Origins and Chemical Properties

PCDDs have been released into the environment in a number of different ways. Sometimes this has been due to the use of a pesticide that is contaminated with them. 2,4,5-T and related phenoxyalkanoic herbicides have been contaminated with them as a consequence of the interaction of chlorophenols used in the manufacturing 

Organic Pollutants An Ecotoxicological Perspective, Second Edition 

FIGURE 7.1 Formation of dioxin and dibenzofuran (from Crosby 1998). 

8-TCDD has been more widely studied than other PCDDs, and will be taken as an example for the whole group of compounds. It is a stable solid with a melting point of 306°C. Its water solubility is very low, which has been estimated to be 0.01-0.2 pg/L its log is 6.6. More highly chlorinated PCDDs are even less soluble in water. 

From here on, these two related groups of pollutants will be treated together. 

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A description is given of a discovery in 1833 by Bartolomeo Bizio, a Venetian chemist, of the origin and chemical properties of Tyrian Purple. This was subsequently shown... 

Rossell, B. (2001) Origins and Chemical Properties, in Oils and Fats, Vol. 2., Animal Carcass Fats (ed. 

The purposes of this paper are then (a) to refer on some additional results obtained, in order to confirm the previously suggested [9, 10 ] involvement of humic free radicals in the cross coupling reactions of humic substances with xenobiotic phenoxy radicals and (b) to discuss comparatively the different behaviours of humic acids in these reactions, as a function of their different origin and chemical properties. 

With minor exceptions the requirements for the physical and chemical properties of asphalt were essentially the same for the three national specifications and included penetration and ductiUty at 25 °C flash point % loss at 163 °C penetration of residue as a % of original solubiUty in carbon disulfide solubiUty in carbon tetrachloride specific gravity at 25°C and softening point. 

Influence of U colloidal transport in organic-poor surface waters has been far less studied. Riotte et al. (2003) reported U losses from 0 to 70% during ultrafiltration experiments for surface waters of Mount Cameroon without nearly any DOC. Even in the low concentration waters, U can be significantly fractionated from other soluble elements by the occurrence of a colloidal phase, probably inorganic in origin. However, such fractionations are not systematic because of the occurrence of various colloidal phases, characterised by different physical and chemical properties, and hence different sorption and/or complexation capacities (Section 2.1). 

Many material properties lend themselves to the authentication of objects the composition and the physical and chemical properties of materials and their decay products provide objective criteria for establishing the authenticity of archaeological objects. Contradictions between the claimed origin or... 

With the rapid development of modem analysis techniques, especially the popularization of single-crystal X-ray diffraction equipment, the origin of various physical and chemical properties, and the clear elucidation of correlations between the structure and properties of Pcs have become possibilities. Together with the maturity and diversification of their modifications, many Pcs have been synthesized and their molecular structures characterized by X-ray diffraction analysis in the past 5 years [15-77]. 

Apart from butter or butter oil most fats that are used in biscuits are defined in terms of their physical and chemical properties. Fat suppliers are skilled at producing products with controlled physical and chemical properties from a range of raw materials. The baker can either buy fat on a physical and chemical specification, e.g. solid fat index, slip melting point, and not to contain lauric fat, or on an origin basis, e.g. to be coconut oil. The advantage of the botanical specification is that the item is a commodity and can be obtained from numerous sources. The disadvantage of this approach is that the product is tailored for a particular use. 

The assessment of health effects due to exposure to the total petroleum hydrocarbons requires much more detailed information than what is provided by a single total petroleum hydrocarbon value. More detailed physical and chemical properties and analytical information on the total petroleum hydrocarbons fraction and its components are required. Indeed, a critical aspect of assessing the toxic effects of the total petroleum hydrocarbons is the measurement of the compounds, and the first task is to appreciate the origin of the various fractions (compounds) of the total petroleum hydrocarbons. Transport fractions are determined by several chemical and physical properties (i.e., solubility, vapor pressure, and propensity to bind with soil and organic particles). These properties are the basis of measures of teachability and volatility of individual hydrocarbons and transport fractions (Chapters 8, 9, and 10). 

Gluing is difficult, needing pre-treatments such as, for example, chemical etching (sulfo-chromic acid etching), flame oxidation or hot-air (500°C) treatment, corona discharge, plasma or UV treatments. The exposure must be brief and superficial and the original and aged properties must be tested. 

Photolysis and pulse radiolysis are powerful methods for producing sizeable amounts of reactive transients whose physical and chemical properties may be examined. Structural information on the transient and the characterization of early (rapid) steps in an overall reaction can be very helpful for understanding the overall mechanism in a complex reaction. Chemical equilibria may be disturbed by photolysis or radiolysis since one of the components may be most affected by the beam and its concentration thereby changed. The original equilibrium will be reestablished on removing the disturbance and the associated change can be examined just as in the relaxation methods. The approach has been more effectively used in laser photolysis and since very short perturbations are possible the rates associated with very labile equilibria may be measured. 

In the subsurface, kerosene volatilization is controlled by the physical and chemical properties of the solid phase and by the water content. Porosity is a major factor in defining the volatilization process. Galin et al. (1990) reported an experiment where neat kerosene at the saturation retention value was recovered from coarse, medium, and fine sands after 1, 5, and 14 days of incubation. The porosity of the sands decreased from coarse to fine. Figure 8.9 presents gas chromatographs obtained after kerosene volatilization. Note the loss of the more volatile hydrocarbons by evaporation in all sands 14 days after application and the lack of resemblance to the original kerosene. It is clear that the pore size of the sands affected the chemical composition of the remaining kerosene. For example, the fractions disap-... 

Subsurface transformations of contaminants comprising multiple components are reflected in the composition of the residual contamination products, which may have different physical and chemical properties than the original pollutant. Differential partitioning-dissolution and volatilization of component mixtures are the main abiotic processes leading to alteration of the original pollutant. 

A formal description of a mineral presents all the physical and chemical properties of the species. In particular, distinctive attributes that might facilitate identification are noted, and usually a chemical analysis of the first or type specimen on which the name was originally bestowed is included. As an example, the complete description of the mineral brucite (Mg(OH)2), as it appears in Dana s System of Mineralogy, is presented as Appendix 3. Note the complexity of this chemically simple species and the range of information available. In the section on Habit (meaning shape or morphology) both acicular and fibrous forms are noted. The fibrous variety, which has the same composition as brucite, is commonly encountered (see Fig. I.ID) and is known by a separate name, nemalite. ... 

Although the compositions used in fountains are usually based on black powder propellant, the sparks that are responsible for the fountain effect originate from other substances within the composition. These substances are known as emitters and it is the physical and chemical properties of the emitters that determine the characteristics of the fountain. Various additives are also used to promote the visual effects or to cheapen the composition. 

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