Surface area approach

Amidon, G. L., Yalkowsky, S. H., Anik, S. T., Leung, S. (1975) Solubility of nonelectrolytes in polar solvents. V. Estimation of the solubility of aliphatic monofunctional compounds in water using a molecular surface area approach. J. Phys. Chem. 9, 2239-2245. 

The other way to express a relative dose in animals or humans is to do so in terms of body surface area. There are many reasons for believing that the surface area approach is more accurate for relating doses between species (Schmidt-Nielson, 1984), and especially between test animals and humans, but this is still a less common approach in safety assessment, although it is the currently accepted norm in several areas carcinogenesis and chemotherapy, for example. 

Monoazo yellow pigments, on the other hand, are products with larger particle sizes and with much smaller specific surface areas. P.Y.74 is the only species of which there are types with specific surface areas approaching those of diarylide yellow pigments (Sec. 2.3.4). 

Traube s rule accommodates the balance between hydrophobicity and hydro-philicity. It has been extended somewhat and formalized with the development of quantitative methods to estimate the surface area of molecules based on their structures [19, 237]. The molecular surface area approach suggests that the number of water molecules that can be packed around the solute molecule plays an important role in the theoretical calculation of the thermodynamic properties of the solution. Hence, the molecular surface area of the solute is an important parameter in the theory. In compounds other than simple normal alkanes, the functional groups will tend to be more or less polar and thus relatively compatible with the polar water matrix [227,240]. Hence, the total surface area of the molecule can be subdivided into functional group surface area and hydro carbonaceous surface area . These quantities maybe determined for simple compounds as an additive function of constituent groups with subtractions made for the areas where intramolecular contact is made and thus no external surface is presented. 

Camilleri, P., Watts, S.A., and Boraston, J. A. A surface area approach to determine partition coefficients,/. Chem. Soc., Perkin Trans. 2 (September 1988), pp. 1699-1707. 

Funasaki, N., Hada, S.,andNeya, S. Partition coefficients of aliphatic ethers-molecular surface area approach,/. Phys. Chem., 89(14) 3046-3049, 1985. 

The reasons for using these three measures and the advantages and disadvantages of their use have been described by Davidson et al. (1986) and Vocci and Farber (1988). In these papers, it is also explained why the body weight can be used in aU three cases. However, the body weight should be taken to the power of 1, 0.67, and 0.75 for the body weight approach, the body surface area approach, and the caloric requirement approach, respectively. These figures indicate that the approach used to correct for differences in body size will clearly affect the value of the NOAEL adjusted to the body size of humans. 

Adjustment for Differences in Body Size Body Surface Area Approach... 

The surface area approach has been proposed as an alternative to correction for differences in body size based on body weight. This approach is founded on the notion that the basal metabolic rate of vertebrates is a fundamental biological parameter, i.e., a final common expression of physiological and biochemical functions, which is remarkably well related to the body surface area across species and within species (Davidson et al. 1986). 

The above-mentioned references thus indicate that the body surface area approach apparently is a more feasible approach than the body weight approach in terms of dose correction for differences in body size between experimental animals and humans. 

Vermeire et al. (1999) have noted that scaling on the basis of surface area or caloric demand can be considered more appropriate compared to extrapolation based on body weight however, they also noted that experimental work did not answer the question regarding which of these two methods is the most correct. Based on theoretical grounds, and supported by their own analyses, Vermeire et al. (1999) concluded that scaling on the basis of caloric demand to adjust oral NOAELs for metabolic size can be considered more appropriate compared with extrapolation based on body weight. It was also noted that an allometric exponent of 0.67, i.e., the body surface area approach, seems to better describe intraspecies relations. 

Gronlund (1992) has investigated methods used for quantitative risk assessment of non-genotoxic substances, with special regard to the selection of assessment factors. Gronlund found that humans, in most cases, seem to be more sensitive to the toxic effects of chemicals than experimental animals, and that the traditional 10-fold factor for interspecies differences apparently is too small in order to cover the real variation. It was also noted that a general interspecies factor to cover all types of chemicals and all types of experimental animals cannot be expected. It was concluded that a 10-fold factor for interspecies variability probably protects a majority, but not all of the population, provided that the dose correction for differences in body size between experimental animals and humans is performed by the body surface area approach (Section 5.3.2.2). If the dose correction is based on the body weight approach (Section 5.3.2.1), the 10-fold factor was considered to be too small in most cases. 

Aerogels that are about 2-5 nm in diameter have large surface/volume ratios on the order of 10 m and high specific surface areas approaching 1000 m /g. Such large surface/volume ratios make the surface particularly active and potential materials as catalysts, absorbents, and catalyst substrates. 

A similar relationship was observed in Germany. Figure 12.36, for example, shows the deviation of the monthly mean ozone concentration after corrections for seasonal variations, long-term trends, the QBO and vortex effects, and the associated particle surface area concentration from 1991 to 1994 (Ansmann et al., 1996). The increase in the particle surface area due to Mount Pinatubo is clear associated with this increase in aerosol particles are negative monthly mean deviations in ozone that persist until fall 1993, when the surface area approaches the preeruption values. Similarly, the decrease in the total column ozone from 1980-1982 to 1993 observed at Edmonton, Alberta, Canada, and shown at the beginning of this chapter in Fig. 12.1 has been attributed to the effects of the Mount Pinatubo eruption (Kerr et al., 1993). 

Amidon, G. L. and S. T. Anik, Application of the Surface Area Approach to the Correlation and Estimation of Aqueous Solubility and Vapor Pressure Alkyl Aromatic Hydrocarbons. J. Chem. Eng. Data, 1981 26, 28-33. 

Camilleri, P., S. A. Watts, and J. A. Boraston, Surface Area Approach to Determination of Partition Coefficients. Chem. Soc. Perkin Trans., 1988 n, 1699ff. 

The activity of biocatalysts, like colloidal silver, is directly proportional to the surface area of the metal. The geometric progression in surface area of silver particles that one obtains by taking a starting point of 1 cm3 of silver and then reducing incrementally into smaller and smaller cubes, produces silver particles having a total surface area approaching six square kilometres ... 

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