It is important
to recognize that human exposure assessment (HEA) is not intended to be performed without
a specific objective or purpose. One objective is to implement exposure/risk surveillance
to ensure that the exposure of a (working) population is indeed at or below a safe level.
Another more commonly-seen objective is to provide the required exposure information to
complete a health risk assessment (RA).
Numerous uncertainties are generally associated
with RA, since toxicity data are almost always derived from animal studies and, as stated
in the last slide, HEA is an art as much as a science. Nonetheless, there are at least two
certainties that can be said about RA. The first is that toxicity level per se,
such as the no-observed-adverse-effect level, is not readily indicative of the risk
involved. Nor is exposure level per se, without any information on toxicity or
potency, a good risk indicator.
In its simplest term, RA is the process of comparing an estimated exposure level to a
level that is pre-established as safe. Insofar as both of these components are estimates,
the resultant risk is likewise an estimate at best. Partly because risk perception differs
among people in all sectors, and in part because RA is such an inexact science, there are
bound to be many ways in which an exposure level can be compared to a safe level. Lecture
9 will discuss at some length many of the risk characterization schemes commonly used
today. Also to be discussed extensively in the next lecture are the uncertainty factors
that are often considered in risk characterization.