Extrapolation of chemical

A wide-ranging compilation of techniques, Extrapolation Practice for Ecotoxicological Effect Characterization of Chemicals describes methods of extrapolation in the framework of ecological risk assessment. The book, informally known as EXPECT, identifies data needs and situations where these extrapolations can be most usefully applied, making it a practical guide to the application of extrapolation procedures. It focuses on the extrapolation of chemical effects and covers the extrapolation of exposures in the context of interactions between toxicants and the matrix. 

Fig. 16. The evaluation of the heat of vaporization for elements 113 and 114 is shown as an example of the extrapolation of chemical and physical properties, as performed by Keller et al. (78)...

The method for extrapolation of chemical potentials to elevated temperatures and pressures is based on the Gibbs-Duhem equation. 

In addition to the well-known monolayer equations already referred to (e.g., the Langmuir, Hill—de Boer and virial equations), there are others such as those associated with the names of Freundlich, Sips, and Toth, which have been applied to physisorption isotherms on microporous solids [11]. These relatively simple, empirical equations are useful for the interpolation and extrapolation of chemical engineering data, but they are not capable of throwing any new light... 

In recent years, the number of elements has increased well beyond 100 as the result of the synthesis of artificial elements. At the time of writing, conclusive evidence has been reported for element 111. Such elements are typically very unstable, and only a few atoms are produced at any time. However, ingenious chemical techniques have been devised that permit the chemical properties of these so-called superheavy elements to be examined and allow one to check whether extrapolations of chemical properties are maintained for such highly massive atoms. On a more philosophical note, the production of these elements allows us to examine whether the periodic law is an exceptionless law, of the same kind as Newton s law of gravitation, or whether deviations to the expected recurrences in chemical properties might take place once a sufficiently high atomic number is reached. No surprises have been found so far, but the question of whether some of these superheavy elements have the expected chemical properties is far from being fully resolved. One important complication that arises in... 

Grice, H.C. (ed.). 1984. Interpretation and Extrapolation of Chemical and Biological Carcinogenicity Data to Establish Human Safety Standards The Use of Short-Term Tests for Mutagenicity and Carcinogenicity on Chemical Hazard Evaluation. New York Springer-Verlag. 

The procedures used for estimating the service life of solid rocket and gun propulsion systems include physical and chemical tests after storage at elevated temperatures under simulated field conditions, modeling and simulation of propellant strains and bond tine characteristics, measurements of stabilizer content, periodic surveillance tests of systems received after storage in the field, and extrapolation of the service life from the detailed data obtained (21—33). 

The standard Gibbs-energy change of reaction AG° is used in the calculation of equilibrium compositions. The standard heat of reaclion AH° is used in the calculation of the heat effects of chemical reaction, and the standard heat-capacity change of reaction is used for extrapolating AH° and AG° with T. Numerical values for AH° and AG° are computed from tabulated formation data, and AC° is determined from empirical expressions for the T dependence of the C° (see, e.g., Eq. [4-142]). 

Extrapolation of KgO data for absorption and stripping to conditions other than those for which the origin measurements were made can be extremely risky, especially in systems involving chemical reactions in the liquid phase. One therefore would be wise to restrict the use of overall volumetric mass-transfer-coefficient data to conditions not too far removed from those employed in the actual tests. The most reh-able data for this purpose would be those obtained from an operating commercial unit of similar design. 

Eor ethylzinc chloride, CH3CH2ZnCl, and ethylzinc bromide, CH3CH2ZnBr, there is a linear relationship between the observed chemical shift and the ratio of ethylzinc halide to diethylzinc. Extrapolation of these lines to x=l (mol fraction of CH3CH2Z11X) gives predicted values for the average chemical shift that closely match those measured for these species. This indicates that for these two organozinc halides, the Schlenk equilibrium lies heavily on the side of the ethylzinc halide in toluene. However, in the case of ethylzinc iodide, CH3CH2ZnI, there is a... 

Two main hazards associated with chemicals are toxicity and flammability. Toxicity measurements in model species and their interpretation are largely the province of life scientists. Chemical engineers can provide assistance in helping life scientists extrapolate their resrrlts in the assessment of chemical hazards. Chemical engineers have the theoretical tools to make important contributions to modehng the transport and transformation of chemical species in the body—from the entry of species into the body to their action at the rrltimate site where they exert their toxic effect. Chemical engineers are also more likely than life scientists to appreciate... 

When students do make an attempt to relate between the three levels of representation, several unexpected trends in their reasoning are revealed. In the majority of explanations given by students about chemical reactions in a review imdertaken by Andersson (1986), there was a clear extrapolation of physical attributes and changes from the macroscopic world to the particle or submicroscopic one. So, when wood bums, wood molecules are also said to bum. If metallic copper is bright reddish-brown, atoms of copper are also imagined to be reddish-brown in colour (Ben-Zvi, Eylon, Silberstein, 1986). One reason for such extrapolation of physical attributes of substances to the particulate level is the tendency of students to assume that the atoms, ions and molecules in a substance are veiy small portions of the continuous substance. 

The student conceptions that were displayed could be categorised into three main types, namely (1) confusion between macroscopic and submicroscopic representations, (2) extrapolation of bulk macroscopic properties of matter to the submicroscopic level and (3) corrfusion over the multi-faceted significance of chemical symbols, chemical formulas as well as chemical and ionic equations. Student conceptions held by at least 10% of the students who were involved in the alternative instractional programme were identified. Several examples of student conceptions involving the use of the triplet relationship are discussed in the next section. 

The extrapolation of physical attributes of substances to the submicroscopic level of representation was evident when students explained the changes in the displacement reaction between zinc powder and aqueous copper(II) sulphate. The decrease in intensity of the blue colour of the solution was attributed by 31% of students to the removal of blue individual Cu + ions from aqueous solution. The suggestion that individual Cu + ions (the submicroscopic level) are blue may be indicative of the extrapolation of the blue colour of the aqueous copper(II) sulphate (the macroscopic level) to the colour of individual Cu + ions (the submicroscopic level). Thirty-one percent of students also suggested that reddish-brown, insoluble individual atoms of copper were produced in this chemical reaction, again suggesting extrapolation of the bulk properties of copper, i.e., being reddish-brown and insolnble in water (the macroscopic level), to individual copper atoms having these properties (the snbmicroscopic level). 

In the chemical reaction between iron(II) oxide powder and dilute hydrochloric acid, the solution changed from colourless to light green. The suggestion by 15% of students that gpeen individual Fe + ions were present in aqueous iron(II) chloride again indicated possible extrapolation of the bulk colour of the pale green aqueous iron(TI) chloride (the macroscopic level) to the colour of individual Fe + ions (the submicroscopic and symbohc levels) in solution. 

PBPK models improve the pharmacokinetic extrapolations used in risk assessments that identify the maximal (i.e., the safe) levels for human exposure to chemical substances (Andersen and Krishnan 1994). PBPK models provide a scientifically sound means to predict the target tissue dose of chemicals in humans who are exposed to environmental levels (for example, levels that might occur at hazardous waste sites) based on the results of studies where doses were higher or were administered in different species. Figure 3-4 shows a conceptualized representation of a PBPK model. 

PBPK/PD models refine our understanding of complex quantitative dose behaviors by helping to delineate and characterize the relationships between (1) the external/exposure concentration and target tissue dose of the toxic moiety, and (2) the target tissue dose and observed responses (Andersen et al. 1987 Andersen and Krishnan 1994). These models are biologically and mechanistically based and can be used to extrapolate the pharmacokinetic behavior of chemical substances from high to low dose, from route to route, between species, and between subpopulations within a species. The biological basis of... 

Fig. 8 (a) Effects of varying the amino acid at fourth position in ELP[V8X2]. (b) Extrapolation of transition temperature for other ratios of Val Xaa. (a) and (b) Reprinted from [24] with permission from American Chemical Society, copyright 1993 (c) Molecular weight dependence of transition temperature. Reprinted from [23] with permission from Elsevier, copyright 2002... 

The above example illustrates the inherent problems that can arise in the use of standardised protocols for assessing chemicals naturally occurring in the food chain. Had work on comparative metabolism and pharmacokinetics been undertaken before any animal bioassay work, it could have given more useful information. The extrapolation of effects obtained in high-dose animal studies to a large number of people exposed to a low dose is not the most effective use of resources. Nor are such experiments consistent with biological reality. There are few chemicals that would not cause illness or death if the daily intake was increased some 100-1000 fold as is the situation in many... 

Cl. Dybing, E. et al.. Hazard characterization of chemicals in food and diet dose response, mechanisms and extrapolation issues. Food Chem. Toxicol, 40, 237, 2002. 

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