fat sample [6]. In this example the matrix is chemically modified to improve the selectivity of the extraction. The fat is first hydrolyzed by refluxing in 1 N ethanolic potassium hydroi prior to the... 

Volatilization. Transfer of chemicals across the air/water interface can result in either a net gain or loss of chemical, although in many cases the bulk concentration in the air above a contaminated water body is low enough to be neglected (20). When the atmosphere is the primary source of the contaminant, as for example polychlorinated biphenyls in some parts of the Laurentian Great Lakes, atmospheric concentrations obviously cannot be neglected. The Whitman two-film or two-resistance approach (21) has been applied to a number of environmental situations (20, 22, 23). Transport across the air/water interface is viewed as a two-stage process, in which both phases of the interface can offer resistance to transport of the chemical. The rate of transfer depends on turbulence in the water body and in the atmosphere, the... 

The important influence that sample container materials can have on seawater sample composition is illustrated next by two examples one concerning the storage of metal solutions in glass and plastic bottles, the other concerning the storage of solutions of phthalic acid esters and polychlorinated biphenyls in glass and plastic. 

Terrence Collins is the Thomas Lord Professor of Chemistry at Carnegie Mellon University who contends that the dangers of chlorine chemistry are not adequately addressed by either academe or industry, and alternatives to chlorine and chlorine processors must be pursued. He notes, Many serious pollution episodes are attributable to chlorine products and processes. This information also belongs in chemistry courses to help avoid related mistakes. Examples include dioxin-contaminated 2,4,5-T, extensively used as a peacetime herbicide and as a component of the Vietnam War s agent orange chlorofluorocarbons (CFCs) polychlorinated biphenyls (PCBs the pesticides aldrin, chlordane, dieldrin, DDT, endrin, heptachlor, hexachlorobenzene, lindane, mirex, and toxaphene pentachlorophe-... 

Procedure 12.7 is an example of a basic approach that has also been used to clean up polycyclic aromatic hydrocarbons, polychlorinated biphenyls, and N-, P-, and Cl-containing pesticides before further analysis [25],... 

For example, chloroanilines and polychlorinated biphenyl congeners have been shown to alter by microbially-mediated reductive dehalogenation in sediment/water systems, yielding less chlorinated congeners [38,48,52,68,105, 116,119,369-371]. 

The potential of modern chemical instrumentation to detect and measure the conposition of coirplex mixtures has made it necessary to consider the use of methods of multivariable data analysis in the overall evaluation of environmental measurements. In a number of instances, the category (chemical class) of the compound that has given rise to a series of signals may be known but the specific entity responsible for a given signal may not be. This is true, for example, for the polychlorinated biphenyls (PCB s) in which the clean-up procedure and use of specific detectors eliminates most possibilities except PCB s. Such hierarchical procedures simplify the problem somewhat but it is still advantageous to apply data reduction methods during the course of the interpretation process. 

XZ/N VI RON MENTAL APPLICATIONS OF CHEMOMETRics are of interest because of the concern about the effects of chemicals on humans. The symposium upon which this book is based served as an important milestone in a process we, the editors, initiated in 1982. As members of the Environmental Protection Agency s Office of Toxic Substances (OTS), we have responsibilities for the acquisition and analysis of human and environmental exposure data in support of the Toxic Substances Control Act. OTS exposure studies invariably are complex and range from evaluating human body burden data (polychlorinated biphenyls in adipose tissue, for example) to documenting airborne asbestos levels in schools. 

Polychlorinated biphenyls (PCBs) are colorless toxic organic substances that cause cancer and birth defects. There are more than 200 different types of PCBs, ranging in consistency from heavy, oily liquids to waxy solids, and each type further varying in the number and location of chlorine atoms attached to its molecular carbon rings. They are fire resistant and do not conduct heat or electricity well. Accordingly they have numerous commercial applications as insulation in electrical systems, for example, for transformers. 

Another example is polychlorinated biphenyls (PCBs), which have 10 hydrogen atoms that can be substituted by chlorine atoms. There are three types of site the four a sites near the bridge between the two phenyl fragments, the four p sites farther... 

Biopiles have some potential limitations. For example, certain chemicals such as polychlorinated biphenyls and other hydrocarbons are resistant to biodegradation. In addition, high concentrations of toxic metals, such as lead, copper, and mercury, may limit treatment using biopiles. 

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