Lethality coefficient

In estimating the total detriment due to stochastic responses in any organ as described above, the probability coefficient for fatal cancers (F) or severe hereditary responses is based on data in humans and animals described in Section 3.2.2.2, and the lethality fraction (k) and relative length of life lost per fatal response (.II) are based on data on responses from all causes in various national populations. The values of F, k, and t/l for different organs, as well as the probability coefficient for severe hereditary responses, assumed by ICRP (1991) and the resulting estimates of total detriment, F((/T)(2 - k ), are summarized in Table 3.2. The two entries for Total in the last row represent the probability coefficient for... 

This is a convenient way of expressing models for the prediction of LC50 values, and is easy to understand since a numerical increase in the response variable means an increase in toxicity (acute lethality in this case). Furthermore, it is apparent that the QSAR relates an increasing toxicity to an increasing partition coefficient. 

Toxicity is measured by the concentration in mg liter-1 of a compound that causes the death of a certain percentage (usually 50 or 100%) of the test population of a chosen organism (e.g., silvery minnows) in a chosen time (e.g., 96 hours). For organic inhibitors, the higher the concentration needed to achieve a lethal dose of 50%, the less toxic the inhibitor. In Table 12.3 the actual lethal concentration (LC50) (at 96 hr) is compared with that calculated by means of a quantitative structure-activity relation (QSAR). The basic calculation is that of the distribution coefficient of the inhibition of the primary alcohol octanol. 

Using Brine Shrimp Nauplii as Food for Test Animals in Aquatic Toxicology Using Octanol-Water Partition Coefficient to Estimate Median Lethal Concentrations for Fish Due to Narcosis... 

Qio values in the range of S to 20 have been found for bacterial spores against saturated steam sterilizing temperatures. These rather high temperature coefficients show that for steam sterilization, a discrepancy of only I or 2 C from the specified temperature may have signiAcant effects on the process lethality. For instance, a deficiency of 2 to 3 C could easily require a tloubling of the exposure time to achieve the same lethality as the specified process. 

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