Chemical interactions, effects

There is no doubt that this dispersion effect occurs but the magnitude of the spectral differences appear in most cases to be considerably larger than would be predicted by dispersion effects. For example, the poly(e-caprolactone) (PCL) and poly (vinyl chloride) (PVC) blend has been studied 252,253) and for this system the refractive indices are identical. In this case, there are obvious frequency shifts and broadening of the carbonyl band as a function of PVC concentration as shown in (Fig. 21). Nine percent of the original area of the carbonyl peak is involved in the shifted frequency absorption. Clearly, for this system, chemical interaction effects are being observed. In fact, PCL can be viewed as a macromolecular plasticizer for PVC. The blend system polyO-propiolactone) PPL and PVC was studied 2S3). In contrast to the PCL/PVC system, the PPL/PVC system was incompatible over the entire range of compositions. 

Materials that produce harmful effects must come into close stmctural or functional relationship with the tissue or organ they may affect. As a result, they can physically or chemically interact with particular biological components in order to effect the toxic response. 

The relinking (14) and self-healing film (3) theories require chemical interaction between the antiozonant and ozonized mbber. The evidence for these interactions is meager (35,36). Overall, there seems to be no clear evidence in the Hterature for PDA derivatives becoming attached to mbber chains as a result of ozone attack. Much fundamental work in this area remains to be done, however. It seems clear at this point that any antiozonant—mbber interaction must be much less important than the scavenging effect of the antiozonant. In summary, the scavenger model is beheved to be the principal mechanism of antiozonant action. Ozone—antiozonant reaction products form a surface film that provides additional protection (37). 

Cross-linked finishes are not permanent in the tme sense of the word however, under optimum conditions the finish can last for the usehil life of the material. Wet abrasion during laundering is probably the principal cause of gradual removal of the finish. In order to retain antistatic protection for extended use, an excess of finish is often appHed The extent of chemical interaction between the durable antistatic agents and the fiber substrates to which they are appHed is not perfectiy understood. Certain oxidizing agents such as hypochlorite bleaches tend to depolymerize and remove some durable antistatic finishes. Some of the durable finishes have also produced undesirable side effects on textile materials, ie, harsh hand, discoloration, and loss of tensile properties. 

Dietary fiber is a mixture of simple and complex polysaccharides and lignin. In intact plant tissue these components are organized into a complex matrix, which is not completely understood. The physical and chemical interactions that sustain this matrix affect its physicochemical properties and probably its physiological effects. Several of the polysaccharides classified as soluble fiber are soluble only after they have been extracted under fairly rigorous conditions. 

Mechanistic studies to identify how endocrine disrupting chemicals interact with hormone systems are required. Although population effects coupled with biomarkers of exposure are strongly suggestive of endocrine disruption, the effect could be secondary to metabolic toxicity. Establishing mechanisms may avoid the need to make decisions on a weight of evidence approach alone. 

The risk sununation tecluiiques assume tliat intakes of individual substances are small. They also assume independence of action by the compounds involved (i.e., tliat there are no synergistic or antagonistic chemical interactions and tliat all chemicals produce the same effect, i.e., cancer). If tliese assumptions are incorrect, over- or mider-estimation of tlie actual multiple-substance risk could result. 

Some Physico-chemical Interactions of Paraquat with Soil Organic Materials and Model Compounds. I. Effects of Temperature, Time and Absorbate Degradation on Paraquat Adsorption, I. G. Bums, M. H. B. Hayes, and M. Stacey, Weed Res., 13 (1973) 67 -78. 

It should be mentioned that the predicted curve at highest benzene level in Figure 13 agrees with classical kinetics (no diffusion-control). It is not clear therefore why measured data at even higher benzene concentrations do not agree with classical kinetics. There may be some subtle chemical interactions at these high solvent levels. Duerksen(lT) fomd similar effects with styrene polymerization in benzene and had to correct kp for solvent. 

Reaction of the environment with the starting material The commonest example of this type of interaction is the protonation of the substrate by acids in the electrolysis medium, but pH effects will be dealt with in a later section. There are, however, other chemical interactions which can occur. For example, the mechanism and products of the oxidation of olefins are changed by the addition of mercuric ion to the electrolysis medium. In its absence, propylene is oxidized to the allyl cation (Clark et al., 1972),... 

Chemical interactions also occur in the condensed phases. Some of these are expected to be quite complex, e.g., the reactions of free radicals on the surfaces of or within aerosol particles. Simpler sorts of interactions also exist. Perhaps the best understood is the acid-base relationship of NH3 with strong acids in aerosol particles and in liquid water (see Chapter 16). Often, the main strong acid in the atmosphere is H2SO4, and one may consider the nature of the system consisting of H2O (liquid), NH3, H2SO4, and CO2 under realistic atmospheric conditions. Carbon dioxide is not usually important to the acidity of atmospheric liquid water (Charlson and Rodhe, 1982) the dominant effects are due to NH3 and H2SO4. The sensitivity the pH of cloud (or rainwater produced from it) to NH3 and... 

Sites of action. When a chemical interacts with one or more of these, there will be a toxic effect on the organism if the concentration exceeds a certain threshold. The chemical has an effect on the organism. 

The sheer complexity of environmental mixtnres of EDCs, possible interactive effects, and capacity of some EDCs to bioaccumulate (e.g., in fish, steroidal estrogens and alkylphenolic chemicals have been shown to be concentrated up to 40,000-fold in the bile [Larsson et al. 1999 Gibson et al. 2005]) raises questions about the adequacy of the risk assessment process and safety margins established for EDCs. There is little question that considerable further work is needed to generate a realistic pictnre of the mixture effects and exposure threats of EDCs to wildlife populations than has been derived from studies on individual EDCs. Further discussion of the toxicity of mixtures will be found in Chapter 2, Section 2.6. 

Walker, C.H. (1998c). The use of biomarkers to measure the interactive effects of chemicals. Ecotoxicology and Environmental Safety 40, 65-70. 

The mechanisms by which the taste (and also the olfactory) system senses chemical compounds is assumed to occur by way of a chemoreceptory system that interacts effectively with a broad, structural variety of stimulant molecules, by means of a receptor epithelium consisting of the mosaic of adjacent, peripheral membranes of many receptor cells, exposed to a medium carrying stimulus molecules. A receptor cell is conveniently and, for our present purpose, sufficiently defined as a cell equipped to interact, according to some mechanism, with stimulus molecules, to convert the effect of this interaction into a signal, and to project this signal into the system. The taste receptor is thus a differentiated, epithelial cell synaptically contact-... 

This model was proposed in early studies of Myasnikov and colleagues [48, 59]. It explains a vast amount of experimental data dealing not only with effect of molecular oxygen on electrophysical characteristics of adsorbents of this type but on effects of numerous other molecular, atom or radical particles capable of chemical interaction with highly active from this stand-point superstoichiometric metal atoms as well. 

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