Chemical sensitivity summary

The theory of how chemical sensitization acts to increase photographic sensitivity and the theory of photolysis and latent image formation are interconnected. The aim in this section is to provide a summary of current experimental information on chemical sensitization as a basis for discussing the various mechanisms that have been suggested for latent image formation. 

In summary, chemical sensitization is dependent upon intact immunological function and the integrity of T lymphocyte responses. It is also dependent upon the ability of the hapten-protein complex to stimulate (in a susceptible individual) an immune response of sufficient vigor and of the right quality such that when that individual is exposed to the inducing chemical for the second time (by an appropriate route) they will mount a more accelerated and more aggressive inflammatory response. 

Question of Multiple Chemical Sensitivity. Fundamental and Applied Toxicology, Vol. 24, pgs. 22-28,1995. (Note This is a critical summary of a Society of Toxicology Rountable Discussion addressing the issue of MCS.)... 

The Chemical Data Summary Sheet (CDSS) is a part of a larger INEEL Chemical Management System (ICMS) — a computerized tracking system for chemical products, chemicals, or hazardous agents (CPCHA). INEEL developed the CDSS as a tool to aid in hazard identification. Chemical safety experts evaluated every CPCHA at INEEL and developed a CDSS for each. Information on the CDSS includes the National Fire Protection Association (NFPA) diamond a listing of all hazards and a compatibility classification, time-sensitive classification, and building code classification for the identified CPCHA. While the CDSS is not a replacement for an MSDS, it does contain site-specific safety information that cannot be found in an MSDS and that information is presented in a standardized format... 

A summary of physical and chemical constants for beryUium is compUed ia Table 1 (3—7). One of the more important characteristics of beryUium is its pronounced anisotropy resulting from the close-packed hexagonal crystal stmcture. This factor must be considered for any property that is known or suspected to be stmcture sensitive. As an example, the thermal expansion coefficient at 273 K of siagle-crystal beryUium was measured (8) as 10.6 x 10 paraUel to the i -axis and 7.7 x 10 paraUel to the i -axis. The actual expansion of polycrystalline metal then becomes a function of the degree of preferred orientation present and the direction of measurement ia wrought beryUium. 

Once the determinative or confirmatory method has been developed to take full advantage of the chemical properties of the analyte molecule, a study is necessary to prove that the method is valid. Criteria for method validation are outlined in guidelines from the US FDA, US EPA, and EU. A summary of the differences in regulatory requirements for method validation is provided in Table 3. The parameters addressed by all of the regulatory guidelines include accuracy, precision, sensitivity, specificity, and practicability. 

From these data, aquatic fate models construct outputs delineating exposure, fate, and persistence of the compound. In general, exposure can be determined as a time-course of chemical concentrations, as ultimate (steady-state) concentration distributions, or as statistical summaries of computed time-series. Fate of chemicals may mean either the distribution of the chemical among subsystems (e.g., fraction captured by benthic sediments), or a fractionation among transformation processes. The latter data can be used in sensitivity analyses to determine relative needs for accuracy and precision in chemical measurements. Persistence of the compound can be estimated from the time constants of the response of the system to chemical loadings. 

A review of the literature on chemical-induced immunosuppression in rats and mice, exposed during the pre- and/or postnatal period, was compared to exposure of adults. Five known immunosuppressants (i.e., TCDD, TBTO, DES, Pb, and diazepam) were reviewed. The data revealed that the developing immune system was more sensitive to chemical exposure than the mature immune system. Based on these evaluations, the authors concluded that it was reasonable to assume that testing only in adults would not provide a sufficient level of sensitivity to define immunotoxicity in the neonate 132. In summary, this chapter provides compelling evidence that the developing, compared to the mature, immune system is more vulnerable to perturbation. 

In summary, chemical contact sensitization will be favored by the selective activation of Thl and Tel cells, whereas immediate type hypersensitivity reactions such as chemical respiratory hypersensitivity are apparently associated with the preferential activation of Th2 (and possibly Tc2) type cells. 

In summary, computational quantum mechanics has reached such a state that its use in chemical kinetics is possible. However, since these methods still are at various stages of development, their routine and direct use without carefully evaluating the reasonableness of predictions must be avoided. Since ab initio methods presently are far too expensive from the computational point of view, and still require the application of empirical corrections, semiempirical quantum chemical methods represent the most accessible option in chemical reaction engineering today. One productive approach is to use semiempirical methods to build systematically the necessary thermochemical and kinetic-parameter data bases for mechanism development. Following this, the mechanism would be subjected to sensitivity and reaction path analyses for the determination of the rank-order of importance of reactions. Important reactions and species can then be studied with greatest scrutiny using rigorous ab initio calculations, as well as by experiments. 

In summary, gas-phase reactions between aldehydes and NOj occur readily and with strong exothermicity. The rate of reaction is largely dependent on the alde-hyde/N02 mixture ratio, and is increased with increasing NO2 concentration for aldehyde-rich mixtures. On the other hand, no appreciable gas-phase reactions involving NO are likely to occur below 1200 K. The overall chemical reaction involving NO appears to be third order, which impUes that it is sensitive to pressure. The reactions discussed above are important in understanding the gas-phase reaction mechanisms of nitropolymer propellants. 

In summary, there is evidence that the multitalented sulfur sensitization product can trap electrons, can trap holes to reduce recombination, can stabilize photolytic silver atoms, and can accelerate reduction sensitization. Conceivably, each of these properties could be of importance for latent image formation under at least some conditions. The silver sulfide centers are not of uniform size, they probably are not uniformly related energetically to the silver halide matrix, and they may differ in chemical consititution. 

Review the reactive chemicals test data summaries for exotherms, shock sensitivity or other indicators of instability or energy release potential. 

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