More than 100,000 chemicals are released into the global environment every year
through their normal production, use, and disposal. To understand and predict the
potential risk that this environmental contamination poses to humans and wildlife,
we must couple our knowledge on the toxicity of a chemical to our knowledge on
how chemicals enter into and behave in the environment. The simple box model
shown in Figure 26.1 illustrates the relationship between a toxicant source, its fate
in the environment, its effective exposure or dose, and resulting biological effects.
A prospective or predictive assessment of a chemical hazard would begin by characterizing
the source of contamination, modeling the chemical ’ s fate to predict
exposure, and using exposure/dose response functions to predict effects (moving
from left to right in Figure 26.1 ). A common application would be to assess the
potential effects of a new waste discharge. A retrospective assessment would proceed
in the opposite direction starting with some observed effect and reconstructing
events to fi nd a probable cause. Assuming that we have reliable dose/exposure
response functions, the key to successful use of this simple relationship is to develop
a qualitative description and quantitative model of the sources and fate of toxicants
in the environment.