What is the key limitation of applying toxicology?
Because the fundamental mechanisms that cause toxic responses are not fully understood,
toxicological findings are largely based on observations, only partially derived directly from humans.
Toxicology is to a large extent supported by information obtained from experiments on animals. When
extrapolated to humans, such test data carry a considerable degree of uncertainty. This lack of
precision is not only evident in using information obtained in one animal species (e.g., the mouse) to
predict toxic action in another (e.g., humans), but also in extrapolating from the high exposures used in
an animal experiment to the low-dose situation usually encountered , with respect to exposure of the
general population. Depending on the mathematical mode used for such extrapolations, the risk
estimates obtained may differ by orders of magnitude. Thus, quantification of the toxicity of a
chemical is associated with a large degree of uncertainty, typically dwarfing the uncertainty inherent in
a scientific analysis of the fate and transport in the environment of the same chemical.
Having said this about the uncertainty associated with toxicological data, it should also be stressed that,
for many chemicals, the toxicological database is sufficient to predict the risks associated with their
presence in the environment. For chemicals without a sufficient database, generally accepted
approaches exist to make a reasonable approximation to provide the basis for selecting appropriate
strategies protective of human and ecological health. Chapter 14 of this textbook presents a systematic
approach for using toxicological and site data to assess in a quantitative fashion the risk posed by
hazardous waste at a site.