The field of exposure assessment has its origins in industrial hygiene. It has evolved rapidly since 1980, and is now used to examine personal contacts with toxicants found in the personal or community environments. The accurate characterizations of exposure to toxic agents can lead to identification of the distribution of exposure and determination of the mean and high-end values, all of which are central to effective risk assessment. The science to conduct exposure analyses and assessments can be placed within a continuum that follows the movement of a toxicant from its source, through to an ultimate health effect. Information on human exposure provides a firm scientific link between the information obtained by traditional environmental sciences, which focus on effluents, and health effects that can result from contact with environmental toxicants. Understanding and interdicting specific pathways for contact are essential in protecting the public health and the environment.
An exposure is defined as "an event consisting of contact at a boundary between a human and the environment at a specific contaminant concentration for a specified interval of time" (National Research Council). Understanding total exposure requires that its fundamental variables of concentration and time are summed over all possible microenvironments where people spend their time.
The data collected to complete an exposure assessment requires both indirect and direct measurements techniques. Direct measurements assess a person's exposure, using monitors attached to the individual, or through the sampling of biological media such as blood or urine. Indirect measurements involve collecting information about where, when, and how people spend their time, and about the concentrations of a contaminant associated with a medium that contributes to important routes of exposure. The data from indirect measurements are used to estimate a person's exposure using both simple and complex models. Detailed exposure and dose analyses frequently use a combination of direct measurements.
Theoretical advances for simulating exposure occurred in the early 1990s, contributing to an understanding of integrated multimedia and multiroute exposures and helping provide initial estimates of exposure within the general population and high-exposure subgroups. All modeling activities, however, must be validated by measurements.
The construction of models of individual or population exposures to contaminants is essential, since it is nearly impossible to measure all exposures experienced by an individual or by the general population. Therefore, statistically representative groups are selected from the population, and measurements from these groups are used to estimate the exposure of the population, using deterministic or fundamental models.
Exposure assessment is particularly pertinent to understanding risks associated with environmental hazards. Risk is a function of both hazard, which is intrinsic to the chemical or physical agent,
PAUL J. LIOY
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