ABSTRACT
Selective toxicity has been used in Chapter 7 in a rather restricted sense but historically it has had other meanings. An all embracing definition is ‘selective toxicity means the injury of one kind of living matter without harming some other kind with which the first is in intimate contact’ (Albert, 1985). This definition fits well with the previous definition that selectivity should be used down to the cell level and specificity for subcellular components; Table 10.1 lists many examples of selectivity. The last few items in the table, selectivity occurring within a species such as effects confined to one tissue or one cell type (class 5), has been considered in Chapters 7 and 8. Class 1 contains substances which are highly toxic to most organisms and are often volatile such as methyl bromide and phosphine; their selectivity is not biological but brought about by their pattern of use. Classes 2 and 3 have been designed to attack an unwanted organism and to be relatively non-toxic by virtue of their biological properties and/or their pattern of use, e.g. rodenticides (Meehan, 1984). Class 4 is the modification of physiology for the benefit of humans or animals. Many of the current drugs are designed to rectify derangements in normal physiology, to modify normal physiology, to remove cells with uncontrolled growth or to substitute deficient (or mutated) genes. Class 5 is relevant to all chemicals in classes 1-4 which may cause unwanted effects during medical treatment and occupational and environmental exposure. Definition of the selectivity of such exposure in terms of organs, cells and subcellular constituents is important in the assessment of risk of exposure. Inherent in these procedures are problems of predicting from animal data what will be the risk of exposure of humans.
